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2008 |
Jörg Hoormann; Stephanie Jainta; Wolfgang Jaschinski The effect of calibration errors on the accuracy of the eye movement recordings Journal Article In: Journal of Eye Movement Research, vol. 1, no. 2, pp. 1–7, 2008. @article{Hoormann2008,For calibrating eye movement recordings, a regression between spatially defined calibration points and corresponding measured raw data is performed. Based on this regression, a confidence interval (CI) of the actually measured eye position can be calculated in order to$backslash$nquantify the measurement error introduced by inaccurate calibration coefficients. For calculating this CI, a standard deviation (SD) - depending on the calibration quality and the$backslash$ndesign of the calibration procedure - is needed.$backslash$nExamples of binocular recordings with separate monocular calibrations illustrate that the SD is almost independent of the number and spatial separation between the calibration points – even though the later was expected from theoretical simulation. Our simulations and recordings demonstrate that the SD depends critically on residuals at certain calibration points, thus robust regressions are suggested. |
Janet Hui-wen Hsiao; Garrison W. Cottrell Two fixations suffice in face recognition Journal Article In: Psychological Science, vol. 19, no. 10, pp. 998–1006, 2008. @article{Hsiao2008,It is well known that there exist preferred landing positions for eye fixations in visual word recogni- tion. However, the existence ofpreferred landing positions in face recognition is less well established. It is also un- known how many fixations are required to recognize a face. To investigate these questions, we recorded eye movements during face recognition. During an otherwise standard face-recognition task, subjects were allowed a variable number of fixations before the stimulus was masked.We found that optimal recognition performance is achieved with two fixations; performance does not improve with additional fixations. The distribution of the first fix- ation is just to the left ofthe center ofthe nose, and that of the second fixation is around the center ofthe nose. Thus, these appear to be the preferred landing positions for face recognition. Furthermore, the fixations made during face learning differ in location from those made during face recognition and are also more variable in duration; this suggests that different strategies are used for face learning and face recognition. |
Manon W. Jones; Mateo Obregón; M. Louise Kelly; Holly P. Branigan Elucidating the component processes involved in dyslexic and non-dyslexic reading fluency: An eye-tracking study Journal Article In: Cognition, vol. 109, no. 3, pp. 389–407, 2008. @article{Jones2008,The relationship between rapid automatized naming (RAN) and reading fluency is well documented (see Wolf, M. & Bowers, P.G. (1999). The double-deficit hypothesis for the developmental dyslexias. Journal of Educational Psychology, 91(3), 415-438, for a review), but little is known about which component processes are important in RAN, and why developmental dyslexics show longer latencies on these tasks. Researchers disagree as to whether these delays are caused by impaired phonological processing or whether extra-phonological processes also play a role (e.g., Clarke, P., Hulme, C., & Snowling, M. (2005). Individual differences in RAN and reading: A response timing analysis. Journal of Research in Reading, 28(2), 73-86; Wolf, M., Bowers, P.G., & Biddle, K. (2000). Naming-speed processes, timing, and reading: A conceptual review. Journal of learning disabilities, 33(4), 387-407). We conducted an eye-tracking study that manipulated phonological and visual information (as representative of extra-phonological processes) in RAN. Results from linear mixed (LME) effects analyses showed that both phonological and visual processes influence naming-speed for both dyslexic and non-dyslexic groups, but the influence on dyslexic readers is greater. Moreover, dyslexic readers' difficulties in these domains primarily emerge in a measure that explicitly includes the production phase of naming. This study elucidates processes underpinning RAN performance in non-dyslexic readers and pinpoints areas of difficulty for dyslexic readers. We discuss these findings with reference to phonological and extra-phonological hypotheses of naming-speed deficits. |
C. -H. Juan; Neil G. Muggleton; Ovid J. L. Tzeng; D. L. Hung; A. Cowey; Vincent Walsh Segregation of visual selection and saccades in human frontal eye fields Journal Article In: Cerebral Cortex, vol. 18, no. 10, pp. 2410–2415, 2008. @article{Juan2008,The premotor theory of attention suggests that target processing and generation of a saccade to the target are interdependent. Temporally precise transcranial magnetic stimulation (TMS) was delivered over the human frontal eye fields, the area most frequently associated with the premotor theory in association with eye movements, while subjects performed a visually instructed pro-/antisaccade task. Visual analysis and saccade preparation were clearly separated in time, as indicated by 2 distinct time points of TMS delivery that resulted in elevated saccade latencies. These results show that visual analysis and saccade preparation, although frequently enacted together, are dissociable processes. |
Johanna K. Kaakinen; Jukka Hyönä Perspective-driven text comprehension Journal Article In: Applied Cognitive Psychology, vol. 22, pp. 319–334, 2008. @article{Kaakinen2008,The present article reports results of an eye‐tracking experiment, which examines whether the perspective‐driven text comprehension framework applies to comprehension of narrative text. Sixty‐four participants were instructed to adopt either a burglar's or an interior designer's perspective. A pilot test showed that readers have more overlapping prior knowledge with the burglar‐relevant than with the interior designer‐relevant information of the experimental text. Participants read either a transparent text version where the (ir)relevance of text segments to the perspective was made apparent, or an opaque text version where no direct mention of the perspective was made. After reading participants wrote a free recall of the text. The results showed that perspective‐related prior knowledge modulates the perspective effects observed in on‐line text processing and that signalling of (ir)relevance helps in encoding relevant information to memory. It is concluded that the proposed framework generalizes to the on‐line comprehension of narrative texts. |
Roger Kalla; Neil G. Muggleton; Chi-Hung Juan; Alan Cowey; Vincent Walsh The timing of the involvement of the frontal eye fields and posterior parietal cortex in visual search Journal Article In: NeuroReport, vol. 19, no. 10, pp. 1069–1073, 2008. @article{Kalla2008,The frontal eye fields (FEFs) and posterior parietal cortex (PPC) are important for target detection in conjunction visual search but the relative timings of their contribution have not been compared directly. We addressed this using temporally specific double pulse transcranial magnetic stimulation delivered at different times over FEFs and PPC during performance of a visual search task. Disruption of performance was earlier (0/40 ms) with FEF stimulation than with PPC stimulation (120/160 ms), revealing a clear and substantial temporal dissociation of the involvement of these two areas in conjunction visual search. We discuss these timings with reference to the respective roles of FEF and PPC in the modulation of extrastriate visual areas and selection of responses. |
Andre Kaminiarz; Bart Krekelberg; Frank Bremmer Expansion of visual space during optokinetic afternystagmus (OKAN) Journal Article In: Journal of Neurophysiology, vol. 99, no. 5, pp. 2470–2478, 2008. @article{Kaminiarz2008,The mechanisms underlying visual perceptual stability are usually investigated using voluntary eye movements. In such studies, errors in perceptual stability during saccades and pursuit are commonly interpreted as mismatches between actual eye position and eye-position signals in the brain. The generality of this interpretation could in principle be tested by investigating spatial localization during reflexive eye movements whose kinematics are very similar to those of voluntary eye movements. Accordingly, in this study, we determined mislocalization of flashed visual targets during optokinetic afternystagmus (OKAN). These eye movements are quite unique in that they occur in complete darkness and are generated by subcortical control mechanisms. We found that during horizontal OKAN slow phases, subjects mislocalize targets away from the fovea in the horizontal direction. This corresponds to a perceived expansion of visual space and is unlike mislocalization found for any other voluntary or reflexive eye movement. Around the OKAN fast phases, we found a bias in the direction of the fast phase prior to its onset and opposite to the fast-phase direction thereafter. Such a biphasic modulation has also been reported in the temporal vicinity of saccades and during optokinetic nystagmus (OKN). A direct comparison, however, showed that the modulation during OKAN was much larger and occurred earlier relative to fast-phase onset than during OKN. A simple mismatch between the current eye position and the eye-position signal in the brain is unlikely to explain such disparate results across similar eye movements. Instead, these data support the view that mislocalization arises from errors in eye-centered position information. |
Annette Kinder; Martin Rolfs; Reinhold Kliegl Sequence learning at optimal stimulus – response mapping: Evidence from a serial reaction time task Journal Article In: Quarterly Journal of Experimental Psychology, vol. 61, no. 2, pp. 203–209, 2008. @article{Kinder2008,We propose a new version of the serial reaction time (SRT) task in which participants merely looked at the target instead of responding manually. As response locations were identical to target locations, stimulus–response compatibility was maximal in this task. We demonstrated that saccadic response times decreased during training and increased again when a new sequence was presented. It is unlikely that this effect was caused by stimulus–response (S–R) learning because bonds between (visual) stimuli and (oculomotor) responses were already well established before the experiment started. Thus, the finding shows that the building ofS–R bonds is not essential for learning in the SRT task. Numerous |
Albrecht W. Inhoff; Matthew S. Solomon; Bradley A. Seymour; Ralph Radach Eye position changes during reading fixations are spatially selective Journal Article In: Vision Research, vol. 48, no. 8, pp. 1027–1039, 2008. @article{Inhoff2008,Intra-fixation location changes were measured when one-line sentences written in lower or aLtErNaTiNg case were read. Intra-fixation location changes were common and their size was normally distributed except for a relatively high proportion of fixations without a discernible location change. Location changes that did occur were systematically biased toward the right when alternating case was read. Irrespective of case type, changes of the right eye were biased toward the right at the onset of sentence reading, and this spatial bias decreased as sentence reading progressed from left to right. The left eye showed a relatively stable right-directed bias. These results show that processing demands can pull the two fixated eyes in the same direction and that the response to this pull can differ for the right and left eye. |
Albrecht W. Inhoff; Matthew S. Starr; Matthew S. Solomon; Lars Placke Eye movements during the reading of compound words and the influence of lexeme meaning Journal Article In: Memory & Cognition, vol. 36, no. 3, pp. 675–687, 2008. @article{Inhoff2008a,We examined the use of lexeme meaning during the processing of spatially unified bilexemic compound words by manipulating both the location and the word frequency of the lexeme that primarily defined the meaning of a compound (i.e., the dominant lexeme). The semantically dominant and nondominant lexemes occupied either the beginning or the ending compound word location, and the beginning and ending lexemes could be either high- or low-frequency words. Three tasks were used–lexical decision, naming, and sentence reading–all of which focused on the effects of lexeme frequency as a function of lexeme dominance. The results revealed a larger word frequency effect for the dominant lexeme in all three tasks. Eye movements during sentence reading further revealed larger word frequency effects for the dominant lexeme via several oculomotor motor measures, including the duration of the first fixation on a compound word. These findings favor theoretical conceptions in which the use of lexeme meaning is an integral part of the compound recognition process. |
Helene Intraub; Christopher A. Dickinson False memory 1/20th of a second later: What the early onset of boundary extension reveals about perception Journal Article In: Psychological Science, vol. 19, no. 10, pp. 1007–1014, 2008. @article{Intraub2008,Errors of commission are thought to be caused by heavy memory loads, confusing information, lengthy retention intervals, or some combination of these factors. We report false memory beyond the boundaries of a view, boundary extension, after less than 1/20th of a second. Photographs of scenes were interrupted by a 42-ms or 250-ms mask, 250 ms into viewing, before reappearing or being replaced with a different view (Experiment 1). Postinterruption photographs that were unchanged were rated as closer up than the original views; when the photographs were changed, the same pair of closer-up and wider-angle views was rated as more similar when the closer view was first, rather than second. Thus, observers remembered preinterruption views with extended boundaries. Results were replicated when the interruption included a saccade (Experiment 2). The brevity of these interruptions has implications for visual scanning; it also challenges the traditional distinction between perception and memory. We offer an alternative conceptualization that shows how source monitoring can explain false memory after an interruption briefer than an eyeblink. |
Stuart Jackson; Fred Cummins; Nuala Brady Rapid perceptual switching of a reversible biological figure Journal Article In: PLoS ONE, vol. 3, no. 12, pp. e3982, 2008. @article{Jackson2008,Certain visual stimuli can give rise to contradictory perceptions. In this paper we examine the temporal dynamics of perceptual reversals experienced with biological motion, comparing these dynamics to those observed with other ambiguous structure from motion (SFM) stimuli. In our first experiment, naïve observers monitored perceptual alternations with an ambiguous rotating walker, a figure that randomly alternates between walking in clockwise (CW) and counter-clockwise (CCW) directions. While the number of reported reversals varied between observers, the observed dynamics (distribution of dominance durations, CW/CCW proportions) were comparable to those experienced with an ambiguous kinetic depth cylinder. In a second experiment, we compared reversal profiles with rotating and standard point-light walkers (i.e. non-rotating). Over multiple test repetitions, three out of four observers experienced consistently shorter mean percept durations with the rotating walker, suggesting that the added rotational component may speed up reversal rates with biomotion. For both stimuli, the drift in alternation rate across trial and across repetition was minimal. In our final experiment, we investigated whether reversals with the rotating walker and a non-biological object with similar global dimensions (rotating cuboid) occur at random phases of the rotation cycle. We found evidence that some observers experience peaks in the distribution of response locations that are relatively stable across sessions. Using control data, we discuss the role of eye movements in the development of these reversal patterns, and the related role of exogenous stimulus characteristics. In summary, we have demonstrated that the temporal dynamics of reversal with biological motion are similar to other forms of ambiguous SFM. We conclude that perceptual switching with biological motion is a robust bistable phenomenon. |
Xu Huang; Jin Jing; Xiao-bing Zou; Meng-Long Wang; Xiu-Hong Li; Ai-Hua Lin Eye movements characteristics of Chinese dyslexic children in picture searching Journal Article In: Chinese Medical Journal, vol. 121, no. 17, pp. 1617–1621, 2008. @article{Huang2008,Background: Reading Chinese, a kind of ideogram, relies more on visual cognition. The visuospatial cognitive deficit of Chinese dyslexia is an interesting topic that has received much attention. The purpose of current research was to explore the visuopatial cognitive characteristics of Chinese dyslexic children by studying their eye movements via a picture searching test. Methods: According to the diagnostic criteria defined by ICD-10, twenty-eight dyslexic children (mean age (10.12±1.42) years) were enrolled from the Clinic of Children Behavioral Disorder in the third affiliated hospital of Sun Yat-sen University. And 28 normally reading children (mean age (10.06±1.29) years), 1:1 matched by age, sex, grade and family condition were chosen from an elementary school in Guangzhou as a control group. Four groups of pictures (cock, accident, canyon, meditate) from Picture Vocabulary Test were chosen as eye movement experiment targets. All the subjects carried out the picture searching task and their eye movement data were recorded by an Eyelink II High-Speed Eye Tracker. The duration time, average fixation duration, average saccade amplitude, fixation counts and saccade counts were compared between the two groups of children. Results: The dyslexic children had longer total fixation duration and average fixation duration (F=7.711, P <0.01; F=4.520, P <0.05), more fixation counts and saccade counts (F=7.498, P <0.01; F=11.040, P <0.01), and a smaller average saccade amplitude (F=29.743, P <0.01) compared with controls. But their performance in the picture vocabulary test was the same as those of the control group. The eye movement indexes were affected by the difficulty of the pictures and words, all eye movement indexes, except saccade amplitude, had a significant difference within groups (P <0.05). Conclusions: Chinese dyslexic children have abnormal eye movements in picture searching, applying slow fixations, more fixations and small and frequent saccades. Their abnormal eye movement mode reflects the poor ability and strategy of visual information processing. |
Wendy E. Huddleston; Edgar A. DeYoe The representation of spatial attention in human parietal cortex dynamically modulates with performance Journal Article In: Cerebral Cortex, vol. 18, no. 6, pp. 1272–1280, 2008. @article{Huddleston2008,The control and allocation of attention is an essential, ubiquitous neural process that gates our awareness of objects and events in the environment. Neural representations of the locus of spatial attention have been previously demonstrated in parietal cortex. However, the behavioral relevance of these neural representations is not known. While undergoing functional magnetic resonance imaging, subjects performed a covert spatial attention task that yielded a wide range of performance values. Voxels in parietal cortex selective for attended target location also dynamically modulated, becoming more or less responsive as performance levels changed. Surprisingly, this relationship was not linear. Responses peaked at intermediate performance levels and dropped both when performance was very high and when it was very low. Such dynamic modulation may represent a mechanism for organizing neural control signals according to behavioral task demands. |
Falk Huettig; Robert J. Hartsuiker When you name the pizza you look at the coin and the bread: Eye movements reveal semantic activation during word production Journal Article In: Memory & Cognition, vol. 36, no. 2, pp. 341–360, 2008. @article{Huettig2008,Two eyetracking experiments tested for activation of category coordinate and perceptually related concepts when speakers prepare the name of an object. Speakers saw four visual objects in a 2 x 2 array and identified and named a target picture on the basis of either category (e.g., "What is the name of the musical instrument?") or visual-form (e.g., "What is the name of the circular object?") instructions. There were more fixations on visual-form competitors and category coordinate competitors than on unrelated objects during name preparation, but the increased overt attention did not affect naming latencies. The data demonstrate that eye movements are a sensitive measure of the overlap between the conceptual (including visual-form) information that is accessed in preparation for word production and the conceptual knowledge associated with visual objects. Furthermore, these results suggest that semantic activation of competitor concepts does not necessarily affect lexical selection, contrary to the predictions of lexical-selection-by-competition accounts (e.g., Levelt, Roelofs, & Meyer, 1999). |
Amelia R. Hunt; Craig S. Chapman; Alan Kingstone Taking a long look at action and time perception Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 34, no. 1, pp. 125–136, 2008. @article{Hunt2008,Everyone has probably experienced chronostasis, an illusion of time that can cause a clock's second hand to appear to stand still during an eye movement. Though the illusion was initially thought to reflect a mechanism for preserving perceptual continuity during eye movements, an alternative hypothesis has been advanced that overestimation of time might be a general effect of any action. Contrary to both of these hypotheses, the experiments reported here suggest that distortions of time perception related to an eye movement are not distinct from temporal distortions for other kinds of responses. Moreover, voluntary action is neither necessary nor sufficient for overestimation effects. These results lead to a new interpretation of chronostasis based on the role of attention and memory in time estimation. |
Keisuke Kawasaki; David L. Sheinberg Learning to recognize visual objects with microstimulation in inferior temporal cortex Journal Article In: Journal of Neurophysiology, vol. 100, no. 1, pp. 197–211, 2008. @article{Kawasaki2008,The malleability of object representations by experience is essential for adaptive behavior. It has been hypothesized that neurons in inferior temporal cortex (IT) in monkeys are pivotal in visual association learning, evidenced by experiments revealing changes in neural selectivity following visual learning, as well as by lesion studies, wherein functional inactivation of IT impairs learning. A critical question remaining to be answered is whether IT neuronal activity is sufficient for learning. To address this question directly, we conducted experiments combining visual classification learning with microstimulation in IT. We assessed the effects of IT microstimulation during learning in cases where the stimulation was exclusively informative, conditionally informative, and informative but not necessary for the classification task. The results show that localized microstimulation in IT can be used to establish visual classification learning, and the same stimulation applied during learning can predictably bias judgments on subsequent recognition. The effect of induced activity can be explained neither by direct stimulation-motor association nor by simple detection of cortical stimulation. We also found that the learning effects are specific to IT stimulation as they are not observed by microstimulation in an adjacent auditory area. Our results add the evidence that the differential activity in IT during visual association learning is sufficient for establishing new associations. The results suggest that experimentally manipulated activity patterns within IT can be effectively combined with ongoing visually induced activity during the formation of new associations. |
Edward L. Keller; Kyoung-Min Lee; Se-Woong Park; Jessica A. Hill Effect of inactivation of the cortical frontal eye field on saccades generated in a choice response paradigm Journal Article In: Journal of Neurophysiology, vol. 100, no. 5, pp. 2726–2737, 2008. @article{Keller2008,Previous studies using muscimol inactivations in the frontal eye fields (FEFs) have shown that saccades generated by recall from working memory are eliminated by these lesions, whereas visually guided saccades are relatively spared. In these experiments, we made reversible inactivations in FEFs in alert macaque monkeys and examined the effect on saccades in a choice response task. Our task required monkeys to learn arbitrary pairings between colored stimuli and saccade direction. Following inactivations, the percentage of choice errors increased as a function of the number of alternative (NA) pairings. In contrast, the percentage of dysmetric saccades (saccades that landed in the correct quadrant but were inaccurate) did not vary with NA. Saccade latency increased postlesion but did not increase with NA. We also made simultaneous inactivations in both FEFs. The results following bilateral lesions showed approximately twice as many choice errors. We conclude that the FEFs are involved in the generation of saccades in choice response tasks. The dramatic effect of NA on choice errors, but the lack of an effect of NA on motor errors or response latency, suggests that two types of processing are interrupted by FEF lesions. The first involves the formation of a saccadic intention vector from associate memory inputs, and the second, the execution of the saccade from the intention vector. An alternative interpretation of the first result is that a role of the FEFs may be to suppress incorrect responses. The doubling of choice errors following bilateral FEF lesions suggests that the effect of unilateral lesions is not caused by a general inhibition of the lesioned side by the intact side. |
Chantal Kemner; Lizet Ewijk; Herman Engeland; Ignace T. C. Hooge Brief report: Eye movements during visual search tasks indicate enhanced stimulus discriminability in subjects with PDD Journal Article In: Journal of Autism and Developmental Disorders, vol. 38, no. 3, pp. 553–558, 2008. @article{Kemner2008,Subjects with PDD excel on certain visuo-spatial tasks, amongst which visual search tasks, and this has been attributed to enhanced perceptual discrimination. However, an alternative explanation is that subjects with PDD show a different, more effective search strategy. The present study aimed to test both hypotheses, by measuring eye movements during visual search tasks in high functioning adult men with PDD and a control group. Subjects with PDD were significantly faster than controls in these tasks, replicating earlier findings in children. Eye movement data showed that subjects with PDD made fewer eye movements than controls. No evidence was found for a different search strategy between the groups. The data indicate an enhanced ability to discriminate between stimulus elements in PDD. |
Dirk Kerzel; Angélique Gauch; Blandine Ulmann Local motion inside an object affects pointing less than smooth pursuit Journal Article In: Experimental Brain Research, vol. 191, no. 2, pp. 187–195, 2008. @article{Kerzel2008,During smooth pursuit eye movements, briefly presented objects are mislocalized in the direction of motion. It has been proposed that the localization error is the sum of the pursuit signal and the retinal motion signal in a ~200 ms interval after flash onset. To evaluate contributions of retinal motion signals produced by the entire object (global motion) and elements within the object (local motion), we asked observers to reach to flashed Gabor patches (Gaussian-windowed sine-wave gratings). Global motion was manipulated by varying the duration of a stationary flash, and local motion was manipulated by varying the motion of the sine-wave. Our results confirm that global retinal motion reduces the localization error. The effect of local retinal motion on object localization was far smaller, even though local and global motion had equal effects on eye velocity. Thus, local retinal motion has differential access to manual and oculomotor control circuits. Further, we observed moderate correlations between smooth pursuit gain and localization error. |
Dirk Kerzel; David Souto; Nathalie E. Ziegler Effects of attention shifts to stationary objects during steady-state smooth pursuit eye movements Journal Article In: Vision Research, vol. 48, no. 7, pp. 958–969, 2008. @article{Kerzel2008a,A number of studies have shown that stationary backgrounds compromise smooth pursuit eye movements. It has been suggested that poor attentional selection of the pursuit target was responsible for reductions of pursuit gain. To quantify the detrimental effects of attention, we instructed observers to either pay attention to background objects or to ignore them. The to-be-attended object was indicated by peripheral or central cues. Strong reductions of pursuit gain occurred when the following conditions were met: (a) the subject payed attention to the object (b) a salient event was present, for instance the onset of the target or cue and (c) the attended target produced retinal motion. Removing any of the three conditions resulted in no or far smaller decreases of pursuit gain. Further, decreases in pursuit gain were present with perceptual discrimination and simple manual detection. |
Andrea E. Martin; Brian McElree A content-addressable pointer mechanism underlies comprehension of verb-phrase ellipsis Journal Article In: Journal of Memory and Language, vol. 58, no. 3, pp. 879–906, 2008. @article{Martin2008,Interpreting a verb-phrase ellipsis (VP ellipsis) requires accessing an antecedent in memory, and then integrating a representation of this antecedent into the local context. We investigated the online interpretation of VP ellipsis in an eye-tracking experiment and four speed-accuracy tradeoff experiments. To investigate whether the antecedent for a VP ellipsis is accessed with a search or direct-access retrieval process, Experiments 1 and 2 measured the effect of the distance between an ellipsis and its antecedent on the speed and accuracy of comprehension. Accuracy was lower with longer distances, indicating that interpolated material reduced the quality of retrieved information about the antecedent. However, contra a search process, distance did not affect the speed of interpreting ellipsis. This pattern suggests that antecedent representations are content-addressable and retrieved with a direct-access process. To determine whether interpreting ellipsis involves copying antecedent information into the ellipsis site, Experiments 3-5 manipulated the length and complexity of the antecedent. Some types of antecedent complexity lowered accuracy, notably, the number of discourse entities in the antecedent. However, neither antecedent length nor complexity affected the speed of interpreting the ellipsis. This pattern is inconsistent with a copy operation, and it suggests that ellipsis interpretation may involve a pointer to extant structures in memory. |
Eric Matheron; Qing Yang; Thanh Thuan Lê; Zoï Kapoula Effects of ocular dominance on the vertical vergence induced by a 2-diopter vertical prism during standing Journal Article In: Neuroscience Letters, vol. 444, no. 2, pp. 176–180, 2008. @article{Matheron2008,This study examined the eye movement responses to vertical disparity induced by a 2-diopter vertical prism base down while in standing position. Vertical vergence movements are known to be small requiring accurate measurement with the head stabilized, and was done with the EyeLink 2. The 2-diopter vertical prism, base down, was inserted in front of either the non-dominant eye (NDE) or dominant eye (DE) at 40 and 200 cm. The results showed that vertical vergence was stronger and excessive relative to the required value (i.e. 1.14°) when the prism was on the NDE for both distances, but more appropriate when the prism was on the DE. The results suggest that sensory disparity process and vertical vergence responses are modulated by eye dominance. |
Alicia Peltsch; Aaron B. Hoffman; I. T. Armstrong; Giovanna Pari; D. P. Munoz Saccadic impairments in Huntington's disease Journal Article In: Experimental Brain Research, vol. 186, no. 3, pp. 457–469, 2008. @article{Peltsch2008,Huntington's disease (HD), a progressive neurological disorder involving degeneration in basal ganglia structures, leads to abnormal control of saccadic eye movements. We investigated whether saccadic impairments in HD (N = 9) correlated with clinical disease severity to determine the relationship between saccadic control and basal ganglia pathology. HD patients and age/sex-matched controls performed various eye movement tasks that required the execution or suppression of automatic or voluntary saccades. In the "immediate" saccade tasks, subjects were instructed to look either toward (pro-saccade) or away from (anti-saccade) a peripheral stimulus. In the "delayed" saccade tasks (pro-/anti-saccades; delayed memory-guided sequential saccades), subjects were instructed to wait for a central fixation point to disappear before initiating saccades towards or away from a peripheral stimulus that had appeared previously. In all tasks, mean saccadic reaction time was longer and more variable amongst the HD patients. On immediate anti-saccade trials, the occurrence of direction errors (pro-saccades initiated toward stimulus) was higher in the HD patients. In the delayed tasks, timing errors (eye movements made prior to the go signal) were also greater in the HD patients. The increased variability in saccadic reaction times and occurrence of errors (both timing and direction errors) were highly correlated with disease severity, as assessed with the Unified Huntington's Disease Rating Scale, suggesting that saccadic impairments worsen as the disease progresses. Thus, performance on voluntary saccade paradigms provides a sensitive indicator of disease progression in HD. |
Angélica Pérez Fornos; Jörg Sommerhalder; Alexandre Pittard; Avinoam B. Safran; Marco Pelizzone Simulation of artificial vision: IV. Visual information required to achieve simple pointing and manipulation tasks Journal Article In: Vision Research, vol. 48, no. 16, pp. 1705–1718, 2008. @article{PerezFornos2008,Retinal prostheses attempt to restore some amount of vision to totally blind patients. Vision evoked this way will be however severely constrained because of several factors (e.g., size of the implanted device, number of stimulating contacts, etc.). We used simulations of artificial vision to study how such restrictions of the amount of visual information provided would affect performance on simple pointing and manipulation tasks. Five normal subjects participated in the study. Two tasks were used: pointing on random targets (LEDs task) and arranging wooden chips according to a given model (CHIPs task). Both tasks had to be completed while the amount of visual information was limited by reducing the resolution (number of pixels) and modifying the size of the effective field of view. All images were projected on a 10° × 7° viewing area, stabilised at a given position on the retina. In central vision, the time required to accomplish the tasks remained systematically slower than with normal vision. Accuracy was close to normal at high image resolutions and decreased at 500 pixels or below, depending on the field of view used. Subjects adapted quite rapidly (in less than 15 sessions) to performing both tasks in eccentric vision (15° in the lower visual field), achieving after adaptation performances close to those observed in central vision. These results demonstrate that, if vision is restricted to a small visual area stabilised on the retina (as would be the case in a retinal prosthesis), the perception of several hundreds of retinotopically arranged phosphenes is still needed to restore accurate but slow performance on pointing and manipulation tasks. Considering that present prototypes afford less than 100 stimulation contacts and that our simulations represent the most favourable visual input conditions that the user might experience, further development is required to achieve optimal rehabilitation prospects. |
Matthew S. Peterson; Melissa R. Beck; Jason H. Wong Were you paying attention to where you looked? The role of executive working memory in visual search Journal Article In: Psychonomic Bulletin & Review, vol. 15, no. 2, pp. 372–377, 2008. @article{Peterson2008,Recent evidence has indicated that performing a working memory task that loads executive working memory leads to less efficient visual search (Han & Kim, 2004). We explored the role that executive functioning plays in visual search by examining the pattern of eye movements while participants performed a search task with or without a secondary executive working memory task. Results indicate that executive functioning plays two roles in visual search: the identification of objects and the control of the disengagement of attention. |
Tobias Pflugshaupt; Thomas Nyffeler; Roman Von Wartburg; Christian W. Hess; René M. Müri Loss of exploratory vertical saccades after unilateral frontal eye field damage Journal Article In: Journal of Neurology, Neurosurgery and Psychiatry, vol. 79, no. 4, pp. 474–477, 2008. @article{Pflugshaupt2008,Despite their relevance for locomotion and social interaction in everyday situations, little is known about the cortical control of vertical saccades in humans. Results from microstimulation studies indicate that both frontal eye fields (FEFs) contribute to these eye movements. Here, we present a patient with a damaged right FEF, who hardly made vertical saccades during visual exploration. This finding suggests that, for the cortical control of exploratory vertical saccades, integrity of both FEFs is indeed important. |
Matthew H. Phillips; Jay A. Edelman The dependence of visual scanning performance on search direction and difficulty Journal Article In: Vision Research, vol. 48, no. 21, pp. 2184–2192, 2008. @article{Phillips2008,Phillips and Edelman [Phillips, M. H., & Edelman, J. A. (2008). The dependence of visual scanning performance on saccade, fixation, and perceptual metrics. Vision Research, 48(7), 926-936] presented evidence that performance variability in a visual scanning task depends on oculomotor variables related to saccade amplitude rather than fixation duration, and that saccade-related metrics reflects perceptual span. Here, we extend these results by showing that even for extremely difficult searches trial-to-trial performance variability still depends on saccade-related metrics and not fixation duration. We also show that scanning speed is faster for horizontal than for vertical searches, and that these differences derive again from differences in saccade-based metrics and not from differences in fixation duration. We find perceptual span to be larger for horizontal than vertical searches, and approximately symmetric about the line of gaze. |
Antonio F. Macedo; Michael D. Crossland; Gary S. Rubin The effect of retinal image slip on peripheral visual acuity Journal Article In: Journal of Vision, vol. 8, no. 14, pp. 1–11, 2008. @article{Macedo2008,Retinal image slip promoted by fixational eye movements prevents image fading in central vision. However, in the periphery a higher amount of movement is necessary to prevent this fading. We assessed the effect of different levels of retinal image slip in peripheral vision by measuring peripheral visual acuity (VA), with and without crowding, while modulating retinal eccentricity. Gaze position was monitored throughout using an infrared eyetracker. The target was presented for up to 500 msec, either with no retinal image slip, with reduced retinal slip, or with increased retinal image slip. Without crowding, peripheral visual acuity improved with increased retinal image slip compared with the other two conditions. IN contrast to the previous result, under crowded conditions, peripheral visual acuity decreased markedly with increased retinal image slip. Therefore, the effects of increased retinal image slip are different for simple (noncrowded) and more complex (crowded) visual tasks. These results provide further evidence for the importance of fixation stability on complex visual tasks when using the peripheral retina. |
James S. Magnuson; Michael K. Tanenhaus; Richard N. Aslin Immediate effects of form-class constraints on spoken word recognition Journal Article In: Cognition, vol. 108, no. 3, pp. 866–873, 2008. @article{Magnuson2008,In many domains of cognitive processing there is strong support for bottom-up priority and delayed top-down (contextual) integration. We ask whether this applies to supra-lexical context that could potentially constrain lexical access. Previous findings of early context integration in word recognition have typically used constraints that can be linked to pair-wise conceptual relations between words. Using an artificial lexicon, we found immediate integration of syntactic expectations based on pragmatic constraints linked to syntactic categories rather than words: phonologically similar "nouns" and "adjectives" did not compete when a combination of syntactic and visual information strongly predicted form class. These results suggest that predictive context is integrated continuously, and that previous findings supporting delayed context integration stem from weak contexts rather than delayed integration. |
George L. Malcolm; Linda J. Lanyon; Andrew J. B. Fugard; Jason J. S. Barton Scan patterns during the processing of facial expression versus identity: An exploration of task-driven and stimulus-driven effects Journal Article In: Journal of Vision, vol. 8, no. 8, pp. 1–9, 2008. @article{Malcolm2008,Perceptual studies suggest that processing facial identity emphasizes upper-face information, whereas processing expressions of anger or happiness emphasizes the lower-face. The two goals of the present study were to determine (a) if the distributions of eye fixations reflect these upper/lower-face biases, and (b) whether this bias is task- or stimulus-driven. We presented a target face followed by a probe pair of morphed faces, neither of which was identical to the target. Subjects judged which of the pair was more similar to the target face while eye movements were recorded. In Experiment 1 the probe pair always differed from each other in both identity and expression on each trial. In one block subjects judged which probe face was more similar to the target face in identity, and in a second block subjects judged which probe face was more similar to the target face in expression. In Experiment 2 the two probe faces differed in either expression or identity, but not both. Subjects were not informed which dimension differed, but simply asked to judge which probe face was more similar to the target face. We found that subjects scanned the upper-face more than the lower-face during the identity task but the lower-face more than the upper-face during the expression task in Experiment 1 (task-driven effects), with significantly less variation in bias in Experiment 2 (stimulus-driven effects). We conclude that fixations correlate with regional variations of diagnostic information in different processing tasks, but that these reflect top-down task-driven guidance of information acquisition more than stimulus-driven effects. |
David Melcher Dynamic, object-based remapping of visual features in trans-saccadic perception Journal Article In: Journal of Vision, vol. 8, no. 14, pp. 1–17, 2008. @article{Melcher2008,Saccadic eye movements can dramatically change the location in which an object is projected onto the retina. One mechanism that might potentially underlie the perception of stable objects, despite the occurrence of saccades, is the "remapping" of receptive fields around the time of saccadic eye movements. Here we examined two possible models of trans-saccadic remapping of visual features: (1) spatiotopic coordinates that remain constant across saccades or (2) an object-based remapping in retinal coordinates. We used form adaptation to test "object" and "space" based predictions for an adapter that changed spatial and/or retinal location due to eye movements, object motion or manual displacement using a computer mouse. The predictability and speed of the object motion was also manipulated. The main finding was that maximum transfer of the form aftereffect in retinal coordinates occurred when there was a saccade and when the object motion was attended and predictable. A small transfer was also found when observers moved the object across the screen using a computer mouse. The overall pattern of results is consistent with the theory of object-based remapping for salient stimuli. Thus, the active updating of the location and features of attended objects may play a role in perceptual stability. |
Xiaochuan Pan; Kosuke Sawa; Ichiro Tsuda; Minoru Tsukada; Masamichi Sakagami Reward prediction based on stimulus categorization in primate lateral prefrontal cortex Journal Article In: Nature Neuroscience, vol. 11, no. 6, pp. 703–712, 2008. @article{Pan2008,To adapt to changeable or unfamiliar environments, it is important that animals develop strategies for goal-directed behaviors that meet the new challenges. We used a sequential paired-association task with asymmetric reward schedule to investigate how prefrontal neurons integrate multiple already-acquired associations to predict reward. Two types of reward-related neurons were observed in the lateral prefrontal cortex: one type predicted reward independent of physical properties of visual stimuli and the other encoded the reward value specific to a category of stimuli defined by the task requirements. Neurons of the latter type were able to predict reward on the basis of stimuli that had not yet been associated with reward, provided that another stimulus from the same category was paired with reward. The results suggest that prefrontal neurons can represent reward information on the basis of category and propagate this information to category members that have not been linked directly with any experience of reward. |
Sebastian Pannasch; Jens R. Helmert; Katharina Roth; Ann-Katrin Herbold; Henrik Walter Visual fixation durations and saccade amplitudes: Shifting relationship in a variety of conditions Journal Article In: Journal of Eye Movement Research, vol. 2, no. 2, pp. 1–19, 2008. @article{Pannasch2008,Is there any relationship between visual fixation durations and saccade amplitudes in free exploration of pictures and scenes? In four experiments with naturalistic stimuli, we compared eye movements during early and late phases of scene perception. Influences of repeated presentation of similar stimuli (Experiment 1), object density (Experiment 2), emotional stimuli (Experiment 3) and mood induction (Experiment 4) were examined. The results demonstrate a systematic increase in the durations of fixations and a decrease for saccadic amplitudes over the time course of scene perception. This relationship was very stable across the variety of studied conditions. It can be interpreted in terms of a shifting balance of the two modes of visual information processing. |
Elmar H. Pinkhardt; Reinhart Jürgens; Wolfgang Becker; Federica Valdarno; Albert C. Ludolph; Jan Kassubek Differential diagnostic value of eye movement recording in PSP-parkinsonism, Richardson's syndrome, and idiopathic Parkinson's disease Journal Article In: Journal of Neurology, vol. 255, no. 12, pp. 1916–1925, 2008. @article{Pinkhardt2008,Vertical gaze palsy is a highly relevant clinical sign in parkinsonian syndromes. As the eponymous sign of progressive supranuclear palsy (PSP), it is one of the core features in the diagnosis of this disease. Recent studies have suggested a further differentiation of PSP in Richardson's syndrome (RS) and PSP-parkinsonism (PSPP). The aim of this study was to search for oculomotor abnormalities in the PSP-P subset of a sample of PSP patients and to compare these findings with those of (i) RS patients, (ii) patients with idiopathic Parkinson's disease (IPD), and (iii) a control group. Twelve cases of RS, 5 cases of PSP-P, and 27 cases of IPD were examined by use of video-oculography (VOG) and compared to 23 healthy normal controls. Both groups of PSP patients (RS, PSP-P) had significantly slower saccades than either IPD patients or controls, whereas no differences in saccadic eye peak velocity were found between the two PSP groups or in the comparison of IPD with controls. RS and PSP-P were also similar to each other with regard to smooth pursuit eye movements (SPEM), with both groups having significantly lower gain than controls (except for downward pursuit); however, SPEM gain exhibited no consistent difference between PSP and IPD. A correlation between eye movement data and clinical data (Hoehn & Yahr scale or disease duration) could not be observed. As PSP-P patients were still in an early stage of the disease when a differentiation from IPD is difficult on clinical grounds, the clear-cut separation between PSP-P and IPD obtained by measuring saccade velocity suggests that VOG could contribute to the early differentiation between these patient groups. |
Alexander Pollatsek; Timothy J. Slattery; Barbara J. Juhasz The processing of novel and lexicalised prefixed words in reading Journal Article In: Language and Cognitive Processes, vol. 23, no. 7-8, pp. 1133–1158, 2008. @article{Pollatsek2008,Two experiments compared how relatively long novel prefixed words (e.g., overfarm) and existing prefixed words were processed in reading. The use of novel prefixed words allows one to examine the roles of whole-word access and decompositional processing in the processing of non-novel prefixed words. The two experiments found that, although there was a large cost to novelty (e.g., gaze durations were about 100 ms longer for novel prefixedwords), the effect of the frequency of the root morpheme on fixation measures was about the same for novel and non-novel prefixed words for most measures. This finding rules out a (‘‘horse-race'') dual-route model of processing for existing prefixed words in which the whole-word and decompositional route are parallel and independent, as such a model would predict a substantially larger root frequency effect for novel words (where whole-word processes do not exist). The most likely model to explain the processing of prefixed words is a parallel interactive one. |
Jason S. McCarley; Christopher Grant State-trace analysis of the effects of a visual illusion on saccade amplitudes and perceptual judgments Journal Article In: Psychonomic Bulletin & Review, vol. 15, no. 5, pp. 1008–1014, 2008. @article{McCarley2008,Visual illusions often appear to have a larger influence on subjective judgments than on visuomotor behavior. Although this effect has been taken as evidence for multiple estimates of stimulus size in the visual brain, dissociations between subjective judgments and visuomotor measures can frequently be reconciled with a single-estimate model. To circumvent this difficulty, we used state-trace analysis in a pair of experiments to examine the effects of the Müller-Lyer illusion on subjective length estimates, voluntary saccade amplitudes, and reflexive saccade amplitudes. All dependent measures were affected by the illusion. However, state-trace analyses revealed nonmonotonic relationships among all three variables, a pattern inconsistent with the possibility of a single underlying estimate of stimulus size. |
Bob McMurray; Richard N. Aslin; Michael K. Tanenhaus; Michael J. Spivey; Dana Subik Gradient sensitivity to within-category variation in words and syllables Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 34, no. 6, pp. 1609–1631, 2008. @article{McMurray2008,Five experiments monitored eye movements in phoneme and lexical identification tasks to examine the effect of within-category subphonetic variation on the perception of stop consonants. Experiment 1 demonstrated gradient effects along voice-onset time (VOT) continua made from natural speech, replicating results with synthetic speech (B. McMurray, M. K. Tanenhaus, & R. N. Aslin, 2002). Experiments 2-5 used synthetic VOT continua to examine effects of response alternatives (2 vs. 4), task (lexical vs. phoneme decision), and type of token (word vs. consonant-vowel). A gradient effect of VOT in at least one half of the continuum was observed in all conditions. These results suggest that during online spoken word recognition, lexical competitors are activated in proportion to their continuous distance from a category boundary. This gradient processing may allow listeners to anticipate upcoming acoustic-phonetic information in the speech signal and dynamically compensate for acoustic variability. |
Bob McMurray; Meghan Clayards; Michael K. Tanenhaus; Richard N. Aslin Tracking the time course of phonetic cue integration during spoken word recognition Journal Article In: Psychonomic Bulletin & Review, vol. 15, no. 6, pp. 1064–1071, 2008. @article{McMurray2008a,Speech perception requires listeners to integrate multiple cues that each contribute to judgments about a phonetic category. Classic studies of trading relations assessed the weights attached to each cue but did not explore the time course of cue integration. Here, we provide the first direct evidence that asynchronous cues to voicing (/b/ vs. /p/) and manner (/b/ vs. /w/) contrasts become available to the listener at different times during spoken word recognition. Using the visual world paradigm, we show that the probability of eye movements to pictures of target and of competitor objects diverge at different points in time after the onset of the target word. These points of divergence correspond to the availability of early (voice onset time or formant transition slope) and late (vowel length) cues to voicing and manner contrasts. These results support a model of cue integration in which phonetic cues are used for lexical access as soon as they are available. |
Rike Steenken; Hans Colonius; Adele Diederich; Stefan Rach Visual-auditory interaction in saccadic reaction time: Effects of auditory masker level Journal Article In: Brain Research, vol. 1220, pp. 150–156, 2008. @article{Steenken2008,Saccadic reaction time (SRT) to a visual target tends to be shorter when auditory stimuli are presented in close temporal and spatial proximity, even when subjects are instructed to ignore the auditory non-target (focused attention paradigm). Observed SRT reductions typically range between 10 and 50 ms and decrease as spatial disparity between the stimuli increases. Previous studies using pairs of visual and auditory stimuli differing in both azimuth and vertical position suggest that the amount of SRT facilitation decreases not with the physical but with the perceivable distance between visual target and auditory accessory. Here we probe this hypothesis by presenting an additional white-noise masker background of 3 s duration. Increasing the masker level had a diametrical effect on SRTs in spatially coincident vs. disparate stimulus configurations: saccadic responses to coincident visual-auditory stimuli are slowed down, whereas saccadic responses to disparate stimuli are speeded up. As verified in a separate auditory localization task, localizability of the auditory accessory decreases with masker level. The SRT results are accounted for by a conceptual model positing that increasing masker level enlarges the area of possible auditory stimulus locations: it implies that perceivable distances decrease for disparate stimulus configurations and increase for coincident stimulus pairs. |
Rike Steenken; Adele Diederich; Hans Colonius Time course of auditory masker effects: Tapping the locus of audiovisual integration? Journal Article In: Neuroscience Letters, vol. 435, no. 1, pp. 78–83, 2008. @article{Steenken2008a,In a focused attention paradigm, saccadic reaction time (SRT) to a visual target tends to be shorter when an auditory accessory stimulus is presented in close temporal and spatial proximity. Observed SRT reductions typically diminish as spatial disparity between the stimuli increases. Here a visual target LED (500 ms duration) was presented above or below the fixation point and a simultaneously presented auditory accessory (2 ms duration) could appear at the same or the opposite vertical position. SRT enhancement was about 35 ms in the coincident and 10 ms in the disparate condition. In order to further probe the audiovisual integration mechanism, in addition to the auditory non-target an auditory masker (200 ms duration) was presented before, simultaneous to, or after the accessory stimulus. In all interstimulus interval (ISI) conditions, SRT enhancement went down both in the coincident and disparate configuration, but this decrement was fairly stable across the ISI values. If multisensory integration solely relied on a feed-forward process, one would expect a monotonic decrease of the masker effect with increasing ISI in the backward masking condition. It is therefore conceivable that the relatively high-energetic masker causes a broad excitatory response of SC neurons. During this state, the spatial audio-visual information from multisensory association areas is fed back and merged with the spatially unspecific excitation pattern induced by the masker. Assuming that a certain threshold of activation has to be achieved in order to generate a saccade in the correct direction, the blurred joint output of noise and spatial audio-visual information needs more time to reach this threshold prolonging SRT to an audio-visual object. |
Timo Stein; Ignacio Vallines; Werner X. Schneider Primary visual cortex repoundsects behavioral performance in the attentional blink Journal Article In: NeuroReport, vol. 19, no. 13, pp. 1277–1281, 2008. @article{Stein2008,When two masked targets are presented in a rapid sequence, attentional limitations are reflected in reduced identification accuracy for the second target (T2). We used functional magnetic resonance imaging to disentangle the distinct neural substrates of T2 processing during this attentional blink phenomenon. Spatially separating the two targets allows the retinotopic localization of the different stimuli's encoding sites in primary visual cortex (V1) and thus enables activation elicited by each target to be differentially measured in V1. The encoding location of the second target mirrored T2 identification accuracy in a retinotopically specific manner. These results are the first evidence for effects of behavioral performance on hemodynamic responses in V1 under conditions of the attentional blink. |
Brian Sullivan; Jelena Jovancevic-Misic; Mary Hayhoe; Gwen Sterns Use of multiple preferred retinal loci in Stargardt's disease during natural tasks: A case study Journal Article In: Ophthalmic and Physiological Optics, vol. 28, no. 2, pp. 168–177, 2008. @article{Sullivan2008,Individuals with central visual field loss often use a preferred retinal locus (PRL) to compensate for their deficit. We present a case study examining the eye movements of a subject with Stargardt's disease causing bilateral central scotomas, while performing a set of natural tasks including: making a sandwich; building a model; reaching and grasping; and catching a ball. In general, the subject preferred to use PRLs in the lower left visual field. However, there was considerable variation in the location and extent of the PRLs used. Our results demonstrate that a well-defined PRL is not necessary to adequately perform this set of tasks and that many sites in the peripheral retina may be viable for PRLs, contingent on task and stimulus constraints. |
Joshua M. Susskind; Daniel H. Lee; Andrée Cusi; Roman Feiman; Wojtek Grabski; Adam K. Anderson Expressing fear enhances sensory acquisition Journal Article In: Nature Neuroscience, vol. 11, no. 7, pp. 843–850, 2008. @article{Susskind2008,It has been proposed that facial expression production originates in sensory regulation. Here we demonstrate that facial expressions of fear are configured to enhance sensory acquisition. A statistical model of expression appearance revealed that fear and disgust expressions have opposite shape and surface reflectance features. We hypothesized that this reflects a fundamental antagonism serving to augment versus diminish sensory exposure. In keeping with this hypothesis, when subjects posed expressions of fear, they had a subjectively larger visual field, faster eye movements during target localization and an increase in nasal volume and air velocity during inspiration. The opposite pattern was found for disgust. Fear may therefore work to enhance perception, whereas disgust dampens it. These convergent results provide support for the Darwinian hypothesis that facial expressions are not arbitrary configurations for social communication, but rather, expressions may have originated in altering the sensory interface with the physical world. |
Giovanni Taibbi; Zhong I. Wang; Louis F. Dell'Osso Infantile nystagmus syndrome : Broadening the high-foveation-quality fi eld with contact lenses Journal Article In: Ophthalmology, vol. 2, no. 3, pp. 585–589, 2008. @article{Taibbi2008,We investigated the effects of contact lenses in broadening and improving the high-foveation-quality fi eld in a subject with infantile nystagmus syndrome (INS). A high-speed, digitized video system was used for the eye-movement recording. The subject was asked to fi xate a far target at different horizontal gaze angles with contact lenses inserted. Data from the subject while fi xating at far without refractive correction and at near (at a convergence angle of 60 PD), were used for comparison. The eXpanded Nystagmus Acuity Function (NAFX) was used to evaluate the foveation quality at each gaze angle. Contact lenses broadened the high- foveation-quality range of gaze angles in this subject. The broadening was comparable to that achieved during 60 PD of convergence although the NAFX values were lower. Contact lenses allowed the subject to see “more” (he had a wider range of high-foveation-quality gaze angles) and “better” (he had improved foveation at each gaze angle). Instead of being contraindicated by INS, contact lenses emerge as a potentially important therapeutic option. Contact lenses employ afferent feedback via the ophthalmic division of the V cranial nerve to damp INS slow phases over a broadened range of gaze angles. This supports the proprioceptive hypothesis of INS improvement. |
Kohske Takahashi; Katsumi Watanabe Persisting effect of prior experience of change blindness Journal Article In: Perception, vol. 37, no. 2, pp. 324–327, 2008. @article{Takahashi2008,Most cognitive scientists know that an airplane tends to lose its engine when the display is flickering. How does such prior experience influence visual search? We recorded eye movements made by vision researchers while they were actively performing a change-detection task. In selected trials, we presented Rensink's familiar 'airplane' display, but with changes occurring at locations other than the jet engine. The observers immediately noticed that there was no change in the location where the engine had changed in the previous change-blindness demonstration. Nevertheless, eye-movement analyses indicated that the observers were compelled to look at the location of the unchanged engine. These results demonstrate the powerful effect of prior experience on eye movements, even when the observers are aware of the futility of doing so. |
Tim J. Smith; John M. Henderson Edit Blindness: The relationship between attention and global change blindness in dynamic scenes Journal Article In: Journal of Eye Movement Research, vol. 2, no. 2, pp. 1–17, 2008. @article{Smith2008,Although we experience the visual world as a continuous, richly detailed space we often fail to notice large and significant changes. Such change blindness has been demonstrated for local object changes and changes to the visual form of whole images, however it is assumed that total changes from one image to another would be easily detected. Film editing presents such total changes several times a minute yet we rarely seem to be aware of them, a phenomenon we refer to here as edit blindness. This phenomenon has never been empirically demonstrated even though film editors believe they have at their disposal techniques that induce edit blindness, the Continuity Editing Rules. In the present study we tested the relationship between Continuity Editing Rules and edit blindness by instructing participants to detect edits while watching excerpts from feature films. Eye movements were recorded during the task. The results indicate that edits constructed according to the Continuity Editing Rules result in greater edit blindness than edits not adhering to the rules. A quarter of edits joining two viewpoints of the same scene were undetected and this increased to a third when the edit coincided with a sudden onset of motion. Some cuts may be missed due to suppression of the cut transients by coinciding with eyeblinks or saccadic eye movements but the majority seem to be due to inattentional blindness as viewers attend to the depicted narrative. In conclusion, this study presents the first empirical evidence of edit blindness and its relationship to natural attentional behaviour during dynamic scene viewing. |
J. F. Soechting; Martha Flanders Extrapolation of visual motion for manual interception Journal Article In: Journal of Neurophysiology, vol. 99, no. 6, pp. 2956–2967, 2008. @article{Soechting2008,A frequent goal of hand movement is to touch a moving target or to make contact with a stationary object that is in motion relative to the moving head and body. This process requires a prediction of the target's motion, since the initial direction of the hand movement anticipates target motion. This experiment was designed to define the visual motion parameters that are incorporated in this prediction of target motion. On seeing a go signal (a change in target color), human subjects slid the right index finger along a touch-sensitive computer monitor to intercept a target moving along an unseen circular or oval path. The analysis focused on the initial direction of the interception movement, which was found to be influenced by the time required to intercept the target and the target's distance from the finger's starting location. Initial direction also depended on the curvature of the target's trajectory in a manner that suggested that this parameter was underestimated during the process of extrapolation. The pattern of smooth pursuit eye movements suggests that the extrapolation of visual target motion was based on local motion cues around the time of the onset of hand movement, rather than on a cognitive synthesis of the target's pattern of motion. |
Alexandra Soliman; Gillian A. O'Driscoll; Jens Pruessner; Anne Lise V. Holahan; Isabelle Boileau; Danny Gagnon; Alain Dagher Stress-induced dopamine release in humans at risk of psychosis: A [ "C] raclopride PET study Journal Article In: Neuropsychopharmacology, vol. 33, no. 8, pp. 2033–2041, 2008. @article{Soliman2008,Drugs that increase dopamine levels in the brain can cause psychotic symptoms in healthy individuals and worsen them in schizophrenic patients. Psychological stress also increases dopamine release and is thought to play a role in susceptibility to psychotic illness. We hypothesized that healthy individuals at elevated risk of developing psychosis would show greater striatal dopamine release than controls in response to stress. Using positron emission tomography and [(11)C]raclopride, we measured changes in synaptic dopamine concentrations in 10 controls and 16 psychometric schizotypes; 9 with perceptual aberrations (PerAb, ie positive schizotypy) and 7 with physical anhedonia (PhysAn, ie negative schizotypy). [(11)C]Raclopride binding potential was measured during a psychological stress task and a sensory-motor control. All three groups showed significant increases in self-reported stress and cortisol levels between the stress and control conditions. However, only the PhysAn group showed significant stress-induced dopamine release. Dopamine release in the entire sample was significantly negatively correlated with smooth pursuit gain, an endophenotype linked to frontal lobe function. Our findings suggest the presence of abnormalities in the dopamine response to stress in negative symptom schizotypy, and provide indirect evidence of a link to frontal function. |
Gianluca U. Sorrento; Denise Y. P. Henriques Reference frame conversions for repeated arm movements Journal Article In: Journal of Neurophysiology, vol. 99, no. 6, pp. 2968–2984, 2008. @article{Sorrento2008,The aim of this study was to further understand how the brain represents spatial information for shaping aiming movements to targets. Both behavioral and neurophysiological studies have shown that the brain represents spatial memory for reaching targets in an eye-fixed frame. To date, these studies have only shown how the brain stores and updates target locations for generating a single arm movement. But once a target's location has been computed relative to the hand to program a pointing movement, is that information reused for subsequent movements to the same location? Or is the remembered target location reconverted from eye to motor coordinates each time a pointing movement is made? To test between these two possibilities, we had subjects point twice to the remembered location of a previously foveated target after shifting their gaze to the opposite side of the target site before each pointing movement. When we compared the direction of pointing errors for the second movement to those of the first, we found that errors for each movement varied as a function of current gaze so that pointing endpoints fell on opposite sides of the remembered target site in the same trial. Our results suggest that when shaping multiple pointing movements to the same location the brain does not use information from the previous arm movement such as an arm-fixed representation of the target but instead mainly uses the updated eye-fixed representation of the target to recalculate its location into the appropriate motor frame. |
Jan L. Souman; Tom C. A. Freeman Motion perception during sinusoidal smooth pursuit eye movements: Signal latencies and non-linearities Journal Article In: Journal of Vision, vol. 8, no. 14, pp. 1–14, 2008. @article{Souman2008,Smooth pursuit eye movements add motion to the retinal image. To compensate, the visual system can combine estimates of pursuit velocity and retinal motion to recover motion with respect to the head. Little attention has been paid to the temporal characteristics of this compensation process. Here, we describe how the latency difference between the eye movement signal and the retinal signal can be measured for motion perception during sinusoidal pursuit. In two experiments, observers compared the peak velocity of a motion stimulus presented in pursuit and fixation intervals. Both the pursuit target and the motion stimulus moved with a sinusoidal profile. The phase and amplitude of the motion stimulus were varied systematically in different conditions, along with the amplitude of pursuit. The latency difference between the eye movement signal and the retinal signal was measured by fitting the standard linear model and a non-linear variant to the observed velocity matches. We found that the eye movement signal lagged the retinal signal by a small amount. The non-linear model fitted the velocity matches better than the linear one and this difference increased with pursuit amplitude. The results support previous claims that the visual system estimates eye movement velocity and retinal velocity in a non-linear fashion and that the latency difference between the two signals is small. |
David Souto; Dirk Kerzel Dynamics of attention during the initiation of smooth pursuit eye movements Journal Article In: Journal of Vision, vol. 8, no. 14, pp. 3–1–16, 2008. @article{Souto2008,Many studies indicate that saccades are necessarily preceded by a shift of attention to the target location. There is no direct evidence for the same coupling during smooth pursuit. If smooth pursuit and attention were coupled, pursuit onset should be delayed whenever attention is focused on a stationary, non-target location. To test this hypothesis, observers were instructed to shift their attention to a peripheral location according to a location cue (Experiments 1 and 2) or a symbolic cue (Experiment 3) around the time of smooth pursuit initiation. Attending to static targets had only negligible effects on smooth pursuit latencies and the early open-loop response but lowered pursuit velocity substantially about the onset of closed-loop pursuit. Around this time, eye velocity reflected the competition between the to-be-tracked and to-be-attended object motion, entailing a reduction of eye velocity by 50% compared to the single task condition. The precise time course of attentional modulation of smooth pursuit initiation was at odds with the idea that an attention shift must precede any voluntary eye movement. Finally, the initial catch-up saccades were strongly delayed with attention diverted from the pursuit target. Implications for models of target selection for pursuit and saccades are discussed. |
Miriam Spering; Anna Montagnini; Karl R. Gegenfurtner Competition between color and luminance for target selection in smooth pursuit and saccadic eye movements Journal Article In: Journal of Vision, vol. 8, no. 15, pp. 1–19, 2008. @article{Spering,Visual processing of color and luminance for smooth pursuit and saccadic eye movements was investigated using a target selection paradigm. In two experiments, stimuli were varied along the dimensions color and luminance, and selection of the more salient target was compared in pursuit and saccades. Initial pursuit was biased in the direction of the luminance component whereas saccades showed a relative preference for color. An early pursuit response toward luminance was often reversed to color by a later saccade. Observers' perceptual judgments of stimulus salience, obtained in two control experiments, were clearly biased toward luminance. This choice bias in perceptual data implies that the initial short-latency pursuit response agrees with perceptual judgments. In contrast, saccades, which have a longer latency than pursuit, do not seem to follow the perceptual judgment of salience but instead show a stronger relative preference for color. These substantial differences in target selection imply that target selection processes for pursuit and saccadic eye movements use distinctly different weights for color and luminance stimuli. |
Benjamin W. Tatler; Benjamin T. Vincent Systematic tendencies in scene viewing Journal Article In: Journal of Eye Movement Research, vol. 2, no. 2, pp. 1–18, 2008. @article{Tatler2008,While many current models of scene perception debate the relative roles of low- and high- level factors in eye guidance, systematic tendencies in how the eyes move may be infor- mative. We consider how each saccade and fixation is influenced by that which preceded or followed it, during free inspection of images of natural scenes. We find evidence to suggest periods of localized scanning separated by ‘global' relocations to new regions of the scene. We also find evidence to support the existence of small amplitude ‘corrective' saccades in natural image viewing. Our data reveal statistical dependencies between suc- cessive eye movements, which may be informative in furthering our understanding of eye guidance. |
Benjamin W. Tatler; Nicholas J. Wade; Kathrin Kaulard Examining art: Dissociating pattern and perceptual influences on oculomotor behaviour Journal Article In: Spatial Vision, vol. 21, no. 1, pp. 165–184, 2008. @article{Tatler2008a,When observing art the viewer's understanding results from the interplay between the marks made on the surface by the artist and the viewer's perception and knowledge of it. Here we use a novel set of stimuli to dissociate the influences of the marks on the surface and the viewer's perceptual experience upon the manner in which the viewer inspects art. Our stimuli provide the opportunity to study situations in which (1) the same visual stimulus can give rise to two different perceptual experiences in the viewer, and (2) the visual stimuli differ but give rise to the same perceptual experience in the viewer. We find that oculomotor behaviour changes when the perceptual experience changes. Oculomotor behaviour also differs when the viewer's perceptual experience is the same but the visual stimulus is different. The methodology used and insights gained from this study offer a first step toward an experimental exploration of the relative influences of the artist's creation and viewer's perception when viewing art and also toward a better understanding of the principles of composition in portraiture. |
T. Teichert; Steffen Klingenhoefer; T. Wachtler; Frank Bremmer Depth perception during saccades Journal Article In: Journal of Vision, vol. 8, no. 14, pp. 1–13, 2008. @article{Teichert2008,A number of studies have investigated the localization of briefly flashed targets during saccades to understand how the brain perceptually compensates for changes in gaze direction. Typical version saccades, i.e., saccades between two points of the horopter, are not only associated with changes in gaze direction, but also with large transient changes of ocular vergence. These transient changes in vergence have to be compensated for just as changes in gaze direction. We investigated depth judgments of perisaccadically flashed stimuli relative to continuously present references and report several novel findings. First, disparity thresholds increased around saccade onset. Second, for horizontal saccades, depth judgments were prone to systematic errors: Stimuli flashed around saccade onset were perceived in a closer depth plane than persistently shown references with the same retinal disparity. Briefly before and after this period, flashed stimuli tended to be perceived in a farther depth plane. Third, depth judgments for upward and downward saccades differed substantially: For upward, but not for downward saccades we observed the same pattern of mislocalization as for horizontal saccades. Finally, unlike localization in the fronto-parallel plane, depth judgments did not critically depend on the presence of visual references. Current models fail to account for the observed pattern of mislocalization in depth. |
Masahiko Terao; Junji Watanabe; Akihiro Yagi; Shin'ya Nishida Reduction of stimulus visibility compresses apparent time intervals Journal Article In: Nature Neuroscience, vol. 11, no. 5, pp. 541–542, 2008. @article{Terao2008,The neural mechanisms underlying visual estimation of subsecond durations remain unknown, but perisaccadic underestimation of interflash intervals may provide a clue as to the nature of these mechanisms. Here we found that simply reducing the flash visibility, particularly the visibility of transient signals, induced similar time underestimation by human observers. Our results suggest that weak transient responses fail to trigger the proper detection of temporal asynchrony, leading to increased perception of simultaneity and apparent time compression. |
Marco Thiel; M. Carmen Romano; Jürgen Kurths; Martin Rolfs; Reinhold Kliegl Generating surrogates from recurrences Journal Article In: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 366, pp. 545–557, 2008. @article{Thiel2008,In this paper, we present an approach to recover the dynamics from recurrences of a system and then generate (multivariate) twin surrogate (TS) trajectories. In contrast to other approaches, such as the linear-like surrogates, this technique produces surrogates which correspond to an independent copy of the underlying system, i.e. they induce a trajectory of the underlying system visiting the attractor in a different way. We show that these surrogates are well suited to test for complex synchronization, which makes it possible to systematically assess the reliability of synchronization analyses. We then apply the TS to study binocular fixational movements and find strong indications that the fixational movements of the left and right eye are phase synchronized. This result indicates that there might be only one centre in the brain that produces the fixational movements in both eyes or a close link between the two centres. |
P. D. Thiem; Jessica A. Hill; K. -M. Lee; Edward L. Keller Behavioral properties of saccades generated as a choice response Journal Article In: Experimental Brain Research, vol. 186, no. 3, pp. 355–364, 2008. @article{Thiem2008,The behavior characterizing choice response decision-making was studied in monkeys to provide background information for ongoing neurophysiological studies of the neural mechanisms underlying saccadic choice decisions. Animals were trained to associate a specific color from a set of colored visual stimuli with a specific spatial location. The visual stimuli (colored disks) appeared briefly at equal eccentricity from a central fixation position and then were masked by gray disks. The correct target association was subsequently cued by the appearance of a colored stimulus at the fixation point. The animal indicated its choice by saccading to the remembered location of the eccentric stimulus, which had matched the color of the cue. The number of alternative associations (NA) varied from 1 to 4 and remained fixed within a block of trials. After the training period, performance (percent correct responses) declined modestly as NA increased (on average 96, 93 or 84% correct for 1, 2 or 4 NA, respectively). Response latency increased logarithmically as a function of NA, thus obeying Hick's law. The spatial extent of the learned association between color and location was investigated by rotating the array of colored stimuli that had remained fixed during the learning phase to various different angles. Error rates in choice saccades increased gradually as a function of the amount of rotation. The learned association biased the direction of the saccadic response toward the quadrant associated with the cue, but saccade direction was always toward one of the actual visual stimuli. This suggests that the learned associations between stimuli and responses were not spatially exact, but instead the association between color and location was distributed with declining strength from the trained locations. These results demonstrate that the saccade system in monkeys also displays the characteristic dependence on NA in choice response latencies, while more basic features of the eye movements are invariant from those in other tasks. The findings also provide behavioral evidence that spatially distributed regions are established for the sensory-to-motor associations during training which are later utilized for choice decisions. |
Shery Thomas; Frank A. Proudlock; Nagini Sarvananthan; Eryl O. Roberts; Musarat Awan; Rebecca J. McLean; Mylvaganam Surendran; A. S. Anil Kumar; Shegufta J. Farooq; Christopher Degg; Richard P. Gale; Robert D. Reinecke; Geoffrey Woodruff; Andrea Langmann; Susanne Lindner; Sunila Jain; Patrick Tarpey; F. Lucy Raymond; Irene Gottlob Phenotypical characteristics of idiopathic infantile nystagmus with and without mutations in FRMD7 Journal Article In: Brain, vol. 131, no. 5, pp. 1259–1267, 2008. @article{Thomas2008,Idiopathic infantile nystagmus (IIN) consists of involuntary oscillations of the eyes. The familial form is most commonly X-linked. We recently found mutations in a novel gene FRMD7 (Xq26.2), which provided an opportunity to investigate a genetically defined and homogeneous group of patients with nystagmus. We compared clinical features and eye movement recordings of 90 subjects with mutation in the gene (FRMD7 group) to 48 subjects without mutations but with clinical IIN (non-FRMD7 group). Fifty-eight female obligate carriers of the mutation were also investigated. The median visual acuity (VA) was 0.2 logMAR (Snellen equivalent 6/9) in both groups and most patients had good stereopsis. The prevalence of strabismus was also similar (FRMD7: 7.8%, non-FRMD7: 10%). The presence of anomalous head posture (AHP) was significantly higher in the non-FRMD7 group (P < 0.0001). The amplitude of nystagmus was more strongly dependent on the direction of gaze in the FRMD7 group being lower at primary position (P < 0.0001), compared to non-FRMD7 group (P = 0.83). Pendular nystagmus waveforms were also more frequent in the FRMD7 group (P = 0.003). Fifty-three percent of the obligate female carriers of an FRMD7 mutation were clinically affected. The VA's in affected females were slightly better compared to affected males (P = 0.014). Subnormal optokinetic responses were found in a subgroup of obligate unaffected carriers, which may be interpreted as a sub-clinical manifestation. FRMD7 is a major cause of X-linked IIN. Most clinical and eye movement characteristics were similar in the FRMD7 group and non-FRMD7 group with most patients having good VA and stereopsis and low incidence of strabismus. Fewer patients in the FRMD7 group had AHPs, their amplitude of nystagmus being lower in primary position. Our findings are helpful in the clinical identification of IIN and genetic counselling of nystagmus patients. |
Aidan A. Thompson; Denise Y. P. Henriques Updating visual memory across eye movements for ocular and arm motor control Journal Article In: Journal of Neurophysiology, vol. 100, no. 5, pp. 2507–2514, 2008. @article{Thompson2008,Remembered object locations are stored in an eye-fixed reference frame, so that every time the eyes move, spatial representations must be updated for the arm-motor system to reflect the target's new relative position. To date, studies have not investigated how the brain updates these spatial representations during other types of eye movements, such as smooth-pursuit. Further, it is unclear what information is used in spatial updating. To address these questions we investigated whether remembered locations of pointing targets are updated following smooth-pursuit eye movements, as they are following saccades, and also investigated the role of visual information in estimating eye-movement amplitude for updating spatial memory. Misestimates of eye-movement amplitude were induced when participants visually tracked stimuli presented with a background that moved in either the same or opposite direction of the eye before pointing or looking back to the remembered target location. We found that gaze-dependent pointing errors were similar following saccades and smooth-pursuit and that incongruent background motion did result in a misestimate of eye-movement amplitude. However, the background motion had no effect on spatial updating for pointing, but did when subjects made a return saccade, suggesting that the oculomotor and arm-motor systems may rely on different sources of information for spatial updating. |
Xoana G. Troncoso; Stephen L. Macknik; Susana Martinez-Conde In: Spatial Vision, vol. 22, pp. 335–348, 2008. @article{Troncoso2008a,When corners are embedded in a luminance gradient, their perceived salience varies linearly with corner angle (Troncoso et al., 2005). Here we hypothesize that this relationship may hold true for all corners, not just corner gradients. To test this hypothesis, we developed a novel variant of the flicker-augmented contrast illusion (Anstis and Ho, 1998) that employs solid (non-gradient) corners of varying angles to modify perceived brightness. We flickered solid corners from dark to light grey (50% luminance over time) against a black or a white background. With this new stimulus, subjects compared the apparent brightness of corners, which did not vary in actual luminance, to non-illusory stimuli that varied in actual luminance. We found that the apparent brightness of corners was linearly related to the sharpness of corner angle. Thus this relationship is not solely an effect of corners embedded in gradients, but may be a general principle of corner perception. These findings may have important repercussions for brain mechanisms underlying the early visual processing of shape and brightness. A large fraction of Vasarely's art showcases the perceptual salience of corners, curvature and terminators. Several of these artworks and their implications for visual processing are discussed. |
Xoana G. Troncoso; Stephen L. Macknik; Susana Martinez-conde Microsaccades counteract perceptual filling-in Journal Article In: Journal of Vision, vol. 8, no. 14, pp. 1–9, 2008. @article{Troncoso2008,Artificial scotomas positioned within peripheral dynamic noise fade perceptually during visual fixation (that is, the surrounding dynamic noise appears to fill-in the scotoma). Because the scotomas' edges are continuously refreshed by the dynamic noise background, this filling-in effect cannot be explained by low-level adaptation mechanisms (such as those that may underlie classical Troxler fading). We recently showed that microsaccades counteract Troxler fading and drive first-order visibility during fixation (S. Martinez-Conde, S. L. Macknik, X. G. Troncoso, & T. A. Dyar, 2006). Here we set out to determine whether microsaccades may counteract the perceptual filling-in of artificial scotomas and thus drive second-order visibility. If so, microsaccades may not only counteract low-level adaptation but also play a role in higher perceptual processes. We asked subjects to indicate, via button press/release, whether an artificial scotoma presented on a dynamic noise background was visible or invisible at any given time. The subjects' eye movements were simultaneously measured with a high precision video system. We found that increases in microsaccade production counteracted the perception of filling-in, driving the visibility of the artificial scotoma. Conversely, decreased microsaccades allowed perceptual filling-in to take place. Our results show that microsaccades do not solely overcome low-level adaptation mechanisms but they also contribute to maintaining second-order visibility during fixation. |
Xoana G. Troncoso; Stephen L. Macknik; Jorge Otero-Millan; Susana Martinez-Conde Microsaccades drive illusory motion in the Enigma illusion Journal Article In: Proceedings of the National Academy of Sciences, vol. 105, no. 41, pp. 16033–16038, 2008. @article{Troncoso2008b,Visual images consisting of repetitive patterns can elicit striking illusory motion percepts. For almost 200 years, artists, psychologists, and neuroscientists have debated whether this type of illusion originates in the eye or in the brain. For more than a decade, the controversy has centered on the powerful illusory motion perceived in the painting Enigma, created by op-artist Isia Leviant. However, no previous study has directly correlated the Enigma illusion to any specific physiological mechanism, and so the debate rages on. Here, we show that microsaccades, a type of miniature eye movement produced during visual fixation, can drive illusory motion in Enigma. We asked subjects to indicate when illusory motion sped up or slowed down during the observation of Enigma while we simultaneously recorded their eye movements with high precision. Before "faster" motion periods, the rate of microsaccades increased. Before "slower/no" motion periods, the rate of microsaccades decreased. These results reveal a direct link between microsaccade production and the perception of illusory motion in Enigma and rule out the hypothesis that the origin of the illusion is purely cortical. |
Manabu Shikauchi; Shin Ishii; Tomohiro Shibata Prediction of aperiodic target sequences by saccades Journal Article In: Behavioural Brain Research, vol. 189, no. 2, pp. 325–331, 2008. @article{Shikauchi2008,Through recording of saccadic eye movements, we investigated whether humans can achieve prediction of aperiodic target sequences which cannot be predicted based solely on memorizing short-length patterns of the target sequence. We proposed a novel experimental paradigm in which Auto-Regressive (AR) processes are used to generate aperiodic target sequences. If subjects can fully utilize the knowledge on the AR dynamics that have generated the target sequence, optimal prediction can be made. As a control task, a completely unpredictable (random) target sequence was generated by shuffling the AR sequences. Behavioral analysis suggested that the prediction of the next target position in the AR sequence was significantly more successful than that by the random guess or the optimal guess for the random sequence. Although their performances were not optimal, learning of the AR dynamics was observed for first-order AR sequences, suggesting that the subjects attempted to predict the next target position based on partially identified AR dynamics. |
Mariano Sigman; Jérôme Sackur; Antoine Del Cul; Stanislas Dehaene Illusory displacement due to object substitution near the consciousness threshold Journal Article In: Journal of Vision, vol. 8, no. 1, pp. 1–10, 2008. @article{Sigman2008,A briefly presented target shape can be made invisible by the subsequent presentation of a mask that replaces the target. While varying the target-mask interval in order to investigate perception near the consciousness threshold, we discovered a novel visual illusion. At some intervals, the target is clearly visible, but its location is misperceived. By manipulating the mask's size and target's position, we demonstrate that the perceived target location is always displaced to the boundary of a virtual surface defined by the mask contours. Thus, mutual exclusion of surfaces appears as a cause of masking. |
Michael A. Silver; Amitai Shenhav; Mark D'Esposito Cholinergic enhancement reduces spatial spread of visual responses in human early visual cortex Journal Article In: Neuron, vol. 60, no. 5, pp. 904–914, 2008. @article{Silver2008,Animal studies have shown that acetylcholine decreases excitatory receptive field size and spread of excitation in early visual cortex. These effects are thought to be due to facilitation of thalamocortical synaptic transmission and/or suppression of intracortical connections. We have used functional magnetic resonance imaging (fMRI) to measure the spatial spread of responses to visual stimulation in human early visual cortex. The cholinesterase inhibitor donepezil was administered to normal healthy human subjects to increase synaptic levels of acetylcholine in the brain. Cholinergic enhancement with donepezil decreased the spatial spread of excitatory fMRI responses in visual cortex, consistent with a role of acetylcholine in reducing excitatory receptive field size of cortical neurons. Donepezil also reduced response amplitude in visual cortex, but the cholinergic effects on spatial spread were not a direct result of reduced amplitude. These findings demonstrate that acetylcholine regulates spatial integration in human visual cortex. |
Xingshan Li; Gordon D. Logan Object-based attention in Chinese readers of Chinese words: Beyond Gestalt principles Journal Article In: Psychonomic Bulletin & Review, vol. 15, no. 5, pp. 945–949, 2008. @article{Li2008,Most object-based attention studies use objects defined bottom-up by Gestalt principles. In the present study, we defined objects top-down, using Chinese words that were seen as objects by skilled readers of Chinese. Using a spatial cuing paradigm, we found that a target character was detected faster if it was in the same word as the cued character than if it was in a different word. Because there were no bottom-up factors that distinguished the words, these results showed that objects defined by subjects' knowledge–in this case, lexical information–can also constrain the deployment of attention. |
Casimir J. H. Ludwig; Adam Ranson; Iain D. Gilchrist Oculomotor capture by transient events: A comparison of abrupt onsets, offsets, motion, and flicker Journal Article In: Journal of Vision, vol. 8, no. 14, pp. 1–16, 2008. @article{Ludwig2008,Attentional and oculomotor capture by some salient visual event gives insight into what types of dynamic signals the human orienting system is sensitive to. We examined the sensitivity of the saccadic eye movement system to 4 types of dynamic, but task-irrelevant, visual events: abrupt onset, abrupt offset, motion onset and flicker onset. We varied (1) the primary task (contrast vs. motion discrimination) and (2) the amount of prior knowledge of the location of the dynamic event. Interference from the irrelevant events was quantified using a discrimination threshold metric. When the primary task involved contrast discrimination, all four events disrupted performance approximately equally, including the sudden disappearance of an old object. However, when motion was the task-relevant dimension, abrupt onsets and offsets did not disrupt performance at all, but motion onset had a strong effect. Providing more spatial certainty to observers decreased the amount of direct oculomotor capture but nevertheless impaired performance. We conclude that oculomotor capture is predominantly contingent upon the channel the observer monitors in order to perform the primary visual task. |
Amy D. Lykins; Marta Meana; Gregory P. Strauss Sex differences in visual attention to erotic and non-erotic stimuli Journal Article In: Archives of Sexual Behavior, vol. 37, no. 2, pp. 219–228, 2008. @article{Lykins2008,It has been suggested that sex differences in the processing of erotic material (e.g., memory, genital arousal, brain activation patterns) may also be reflected by differential attention to visual cues in erotic material. To test this hypothesis, we presented 20 heterosexual men and 20 heterosexual women with erotic and non-erotic images of heterosexual couples and tracked their eye movements during scene presentation. Results supported previous findings that erotic and non-erotic information was visually processed in a different manner by both men and women. Men looked at opposite sex figures significantly longer than did women, and women looked at same sex figures significantly longer than did men. Within-sex analyses suggested that men had a strong visual attention preference for opposite sex figures as compared to same sex figures, whereas women appeared to disperse their attention evenly between opposite and same sex figures. These differences, however, were not limited to erotic images but evidenced in non-erotic images as well. No significant sex differences were found for attention to the contextual region of the scenes. Results were interpreted as potentially supportive of recent studies showing a greater non-specificity of sexual arousal in women. This interpretation assumes there is an erotic valence to images of the sex to which one orients, even when the image is not explicitly erotic. It also assumes a relationship between visual attention and erotic valence. |
K. -M. Lee; Edward L. Keller Neural activity in the frontal eye fields modulated by the number of alternatives in target choice Journal Article In: Journal of Neuroscience, vol. 28, no. 9, pp. 2242–2251, 2008. @article{Lee2008,Selection of identical responses may not use the same neural mechanisms when the number of alternatives (NA) for the selection changes, as suggested by Hick's law. For elucidating the choice mechanisms, frontal eye field (FEF) neurons were monitored during a color-to-location choice saccade task as the number of potential targets was varied. Visual responses to alternative targets decreased as NA increased, whereas perisaccade activities increased with NA. These modulations of FEF activities seem closely related to the choice process because the activity enhancements coincided with the timing of target selection, and the neural modulation was greater as NA increased, features expected of neural correlates for a choice process from the perspective of Hick's law. Our current observations suggest two novel notions of FEF neuronal behavior that have not been reported previously: (1) cells called "phasic visual" that do not discharge in the perisaccade interval in a delayed-saccade paradigm show such activity in a choice response task at the time of the saccade; and (2) the activity in FEF visuomotor cells display an inverse relationship between perisaccadic activity and the time of saccade triggering with higher levels of activity leading to longer saccade reaction times. These findings support the area's involvement in sensory-motor translation for target selection through coactivation and competitive interaction of neural populations that code for alternative action sets. |
Vaia Lestou; Frank E. Pollick; Zoe Kourtzi Neural substrates for action understanding at different description levels in the human brain Journal Article In: Journal of Cognitive Neuroscience, vol. 20, no. 2, pp. 324–341, 2008. @article{Lestou2008,Understanding complex movements and abstract action goals is an important skill for our social interactions. Successful social interactions entail understanding of actions at different levels of action description, ranging from detailed movement trajectories that support learning of complex motor skills through imitation to distinct features of actions that allow us to discriminate between action goals and different action styles. Previous studies have implicated premotor, parietal, and superior temporal areas in action understanding. However, the role of these different cortical areas in action understanding at different levels of action description remains largely unknown. We addressed this question using advanced animation and stimulus generation techniques in combination with sensitive functional magnetic resonance imaging adaptation or repetition suppression methods. We tested the neural sensitivity of fronto-parietal and visual areas to differences in the kinematics and goals of actions using kinematic morphs of arm movements. Our findings provide novel evidence for differential involvement of ventral premotor, parietal, and temporal regions in action understanding. We show that the ventral premotor cortex encodes the physical similarity between movement trajectories and action goals that are important for exact copying of actions and the acquisition of complex motor skills. In contrast, whereas parietal regions and the superior temporal sulcus process the perceptual similarity between movements and may support the perception and imitation of abstract action goals and movement styles. Thus, our findings propose that fronto-parietal and visual areas involved in action understanding mediate a cascade of visual-motor processes at different levels of action description from exact movement copies to abstract action goals achieved with different movement styles. |
P. Christiaan Klink; Raymond Van Ee; M. M. Nijs; G. J. Brouwer; A. J. Noest; Richard J. A. Wezel Early interactions between neuronal adaptation and voluntary control determine perceptual choices in bistable vision Journal Article In: Journal of Vision, vol. 8, no. 5, pp. 1–18, 2008. @article{Klink2008,At the onset of bistable stimuli, the brain needs to choose which of the competing perceptual interpretations willfi rst reach awareness. Stimulus manipulations and cognitive control both infl uence this choice process, but the underlying mechanisms and interactions remain poorly understood. Using intermittent presentation of bistable visual stimuli, we demonstrate that short interruptions cause perceptual reversals upon the next presentation, whereas longer interstimulus intervals stabilize the percept. Top-down voluntary control biases this process but does not override the timing dependencies. Extending a recently introduced low-level neural model, we demonstrate that percept-choice dynamics in bistable vision can be fully understood with interactions in early neural processing stages. Our model includes adaptive neural processing preceding a rivalry resolution stage with cross-inhibition, adaptation, and an interaction of the adaptation levels with a neural baseline. Most importantly, ourfi ndings suggest that top-down attentional control over bistable stimuli interacts with low-level mechanisms at early levels of sensory processing before perceptual confl icts are resolved and perceptual choices about bistable stimuli are made. |
Stefan Klöppel; Bogdan Draganski; Charlotte V. Golding; Carlton Chu; Zoltan Nagy; Philip A. Cook; Stephen L. Hicks; Christopher Kennard; Daniel C. Alexander; Geoff J. M. Parker; Sarah J. Tabrizi; Richard S. J. Frackowiak White matter connections reflect changes in voluntary-guided saccades in pre-symptomatic Huntington's disease Journal Article In: Brain, vol. 131, no. 1, pp. 196–204, 2008. @article{Kloeppel2008,Huntington's disease is caused by a known genetic mutation and so potentially can be diagnosed many years before the onset of symptoms. Neuropathological changes have been found in both striatum and frontal cortex in the pre-symptomatic stage. Disruption of cortico-striatal white matter fibre tracts is therefore likely to contribute to the first clinical signs of the disease. We analysed diffusion tensor MR image (DTI) data from 25 pre-symptomatic gene carriers (PSCs) and 20 matched controls using a multivariate support vector machine to identify patterns of changes in fractional anisotropy (FA). In addition, we performed probabilistic fibre tracking to detect changes in 'streamlines' connecting frontal cortex to striatum. We found a pattern of structural brain changes that includes putamen bilaterally as well as anterior parts of the corpus callosum. This pattern was sufficiently specific to enable us to correctly classify 82% of scans as coming from a PSC or control subject. Fibre tracking revealed a reduction of frontal cortico-fugal streamlines reaching the body of the caudate in PSCs compared to controls. In the left hemispheres of PSCs we found a negative correlation between years to estimated disease onset and streamlines from frontal cortex to body of caudate. A large proportion of the fibres to the caudate body originate from the frontal eye fields, which play an important role in the control of voluntary saccades. This type of saccade is specifically impaired in PSCs and is an early clinical sign of motor abnormalities. A correlation analysis in 14 PSCs revealed that subjects with greater impairment of voluntary-guided saccades had fewer fibre tracking streamlines connecting the frontal cortex and caudate body. Our findings suggest a specific patho-physiological basis for these symptoms by indicating selective vulnerability of the associated white matter tracts. |
Christopher M. Knapp; Irene Gottlob; Rebecca J. McLean; Frank A. Proudlock Horizontal and vertical look and stare optokinetic nystagmus symmetry in healthy adult volunteers Journal Article In: Investigative Ophthalmology & Visual Science, vol. 49, no. 2, pp. 581–588, 2008. @article{Knapp2008,PURPOSE: Look optokinetic nystagmus (OKN) consists of voluntary tracking of details in a moving visual field, whereas stare OKN is reflexive and consists of shorter slow phases of lower gain. Horizontal OKN is symmetrical in healthy adults, whereas symmetry of vertical OKN is controversial. Horizontal and vertical look and stare OKN symmetry was measured, and the consistency of individual asymmetries and the effect of varying stimulus conditions were investigated.METHODS: Horizontal and vertical look and stare OKN gains were recorded in 15 healthy volunteers (40 degrees /s) using new methods to delineate look and stare OKN. Responses with right and left eye viewing were compared to investigate consistency of individual OKN asymmetry. In a second experiment, the symmetry of stare OKN was measured in nine volunteers varying velocity (20 degrees /s and 40 degrees /s), contrast (50% and 100%), grating contrast profile (square or sine wave), and stimulus shape (full screen or circular vignetted).RESULTS: There was no horizontal or vertical asymmetry in look or stare OKN gain for all volunteers grouped together. However, individual vertical asymmetries were strongly correlated for left and right eye viewing (look: r = 0.77 |
John D. Koehn; Elizabeth Roy; Jason J. S. Barton The "diagonal effect": A systematic error in oblique antisaccades Journal Article In: Journal of Neurophysiology, vol. 100, no. 2, pp. 587–597, 2008. @article{Koehn2008,Antisaccades are known to show greater variable error and also a systematic hypometria in their amplitude compared with visually guided prosaccades. In this study, we examined whether their accuracy in direction (as opposed to amplitude) also showed a systematic error. We had human subjects perform prosaccades and antisaccades to goals located at a variety of polar angles. In the first experiment, subjects made prosaccades or antisaccades to one of eight equidistant locations in each block, whereas in the second, they made saccades to one of two equidistant locations per block. In the third, they made antisaccades to one of two locations at different distances but with the same polar angle in each block. Regardless of block design, the results consistently showed a saccadic systematic error, in that oblique antisaccades (but not prosaccades) requiring unequal vertical and horizontal vector components were deviated toward the 45 degrees diagonal meridians. This finding could not be attributed to range effects in either Cartesian or polar coordinates. A perceptual origin of the diagonal effect is suggested by similar systematic errors in other studies of memory-guided manual reaching or perceptual estimation of direction, and may indicate a common spatial bias when there is uncertain information about spatial location. |
Christof Körner; Iain D. Gilchrist Memory processes in multiple-target visual search Journal Article In: Psychological Research, vol. 72, no. 1, pp. 99–105, 2008. @article{Koerner2008,Gibson, Li, Skow, Brown, and Cooke (Psychological Science, 11, 324–327, 2000) had participants carry out a search task in which they were required to detect the presence of one or two targets. In order to successfully perform such a multiple-target visual search task, participants had to remember the location of the Wrst target while searching for the second target. In two experiments we investigated the cost of remembering this target location. In Experiment 1, we compared performance on the Gibson et al. task with performance on a more conventional present–absent search task. The comparison suggests a substantial performance cost as measured by reaction time, number of Wxations and slope of the search functions. In Experment 2, we looked in detail at reWxations of distractors, which are a direct measure of attentional deployment. We demonstrated that the cost in this multiple-target visual search task was due to an increased number of reWxations on previously visited distractors. Such reWxations were present right from the start of the search. This change in search behaviour may be caused by the necessity of having to remember a target-allocating memory for the upcoming target may consume memory capacity that may otherwise be available for the tagging of distractors. These results support the notion of limited capacity memory processes in search. Introduction |
Victor Kuperman; Raymond Bertram; R. Harald Baayen Morphological dynamics in compound processing Journal Article In: Language and Cognitive Processes, vol. 23, no. 7-8, pp. 1089–1132, 2008. @article{Kuperman2008,This paper explores the time-course of morphological processing of trimorphemic Finnish compounds. We find evidence for the parallel access to full- forms and morphological constituents diagnosed by the early effects of compound frequency, as well as early effects of left constituent frequency and family size. We also observe an interaction between compound frequency and both the left and the right constituent family sizes. Furthermore, our data show that suffixes embedded in the derived left constituent of a compound are efficiently used for establishing the boundary between compounds' constituents. The success of segmentation of a compound is demonstrably modulated by the affixal salience of the embedded suffixes. We discuss implications of these findings for current models of morphological processing and propose a new model that views morphemes, combinations of morphemes and morphological paradigms as probabilistic sources of information that are interactively used in recognition of complex words. |
Jochen Laubrock; Ralf Engbert; Reinhold Kliegl Fixational eye movements predict the perceived direction of ambiguous apparent motion Journal Article In: Journal of Vision, vol. 8, no. 14, pp. 1–17, 2008. @article{Laubrock2008,Neuronal activity in area LIP is correlated with the perceived direction of ambiguous apparent motion (Z. M. Williams, J. C. Elfar, E. N. Eskandar, L. J. Toth, & J. A. Assad, 2003). Here we show that a similar correlation exists for small eye movements made during fixation. A moving dot grid with superimposed fixation point was presented through an aperture. In a motion discrimination task, unambiguous motion was compared with ambiguous motion obtained by shifting the grid by half of the dot distance. In three experiments we show that (a) microsaccadic inhibition, i.e., a drop in microsaccade frequency precedes reports of perceptual flips, (b) microsaccadic inhibition does not accompany simple response changes, and (c) the direction of microsaccades occurring before motion onset biases the subsequent perception of ambiguous motion. We conclude that microsaccades provide a signal on which perceptual judgments rely in the absence of objective disambiguating stimulus information. |
Angelika Lingnau; Jens Schwarzbach; Dirk Vorberg Adaptive strategies for reading with a forced retinal location Journal Article In: Journal of Vision, vol. 8, no. 5, pp. 1–18, 2008. @article{Lingnau2008,Forcing normal-sighted participants to use a distinct parafoveal retinal location for reading, we studied which part of the visual field is best suited to take over functions of the fovea during early stages of macular degeneration (MD). A region to the right of fixation lead to best reading performance and most natural gaze behavior, whereas reading performance was severely impaired when a region to the left or below fixation had to be used. An analysis of the underlying oculomotor behavior revealed that practice effects were accompanied by a larger number of saccades in text direction and decreased fixation durations, whereas no adjustment of saccade amplitudes was observed. We provide an explanation for the observed performance differences at different retinal locations based on the interplay of attention and eye movements. Our findings have important implications for the development of training methods for MD patients targeted at reading, suggesting that it would be beneficial for MD patients to use a region to the right of their central scotoma. |
Marine Vernet; Qing Yang; Gintautas Daunys; Christophe Orssaud; Thomas Eggert; Zoï Kapoula How the brain obeys Hering's law: A TMS study of the posterior parietal cortex Journal Article In: Investigative Ophthalmology & Visual Science, vol. 49, no. 1, pp. 230–237, 2008. @article{Vernet2008,PURPOSE: Human ocular saccades are not perfectly yoked; the origin of this disconjugacy (muscular versus central) remains controversial. The purpose of this study was to test a cortical influence on the binocular coordination of saccades. METHODS: The authors used a gap paradigm to elicit vertical or horizontal saccades of 10 degrees , randomly interleaved; transcranial magnetic stimulation (TMS) was applied on the posterior parietal cortex (PPC) 100 ms after the target onset. RESULTS: TMS of the left or right PPC increased (i) the misalignment of the eyes during the presaccadic fixation period; (ii) the size difference between the saccades of the eyes, called disconjugacy; the increase of disconjugacy was significant for rightward and downward saccades after TMS of the right PPC and for downward saccades after TMS of the left PPC. CONCLUSIONS: The authors conclude that the PPC is actively involved in maintaining eye alignment during fixation and in the control of binocular coordination of saccades. |
Marine Vernet; Qing Yang; Gintautas Daunys; Christophe Orssaud; Zoï Kapoula TMS of the posterior parietal cortex delays the latency of unpredictable saccades but not when they are combined with predictable divergence Journal Article In: Brain Research Bulletin, vol. 76, no. 1-2, pp. 50–56, 2008. @article{Vernet2008a,This study tests the influence of transcranial magnetic stimulation (TMS) of the posterior parietal cortex (PPC) on the initiation of horizontal and vertical saccades, alone or combined with a predictable divergence. A gap paradigm was used; TMS was applied 100 ms after target onset. TMS of the left PPC increased the latency of unpredictable rightward saccades, while TMS of the right PPC increased the latency of unpredictable downward saccades. Yet, when unpredictable saccades were combined with predictable divergence, neither component was affected. We suggest that in the latter case, the initiation of both components was taken in charge by another area, e.g. frontal. Thus, even when one component was predictable, a common mechanism controls the initiation of both components. The results confirm that TMS only modifies the latency when the cortical area stimulated is involved in the triggering of the eye movement. |
Marine Vernet; Qing Yang; Gintautas Daunys; Christophe Orssaud; Zoï Kapoula Divergence influences triggering of both vertical and horizontal saccades Journal Article In: Optometry and Vision Science, vol. 85, no. 3, pp. 187–195, 2008. @article{Vernet2008b,Purpose. In real life, divergence is frequently combined with vertical saccades. The purpose of this study was to examine the initiation of vertical and horizontal saccades, pure or combined with divergence. Methods. We used a gap paradigm to elicit vertical or horizontal saccades (10 degrees), pure or combined with a predictable divergence (10 degrees). Eye movements from 12 subjects were recorded with EyeLink II. Results. The major results were (i) when combined with divergence, the latency of horizontal saccades increased but not the latency of vertical saccades; (ii) for both vertical and horizontal saccades, a tight correlation between the latency of saccade and divergence was found; (iii) when the divergence was anticipated, the saccade was delayed. Conclusion. We conclude that the initiation of both components of combined movements is interdependent. |
Julius Verrel; Harold Bekkering; Bert Steenbergen Eye-hand coordination during manual object transport with the affected and less affected hand in adolescents with hemiparetic cerebral palsy Journal Article In: Experimental Brain Research, vol. 187, no. 1, pp. 107–116, 2008. @article{Verrel2008,In the present study we investigated eye-hand coordination in adolescents with hemiparetic cerebral palsy (CP) and neurologically healthy controls. Using an object prehension and transport task, we addressed two hypotheses, motivated by the question whether early brain damage and the ensuing limitations of motor activity lead to general and/or effector-specific effects in visuomotor control of manual actions. We hypothesized that individuals with hemiparetic CP would more closely visually monitor actions with their affected hand, compared to both their less affected hand and to control participants without a sensorimotor impairment. A second, more speculative hypothesis was that, in relation to previously established deficits in prospective action control in individuals with hemiparetic CP, gaze patterns might be less anticipatory in general, also during actions performed with the less affected hand. Analysis of the gaze and hand movement data revealed the increased visual monitoring of participants with CP when using their affected hand at the beginning as well as during object transport. In contrast, no general deficit in anticipatory gaze control in the participants with hemiparetic CP could be observed. Collectively, these findings are the first to directly show that individuals with hemiparetic CP adapt eye-hand coordination to the specific constraints of the moving limb, presumably to compensate for sensorimotor deficits. |
Suiping Wang; Hsuan-Chih Chen; Jinmian Yang; Lei Mo Immediacy of integration in discourse comprehension: Evidence from Chinese readers' eye movements Journal Article In: Language and Cognitive Processes, vol. 23, no. 2, pp. 241–257, 2008. @article{Wang2008a,An eye-movement study was conducted to examine whether Chinese readers immediately activate and integrate related background information during discourse comprehension. Participants were asked to read short passages, each containing a critical word that fitted well within the local context but was inconsistent or neutral with background information from the early part of the passage. This manipulation of textual consistency produced reliable effects on both first-pass reading fixations in the target region and second-pass reading times in the pre-target and target regions. These results indicate that integration processes start very rapidly in reading text in a writing system with properties that encourage delayed processing, suggesting that immediate processing is likely a universal principle in discourse comprehension. |
Z. I. Wang; Louis F. Dell'Osso Tenotomy procedure alleviates the "slow to see" phenomenon in infantile nystagmus syndrome: Model prediction and patient data Journal Article In: Vision Research, vol. 48, no. 12, pp. 1409–1419, 2008. @article{Wang2008,Our purpose was to perform a systematic study of the post-four-muscle-tenotomy procedure changes in target acquisition time by comparing predictions from the behavioral ocular motor system (OMS) model and data from infantile nystagmus syndrome (INS) patients. We studied five INS patients who underwent only tenotomy at the enthesis and reattachment at the original insertion of each (previously unoperated) horizontal rectus muscle for their INS treatment. We measured their pre- and post-tenotomy target acquisition changes using data from infrared reflection and high-speed digital video. Three key aspects were calculated and analyzed: the saccadic latency (Ls), the time to target acquisition after the target jump (Lt) and the normalized stimulus time within the cycle. Analyses were performed in MATLAB environment (The MathWorks, Natick, MA) using OMLAB software (OMtools, available from http://www.omlab.org). Model simulations were performed in MATLAB Simulink environment. The model simulation suggested an Lt reduction due to an overall foveation-quality improvement. Consistent with that prediction, improvement in Lt, ranging from ∼200 ms to ∼500 ms (average ∼ 280 ms), was documented in all five patients post-tenotomy. The Lt improvement was not a result of a reduced Ls. INS patients acquired step-target stimuli faster post-tenotomy. This target acquisition improvement may be due to the elevated foveation quality resulting in less inherent variation in the input to the OMS. A refined behavioral OMS model, with "fast" and "slow" motor neuron pathways and a more physiological plant, successfully predicted this improved visual behavior and again demonstrated its utility in guiding ocular motor research. |
Tessa Warren; Kerry McConnell; Keith Rayner Effects of context on eye movements when reading about possible and impossible events Journal Article In: Journal of Experimental Psychology: Learning, Memory, and Cognition, vol. 34, no. 4, pp. 1001–1010, 2008. @article{Warren2008,Plausibility violations resulting in impossible scenarios lead to earlier and longer lasting eye movement disruption than violations resulting in highly unlikely scenarios (K. Rayner, T. Warren, B. J. Juhasz, & S. P. Liversedge, 2004; T. Warren & K. McConnell, 2007). This could reflect either differences in the timing of availability of different kinds of information (e.g., selectional restrictions, world knowledge, and context) or differences in their relative power to guide semantic interpretation. The authors investigated eye movements to possible and impossible events in real-world and fantasy contexts to determine when contextual information influences detection of impossibility cued by a semantic mismatch between a verb and an argument. Gaze durations on a target word were longer to impossible events independent of context. However, a measure of the time elapsed from first fixating the target word to moving past it showed disruption only in the real-world context. These results suggest that contextual information did not eliminate initial disruption but moderated it quickly thereafter. |
Yuan-Chi Tseng; Chiang-Shan Ray Li The effects of response readiness and error monitoring on saccade countermanding Journal Article In: The Open Psychology Journal, vol. 1, no. 1, pp. 18–25, 2008. @article{Tseng2008,The stop-signal task (SST) and anti-saccade tasks are both widely used to explore cognitive inhibitory control. Our previous work on a manual SST showed that subjects' readiness to respond to the go signal and the extent to which subjects monitor their errors need to be considered in order to attribute impaired performance to deficits in response inhi- bition. Here we examine whether these same task-related variables similarly influence oculomotor SST and anti-saccade performance. Thirty-six and sixty healthy, adult subjects participated in an oculomotor SST and anti-saccade task, respec- tively, in which the fore-period (FP) of imperative stimulus varied randomly from trial to trial. We computed a FP effect to index response readiness to the imperative stimulus and a post-error slowing (PES) effect to index error monitoring. Contrary to what we had anticipated, other than a weak but negative association between the FP effect and anti-saccade errors, these behavioral variables did not correlate with SST or anti-saccade performance. |
Geoffrey Underwood; Emma Templeman; Laura Lamming; Tom Foulsham Is attention necessary for object identification? Evidence from eye movements during the inspection of real-world scenes Journal Article In: Consciousness and Cognition, vol. 17, no. 1, pp. 159–170, 2008. @article{Underwood2008,Eye movements were recorded during the display of two images of a real-world scene that were inspected to determine whether they were the same or not (a comparative visual search task). In the displays where the pictures were different, one object had been changed, and this object was sometimes taken from another scene and was incongruent with the gist. The experiment established that incongruous objects attract eye fixations earlier than the congruous counterparts, but that this effect is not apparent until the picture has been displayed for several seconds. By controlling the visual saliency of the objects the experiment eliminates the possibility that the incongruency effect is dependent upon the conspicuity of the changed objects. A model of scene perception is suggested whereby attention is unnecessary for the partial recognition of an object that delivers sufficient information about its visual characteristics for the viewer to know that the object is improbable in that particular scene, and in which full identification requires foveal inspection. |
Seppo Vainio; Jukka Hyönä; Anneli Pajunen Processing modifier-head agreement in reading: Evidence for a delayed effect of agreement Journal Article In: Memory & Cognition, vol. 36, no. 2, pp. 329–340, 2008. @article{Vainio2008,The present study examined whether type of inflectional case (semantic or grammatical) and phonological and morphological transparency affect the processing of Finnish modifier-head agreement in reading. Readers' eye movement patterns were registered. In Experiment 1, an agreeing modifier condition (agreement was transparent) was compared with a no-modifier condition, and in Experiment 2, similar constructions with opaque agreement were used. In both experiments, agreement was found to affect the processing of the target noun with some delay. In Experiment 3, unmarked and case-marked modifiers were used. The results again demonstrated a delayed agreement effect, ruling out the possibility that the agreement effects observed in Experiments 1 and 2 reflect a mere modifier-presence effect. We concluded that agreement exerts its effect at the level of syntactic integration but not at the level of lexical access. |
Matteo Valsecchi; Sven Saage; Brian J. White; Karl R. Gegenfurtner Advantage in reading lexical bundles is reduced in non-native speakers Journal Article In: Journal of Eye Movement Research, vol. 6, no. 5:2, pp. 1–15, 2008. @article{Valsecchi2008,Formulaic sequences such as idioms, collocations, and lexical bundles, which may be processed as holistic units, make up a large proportion of natural language. For language learners, however, formulaic patterns are a major barrier to achieving native like compe- tence. The present study investigated the processing of lexical bundles by native speakers and less advanced non-native English speakers using corpus analysis for the identification of lexical bundles and eye-tracking to measure the reading times. The participants read sentences containing 4-grams and control phrases which were matched for sub-string fre- quency. The results for native speakers demonstrate a processing advantage for formulaic sequences over the matched control units. We do not find any processing advantage for non-native speakers which suggests that native like processing of lexical bundles comes only late in the acquisition process |
Katsumi Watanabe; Kenji Yokoi Dynamic distortion of visual position representation around moving objects Journal Article In: Journal of Vision, vol. 8, no. 3, pp. 1–11, 2008. @article{Watanabe2008,The relative visual positions of briefly flashed stimuli are systematically modified in the presence of motion signals (R. Nijhawan, 2002; D. Whitney, 2002). Previously, we investigated the two-dimensional distortion of relative-position representations between moving and flashed stimuli. The results showed that the perceived position of a flash is not uniformly displaced but shifted toward a single convergent point back along the trajectory of a moving object (K. Watanabe & K. Yokoi, 2006, 2007). In the present study, we examined the temporal dynamics of the anisotropic distortion of visual position representation. While observers fixated on a stationary cross, a black disk appeared, moved along a horizontal trajectory, and disappeared. A white dot was briefly flashed at various positions relative to the moving disk and at various timings relative to the motion onset/offset. The temporal emerging-waning pattern of anisotropic mislocalization indicated that position representation in the space ahead of a moving object differs qualitatively from that in the space behind it. Thus, anisotropic mislocalization cannot be explained by either a spatially or a temporally homogeneous process. Instead, visual position representation is anisotropically influenced by moving objects in both space and time. |
Mark Wexler; Nizar Ouarti Depth affects where we look Journal Article In: Current Biology, vol. 18, no. 23, pp. 1872–1876, 2008. @article{Wexler2008,Understanding how we spontaneously scan the visual world through eye movements is crucial for characterizing both the strategies and inputs of vision [1-27]. Despite the importance of the third or depth dimension for perception and action, little is known about how the specifically three-dimensional aspects of scenes affect looking behavior. Here we show that three-dimensional surface orientation has a surprisingly large effect on spontaneous exploration, and we demonstrate that a simple rule predicts eye movements given surface orientation in three dimensions: saccades tend to follow surface depth gradients. The rule proves to be quite robust: it generalizes across depth cues, holds in the presence or absence of a task, and applies to more complex three-dimensional objects. These results not only lead to a more accurate understanding of visuo-motor strategies, but also suggest a possible new oculomotor technique for studying three-dimensional vision from a variety of depth cues in subjects-such as animals or human infants-that cannot explicitly report their perceptions. |
Brian J. White; Martin Stritzke; Karl R. Gegenfurtner Saccadic facilitation in natural backgrounds Journal Article In: Current Biology, vol. 18, no. 2, pp. 124–128, 2008. @article{White2008,In visual systems with a fovea, only a small portion of the visual field can be analyzed with high accuracy. Saccadic eye movements shift that center of gaze around several times a second. Saccades have been characterized in great detail and depend critically on a number of visual properties of the stimuli [1-5]. However, typical experiments have used bright spots on dark backgrounds, while our natural environment has a highly characteristic rich spatial structure [6, 7]. Here we show that the saccadic system, unlike the perceptual system, is able to compensate for the masking caused by structured backgrounds. Consequently, saccadic latencies in the context of natural backgrounds are much faster than unstructured backgrounds at equal levels of visibility. The results suggest that whenever a structured background acts to mask the visibility of the saccade target, it simultaneously preactivates saccadic circuitry and thus ensures a fast reaction to potentially critical stimuli that are difficult to detect in our environment. © 2008 Elsevier Ltd. All rights reserved. |
Sarah J. White; Raymond Bertram; Jukka Hyönä Semantic processing of previews within compound words Journal Article In: Journal of Experimental Psychology: Learning, Memory, and Cognition, vol. 34, no. 4, pp. 988–993, 2008. @article{White2008a,Previous studies have suggested that previews of words prior to fixation can be processed orthographically, but not semantically, during reading of sentences (K. Rayner, D. A. Balota, & A. Pollatsek, 1986). The present study tested whether semantic processing of previews can occur within words. The preview of the second constituent of 2-constituent Finnish compound nouns was manipulated. The previews were either identical to the 2nd constituent or they were incorrect in the form of a semantically related word, a semantically unrelated word, or a semantically meaningless nonword. The results indicate that previews of 2nd constituents within compound words can be semantically processed. The results have important implications for understanding the nature of preview and compound word processing. These issues are crucial to developing comprehensive models of eye-movement control and word recognition during reading. |
Christian Vorstius; Ralph Radach; Alan R. Lang; Christina J. Riccardi Specific visuomotor deficits due to alcohol intoxication: evidence from the pro- and antisaccade paradigms. Journal Article In: Psychopharmacology, vol. 196, no. 2, pp. 201–210, 2008. @article{Vorstius2008,RATIONALE: Alcohol affects a variety of human behaviors, including visual perception and motor control. Although recent research has begun to explore mechanisms that mediate these changes, their exact nature is still not well understood. OBJECTIVES: The present study used two basic oculomotor tasks to examine the effect of alcohol on different levels of visual processing within the same individuals. A theoretical framework is offered to integrate findings across multiple levels of oculomotor control. MATERIALS AND METHODS: Twenty-four healthy participants were asked to perform eye movements in reflexive (pro-) and voluntary (anti-) saccade tasks. In one of two counterbalanced sessions, performance was measured after alcohol administration (mean BrAC=69 mg%); the other served as a within-subjects no-alcohol comparison condition. RESULTS: Error rates were not influenced by alcohol intoxication in either task. However, there were significant effects of alcohol on saccade latency and peak velocity in both tasks. Critically, a specific alcohol-induced impairment (hypermetria) in saccade amplitudes was observed exclusively in the anti-saccade task. CONCLUSIONS: The saccade latency data strongly suggest that alcohol intoxication impairs temporal aspects of saccade generation, irrespective of the level of processing triggering the saccade. The absence of effects on anti-saccade errors calls for further research into the notion of alcohol-induced impairment of the ability to inhibit prepotent responses. Furthermore, the specific impairment of saccade amplitude in the anti-saccade task under alcohol suggests that higher level processes involved in the spatial remapping of target location in the absence of a visually specified saccade goal are specifically affected by alcohol intoxication. |
Robin Walker; Eugene McSorley The influence of distractors on saccade target selection: Saccade trajectory effects Journal Article In: Journal of Eye Movement Research, vol. 2, no. 3, pp. 1–13, 2008. @article{Walker2008,It has long been known that the path (trajectory) taken by the eye to land on a target is rarely straight (Yarbus, 1967). Furthermore, the magnitude and direction of this natural tendency for curvature can be modulated by the presence of a competing distractor stimulus presented along with the saccade target. The distractorrelated modulation of saccade trajectories provides a subtle measure of the underlying competitive processes involved in saccade target selection. Here we review some of our own studies into the effects distractors have on saccade trajectories, which can be regarded as a way of probing the competitive balance between target and distractor salience. |
Claudia Wilimzig; Naotsugu Tsuchiya; Manfred Fahle; Wolfgang Einhäuser; Christof Koch Spatial attention increases performance but not subjective confidence in a discrimination task Journal Article In: Journal of Vision, vol. 8, no. 5, pp. 7, 2008. @article{Wilimzig2008,Selective attention to a target yields faster and more accurate responses. Faster response times, in turn, are usually associated with increased subjective confidence. Could the decrease in reaction time in the presence of attention therefore simply reflect a shift toward more confident responses? We here addressed the extent to which attention modulates accuracy, processing speed, and confidence independently. To probe the effect of spatial attention on performance, we used two attentional manipulations of a visual orientation discrimination task. We demonstrate that spatial attention significantly increases accuracy, whereas subjective confidence measures reveal overconfidence in non-attended stimuli. At constant confidence levels, reaction times showed a significant decrease (by 15-49%, corresponding to 100-250 ms). This dissociation of objective performance and subjective confidence suggests that attention and awareness, as measured by confidence, are distinct, albeit related, phenomena. |
Amanda H. Wilson; Adam Wilson; Martin W. Hove; Martin Paré; Kevin G. Munhall Loss of central vision and audiovisual speech perception Journal Article In: Visual Impairment Research, vol. 10, no. 1, pp. 23–34, 2008. @article{Wilson2008,Communication impairments pose a major threat to an individual's quality of life. However, the impact of visual impairments on communication is not well understood, despite the important role that vision plays in the perception of speech. Here we present 2 experiments examining the impact of discrete central scotomas on speech perception. In the first experiment, 4 patients with central vision loss due to unilateral macular holes identified utterances with conflicting auditory-visual information, while simultaneously having their eye movements recorded. Each eye was tested individually. Three participants showed similar speech perception with both the impaired eye and the unaffected eye. For 1 participant, speech perception was disrupted by the scotoma because the participant did not shift gaze to avoid obscuring the talker's mouth with the scotoma. In the second experiment, 12 undergraduate students with gaze-contingent artificial scotomas (10 visual degrees in diameter) identified sentences in background noise. These larger scotomas disrupted speech perception, but some participants overcame this by adopting a gaze strategy whereby they shifted gaze to prevent obscuring important regions of the face such as the mouth. Participants who did not spontaneously adopt an adaptive gaze strategy did not learn to do so over the course of 5 days; however, participants who began with adaptive gaze strategies became more consistent in their gaze location. These findings confirm that peripheral vision is sufficient for perception of most visual information in speech, and suggest that training in gaze strategy may be worthwhile for individuals with communication deficits due to visual impairments. |
D. A. Wismeijer; Raymond Van Ee; Casper J. Erkelens Depth cues, rather than perceived depth, govern vergence Journal Article In: Experimental Brain Research, vol. 184, no. 1, pp. 61–70, 2008. @article{Wismeijer2008,We studied the influence of perceived surface orientation on vergence accompanying a saccade while viewing an ambiguous stimulus. We used the slant rivalry stimulus, in which perspective foreshortening and disparity specified opposite surface orientations. This rivalrous configuration induces alternations of perceived surface orientation, while the slant cues remain constant. Subjects were able to voluntarily control their perceptual state while viewing the ambiguous stimulus. They were asked to make a saccade across the perceived slanted surface. Our data show that vergence responses closely approximated the vergence response predicted by the disparity cue, irrespective of voluntarily controlled perceived orientation. However, comparing the data obtained while viewing the ambiguous stimulus with data from an unambiguous stimulus condition (when disparity and perspective specified similar surface orientations) revealed an effect of perspective cues on vergence. Collectively our results show that depth cues rather than perceived depth govern vergence. |