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2004 |
Jillian H. Fecteau; Crystal Au; Irene T. Armstrong; Douglas P. Munoz Sensory biases produce alternation advantage found in sequential saccadic eye movement tasks Journal Article In: Experimental Brain Research, vol. 159, no. 1, pp. 84–91, 2004. @article{Fecteau2004, In two-choice reaction time tasks, participants respond faster when the correct decision switches across consecutive trials. This alternation advantage has been interpreted as the guessing strategies of participants. Because the participants expect that the correct decision will switch across consecutive trials, they respond faster when this expectation is confirmed and they respond more slowly when it is disconfirmed. In this study, we evaluated the veracity of this expectancy interpretation. After replicating a long-lasting alternation advantage in saccadic reaction times (Experiment 1), we show that reducing the participants' ability to guess with a challenging mental rotation task does not change the alternation advantage, which suggests that expectancy is not responsible for the effect (Experiment 2). Next, we used prosaccade and antisaccade responses to dissociate between the sensory and motor contributions of the alternation advantage (Experiment 3) and we found that the alternation advantage originates from sensory processing. The implications of these findings are discussed with regard to guessing strategies, sensory processing, and how these findings may relate to inhibition of return. |
A. Caspi; B. R. Beutter; Miguel P. Eckstein The time course of visual information accrual guiding eye movement decisions Journal Article In: Proceedings of the National Academy of Sciences, vol. 101, no. 35, pp. 13086–13090, 2004. @article{Caspi2004, Saccadic eye movements are the result of neural decisions about where to move the eyes. These decisions are based on visual information accumulated before the saccade; however, during an approximately 100-ms interval immediately before the initiation of an eye movement, new visual information cannot influence the decision. Does the brain simply ignore information presented during this brief interval or is the information used for the subsequent saccade? Our study examines how and when the brain integrates visual information through time to drive saccades during visual search. We introduce a new technique, saccade-contingent reverse correlation, that measures the time course of visual information accrual driving the first and second saccades. Observers searched for a contrast-defined target among distractors. Independent contrast noise was added to the target and distractors every 25 ms. Only noise presented in the time interval in which the brain accumulates information will influence the saccadic decisions. Therefore, we can retrieve the time course of saccadic information accrual by averaging the time course of the noise, aligned to saccade initiation, across all trials with saccades to distractors. Results show that before the first saccade, visual information is being accumulated simultaneously for the first and second saccades. Furthermore, information presented immediately before the first saccade is not used in making the first saccadic decision but instead is stored and used by the neural processes driving the second saccade. |
Paul Dassonville; Jagdeep Bala Bala Perception, action, and Roelofs effect: A mere illusion of dissociation. Journal Article In: PLoS Biology, vol. 2, pp. 1936–1945, 2004. @article{Dassonville2004, A prominent and influential hypothesis of vision suggests the existence of two separate visual systems within the brain, one creating our perception of the world and another guiding our actions within it. The induced Roelofs effect has been described as providing strong evidence for this perception/action dissociation: When a small visual target is surrounded by a large frame positioned so that the frame's center is offset from the observer's midline, the perceived location of the target is shifted in the direction opposite the frame's offset. In spite of this perceptual mislocalization, however, the observer can accurately guide movements to the target location. Thus, perception is prone to the illusion while actions seem immune. Here we demonstrate that the Roelofs illusion is caused by a frame-induced transient distortion of the observer's apparent midline. We further demonstrate that actions guided to targets within this same distorted egocentric reference frame are fully expected to be accurate, since the errors of target localization will exactly cancel the errors of motor guidance. These findings provide a mechanistic explanation for the various perceptual and motor effects of the induced Roelofs illusion without requiring the existence of separate neural systems for perception and action. Given this, the behavioral dissociation that accompanies the Roelofs effect cannot be considered evidence of a dissociation of perception and action. This indicates a general need to re-evaluate the broad class of evidence purported to support this hypothesized dissociation. |
Paul Dassonville; Bruce Bridgeman; Jagdeep Kaur Bala; Paul Thiem; Anthony Sampanes The induced Roelofs effect: Two visual systems of the shift of a single reference frame? Journal Article In: Vision Research, vol. 44, pp. 603–611, 2004. @article{Dassonville2004a, Cognitive judgments about an object's location are distorted by the presence of a large frame offset left or right of an observer's midline. Sensorimotor responses, however, seem immune to this induced Roelofs illusion, with observers able to accurately point to the target's location. These findings have traditionally been used as evidence for a dissociation of the visual processing required for cognitive judgments and sensorimotor responses. However, a recent alternative hypothesis suggests that the behavioral dissociation is expected if the visual system uses a single frame of reference whose origin (the apparent midline) is biased toward the offset frame. The two theories make qualitatively distinct predictions in a paradigm in which observers are asked to indicate the direction symmetrically opposite the target's position. The collaborative findings of two laboratories clearly support the biased-midline hypothesis. |
Agnieszka Bojko; Arthur F. Kramer; Matthew S. Peterson Age equivalence in switch costs for prosaccade and antisaccade tasks Journal Article In: Psychology and Aging, vol. 19, no. 1, pp. 226–234, 2004. @article{Bojko2004, This study examined age differences in task switching using prosaccade and antisaccade tasks. Significant specific and general switch costs were found for both young and old adults, suggesting the existence of 2 types of processes: those responsible for activation of the currently relevant task set and deactivation of the previously relevant task set and those responsible for maintaining more than 1 task active in working memory. Contrary to the findings of previous research, which used manual response tasks with arbitrary stimulus-response mappings to study task-switching performance, no age-related deficits in either type of switch costs were found. These data suggest age-related sparing of task-switching processes in situations in which memory load is low and stimulus-response mappings are well learned. |
Walter R. Boot; Jason S. McCarley; Arthur F. Kramer; Matthew S. Peterson Automatic and intentional memory processes in visual search Journal Article In: Psychonomic Bulletin & Review, vol. 11, no. 5, pp. 854–861, 2004. @article{Boot2004, Previous research has indicated that saccade target selection during visual search is influenced by scanning history. Already inspected items are less likely to be chosen as saccade targets as long as the number intervening saccades is small. Here, we adapted Jacoby's (1991) process dissociation procedure to assess the role of intentional and automatic processes in saccade target selection. Results indicate a large automatic component biasing participants to move their eyes to unexamined locations. However, an intentional component allowed participants to both reinspect old items and aid their selection of new items. A second experiment examined inhibition of return (IOR) as a candidate for the observed automatic component. IOR was found for items that had been previously examined. It is concluded that both automatic and intentional memory traces are available to guide the eyes during search. |
Yuan-Chi Tseng; Chiang-Shan Ray Li Oculomotor correlates of context-guided learning in visual search Journal Article In: Perception and Psychophysics, vol. 66, no. 8, pp. 1363–1378, 2004. @article{Tseng2004, Previous studies have shown that context-facilitated visual search can occur through implicit learning. In the present study, we have explored its oculomotor correlates as a step toward unraveling the mechanisms that underlie such learning. Specifically, we examined a number of oculomotor parameters that might accompany the learning of context-guided search. The results showed that a decrease in the number of saccades occurred along with a fall in search time. Furthermore, we identified an effective search period in which each saccade monotonically brought the fixation closer to the target. Most important, the speed with which eye fixation approached the target did not change as a result of learning. We discuss the general implications of these results for visual search. |
Geoffrey Underwood; Lorraine Jebbett; Katharine Roberts Inspecting pictures for information to verify a sentence: Eye movements in general encoding and in focused search Journal Article In: Quarterly Journal of Experimental Psychology, vol. 57, no. 1, pp. 165–182, 2004. @article{Underwood2004, When we see combinations of text & graphics, such as photographs & their captions in printed media, how do we compare the information in the two components? Two experiments used a sentence-picture verification task in which statements about photographs of natural scenes were read in order to make a true/false decision about the validity of the sentence, & in which eye movements were recorded. In experiment 1, the sentence & the picture were presented concurrently, & objects & words could be inspected in any order. In experiment 2, the two components were presented one after the other, either picture first or sentence first. Fixation durations on pictures were characteristically longer than those on sentences in both experiments, & fixations on sentences varied according to whether they were being encoded as abstract propositions or as coreferents of objects depicted in a previously inspected picture. The decision time data present a difficulty for existing models of sentence verification tasks, with an inconsistent pattern of differences between true & false trials. |
Wieske Zoest; Mieke Donk; Jan Theeuwes The role of stimulus-driven and goal-driven control in saccadic visual selection Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 30, no. 4, pp. 746–759, 2004. @article{Zoest2004, Four experiments were conducted to investigate the role of stimulus-driven and goal-driven control in saccadic eye movements. Participants were required to make a speeded saccade toward a predefined target presented concurrently with multiple nontargets and possibly 1 distractor. Target and distractor were either equally salient (Experiments 1 and 2) or not (Experiments 3 and 4). The results uniformly demonstrated that fast eye movements were completely stimulus driven, whereas slower eye movements were goal driven. These results are in line with neither a bottom-up account nor a top-down notion of visual selection. Instead, they indicate that visual selection is the outcome of 2 independent processes, one stimulus driven and the other goal driven, operating in different time windows. |
Michael Varsori; Angelica Perez-Fornos; Avinoam B. Safran; Andrew R. Whatham Development of a viewing strategy during adaptation to an artificial central scotoma Journal Article In: Vision Research, vol. 44, no. 23, pp. 2691–2705, 2004. @article{Varsori2004, Although many individuals with a central scotoma develop eccentric fixation most often beneath or left of the scotoma, little is known about how they come to develop a particular viewing strategy. We investigated this by asking eight subjects with normal vision to read isolated letters, words and text passages while an artificial scotoma covered a central portion of the visual field. We quantified viewing strategy and analysed changes in their viewing behaviour over 8â€"10 sessions within a two-week period. Subjects read while either a horizontal (n = 4) or vertical bar scotoma (n = 4), 10° wide, covered the entire horizontal or vertical meridian of the stimulus field.For the horizontal scotoma group: (1) there was an increasing preference to use the inferior visual field for isolated letters/words and text passages, which was essentially complete within the test period; (2) the superior visual field was preferred when reading letters/words initially presented in upper visual space and the inferior visual field when reading letters/words initially presented in lower visual space; (3) in general, variation in viewing strategy according to stimulus position diminished over the sessions for all stimuli.For the vertical scotoma group: (1) two subjects used the left and right visual fields in approximately equal proportion to view isolated letters/words, one subject showed a weak preference to use the left visual field and one subject developed a strong preference for using the right visual field; (2) the text passages could be read with combined use of left and right visual fields in a specific manner; (3) the left visual field was preferred to view stimuli initially presented in left visual space while the right visual field was preferred for words initially presented in right visual space. This effect diminished across sessions.Overall, these findings indicate that (1) a specific viewing strategy can be developed through as little as 5 hours of reading experience without guided training; (2) two distinctly separate retinal areas can be used in an integrated manner during reading; (4) stimulus position in visual space can influence viewing strategy; (5) in general, reading encourages a preference for the inferior over the superior visual field, but not the left over right visual field. Letter/word/text recognition and reading speeds increased progressively across sessions, even after scotoma lateralisation appeared stabilised suggesting that multiple mechanism are involved in adaptive changes. |
Wolf Schwarz; Inge M. Keus Moving the eyes along the mental number line: Comparing SNARC effects with saccadic and manual responses Journal Article In: Perception and Psychophysics, vol. 66, no. 4, pp. 651–664, 2004. @article{Schwarz2004, Bimanual parityjudgments about numerically small (large) digits are faster with the left (right) hand, even though parity is unrelated to numerical magnitude per se (the SNARC effect; Dehaene, Bossini, & Giraux, 1993). According to one model, this effect reflects a space-related representation of numerical magnitudes (mental number line) with a genuine left-to-right orientation. Alternatively, it may simply reflect an overlearned motor association between numbers and manual responses–as, for example, on typewriters or computer keyboards–in which case it should be weaker or absent with effectors whose horizontal response component is less systematically associated with individual numbers. Two experiments involving comparisons of saccadic and manual parity judgment tasks clearly support the first view; they also establish a vertical SNARC effect, suggesting that our magnitude representation resembles a number map, rather than a number line. |
Jan Theeuwes; Richard Godijn Inhibition of return and oculomotor interference Journal Article In: Vision Research, vol. 44, pp. 1485–1492, 2004. @article{Theeuwes2004, The present study shows that inhibition-of-return reduces competition for selection within the oculomotor system. We examined the effect of a distractor when it was presented at an inhibited location (IOR). The results show that due to IOR distractors cause less interference. This was evident in all three measures. First, there was less oculomotor capture when a distractor was presented at an inhibited location. Second, the saccade latency to the target was shorter when a distractor appeared at an inhibited location than when it appeared at a non-inhibited location. Third, there was less curvature towards the distractor when it was presented at inhibited location relative to a non-inhibited location. The observation that there is less interference for a distractor presented at an inhibited location suggests that IOR reduces the exogenous activation of the distractor within the saccade map. |
Jan Theeuwes; Richard Godijn; Jay Pratt A new estimation of the duration of attentional dwell time Journal Article In: Psychonomic Bulletin & Review, vol. 11, no. 1, pp. 60–64, 2004. @article{Theeuwes2004a, How rapidly can attention move from one object to the next? Previous studies in which the dwell time paradigm was used have estimated attentional switch times of 200-500 msec, results incompatible with the search rate estimates of 25-50 msec shown in numerous visual search studies. It has been argued that dwell times are so long in the dwell time paradigm because the attentional shifts measured are unlike those used in visual search. In the present experiment, a variation of a visual search task was used, in which serial endogenous (volitional) deployments of attention were measured directly by means of a probe reaction time task. The experiment revealed a dwell time of about 250 msec, consistent with the faster estimates from other dwell time studies. This result suggests that endogenous shifts of attention may be relatively slow and that the faster attentional shifts estimated from visual search tasks may be due to the involvement of bottom-up processes. |
John T. Serences; Jens Schwarzbach; Susan M. Courtney; Xavier Golay; Steven Yantis Control of object-based attention in human cortex Journal Article In: Cerebral Cortex, vol. 14, no. 12, pp. 1346–1357, 2004. @article{Serences2004, Visual attention is a mechanism by which observers select relevant or important information from the current visual array. Previous investigations have focused primarily on the ability to select a region of space for further visual analysis. These studies have revealed a distributed frontoparietal circuit that is responsible for the control of spatial attention. However, vision must ultimately represent objects and in real scenes objects often overlap spatially; thus attention must be capable of selecting objects and their properties nonspatially. Little is known about the neural basis of object-based attentional control. In two experiments, human observers shifted attention between spatially superimposed faces and houses. Event-related functional magnetic resonance imaging (fMRI) revealed attentional modulation of activity in face- and house-selective cortical regions. Posterior parietal and frontal regions were transiently active when attention was shifted between spatially superimposed perceptual objects. The timecourse of activity provides insight into the functional role that these brain regions play in attentional control processes. |
Bhavin R. Sheth; Shinsuke Shimojo Sound-aided recovery from and persistence against visual filling-in Journal Article In: Vision Research, vol. 44, no. 16, pp. 1907–1917, 2004. @article{Sheth2004, Disappearance phenomena, in which salient visual stimuli do not register consciously, have been known to occur. Recovery from such phenomena typically occurs through change in some visual attribute, such as increase in luminance contrast or stimulus duration. Thus far, there have been no reports of cross-modal modulation of disappearance phenomena. In particular, what effect a cross-modal attentional cue has on sensory suppression is unknown. Here, we show that an adapted, flickered visual target that is synchronous with a brief sound appears more vivid than a similarly adapted, otherwise identical, visual target that is offset in time by more than 200 ms from the auditory cue. We argue that the brief auditory stimuli momentarily boost the concurrent signal of the adapted visual stimulus at a site downstream of the visual adaptation, thus causing the transient recovery from the visual adaptation. Repetitive visual cues cause significantly less recovery from visual adaptation than repetitive auditory cues, implying that there are functions a cross-modal cue can perform that a cue of the same modality cannot. Moreover repetitive auditory cues selectively prevent synchronous visual targets from undergoing visual adaptation. Ours is the first report of cross-modal modulation of a disappearance phenomenon. |
Marcus Kaiser; Markus Lappe Perisaccadic mislocalization orthogonal to saccade direction. Journal Article In: Neuron, vol. 41, pp. 293–300, 2004. @article{Kaiser2004, Saccadic eye movements transiently distort perceptual space. Visual objects flashed shortly before or during a saccade are mislocalized along the saccade direction, resembling a compression of space around the saccade target. These mislocalizations reflect transient errors of processes that construct spatial stability across eye movements. They may arise from errors of reference signals associated with saccade direction and amplitude or from visual or visuomotor remapping processes focused on the saccade target's position. The second case would predict apparent position shifts toward the target also in directions orthogonal to the saccade. We report that such orthogonal mislocalization indeed occurs. Surprisingly, however, the orthogonal mislocalization is restricted to only part of the visual field. This part comprises distant positions in saccade direction but does not depend on the target's position. Our findings can be explained by a combination of directional and positional reference signals that varies in time course across the visual field. |
Mika Koivisto; Jukka Hyönä; Antti Revonsuo The effects of eye movements, spatial attention, and stimulus features on inattentional blindness Journal Article In: Vision Research, vol. 44, no. 27, pp. 3211–3221, 2004. @article{Koivisto2004, Observers often fail to detect the appearance of an unexpected visual object ("inattentional blindness"). Experiment 1 studied the effects of fixation position and spatial attention on inattentional blindness. Eye movements were measured. We found strong inattentional blindness to the unexpected stimulus even when it was fixated and appeared in one of the expected positions. The results suggest that spatial attention is not sufficient for attentional capture and awareness. Experiment 2 showed that the stimulus was easier to consciously detect when it was colored but the relation of the color to the color of the attended objects had no effect on detection. The unexpected stimulus was easiest to detect, when it represented the same category as the attended objects. |
Christof Körner; Iain D. Gilchrist Eye movements in a simple spatial reasoning task Journal Article In: Perception, vol. 33, no. 4, pp. 485–494, 2004. @article{Koerner2004a, We report two experiments in which participants read a question about the spatial relationship between two letters, then viewed a visual display containing the letters and were required to respond to the question. The format of the question influenced the nature of the eye movements generated to the visual display. Participants also had a tendency to make additional eye movements in order to generate a fixation sequence that corresponded to the order of the letters in the question. This demonstrates an influence of stored information on eye movement generation, and suggests that the scanpath plays a role in structuring the visual information to facilitate reasoning. |
Timothy L. Hodgson; Charlotte Golding; Dimitra Molyva; Clive R. Rosenthal; Christopher Kennard Eye movements during task switching: Reflexive, symbolic, and affective contributions to response selection Journal Article In: Journal of Cognitive Neuroscience, vol. 16, no. 2, pp. 318–330, 2004. @article{Hodgson2004, Active vision is a dynamic process involving the flexible coordination of different gaze strategies to achieve behavioral goals. Although many complex behaviors rely on an ability to efficiently switch between gaze-control strategies, few studies to date have examined mechanisms of task level oculomotor control in detail. Here, we report five experiments in which subjects alternated between conflicting stimulus-saccade mappings within a block of trials. The first experiment showed that there is no performance cost associated with switching between pro and anti saccades. However, follow-up experiments demonstrate that whenever subjects alternate between arbitrary stimulus-saccade mappings, latency costs are apparent on the first trial after a task change. More detailed analysis of switch costs showed that latencies were particularly elevated for saccades directed toward the same location that had been the target for a saccade on the preceeding trial. This saccade "inhibition of return" effect was most marked when unexpected error feedbacks cued task switches, suggesting that saccade selection processes are modulated by reward. We conclude that there are two systems for saccade control that differ in their characteristics following a task switch. The "reflexive" control system can be enabled/disabled in advance of saccade execution without incurring any performance cost. Switch costs are only observed when two or more arbitrary stimulus-saccade mappings have to be coordinated by a "symbolic" control system. |
Dirk Kerzel Attentional load modulates mislocalization of moving stimuli, but does not eliminate the error Journal Article In: Psychonomic Bulletin & Review, vol. 11, no. 5, pp. 848–853, 2004. @article{Kerzel2004, Localization of the onset and offset of a moving target is subject to a number of errors that have to be attributed to events following or preceding the target event. Apparently, observers are unable to ignore the spatiotemporal context surrounding the target event. In two experiments, observers' attention was directed toward a single position along a trajectory, two positions along a single trajectory, or two positions along two different trajectories. In the latter condition, attention to details of a single trajectory was reduced. At the same time, motion type was manipulated by varying the temporal interval between successive target presentations. The localization error was not affected by attentional load; however, effects of motion type were eliminated when two trajectories had to be attended to. It may be sufficient to notice that the target has moved for localization errors to occur, while specifics of the trajectory are ignored. |
2003 |
Dirk Kerzel Mental extrapolation of target position is strongest with weak motion signals and motor responses Journal Article In: Vision Research, vol. 43, no. 25, pp. 2623–2635, 2003. @article{Kerzel2003, Some accounts hold that the position of moving objects is extrapolated either in visual perception or visual short-term memory ("representational momentum"). However, some studies did not find forward displacement of the final position when smooth motion was used, whereas reliable displacement was observed with implied motion. To resolve this conflict, the frequency of position changes was varied to sample motion types between the extreme cases of implied and smooth motion. A continuous function relating frequency of target change and displacement was found: Displacement increased when the frequency of position changes was reduced. Further, the response mode was varied. Probe judgments produced less forward displacement than motor judgments such as mouse or natural pointing movements. Also, localization judgments were susceptible to motion context, but not to variations of probe shape or expectancy about trajectory length. It is suggested that forward displacement results from the extrapolation of the next step in the observed motion sequence. |
Dirk Kerzel; Karl R. Gegenfurtner Neuronal processing delays are compensated in the sensorimotor Journal Article In: Current Biology, vol. 13, no. 22, pp. 1975–1978, 2003. @article{Kerzel2003a, Moving objects change their position until signals from the photoreceptors arrive in the visual cortex. Nonetheless, motor responses to moving objects are accurate and do not lag behind the real-world position. The questions are how and where neural delays are compensated for. It was suggested that compensation is achieved within the visual system by extrapolating the position of moving objects. A visual illusion supports this idea: when a briefly flashed object is presented in the same position as a moving object, it appears to lag behind. However, moving objects do not appear ahead of their final or reversal points. We investigated a situation where participants localized the final position of a moving stimulus. Visual perception and short-term memory of the final target position were accurate, but reaching movements were directed toward future positions of the target beyond the vanishing point. Our results show that neuronal latencies are not compensated for at early stages of visual processing, but at a late stage when retinotopic information is transformed into egocentric space used for motor responses. The sensorimotor system extrapolates the position of moving targets to allow for precise localization of moving targets despite neuronal latencies. |
Masud Husain; Andrew Parton; Timothy L. Hodgson; Dominic J. Mort; Geraint Rees Self-control during response conflict by human supplementary eye field Journal Article In: Nature Neuroscience, vol. 6, no. 2, pp. 117–118, 2003. @article{Husain2003, Although medial frontal cortex is considered to have an important role in planning behavior and monitoring errors, the specific contributions of regions within it are poorly understood1, 2, 3. Here we report that a patient with a highly selective lesion of a medial frontal motor area—the supplementary eye field (SEF)—lacked control in changing the direction of his eye movement from either a previous intention or behavioral 'set'; however, he monitored his errors well and corrected them quickly. The results indicate a key new role for the SEF and show that medial frontal mechanisms for self-control of action may be highly specific, with the SEF critically involved in implementing oculomotor control during response conflict, but not in error monitoring. |
Toshihide Imaruoka; Toshio Yanagida; Satoru Miyauchi Attentional set for external information activates the right intraparietal area Journal Article In: Cognitive Brain Research, vol. 16, no. 2, pp. 199–209, 2003. @article{Imaruoka2003, Visual attention can be allocated to a location or an object by using two different types of information: internal information and external information. The results of recent psychological studies [Bagon and Egeth, Percept. Psychophys. 55 (1994) 485] suggest that an observer's attentional set determines how these two kinds of information are used in visual tasks. In this study, we measured brain activities during two modes of visual search; one is the feature search mode, in which an attentional set for knowledge of a target item (internal information) is used, and the other is the singleton detection mode, in which an attentional set for oddness in the visual scene (external information) is used. We found extended activation in the frontal and parietal areas for both search modes. In addition, a direct comparison of brain activity during the singleton detection mode and the feature search mode revealed that the areas around the right intraparietal sulcus were more involved in the attentional set for oddness. These results suggest that the human right intraparietal cortex is related to the attentional set for external information. |
Junji Ito; Andrey R. Nikolaev; Marjolein Luman; Maartje F. Aukes; Chie Nakatani; Cees Van Leeuwen Perceptual switching, eye movements, and the bus paradox Journal Article In: Perception, vol. 32, no. 6, pp. 681–698, 2003. @article{Ito2003, According to a widely cited finding by Ellis and Stark (1978 Perception 7 575-581), the duration of eye fixations is longer at the instant of perceptual reversal of an ambiguous figure than before or after the reversal. However, long fixations are more likely to include samples of an independent random event than are short fixations. This sampling bias would produce the pattern of results also when no correlation exists between fixation duration and perceptual reversals. When an appropriate correction is applied to the measurement of fixation durations, the effect disappears. In fact, there are fewer actual button-presses during the long intervals than would be expected by chance. Moving-window analyses performed on eye-fixation data reveal that no unique eye event is associated with switching behaviour. However, several indicators, such as blink frequency, saccade frequency, and the direction of the saccade, are each differentially sensitive to perceptual and response-related aspects of the switching process. The time course of these indicators depicts switching behaviour as a process of cascaded stages. |
Charissa R. Lansing; George W. McConkie Word identification and eye fixation locations in visual and visual-plus-auditory presentations of spoken sentences Journal Article In: Perception and Psychophysics, vol. 65, no. 4, pp. 536–552, 2003. @article{Lansing2003, In this study, we investigated where people look on talkers' faces as they try to understand what is being said. Sixteen young adults with normal hearing and demonstrated average speechreading proficiency were evaluated under two modality presentation conditions: vision only versus vision plus low-intensity sound. They were scored for the number of words correctly identified from 80 unconnected sentences spoken by two talkers. The results showed two competing tendencies: an eye primacy effect that draws the gaze to the talkers eyes during silence and an information source attraction effect that draws the gaze to the talker's mouth during speech periods. Dynamic shifts occur between eyes and mouth prior to speech onset and following the offset of speech, and saccades tend to be suppressed during speech periods. The degree to which the gaze is drawn to the mouth during speech and the degree to which saccadic activity is suppressed depend on the difficulty of the speech identification task. Under the most difficult modality presentation condition, vison only, accuracy was related to average sentence difficulty and individual proficiency in visual speech perception, but not to the proportion of gaze time directed toward the talkers mouth or toward other parts of the talker's face. |
Yuki Kamide; Gerry T. M. Altmann; Sarah L. Haywood The time-course of prediction in incremental sentence processing: Evidence from anticipatory eye movements Journal Article In: Journal of Memory and Language, vol. 49, no. 1, pp. 133–156, 2003. @article{Kamide2003, Three eye-tracking experiments using the 'visual-world' paradigm are described that explore the basis by which thematic dependencies can be evaluated in advance of linguistic input that unambiguously signals those dependencies. Following Altmann and Kamide (1999), who found that selectional information conveyed by a verb can be used to anticipate an upcoming Theme, we attempt to draw here a more precise picture of the basis for such anticipatory processing. Our data from two studies in English and one in Japanese suggest that (a) verb-based information is not limited to anticipating the immediately following (grammatical) object, but can also anticipate later occurring objects (e.g., Goals), (b) in combination with information conveyed by the verb, a pre-verbal argument (Agent) can constrain the anticipation of a subsequent Theme, and (c) in a head-final construction such as that typically found in Japanese, both syntactic and semantic constraints extracted from pre-verbal arguments can enable the anticipation, in effect, of a further forthcoming argument in the absence of their head (the verb). We suggest that such processing is the hallmark of an incremental processor that is able to draw on different sources of information (some non-linguistic) at the earliest possible opportunity to establish the fullest possible interpretation of the input at each moment in time. |
Monika Harvey; Iain D. Gilchrist; Bettina Olk; Keith Muir Eye-movement patterns do not mediate size distortion effects in hemispatial neglect: Looking without seeing Journal Article In: Neuropsychologia, vol. 41, no. 8, pp. 1114–1121, 2003. @article{Harvey2003, Over the last decade a range of studies have shown that some patients with hemispatial neglect subjectively underestimate the size of objects presented in their contralesional hemispace. Recently, it has been suggested that the effect is simply due to either hemianopia [Brain 124 (2001) 527], or the combination of neglect and hemianopia [Neurology 52 (1999) 1845]. In the current study we asked right hemisphere lesioned patients with and without neglect and hemianopia as well as healthy controls to judge either two horizontal or vertical lines presented simultaneously in right and left hemispace and monitored their eye movements. Three out of the six patients showed the predicted size distortion effect for horizontal lines. We found no evidence that the effect was mediated by eye movements. The two neglect patients who showed the strongest left side underestimation showed symmetrical (left, right) scanning of the lines both in terms of number of fixations and fixation time, yet they still failed to judge the relative size veridically. In addition, we did not find strong evidence for a link with hemianopia. We therefore propose that the effect reflects a computational/representational failure of processing for horizontal extent. |
Katia Duscherer; Daniel Holender Semantic priming from flanker words: Some limitations to automaticity Journal Article In: Psychologica Belgica, vol. 43, no. 3, pp. 153–179, 2003. @article{Duscherer2003, We explore under which conditions words flanking a centrally presented digit in the prime display can elicit semantic priming on the lexical decision to a subsequent letter string appearing at fixation about 1 sec later. No significant priming is found when the prime display requires an immediate odd/even classification of a digit (Experiment 1), a delayed recall of a digit (Experiment 3), or the detection of an infrequent change from the digit 4 to the letter A (Experiment 4). It is only in Experiment 2, in which nothing is presented at fixation during the prime display in positive lexical decision trials, that a positive semantic priming effect is found. These results are discussed in the framework of quantitative and qualitative limitations to processing automaticity. |
Elizabeth Gilman; Geoffrey Underwood Restricting the field of view to investigate the perceptual spans of pianists Journal Article In: Visual Cognition, vol. 10, no. 2, pp. 201–232, 2003. @article{Gilman2003, An experiment is reported, which was designed to determine how the perceptual span of pianists varies with developing skill and cognitive load. Eye-movements were recorded as musical phrases were presented through a gaze-contingent window, which contained one beat, two beats, or four beats. In a control condition, the music was presented without a window. The pianists were required to perform three tasks of varying cognitive load: An error-detection task (low load); a sight- reading task (medium load); and a transposition task (high load). Measures taken comprised fixation duration, fixation frequency, saccade length, fixation locations, performance duration, note duration, position of first error, number of errors, and eye±hand span. The results indicate that good and poor sight-readers do not differ in terms of perceptual span. However, good sight-readers were found to have larger eye±hand spans. Furthermore, the results show that increasing cognitive load decreases eye±hand span, but has little effect on perceptual span. |
Richard Godijn; Jan Theeuwes Parallel allocation of attention prior to the execution of saccade sequences Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 29, no. 5, pp. 882–896, 2003. @article{Godijn2003, In a series of 5 experiments, the allocation of attention prior to the execution of saccade sequences was examined by using a dual-task paradigm. In the primary task, participants were required to execute a sequence of 2 endogenous saccades. The secondary task was a forced-choice letter identification task. During the programming of the saccade sequences, letters were briefly presented at the saccade goals and at no-saccade locations. The results showed that performance was better for letters presented at any of the saccade goals than for letters presented at any of the no-saccade locations. The results support a spatial model that assumes that prior to the execution of a saccade sequence, attention is allocated in parallel to all saccade goals. |
Junghyun Park; Madeleine Schlag-Rey; John Schlag Spatial localization precedes temporal determination in visual perception Journal Article In: Vision Research, vol. 43, no. 15, pp. 1667–1674, 2003. @article{Park2003a, The temporal order of two spots of light successively appearing in the dark, just before a saccade, influences their perceived spatial relation. Both spots are mislocalized in the saccade direction - the second more so than the first - because mislocalization grows as time elapses from stimulus to saccade onset. On the other hand, the perceived order of the two spots may be altered if the second spot is at the focus of spatial attention. How would these illusory perceptions of space and time interact when they are brought to play together? Could they be independent or could one perception depend on the other? Here we show that perceived location of stimuli is not affected by illusory temporal order, whereas perceived temporal order is affected by misperceived location. The results suggest that the brain processes spatial location of visual stimuli before processing their temporal order. |
Junghyun Park; Madeleine Schlag-Rey; John Schlag Voluntary action expands perceived duration of its sensory consequence Journal Article In: Experimental Brain Research, vol. 149, no. 4, pp. 527–529, 2003. @article{Park2003, When we look at a clock with a hand showing seconds, the hand sometimes appears to stay longer at its first-seen position than at the following positions, evoking an illusion of chronostasis. This illusory extension of perceived duration has been shown to be coupled to saccadic eye movement and it has been suggested to serve as a mechanism of maintaining spatial stability across the saccade. Here, we examined the effects of three kinds of voluntary movements on the illusion of chronostasis: key press, voice command, and saccadic eye movement. We found that the illusion can occur with all three kinds of voluntary movements if such movements start the clock immediately. When a delay is introduced between the voluntary movement and the start of the clock, the delay itself is overestimated. These results indicate that the illusion of chronostasis is not specific to saccadic eye movement, and may therefore involve a more general mechanism of how voluntary action influences time perception. |
Taosheng Liu; Scott D. Slotnick; John T. Serences; Steven Yantis Cortical mechanisms of feature-based attentional control Journal Article In: Cerebral Cortex, vol. 13, no. 12, pp. 1334–1343, 2003. @article{Liu2003, A network of fronto-parietal cortical areas is known to be involved in the control of visual attention, but the representational scope and specific function of these areas remains unclear. Recent neuroimaging evidence has revealed the existence of both transient (attention-shift) and sustained (attention-maintenance) mechanisms of space-based and object-based attentional control. Here we investigate the neural mechanisms of feature-based attentional control in human cortex using rapid event-related functional magnetic resonance imaging (fMRI). Subjects viewed an aperture containing moving dots in which dot color and direction of motion changed once per second. At any given moment, observers attended to either motion or color. Two of six motion directions and two of six colors embedded in the stimulus stream cued subjects either to shift attention from the currently attended to the unattended feature or to maintain attention on the currently attended feature. Attentional modulation of the blood oxygenation level dependent (BOLD) fMRI signal was observed in early visual areas that are selective for motion and color. More importantly, both transient and sustained BOLD activity patterns were observed in different fronto-parietal cortical areas during shifts of attention. We suggest these differing temporal profiles reflect complementary roles in the control of attention to perceptual features. |
Jason S. McCarley; Arthur F. Kramer; Gregory J. DiGirolamo Differential effects of the Müller-Lyer illusion on reflexive and voluntary saccades Journal Article In: Journal of Vision, vol. 3, no. 11, pp. 751–760, 2003. @article{McCarley2003, Research has produced conflicting evidence as to whether saccade programming is or is not biased by perceptual illusions. However, previous studies have generally not distinguished between effects of illusory percepts on reflexive saccades, programmed automatically in response to an external visual signal, and voluntary saccades, programmed purposively to a location where no signal has occurred. Here we find that voluntary and reflexive saccades are differentially susceptible to the Müller-Lyer illusion; reflexive movements are reliably but modestly affected by the illusion, whereas voluntary movements show an effect similar to that of perceptual judgments. Results suggest that voluntary saccade programming occurs within a non-retinotopic spatial representation similar to that of visual consciousness, whereas reflexive saccade programming occurs within a representation integrating retinotopic and higher level spatial frames. The effects of the illusion on reflexive saccades are not subject to endogenous control, nor are they modulated by the strength of an exogenous target signal. |
Jason S. Mccarley; Ranxiao F. Wang; Arthur F. Kramer; David E. Irwin; Matthew S. Peterson How much memory does oculomotor search have? Journal Article In: Psychological Science, vol. 14, no. 5, pp. 422–426, 2003. @article{Mccarley2003b, Research has demonstrated that oculomotor visual search is guided by memory for which items or locations within a display have already been inspected. In the study reported here, we used a gaze-contingent search paradigm to examine properties of this memory. Data revealed a memory buffer for search history of three to four items. This buffer was effected in part by a space-based trace attached to a location independently of whether the object that had been seen at that position remained visible, and was subject to interference from other stimuli seen in the course of a trial. |
Casimir J. H. Ludwig; Iain D. Gilchrist Target similarity affects saccade curvature away from irrelevant onsets Journal Article In: Experimental Brain Research, vol. 152, no. 1, pp. 60–69, 2003. @article{Ludwig2003, Saccade curvature away from visual distractors is a measure of the salience of these distractors for the oculomotor system. Three experiments are reported in which the integration of luminance onset signals and target similarity signals is examined, using a saccade curvature paradigm. Observers made saccades to a no-onset colour target in one of two positions on the vertical meridian. On most trials, an abrupt onset distractor that was either similar or dissimilar to the target appeared left or right on the horizontal midline. Saccades curved away from the irrelevant onsets; however, the amount of curvature was modulated by target similarity only when the onset appeared before the target (experiment 2) or when saccade initiation was delayed (experiment 3). These results suggest that the initial response to the onset is stimulus-driven and mediated by its transient component. Over time, the response is integrated with and augmented by top-down inputs. Visual and non-visual signals converge onto a common motor map to determine an item's salience. |
Casimir J. H. Ludwig; Iain D. Gilchrist Goal-driven modulation of oculomotor capture Journal Article In: Perception and Psychophysics, vol. 65, no. 8, pp. 1243–1251, 2003. @article{Ludwig2003a, In a recent study, Ludwig and Gilchrist (2002) showed that stimulus-driven oculomotor capture by abrupt onset distractors was modulated by distractor-target similarity: Participants were more likely to fixate an irrelevant onset when it shared the target color. Here we test whether this pattern of performance is the result of (1) inhibition of all items in the distractor color, (2) a response bias to local color discontinuities, or (3) the integration of stimulus-driven abrupt onset signals with goal-driven information about the target features. The results of two experiments clearly support the third explanation. We conclude that oculomotor capture is modulated by, but not contingent upon, top-down control, and our findings argue for an integrative view of the saccadic system. |
Lars Lünenburger; Klaus-Peter Hoffmann Arm movement and gap as factors influencing the reaction time of the second saccade in a double-step task Journal Article In: European Journal of Neuroscience, vol. 17, no. 11, pp. 2481–91, 2003. @article{Luenenburger2003, To guide our hand for reaching, we explore our visual environment by sequences of saccades. In the present paper, we studied the eye and hand movements of human subjects looking or looking and pointing at a target that is instantaneously displaced two times (double-step task). It was previously shown that the second saccade has a much longer reaction time than the first one [Feinstein & Williams (1972) Vision Res., 12, 33-44]. The second reaction time is even longer if the subject also has to point to the target with the hand [Lünenburger et al. (2000) Eur. J. Neurosci., 12, 4107-4116]. The conditions and objective for these effects are further examined in the present paper. It is shown that vision of the hand reduces the first and second saccadic reaction times in parallel. The second reaction time is prolonged for shorter delays between both target steps as well as for larger amplitudes of the second saccade. However, the long second reaction time does not reflect an absolute saccadic refractory period, because a gap before the second target step reduces the second reaction time to a value similar to the first. Hand response time and average hand velocity were increased when the second target step was larger. The response time for the eyes was about 30% of the response time of the hand. We argue that the observed effects reflect the coordination of eye and hand movement to allow a precise and efficient reaching behaviour. |
Ervin Poljac; Albert V. Berg Representation of heading direction in far and near head space Journal Article In: Experimental Brain Research, vol. 151, no. 2, pp. 501–513, 2003. @article{Poljac2003, Manipulation of objects around the head requires an accurate and stable internal representation of their locations in space, also during movements such as that of the eye or head. For far space, the representation of visual stimuli for goal-directed arm movements relies on retinal updating, if eye movements are involved. Recent neurophysiological studies led us to infer that a transformation of visual space from retinocentric to a head-centric representation may be involved for visual objects in close proximity to the head. The first aim of this study was to investigate if there is indeed such a representation for remembered visual targets of goal-directed arm movements. Participants had to point toward an initially foveated central target after an intervening saccade. Participants made errors that reflect a bias in the visuomotor transformation that depends on eye displacement rather than any head-centred variable. The second issue addressed was if pointing toward the centre of a wide-field expanding motion pattern involves a retinal updating mechanism or a transformation to a head-centric map and if that process is distance dependent. The same pattern of pointing errors in relation to gaze displacement was found independent of depth. We conclude that for goal-directed arm movements, representation of the remembered visual targets is updated in a retinal frame, a mechanism that is actively used regardless of target distance, stimulus characteristics or the requirements of the task. |
Marc Pomplun; Eyal M. Reingold; Jiye Shen Area activation: A computational model of saccadic selectivity in visual search Journal Article In: Cognitive Science, vol. 27, no. 2, pp. 299–312, 2003. @article{Pomplun2003, The Area Activation Model (Pomplun, Reingold, Shen, & Williams, 2000) is a computational model predicting the statistical distribution of saccadic endpoints in visual search tasks. Its basic assumption is that saccades in visual search tend to foveate display areas that provide a maximum amount of task-relevant information for processing during the subsequent fixation. In the present study, a counterintuitive prediction by the model is empirically tested, namely that saccadic selectivity towards stimulus features depends on the spatial arrangement of search items. We find good correspondence between simulated and empirically observed selectivity patterns, providing strong support for the Area Activation Model. |
Dimitris Agrafiotis; Nishan Canagarajah; David R. Bull; Matthew Dye Perceptually optimised sign language video coding based on eye tracking analysis Journal Article In: Electronics Letters, vol. 39, pp. 1–2, 2003. @article{Agrafiotis2003, A perceptually optimised approach to sign language video coding is presented. The proposed approach is based on the results (included) of an eye tracking study in the visual attention of sign language viewers. Results show reductions in bit rate of over 30% with very good subjective quality. |
Helena Ojanpää; Risto Näsänen Utilisation of spatial frequency information in face search Journal Article In: Vision Research, vol. 43, no. 24, pp. 2505–2515, 2003. @article{Ojanpaeae2003a, In previous studies the utilisation of spatial frequency information in face perception has been investigated by using static recognition tasks. In this study we used a visual search task, which requires eye movements and fast identification of previously learned facial photographs. Using Fourier phase randomisation, spatial information was selectively removed without changing the amplitude spectrum of the image. Fourier phase was randomised within one-octave wide bands of nine different centre spatial frequencies (2-32 c/face width, 0.63-10.1 c/deg). In a control condition no randomisation was used. All stimuli had similar contrast. Search times and eye movements during the search were measured. The removal of spatial information by phase randomisation at medium spatial frequencies resulted in a considerable increase of search times. In the main experiment the maximum of the search times occurred between 8 and 11 c/ face width. The number of eye fixations behaved similarly. In an additional experiment with a threefold viewing distance the search times increased and the maximum of the search times shifted slightly to lower object spatial frequencies (5.6-8 c/face width). This suggests that the band of spatial frequencies used in face search is not completely scale invariant. The results show that information most important to face search is located at a limited band of mid spatial frequencies. This is consistent with earlier studies, in which non-dynamical face recognition tasks and low-contrast stimuli have been used. |
Dominic J. Mort; Richard J. Perry; Sabira K. Mannan; Timothy L. Hodgson; Elaine Anderson; Rebecca Quest; Donald McRobbie; Alan McBride; Masud Husain; Christopher Kennard Differential cortical activation during voluntary and reflexive saccades in man Journal Article In: NeuroImage, vol. 18, no. 2, pp. 231–246, 2003. @article{Mort2003, A saccade involves both a step in eye position and an obligatory shift in spatial attention. The traditional division of saccades into two types, the "reflexive" saccade made in response to an exogenous stimulus change in the visual periphery and the "voluntary" saccade based on an endogenous judgement to move gaze, is supported by lines of evidence which include the longer onset latency of the latter and the differential effects of lesions in humans and primates on each. It has been supposed that differences between the two types of saccade derive from differences in how the spatial attention shifts involved in each are processed. However, while functional imaging studies have affirmed the close link between saccades and attentional shifts by showing they activate overlapping cortical networks, attempts to contrast exogenous with endogenous ("covert") attentional shifts directly have not revealed separate patterns of cortical activation. We took the "overt" approach, contrasting whole reflexive and voluntary saccades using event-related fMRI. This demonstrated that, relative to reflexive saccades, voluntary saccades produced greater activation within the frontal eye fields and the saccade-related area of the intraparietal sulci. The reverse contrast showed reflexive saccades to be associated with relative activation of the angular gyrus of the inferior parietal lobule, strongest in the right hemisphere. The frequent involvement of the right inferior parietal lobule in lesions causing hemispatial neglect has long implicated this parietal region in an important, though as yet uncertain, role in the awareness and exploration of space. This is the first study to demonstrate preferential activation of an area in its posterior part, the right angular gyrus, during production of exogenously triggered rather than endogenously generated saccades, a finding which we propose is consistent with an important role for the angular gyrus in exogenous saccadic orienting. |
Karen Mortier; Mieke Donk; Jan Theeuwes Attentional capture within and between objects Journal Article In: Acta Psychologica, vol. 113, pp. 133–145, 2003. @article{Mortier2003, The present study addressed the question whether attentional capture by abrupt onsets is affected by object-like properties of the stimulus field. Observers searched for a target circle at one of four ends of two solid rectangles. In the focused attention condition the location of the upcoming target was cued by means of a central arrowhead, whereas in the divided attention condition, the target location was not cued. Irrelevant abrupt onsets could appear either within the attended or within the non-attended object. The results showed that in the focused attention condition, onsets ceased to capture attention irrespective of whether the onset appeared within an attended object or within a non-attended object. © 2003 Elsevier Science B.V. All rights reserved. |
I. T. Armstrong; Douglas P. Munoz Inhibitory control of eye movements during oculomotor countermanding in adults with attention-deficit hyperactivity disorder Journal Article In: Experimental Brain Research, vol. 152, no. 4, pp. 444–452, 2003. @article{Armstrong2003a, Children with attention-deficit hyperactivity disorder (ADHD) are impulsive, and that impulsiveness can be measured using a countermanding task. Although the overt behaviors of ADHD attenuate with age, it is not clear how well impulsiveness is controlled in adults with ADHD. We tested ADHD adults with an oculomotor countermanding task. The task included two conditions: on 75% of the trials, participants viewed a central fixation marker and then looked to an eccentric target that appeared simultaneous with the disappearance of the fixation marker; on 25% of the trials, a signal was presented at variable delays after target appearance. The signal instructed subjects to stop, or countermand, an eye movement to the target. A correct movement in this case would be to hold gaze at the central fixation location. We expected ADHD participants to be impulsive in their countermanding performance. Additionally, we expected that a visual stop signal at the central fixation location would assist oculomotor countermanding because the signal is presented in the "stop" location, at fixation. To test whether a central stop signal positively biased countermanding, we used a three types of stop signal to instruct the stop: a central visual marker, a peripheral visual signal, and a non-localized sound. All subjects performed best with the central visual stop signal. Subjects with ADHD were less able to countermand eye movements and were influenced more negatively by the non-central signals. Oculomotor countermanding may be useful for quantifying impulsive dysfunction in adults with ADHD especially if a non-central stop signal is applied. |
Michael Coesmans; Peter A. Sillevis Smitt; David J. Linden; Ryuichi Shigemoto; Tomoo Hirano; Yoshinori Yamakawa; Adriaan M. Alphen; Chongde Luo; Josef N. Geest; Johan M. Kros; Carlos A. Gaillard; Maarten A. Frens; Chris I. De Zeeuw Mechanisms underlying cerebellar motor deficits due to mGluR1-autoantibodies Journal Article In: Annals of Neurology, vol. 53, no. 3, pp. 325–336, 2003. @article{Coesmans2003, Patients with Hodgkin's disease can develop paraneoplastic cerebellar ataxia because of the generation of autoantibodies against mGluR1 (mGluR1-Abs). Yet, the pathophysiological mechanisms underlying their motor coordination deficits remain to be elucidated. Here, we show that application of IgG purified from the patients' serum to cerebellar slices of mice acutely reduces the basal activity of Purkinje cells, whereas application to the flocculus of mice in vivo evokes acute disturbances in the performance of their compensatory eye movements. In addition, the mGluR1-Abs block induction of long-term depression in cultured mouse Purkinje cells, whereas the cerebellar motor learning behavior of the patients is affected in that they show impaired adaptation of their saccadic eye movements. Finally, postmortem analysis of the cerebellum of a paraneoplastic cerebellar ataxia patient showed that the number of Purkinje cells was significantly reduced by approximately two thirds compared with three controls. We conclude that autoantibodies against mGluR1 can cause cerebellar motor coordination deficits caused by a combination of rapid effects on both acute and plastic responses of Purkinje cells and chronic degenerative effects. |
Elliot M. Frohman; Padraig O'Suilleabhain; Richard B. Dewey; Teresa C. Frohman; Phillip D. Kramer A new measure of dysconjugacy in INO: The first-pass amplitude Journal Article In: Journal of the Neurological Sciences, vol. 210, no. 1-2, pp. 65–71, 2003. @article{Frohman2003, Background: The ratios of abducting to adducting eye movements (versional dysconjugacy index, VDI) for saccadic velocity and acceleration have been useful measures by which to objectively characterize internuclear ophthalmoparesis (INO). Amplitude measures of dysconjugacy have been less useful, given that many patients maintain the ability to ultimately reach a centrifugal fixation target and that traditional amplitude measures of VDI have focused on this 'final amplitude' (FA) position. Methods: We utilized infrared oculography to define a new amplitude measure of dysconjugacy in 42 multiple sclerosis (MS) patients with INO. The first-pass amplitude (FPA)-VDI is the ratio of abduction/adduction eye movement amplitudes computed at the time when the abducting eye initially achieves the centrifugal horizontal fixation target. Results: FPA-VDI values were significantly more sensitive and specific than FA-VDI values in demonstrating dysconjugacy in INO, and there was a 14-fold increase in dysconjugacy as measured by FPA-VDI Z-scores when compared to FA-VDI Z-scores. Conclusion: Consideration of velocity (pulse) and amplitude (step) components of dysconjugacy in patients with INO can provide a greater understanding of the dynamic aspects of this syndrome. We propose to characterize the relationship between the pathophysiology of INO and neuroradiologic measures of tissue injury in MS. |
Teresa C. Frohman; Elliot M. Frohman; Padraig O'Suilleabhain; A. R. Salter; Richard B. Dewey; N. Hogan; S. Galetta; A. G. Lee; D. Straumann; J. Noseworthy; D. Zee; J. Corbett; J. Corboy; V. M. Rivera; Phillip D. Kramer Accuracy of clinical detection of INO in MS: Corroboration with quantitative infrared oculography Journal Article In: Neurology, vol. 61, no. 6, pp. 848–850, 2003. @article{Frohman2003a, The authors compared the accuracy of clinical detection (by 279 physician observers) of internuclear ophthalmoparesis (INO) with that of quantitative infrared oculography. For the patients with mild adduction slowing, INO was not identified by 71%. Intermediate dysconjugacy was not detected by 25% of the evaluators. In the most severe cases, INO was not identified by only 6%. Oculographic techniques significantly enhance the precision of INO detection compared to the clinical exam. |
N. J. Upton; Timothy L. Hodgson; G. T. Plant; Richard J. S. Wise; Alexander P. Leff "Bottom-up" and "top-down" effects on reading saccades: A case study Journal Article In: Journal of Neurology, Neurosurgery and Psychiatry, vol. 74, no. 10, pp. 1423–1428, 2003. @article{Upton2003, OBJECTIVE: To investigate the role right foveal/parafoveal sparing plays in reading single words, word arrays, and eye movement patterns in a single case with an incongruous hemianopia. METHODS: The patient, a 48-year-old right handed male with a macular sparing hemianopia in his left eye and a macular splitting hemianopia in his right eye, performed various reading tasks. Single word reading speeds were monitored using a "voice-trigger" system. Eye movements were recorded while reading three passages of text, and PET data were gathered while the subject performed a variety of reading tasks in the camera. RESULTS: The patient was faster at reading single words and text with his left eye compared with his right. A small word length effect was present in his right eye but not his left. His eye movement patterns were more orderly when reading text with his left eye, making fewer saccades. The PET data provided evidence of "top-down" processes involved in reading. Binocular single word reading produced activity in the representation of foveal V1 bilaterally; however, text reading with the left eye only was associated with activation in left but not right parafoveal V1, despite there being visual stimuli in both visual fields. CONCLUSIONS: The presence of a word length effect (typically associated with pure alexia) can be caused by a macular splitting hemianopia. Right parafoveal vision is not critically involved in single word identification, but is when planning left to right reading saccades. The influence of top-down attentional processes during text reading can be visualised in parafoveal V1 using PET. |
I. T. Armstrong; Douglas P. Munoz Attentional blink in adults with attention-deficit hyperactivity disorder: Influence of eye movements Journal Article In: Experimental Brain Research, vol. 152, no. 2, pp. 243–250, 2003. @article{Armstrong2003, The attentional blink paradigm tests attention by overloading it: a list of stimuli is presented very rapidly one after another at the same location on a computer screen, each item overwriting the last, and participants monitor the list using two criteria [e.g. detect the target (red letter) and identify the probe (letter p)]. If the interval between the target and the probe is greater than about 500 ms, both are usually reported correctly, but, when the interval between the target and the probe is within 200-500 ms, report of the probe declines. This decline is the attentional blink, an interval of time when attention is supposedly switching from the first criterion to the second. The attentional blink paradigm should be difficult to perform correctly without vigilantly attending to the rapidly presented list. Vigilance tasks are often used to assess attention-deficit hyperactivity disorder (ADHD). Symptoms of the disorder include hyperactivity and attentional dysfunction; however, some people with ADHD also have difficulty maintaining gaze at a fixed location. We tested 15 adults with ADHD and their age- and sex-matched controls, measuring accuracy and gaze stability during the attentional blink task. ADHD participants reported fewer targets and probes, took longer to recover from the attentional blink, made more eye movements, and made identification errors consistent with non-perception of the letter list. In contrast, errors made by control participants were consistent with guessing (i.e., report of a letter immediately preceding or succeeding the correct letter). Excessive eye movements result in poorer performance for all participants; however, error patterns confirm that the weak performance of ADHD participants may be related to gaze instability as well as to attentional dysfunction. |
Caroline J. Ketcham; Timothy L. Hodgson; Christopher Kennard; George E. Stelmach Memory-motor transformations are impaired in Parkinson s disease Journal Article In: Experimental Brain Research, vol. 149, pp. 30–39, 2003. @article{Ketcham2003, Parkinson's disease patients are known to suffer loss of dopaminergic input to the rostral caudate nucleus. Recent functional magnetic resonance imaging (fMRI) studies have implicated this structure in the transformation of spatial information in memory to guide action, suggesting that memory to motor transformations may be selectively impaired in Parkinson's disease. In order to investigate this possibility we tested a group of Parkinson's disease patients (PDs) using a memory- guided pointing task. Of interest was whether patients showed reduced accuracy in the task as a function of memory load. Twelve PD patients and 13 elderly controls were asked to recall single or four step target sequences with 2 time delays (500 and 3,500 ms). In all memory- guided conditions PD patients showed increased variabil- ity in memory-guided movement end-points. This effect was not affected by delay, number of items, or the sequence familiarity. The results are consistent with increased variability in memory-motor transformations in early PD, due to dopamine depletion within the rostral caudate nucleus. |
Jiye Shen; Eyal M. Reingold; Marc Pomplun Guidance of eye movements during conjunctive visual search: The distractor-ratio effect Journal Article In: Canadian Journal of Experimental Psychology, vol. 57, no. 2, pp. 76–96, 2003. @article{Shen2003, The distractor-ratio effect refers to the finding that search performance in a conjunctive visual search task depends on the relative frequency of two types or subsets of distractors when the total number of items in a display is fixed. Previously, Shen, Reingold, and Pomplun (2000) examined participants' patterns of eye movements in a distractor-ratio paradigm and demonstrated that on any given trial saccadic endpoints were biased towards the smaller subset of distractors and participants flexibly switched between different subsets across trials. The current study explored the boundary conditions of this tendency to flexibly search through a smaller subset of distractors by examining the influence of several manipulations known to modulate search efficiency, including stimulus discriminability (Experiment 1), within-dimension versus cross-dimension conjunction search and distractor heterogeneity (Experiment 2). The results indicated that the flexibility of visual guidance and saccadic bias exemplified by the distractor-ratio effect is a robust phenomenon that mediates search efficiency by adapting to changes in the relative informativeness of stimulus dimensions and features. |
Shinsuke Shimojo; Claudiu Simion; Eiko Shimojo; Christian Scheier Gaze bias both reflects and influences preference Journal Article In: Nature Neuroscience, vol. 6, no. 12, pp. 1317–1322, 2003. @article{Shimojo2003, Emotions operate along the dimension of approach and aversion, and it is reasonable to assume that orienting behavior is intrinsically linked to emotionally involved processes such as preference decisions. Here we describe a gaze 'cascade effect' that was present when human observers were shown pairs of human faces and instructed to decide which face was more attractive. Their gaze was initially distributed evenly between the two stimuli, but then gradually shifted toward the face that they eventually chose. Gaze bias was significantly weaker in a face shape discrimination task. In a second series of experiments, manipulation of gaze duration, but not exposure duration alone, biased observers' preference decisions. We thus conclude that gaze is actively involved in preference formation. The gaze cascade effect was also present when participants compared abstract, unfamiliar shapes for attractiveness, suggesting that orienting and preference for objects in general are intrinsically linked in a positive feedback loop leading to the conscious choice. |
Andreas Schiegg; Heiner Deubel; Werner X. Schneider Attentional selection during preparation of prehension movements Journal Article In: Visual Cognition, vol. 10, no. 4, pp. 409–431, 2003. @article{Schiegg2003, In two experiments coupling between dorsal attentional selection for action and ventral attentional selection for perception during preparation of prehension movements was examined. In a dual-task paradigm subjects had to grasp an "X"-shaped object with either the left or the right hand's thumb and index finger. Simultaneously a discrimination task was used to measure visual attention prior to the execution of the prehension movements: Mask items transiently changed into distractors or discrimination targets. There was exactly one discrimination target per trial, which appeared at one of the four branch ends of the object. In Experiment 1 target position varied randomly while in Experiment 2 it was constant and known to subjects in each block of trials. In both experiments discrimination performance was significantly better for discrimination target positions at to-be-grasped branch ends than for not-to-be-grasped branch ends. We conclude that during preparation of prehension movements visual attention is largely confined to those parts of an object that will be grasped. |
Scott D. Slotnick; Jens Schwarzbach; Steven Yantis Attentional inhibition of visual processing in human striate and extrastriate cortex Journal Article In: NeuroImage, vol. 19, no. 4, pp. 1602–1611, 2003. @article{Slotnick2003, Allocating attention to a spatial location in the visual field is associated with an increase in the cortical response evoked by a stimulus at that location, compared to when the same stimulus is unattended. We used event-related functional magnetic resonance imaging to investigate attentional modulation of the cortical response to a stimulus probe at an attended location and to multiple probes at unattended locations. A localizer task and retinotopic mapping were used to precisely identify the cortical representations of each probe within striate (V1) and extrastriate cortex (V2, VP, V3, V4v, and V3A). The magnitude and polarity of attentional modulation were assessed through analysis of event-related activity time-locked to shifts in spatial attention. Attentional facilitation at the attended location was observed in striate and extrastriate cortex, corroborating earlier findings. Attentional inhibition of visual stimuli near the attended location was observed in striate cortex, and attentional inhibition of more distant stimuli occurred in both striate and extrastriate cortex. These findings indicate that visual attention operates both through facilitation of visual processing at the attended location and through inhibition of unattended stimulus representations in striate and extrastriate cortex. |
Mike Rinck; Elena Gámez; José M. Díaz; Manuel De Vega Processing of temporal information: Evidence from eye movements Journal Article In: Memory & Cognition, vol. 31, no. 1, pp. 77–86, 2003. @article{Rinck2003, In two experiments, we recorded eye movements to study how readers monitor temporal order information contained in narrative texts. Participants read short texts containing critical temporal information in the sixth sentence, which could be either consistent or inconsistent with temporal order information given in the second sentence. In Experiment 1, inconsistent sentences yielded more regressions to the second sentence and longer refixations of it. In Experiment 2, this pattern of eye movements was shown only by readers who noticed the inconsistency and were able to report it. Theoretical and methodological implications of the results for research on text comprehension are discussed. |
Jan Theeuwes; Giel Jan De Vries; Richard Godijn Attentional and oculomotor capture with static singletons Journal Article In: Perception and Psychophysics, vol. 65, no. 5, pp. 735–746, 2003. @article{Theeuwes2003, Previous research has shown that in visual search static singletons have the ability to capture attention (Theeuwes, 1991a, 1992). The present study investigated whether these singletons also have the ability to capture the eyes. Participants had to make an eye movement and respond manually to a shape singleton while a color singleton was present. When participants searched for a unique shape while a unique color singleton was present there was strong attentional and oculomotor capture (Experiment 1). However, when participants searched for a specific-shape singleton (a green circle) when a specific-color singleton (a red element) had to be ignored, there was attentional capture but no oculomotor capture (Experiment 2). The results suggest that an attentional set for a specific feature value defining both the target and the distractor (as in Experiment 2) allows such a fast disengagement of attention from the location of the distractor that a saccade execution to that location is prevented. |
Yutaka Sakaguchi Visual field anisotropy revealed by perceptual filling-in Journal Article In: Vision Research, vol. 43, no. 19, pp. 2029–2038, 2003. @article{Sakaguchi2003, Four experiments were performed to investigate how the time required for perceptual filling-in varies with the position of the target in the visual field. Conventional studies have revealed that filling-in is facilitated by a target with greater eccentricity, while no systematic studies have examined the effect of polar angle. Experiment 1 examined the effect of polar angle when the target and surround differed in luminance. Filling-in was facilitated as the target position changed from the horizontal to the vertical meridian. This dependency was more prominent in the upper field than in the lower, although no asymmetry was found between the left and right visual fields. These features were observed in both monocular and binocular viewing. These results were replicated in a modified stimulus configuration, in which the surround was a circular region concentric with the target (Experiment 2). Moreover, it was confirmed that the asymmetry was not due to fluctuation in the retinal image (i.e., eye movement) (Experiment 3). Finally, Experiment 4 examined whether this anisotropy was observed when two differently oriented gratings were presented in the target and surround regions. Again, filling-in was facilitated for a target close to the vertical meridian, irrespective of the relationship between the target and surround orientations. The underlying mechanism of this anisotropy is discussed from the viewpoints of cortical magnification and neural connections in the visual cortex. |
Kathryn Bock; David E. Irwin; Douglas J. Davidson; Willem J. M. Levelt Minding the clock Journal Article In: Journal of Memory and Language, vol. 48, no. 4, pp. 653–685, 2003. @article{Bock2003, Telling time is an exercise in coordinating language production with visual perception. By coupling different ways of saying times with different ways of seeing them, the performance of time-telling can be used to track cognitive transformations from visual to verbal information in connected speech. To accomplish this, we used eyetracking measures along with measures of speech timing during the production of time expressions. Our findings suggest that an effective interface between what has been seen and what is to be said can be constructed within 300 ms. This interface underpins a preverbal plan or message that appears to guide a comparatively slow, strongly incremental formulation of phrases. The results begin to trace the divide between seeing and saying - or thinking and speaking - that must be bridged during the creation of even the most prosaic utterances of a language. |
Leonardo Chelazzi; Elisabeth Moores; Liana Laiti Associative knowledge controls deployment of visual selective attention Journal Article In: Nature neuroscience, vol. 6, no. 2, pp. 182–189, 2003. @article{Chelazzi2003, According to some models of visual selective attention, objects in a scene activate corresponding neural representations, which compete for perceptual awareness and motor behavior. During a visual search for a target object, top-down control exerted by working memory representations of the target's defining properties resolves competition in favor of the target. These models, however, ignore the existence of associative links among object representations. Here we show that such associations can strongly influence deployment of attention in humans. In the context of visual search, objects associated with the target were both recalled more often and recognized more accurately than unrelated distractors. Notably, both target and associated objects competitively weakened recognition of unrelated distractors and slowed responses to a luminance probe. Moreover, in a speeded search protocol, associated objects rendered search both slower and less accurate. Finally, the first saccades after onset of the stimulus array were more often directed toward associated than control items. |
Heiner Deubel; Werner X. Schneider Delayed saccades, but not delayed manual aiming movements, require visual attention shifts Journal Article In: Annals of the New York Academy of Sciences, vol. 1004, pp. 289–296, 2003. @article{Deubel2003, Several studies have shown that during the preparation of a goal-directed movement, perceptual selection (i.e., visual attention) and action selection (the selection of the movement target) are closely coupled. Here, we study attentional selection in situations in which delayed saccadic eye movements and delayed manual movements are prepared. A dual-task paradigm was used which combined the movement preparation with a perceptual discrimination task. The results demonstrate a fundamental difference between the preparation of saccades and of manual reaching. For delayed saccades, attention is pinned to the saccade target until the onset of the response. This does not hold for manual reaching, however. Although fast reaching movements require attention, reaches delayed more than 300 ms after movement cue onset can be already performed "off-line"; that is, attention can be withdrawn from the movement target. |
Hendrik Chris Dijkerman; Robert D. McIntosh; David Milner; Yves Rossetti; Caroline Tilikete; Richard C. Roberts Ocular scanning and perceptual size distortion in hemispatial neglect: Effects of prism adaptation and sequential stimulus presentation Journal Article In: Experimental Brain Research, vol. 153, no. 2, pp. 220–230, 2003. @article{Dijkerman2003, When asked to compare two lateralized shapes for horizontal size, neglect patients often indicate the left stimulus to be smaller. Gainotti and Tiacci (1971) hypothesized that this phenomenon might be related to a rightward bias in the patients' gaze. This study aimed to assess the relation between this size underestimation and oculomotor asymmetries. Eye movements were recorded while three neglect patients judged the horizontal extent of two rectangles. Two experimental manipulations were performed to increase the likelihood of symmetrical scanning of the stimulus display. The first manipulation entailed a sequential, rather than simultaneous presentation of the two rectangles. The second required adaptation to rightward displacing prisms, which is known to reduce many manifestations of neglect. All patients consistently underestimated the left rectangle, but the pattern of verbal responses and eye movements suggested different underlying causes. These include a distortion of space perception without ocular asymmetry, a failure to view the full leftward extent of the left stimulus, and a high-level response bias. Sequential presentation of the rectangles and prism adaptation reduced ocular asymmetries without affecting size underestimation. Overall, the results suggest that leftward size underestimation in neglect can arise for a number of different reasons. Incomplete leftward scanning may perhaps be sufficient to induce perceptual size distortion, but it is not a necessary prerequisite. |
Nicholas D. Cassavaugh; Arthur F. Kramer; David E. Irwin Influence of task-irrelevant onset distractors on the visual search performance of young and old adults Journal Article In: Aging, Neuropsychology, and Cognition, vol. 10, no. 1, pp. 44–60, 2003. @article{Cassavaugh2003, We examined potential age-related differences in attentional and oculomotor capture by single and multiple abrupt onsets in a singleton search paradigm. 24 participants were instructed to move their eyes as quickly as possible to a color singleton target and to identify a small letter located inside it. Either single or dual onset task-irrelevant distractors were presented simultaneously with the color change that defined the target, or one onset distractor was presented prior to and another onset distractor was presented during the participant's initial eye movement away from fixation. Young and old adults misdirected their eyes to the single and dual onset task-irrelevant distractors, on an equivalent proportion of trials, relative to control trials. However, older adults' saccade latencies and RTs were influenced to a greater extent by onsets compared to younger adults'. These data are discussed in terms of age-related differences in attentional control and oculomotor capture. |
Johannes M. Zanker; Melanie Doyle; Robin Walker Gaze stability of observers watching Op Art pictures Journal Article In: Perception, vol. 32, no. 9, pp. 1037–1049, 2003. @article{Zanker2003, It has been the matter of some debate why we can experience vivid dynamic illusions when looking at static pictures composed from simple black and white patterns. The impression of illusory motion is particularly strong when viewing some of the works of 'Op Artists, such as Bridget Riley's painting Fall. Explanations of the illusory motion have ranged from retinal to cortical mechanisms, and an important role has been attributed to eye movements. To assess the possible contribution of eye movements to the illusory-motion percept we studied the strength of the illusion under different viewing conditions, and analysed the gaze stability of observers viewing the Riley painting and control patterns that do not produce the illusion. Whereas the illusion was reduced, but not abolished, when watching the painting through a pinhole, which reduces the effects of accommodation, it was not perceived in flash afterimages, suggesting an important role for eye movements in generating the illusion for this image. Recordings of eye movements revealed an abundance of small involuntary saccades when looking at the Riley pattern, despite the fact that gaze was kept within the dedicated fixation region. The frequency and particular characteristics of these rapid eye movements can vary considerably between different observers, but, although there was a tendency for gaze stability to deteriorate while viewing a Riley painting, there was no significant difference in saccade frequency between the stimulus and control patterns. Theoretical considerations indicate that such small image displacements can generate patterns of motion signals in a motion-detector network, which may serve as a simple and sufficient, but not necessarily exclusive, explanation for the illusion. Why such image displacements lead to perceptual results with a group of Op Art and similar patterns, but remain invisible for other stimuli, is discussed. |
Thomas Wynn; Frederick Coolidge The role of working memory in the evolution of managed foraging Journal Article In: Before Farming, no. 2, pp. 1–16, 2003. @article{Wynn2003, This article proposes that a relatively simple evolutionary development in human cognition enabled the develop- ment of managed foraging systems and, ultimately, agriculture. This development, an increase in the capacity of working memory, resulted in an enhancement of such specific cognitive abilities as response inhibition, response preparation, resistance to interference, and the ability to integrate action across space and time. All are required for modern managed foraging systems, including hunting and gathering and agriculture. Archaeological evidence provides strong evidence for managed foraging by the middle of the European Upper Palaeolithic and South African Later Stone Age, and independent evidence for enhanced working memory capacity slightly earlier. This fits the hypothesis that enhanced working memory capacity was a relatively recent development in human evolu- tion, and one that enabled not just managed foraging, but perhaps modern culture itself. |
2002 |
Steven Yantis; Jens Schwarzbach; John T. Serences; Robert L. Carlson; Michael A. Steinmetz; James J. Pekar; Susan M. Courtney Transient neural activity in human parietal cortex during spatial attention shifts Journal Article In: Nature Neuroscience, vol. 5, no. 10, pp. 995–1002, 2002. @article{Yantis2002, Observers viewing a complex visual scene selectively attend to relevant locations or objects and ignore irrelevant ones. Selective attention to an object enhances its neural representation in extrastriate cortex, compared with those of unattended objects, via top-down attentional control signals. The posterior parietal cortex is centrally involved in this control of spatial attention. We examined brain activity during attention shifts using rapid, event-related fMRI of human observers as they covertly shifted attention between two peripheral spatial locations. Activation in extrastriate cortex increased after a shift of attention to the contralateral visual field and remained high during sustained contralateral attention. The time course of activity was substantially different in posterior parietal cortex, where transient increases in activation accompanied shifts of attention in either direction. This result suggests that activation of the parietal cortex is associated with a discrete signal to shift spatial attention, and is not the source of a signal to continuously maintain the current attentive state. |
Boris M. Velichkovsky; Alexandra Rothert; Mathias Kopf; Sascha M. Dornhoefer; Markus Joos Towards an express-diagnostics for level of processing and hazard perception Journal Article In: Transportation Research Part F: Traffic Psychology and Behaviour, vol. 5, no. 2, pp. 145–156, 2002. @article{Velichkovsky2002a, The analysis of eye movements can provide rich information about driver's attention and the course of behaviour in hazardous situations. We present data from a driving simulation study showing that the switching between preattentive and attentive processing is reflected in visual fixations. For this initial analysis, we considered fixations from the perspective of their duration and the amplitude of related saccades. Since fixation durations may change instantaneously from one fixation to the next, we further selected the temporal vicinity of the emerging hazard for a closer analysis of fixations around this time. With this second type of analysis, the fixations that actually "detect" a critical event can be discovered and their duration measured. Upon detection of an immediate hazard, there is an increase in fixation duration and a corresponding increase in occurrence of attentive fixations on the cost of preattentive ones. This switching from one level of processing to another is recognisable on a short, phasic time scale. We finally discuss attentional conditions where overlooked or not sufficiently processed hazards do not lead to the appropriate breaking reaction on the part of the driver. |
Harold Bekkering; Sebastiaan F. W. Neggers Visual search is modulated by action intentions Journal Article In: Psychological Science, vol. 13, no. 4, pp. 370–374, 2002. @article{Bekkering2002, The influence of action intentions on visual selection processes was investigated in a visual search paradigm. A predefined target object with a certain orientation and color was presented among distractors, and subjects had to either look and point at the target or look at and grasp the target. Target selection processes prior to the first saccadic eye movement were modulated by the different action intentions. Specifically, fewer saccades to objects with the wrong orientation were made in the grasping condition than in the pointing condition, whereas the number of saccades to an object with the wrong color was the same in the two conditions. Saccadic latencies were similar under the different task conditions, so the results cannot be explained by a speed-accuracy trade-off. The results suggest that a specific action intention, such as grasping, can enhance visual processing of action-relevant features, such as orientation. Together, the findings support the view that visual attention can be best understood as a selection-for-action mechanism. |
Eva Belke; Antje S. Meyer In: European Journal of Cognitive Psychology, vol. 14, no. 2, pp. 237–266, 2002. @article{Belke2002, We investigated the time course of conjunctive ''same''–''different'' judgements for visually presented object pairs by means of combined reaction time and on-line eye movement measurements. The analyses of viewing patterns, viewing times, and reaction times showed that participants engaged in a parallel self-terminating search for differences. In addition, the results obtained for objects differing in only one dimension suggest that processing times may depend on the relative codability of the stimulus dimensions. The results are reviewed in a broader framework in view of higher-order processes. We propose that overspecifications of colour, often found in object descriptions, may have an ''early'' visual rather than a ''late'' linguistic origin. In a parallel assessment of the detection materials, participants overspecified the objects' colour substantially more often than their size. We argue that referential overspecifications of colour are largely attributable to mechanisms of visual discrimination. |
Sebastiaan F. W. Neggers; H. Bekkering Coordinated control of eye and hand movements in dynamic reaching Journal Article In: Human Movement Science, vol. 21, no. 3, pp. 37–64, 2002. @article{Neggers2002, In the present study, we integrated two recent, at first sight contradictory findings regarding the question whether saccadic eye movements can be generated to a newly presented target during an ongoing hand movement. Saccades were measured during so-called adaptive and sustained pointing conditions. In the adapted pointing condition, subjects had to direct both their gaze and arm movements to a displaced target location. The results showed that the eyes could fixate the new target during pointing. In addition, a temporal coupling of these corrective saccades was found with changes in arm movement trajectories when reaching to the new target. In the sustained pointing condition, however, the same subjects had to point to the initial target, while trying to deviate their gaze to a new target that appeared during pointing. It was found that the eyes could not fixate the new target before the hand reached the initial target location. Together, the results indicate that ocular gaze is always forced to follow the target intended by a manual arm movement. A neural mechanism is proposed that couples ocular gaze to the target of an arm movement. Specifically, the mechanism includes a reach neuron layer besides the well-known saccadic layer in the primate superior colliculus. Such a tight, sub-cortical coupling of ocular gaze to the target of a reaching movement can explain the contrasting behavior of the eyes in dependency of whether the eye and hand share the same target position or attempt to move to different locations. |
Jason P. Mitchell; C. Neil MacRae; Iain D. Gilchrist Working memory and the suppression of reflexive saccades Journal Article In: Journal of Cognitive Neuroscience, vol. 14, no. 1, pp. 95–103, 2002. @article{Mitchell2002, Conscious behavioral intentions can frequently fail under conditions of attentional depletion. In attempting to trace the cognitive origin of this effect, we hypothesized that failures of action control–specifically, oculomotor movement–can result from the imposition of fronto-executive load. To evaluate this prediction, participants performed an antisaccade task while simultaneously completing a working-memory task that is known to make variable demands on prefrontal processes (n-back task, see Jonides et al., 1997). The results of two experiments are reported. As expected, antisaccade error rates were increased in accordance with the fronto-executive demands of the n-back task (Experiment 1). In addition, the debilitating effects of working-memory load were restricted to the inhibitory component of the antisaccade task (Experiment 2). These findings corroborate the view that working memory operations play a critical role in the suppression of prepotent behavioral responses. |
Helena Ojanpää; Risto Näsänen; Ilpo Kojo Eye movements in the visual search of word lists Journal Article In: Vision Research, vol. 42, no. 12, pp. 1499–1512, 2002. @article{Ojanpaeae2002, The word identification span refers to the area of the visual field in which words can be identified during a single fixation. The purpose of the study was to estimate the vertical word identification span in a visual word search task, in which words were arranged in a vertical list. In addition, we studied the effect of list layout (orientation, length, and line spacing) on the speed of search and eye movements. The task of the observer was to identify a target word in a word list, where the other words were distracters. Threshold search time, that is, stimulus presentation time for correct identification at a probability level of 0.79, was determined by using a multiple alternative staircase method. Eye movements were recorded simultaneously. The results showed that, in vertical lists, 4-5 words could be identified during a single fixation. Thus, the vertical word identification span was 4-5 character spaces, whereas according to previous studies the horizontal word identification span is about 10 character spaces, which corresponds to 1-2 words. There were fewer fixations and the saccade amplitudes were smaller for vertical than for horizontal lists of the same length. However, search times did not depend on list orientation. This was due to longer fixation times for vertical lists. Further, since average fixation duration for vertical lists was longer than for horizontal lists, processing time seems to depend on the number of items within the span. © 2002 Elsevier Science Ltd. All rights reserved. |
Richard Godijn; Jan Theeuwes Oculomotor capture and Inhibition of Return: Evidence for an oculomotor suppression account of IOR Journal Article In: Psychological Research, vol. 66, no. 4, pp. 234–246, 2002. @article{Godijn2002a, Previous research has shown that when subjects search for a particular target object the sudden appearance of a new object captures the eyes on a large proportion of trials. The present study examined whether the onset affects the oculomotor system even when the eyes move directly towards the target. Ten participants ranging in age from 18-28 yrs served as paid volunteers. Using a modified version of the oculomotor paradigm (see Theeuwes, Kramer, Hahn, & Irwin, 1998) we show that when the eyes moved to the target object, subsequent saccades were inhibited from moving to a location at which a new object had previously appeared (inhibition-of-return; IOR). Whether or not a saccade to the onset was executed had no effect on the size of the inhibition. In particular conditions, the trajectories of saccades to the target objects were slightly curved in the opposite direction of the onset. The data are interpreted in the context of a novel hypothesis regarding oculomotor IOR. |
Richard Godijn; Jan Theeuwes Programming of endogenous and exogenous saccades: Evidence for a competitive integration model Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 28, no. 5, pp. 1039–1054, 2002. @article{Godijn2002b, Participants were required to make a saccade to a uniquely colored target while ignoring the presentation of an onset distractor. The results provide evidence for a competitive integration model of saccade programming that assumes endogenous and exogenous saccades are programmed in a common saccade map. The model incorporates a lateral interaction structure in which saccade-related activation at a specific location spreads to neighboring locations but inhibits distant locations. In addition, there is top-down, location-specific inhibition of locations to which the saccade should not go. The time course of exogenous and endogenous activation in the saccade map can explain a variety of eye movement data, including endpoints, latencies, and trajectories of saccades and the well-known global effect. |
Veerle Gysen; Peter De Graef; Karl Verfaillie Detection of intrasaccadic displacements and depth rotations of moving objects Journal Article In: Vision Research, vol. 42, no. 3, pp. 379–391, 2002. @article{Gysen2002, In a display with a stationary and a moving object, subjects saccaded towards one of the objects and had to detect intrasaccadic changes in position or orientation of either the saccade target or the saccade flanker. Compared to performance for stationary objects, displacement detection for translating objects was better and unaffected by saccadic status of the changed object. This pattern proved to be specific to position changes in translating objects and did not generalize to other types of motion (i.e., rotation) or to other types of intrasaccadic changes (i.e., orientation shifts). Superior transsaccadic coding of the position of a translating object was also observed in control experiments with only a single object present on each trial. Possible accounts in terms of selective attention to moving objects and perceptual relevance of object position are pitted against the data, suggesting qualitative differences in the transsaccadic representation of translating and stationary objects. |
Veerle Gysen; Karl Verfaillie; Peter De Graef The effect of stimulus blanking on the detection of intrasaccadic displacements of translating objects Journal Article In: Vision Research, vol. 42, no. 16, pp. 2021–2030, 2002. @article{Gysen2002a, In a display with a stationary and a translating object, subjects made a saccade towards one of the objects and had to detect intrasaccadic changes in the position of either the saccade target or the saccade flanker. Sensitivity for displacements of the stationary and moving objects was measured in conditions with (60 and 220 ms) and without blanking. In the conditions without blanking, displacement detection for translating objects was better than detection for stationary objects, which confirmed previous results (Vis. Res. 42 (2002) 379). This pattern was reversed in the blanking conditions: Sensitivity for intrasaccadic displacements of the translating object decreased drastically in comparison to conditions without a blank and was even lower than sensitivity for the stationary object. The results suggest differences in the transsaccadic spatial representation of translating and stationary objects. While a change in the spatial position of a stationary object can be detected after a blank period of 60 and 220 ms, this seems impossible for a translating object, indicating timing differences in postsaccadic spatial localization processes. Accounts in terms of a fast and accurate motion processing mechanism that possibly makes use of gain control are discussed. © 2002 Elsevier Science Ltd. All rights reserved. |
Veerle Gysen; Karl Verfaillie; Peter De Graef Transsaccadic perception of translating objects: Effects of landmark objects and visual field position Journal Article In: Vision Research, vol. 42, no. 14, pp. 1785–1796, 2002. @article{Gysen2002b, Previously Gysen, De Graef, and Verfaillie [Vision Research 42 (2002) 379] showed that, with stimulus displays presenting one stationary and one translating object, sensitivity for intrasaccadic displacements was higher for translating than for stationary objects. In the present paper the importance of the relative encoding of the path of the translating object towards the stationary object is investigated. In three experiments we compared detection of intrasaccadic displacements of translating objects in relative motion (moving towards the landmark object) and translating objects moving in isolation. No 'facilitatory' effect of relative motion was found. However a visual field effect was present. Performance was always better for the translating object presented in the lower part in comparison to the upper part of the visual field. A fourth experiment investigated the sensitivity for intrasaccadic displacements of stationary and translating objects presented in the upper as well as in the lower visual field. A lower visual field advantage was observed. The superior performance for translating objects, as was found previously, was confirmed in the lower and upper visual field. |
Martin Greschner; Markus Bongard; Pal Rujan; Josef Ammermüller Retinal ganglion cell synchronization by fixational eye movements improves feature estimation Journal Article In: Nature Neuroscience, vol. 5, no. 4, pp. 341–347, 2002. @article{Greschner2002, Image movements relative to the retina are essential for the visual perception of stationary objects during fixation. Here we have measured fixational eye and head movements of the turtle, and determined their effects on the activity of retinal ganglion cells by simulating the movements on the isolated retina. We show that ganglion cells respond mainly to components of periodic eye movement that have amplitudes of roughly the diameter of a photoreceptor. Drift or small head movements have little effect. Driven cells that are located along contrast borders are synchronized, which reliably signals a preceding movement. In an artificial neural network, the estimation of spatial frequencies for various square wave gratings improves when timelocked to this synchronization. This could potentially improve stimulus feature estimation by the brain. |
Danny Gagnon; Gillian A. O'Driscoll; Michael Petrides; G. B. Pike The effect of spatial and temporal information on saccades and neural activity in oculomotor structures Journal Article In: Brain, vol. 125, no. 1, pp. 123–139, 2002. @article{Gagnon2002, It has been argued that saccade generation is supported by two systems, a'where' system that decides the direction and extent of an impending saccade, and a 'when' system that is involved in the timing of the release of fixation. We evaluated the contributions of these systems to saccade latencies, and used functional MRI to identify the neural substrates of these systems. We found that advance knowledge of the direction and the timing of an impending target movement had both overlapping and discrete effects on saccade latencies and on neural activation. Knowledge of either factor decreased regular saccade latencies. However, knowledge of target direction increased the number of predictive and express saccades while knowledge of target timing did not. The brain activation data showed that advance knowledge of the direction or the timing of the target movement activated primarily overlapping structures. The precentral gyrus, in the region of the frontal eye fields, was more active in conditions in which some aspect of the target movement was predictable than in saccade control and fixation conditions. In the basal ganglia, activation discriminated between advance knowledge of target timing and target direction. The lenticular nuclei were more active when only target timing was known in advance, while the caudate was more active when only target direction was known in advance. These data suggest that the neural structures supporting the 'where' and 'when' systems are highly overlapping, although there is some dissociation sub-cortically. Knowledge of target timing and target direction converge in precentral gyrus, a region where there is strong evidence of context-dependent modulation of neural activity. |
Timothy L. Hodgson; Dominic J. Mort; M. M. Chamberlain; Samuel B. Hutton; K. S. O'Neill; Christopher Kennard Orbitofrontal cortex mediates inhibition of return Journal Article In: Neuropsychologia, vol. 40, no. 12, pp. 1891–1901, 2002. @article{Hodgson2002, Recent accounts have proposed that orbitofrontal cerebral cortex mediates the control of behavior based on emotional feedback and its somatic correlates. Here, we describe the performance of a patient with circumscribed damage to orbitofrontal cortex during a task that requires switching between sensory-motor mappings, contingent on the occurrence of positive and negative reward feedbacks. In this test, normal subjects and other patients with prefrontal damage show an increase in latencies for eye movements towards locations at which a negative feedback was presented on the preceding trial. In contrast, our patient does not show this reward-dependent inhibition of return effect on saccades. She was also found to make an increased rate of ocular refixations during visual search and used a disorganized search strategy in a token foraging task. These findings suggest that orbital regions of the prefrontal cortex mediate an inhibitory effect on actions directed towards locations that have been subject to negative reinforcement. Further, this mechanism seems to play a role in controlling natural search and foraging behavior. |
Amelia R. Hunt; Raymond M. Klein Eliminating the cost of task set reconfiguration Journal Article In: Memory & Cognition, vol. 30, no. 4, pp. 529–539, 2002. @article{Hunt2002, With insufficient time to fully prepare for a switch in task, a deterioration in performance on the first trial of a new task would be expected. The interest of researchers has been captured by the residual switch costs that, surprisingly, remain despite sufficient time to prepare. We used avery simple task to investigate the costs to reaction time and accuracy associated with changing between two different instructional sets every eight trials. Subjects responded to left and right visual targets by making either spatially compatible or incompatible eye movements (Experiment 1) or buttonpress responses (Experiment 2). The subjects were cued as to whether to make the compatible or the incompatible response by the color of a border appearing on the perimeter of the display. In cases in which the subject alternated between making pro- and antisaccades, the large costs to reaction time and accuracy at the short cue-target stimulus onset asynchrony were completely eliminated when sufficient time was provided to prepare for the switch. This complete elimination of residual switch costs was not obtained when the same alternation was applied to manual responses. This pattern of results links residual costs to response selection processes and suggests that they are not a necessary component of the switch process. We propose that the elimination of "stubborn" residual switch costs is rooted in our use of a hypercompatible task (making saccades toward targets) that places minimal demands on response selection. |
Chiang-Shan Ray Li; Shih Chieh Lin A perceptual level mechanism of the inhibition of return in oculomotor planning Journal Article In: Cognitive Brain Research, vol. 14, no. 2, pp. 269–276, 2002. @article{Li2002, A motor response to a visual target presented at a precued spatial location is facilitated if the target is presented shortly after the cue and inhibited when the cue target onset asynchrony approaches a few hundred milliseconds. The latter effect is termed inhibition of return (IOR). It is suggested that IOR provides an important strategy for effective search in our visual environment. Despite studies demonstrating IOR in a number of behavioral tasks, its neural mechanism has remained elusive. As a fundamental step toward understanding these mechanisms, the current study examines whether IOR mainly involves a perceptual or a motor process. We conducted a series of experiments, in which the target instructed saccades to the cued or to a different location. In each experiment, we observed a similar pattern of IOR when the target followed the cue, but not when the saccade was directed to the cued location. In another two experiments, we demonstrated that the magnitude and temporal profile of IOR varied depending on whether an eye movement or a manual response was involved. Overall, the present study suggests that IOR results predominantly from a perceptual level mechanism, with its magnitude and time course modulated by the activation of specific motor effectors. We discuss the implications of these results for attention gating of perceptual inputs and for mechanisms of visuomotor control. |
Chiang-Shan Ray Li; Shih Chieh Lin Inhibition of return in temporal order saccades Journal Article In: Vision Research, vol. 42, no. 17, pp. 2089–2093, 2002. @article{Li2002a, Inhibition of return (IOR) is an attention mechanism that expedites the search of an object in our environment. Results in different studies support either a perceptual or motor account of IOR. One problem with the perceptual account is that IOR has not been observed in temporal order judgment. Here we demonstrate that IOR can be observed in a temporal order saccade task where eye movement instead of manual response is used to select the target. The result suggests the importance of monitoring eye movement in studies of IOR. |
Matthew S. Peterson; Arthur F. Kramer; David E. Irwin; Sowon Hahn Modulation of oculomotor capture by abrupt onsets during attentionally demanding visual search Journal Article In: Visual Cognition, vol. 9, no. 6, pp. 755–791, 2002. @article{Peterson2002, The influence of abrupt onsets on attentionally demanding visual search (i.e., search for a letter target among heterogeneous letter distractors), as indexed by performance and eye movement measures, was investigated in a series of studies. In Experiments 1 and 2 we examined whether onsets would capture the eyes when the appearance of an onset predicted neither the location nor the identity of the target. Subjects did direct their eyes to the abrupt onsets on a disproportionate number of trials in these studies. Interestingly, however, onset capture was modulated by subjects' scan strategies. Furthermore, onsets captured the eyes less frequently than would have been predicted by paradigms showing attentional capture when no eye movements are required. Experiment 3 examined the question of whether onsets would capture the eyes in a situation in which they never served as the target. Capture was observed in this study. However, the magnitude of capture effects was substantially diminished as compared to previous behavioural studies in which the onset had a chance probability of serving as the target. These data are discussed in terms of the influence of top-down constraints on stimulus-driven attentional and oculomotor capture by abrupt onset stimuli. |
Casimir J. H. Ludwig; Iain D. Gilchrist Stimulus-driven and goal-driven control over visual selection Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 28, no. 4, pp. 902–912, 2002. @article{Ludwig2002a, This article explored the extent to which stimulus-driven control over visual selection is modulated by goal-driven factors. Observers searched for a no-onset color target among 3 distractors and signaled its location either manually or with a saccade. Additional distractors appeared either with or without an abrupt onset and were either similar or dissimilar to the target. Abrupt onsets disrupted saccades to the target, especially when they shared the target color. Irrelevant onsets also interfered with the manual responses, but this interference was dependent on the particular type of manual response. Stimulus-driven and contingent capture can occur within a single paradigm, but the extent and nature of these effects depend on the specific response required. |
Jason S. Carley; Arthur F. Kramer; Matthew S. Peterson Overt and covert object based attention Journal Article In: Psychonomic Bulletin & Review, vol. 9, no. 4, pp. 751–758, 2002. @article{Carley2002, To examine the role of perceptual object representations in the control of eye movements and attention, a pair of experiments adapted the object-cuing paradigm of Egly, Driver, and Rafal (1994) to require eye movements. Displays were pairs of adjacent rectangles, each containing two characters. Observers were asked to make a speeded judgment of a target character's orientation, and a cue was provided prior to target/distractor onset to indicate the target's likely location. Gaze-contingent presentation of target and distractors was used to demand overt scanning of displays. Eye movements during task perfor- mance evinced two forms of object-based effects. First, saccades following fixation on an invalidly cued item were more likely to be made within the cued rectangle than between rectangles. Second, sac- cades within the cued rectangle were preceded by shorter dwell times than saccades between rectan- gles. Extrafoveal processing of stimuli within the cued rectangle, however, was not facilitated, suggest- ing that covert attention was not allocated more densely within the cued than within the uncued object. |
Emanuela Bricolo; Tiziana Gianesini; Alessandra Fanini; Claus Bundesen; Leonardo Chelazzi Serial attention mechanisms in visual search: A direct behavioral demonstration Journal Article In: Journal of Cognitive Neuroscience, vol. 14, no. 7, pp. 980–993, 2002. @article{Bricolo2002, In visual search, inefficient performance of human observers is typically characterized by a steady increase in reaction time with the number of array elements-the so-called set-size effect. In general, set-size effects are taken to indicate that processing of the array elements depends on limited-capacity resources, that is, it involves attention. Contrasting theories have been proposed to account for this attentional involvement, however. While some theories have attributed set-size effects to the intervention of serial attention mechanisms, others have explained set-size effects in terms of parallel, competitive architectures. Conclusive evidence in favor of one or the other notion is still lacking. Especially in view of the wide use of visual search paradigms to explore the functional neuroanatomy of attentional mechanisms in the primate brain, it becomes essential that the nature of the attentional involvement in these paradigms be clearly defined at the behavioral level. Here we report a series of experiments showing that highly inefficient search indeed recruits serial attention deployment to the individual array elements. In addition, we describe a number of behavioral signatures of serial attention in visual search that can be used in future investigations to attest a similar involvement of serial attention in other search paradigms. We claim that only after having recognized these signatures can one be confident that truly serial mechanisms are engaged in a given visual search task, thus making it amenable for exploring the functional neuroanatomy underlying its performance. |
Tanja R. M. Coeckelbergh The effect of visual field defects on driving performance Journal Article In: Archives of Ophthalmology, vol. 120, no. 11, pp. 1509–1516, 2002. @article{Coeckelbergh2002a, Objectives: To investigate the effect of visual field de-fects on driving performance, and to predict practical fit-ness to drive. Methods: The driving performance of 87 subjects with visual field defects due to ocular abnormalities was as-sessed on a driving simulator and during an on-road driv-ing test. Outcome Measures: The final score on the on-road driving test and simulator indexes, such as driving speed, viewing behavior, lateral position, time-headway, and time to collision. Results: Subjects with visual field defects showed dif-ferential performance on measures of driving speed, steer-ing stability, lateral position, time to collision, and time-headway. Effective compensation consisted of reduced driving speed in cases of central visual field defects and increased scanning in cases of peripheral visual field de-fects. The sensitivity and specificity of models based on vision, visual attention, and compensatory viewing effi-ciency were increased when the distance at which the sub-ject started to scan was taken into account. Conclusions: Subjects with visual field defects demon-strated differential performance on several driving simu-lator indexes. Driving examiners considered reduced speed and increased scanning to be valid compensation for cen-tral and peripheral visual field defects, respectively. Pre-dicting practical fitness to drive was improved by taking driving simulator indexes into account. |
Lana Dépatie; Gillian A. O'Driscoll; Anne Lise V. Holahan; Victoria Atkinson; Joseph X. Thavundayil; N. Ng Ying Kin; Samarthji Lal Nicotine and behavioral markers of risk for schizophrenia: A double-blind, placebo-controlled, cross-over study Journal Article In: Neuropsychopharmacology, vol. 27, no. 6, pp. 1056–1070, 2002. @article{Depatie2002, We investigated the effect of nicotine on three behavioral markers of risk for schizophrenia: sustained attention (using the Continuous Performance Task (CPT)), antisaccade performance, and smooth pursuit. Smooth pursuit was investigated in two conditions, one in which attention was enhanced (monitoring target changes) and one in which attention was not enhanced (no monitoring). Patients with schizophrenia (n = 15) and controls (n = 14) were given a 14-mg nicotine patch in a double-blind, placebo-controlled, crossover design and plasma nicotine concentrations were monitored. Nicotine concentrations were similar in both groups. A Group X Drug interaction (p < .02) on CPT hits indicated that nicotine improved sustained attention in patients but not in controls. Nicotine significantly decreased antisaccade errors (p < .01) in both groups. A Drug X Monitoring condition interaction (p < .01) on pursuit gain indicated that nicotine significantly increased pursuit gain in the no-monitoring condition in patients and controls equally, but did not improve pursuit in the monitoring condition. Thus, improvement in pursuit may have been mediated via an effect on attention rather than by an effect on oculomotor function per se. In patients, the magnitude of improvement in attention on nicotine was correlated with the improvement on eye movement tasks. Thus, nicotine improves performance on both attention and oculomotor markers of risk for schizophrenia, possibly via common mechanisms. |
Timothy L. Hodgson; B. Tiesman; Adrian M. Owen; Christopher Kennard Abnormal gaze strategies during problem solving in Parkinson's disease Journal Article In: Neuropsychologia, vol. 40, no. 4, pp. 411–422, 2002. @article{Hodgson2002a, We have taken a novel approach to the study of problem solving involving the detailed analysis of natural scanning eye movements during the 'one touch' Tower of London task. Control subjects and patients with idiopathic Parkinson's disease (PDs) viewed a series of pictures depicting two arrangements of coloured balls in pockets within the upper and lower halves of a computer display. The task was to plan (but not execute) the shortest movement sequence required to rearrange the balls in one half of the display (the Workspace) to match the arrangement in the opposite half (the Goalspace) and indicate the number of moves required for problem solution. As problem complexity increased, control subjects spent proportionally more time fixating the Workspace region. This pattern was found regardless of whether subjects were instructed to solve problems by rearranging balls in the lower or upper visual fields. The distribution of gaze within the Workspace was also found to be problem dependent, with gaze being selectively directed towards the problem critical balls. In contrast, PDs were found to make more errors in the task and failed to show any dissociation in the amount of time fixating the two halves of the display. This pattern suggests that the patients had difficulty in encoding and/or maintaining current goals during problem solving, consistent with a role for fronto-striatal circuits in mechanisms of working memory and attention. |
Sunila Jain; Frank A. Proudlock; Cris S. Constantinescu; Irene Gottlob Combined pharmacologic and surgical approach to acquired nystagmus due to multiple sclerosis Journal Article In: American Journal of Ophthalmology, vol. 134, no. 5, pp. 780–782, 2002. @article{Jain2002, PURPOSE: To describe a combined pharmacological and surgical approach to treating acquired nystagmus in a patient with multiple sclerosis. DESIGN: Interventional case report. METHODS: A 40-year-old patient with acquired horizontal and vertical nystagmus and severe oscillopsia secondary to multiple sclerosis had combined treatment with gabapentin and a vertical Kestenbaum-type procedure. RESULTS: After gabapentin treatment (3,000 mg orally daily) the horizontal nystagmus was significantly reduced, and the patient developed a marked chin-up position. The vertical nystagmus remained unchanged, dampening on downgaze. A recession of both inferior rectus muscles reduced the nystagmus significantly in primary position, the abnormal head position disappeared, and oscillopsia completely resolved. Treatment increased visual acuity from 6/24 in the right eye and 6/60 in the left eye to 6/9 in both eyes. CONCLUSIONS: Acquired nystagmus in multiple sclerosis can be significantly improved by using a combined pharmacological and surgical approach. |
Elliot M. Frohman; Teresa C. Frohman; Padraig O'Suilleabhain; H. Zhang; K. Hawker; M. K. Racke; W. Frawley; J. T. Phillips; Phillip D. Kramer Quantitative oculographic characterisation of internuclear ophthalmoparesis in multiple sclerosis: The versional dysconjugacy index Z score Journal Article In: Journal of Neurology, Neurosurgery and Psychiatry, vol. 73, pp. 51–55, 2002. @article{Frohman2002, Background: There is a poor correlation between multiple sclerosis disease activity, as measured by magnetic resonance imaging, and clinical disability. Objective: To establish oculographic criteria for the diagnosis and severity of internuclear ophthalmoparesis (INO), so that future studies can link the severity of ocular dysconjugacy with neuro- radiological abnormalities within the dorsomedial brain stem tegmentum. Methods: The study involved 58 patients with multiple sclerosis and chronic INO and 40 normal sub- jects. Two dimensional infrared oculography was used to derive the versional dysconjugacy index (VDI)—the ratio of abducting to adducting eye movements for peak velocity and acceleration. Diagnostic criteria for the diagnosis and severity of INO were derived using a Z score and histogram analysis, which allowed comparisons of the VDI from multiple sclerosis patients and from a control population. Results: For a given saccade, the VDI was typically higher for acceleration v velocity, whereas the Z scores for velocity measures were always higher than values derived from comparable acceleration VDI measures; this was related to the greater variability of acceleration measures. Thus velocity was a more reliable measure from which to determine Z scores and thereby the criteria for INO and its level of severity. The mean (SD) value of the VDI velocity derived from 40 control subjects was 0.922 (0.072). The highest VDI for velocity from a normal control subject was 1.09, which was 2.33 SD above the normal control mean VDI. We therefore chose 2 SD beyond this value (that is, a Z score of 4.33) as the minimum criterion for the oculographic confirmation of INO. Of patients thought to have unilateral INO on clinical grounds, 70% (16/23) were found to have bilateral INO on oculographic assessment. Conclusions: INO can be confirmed and characterised by level of severity using Z score analysis of quantitative oculography. Such assessments may be useful for linking the level of severity of a specific clinical disability with neuroradiological measures of brain tissue pathology in multiple sclerosis. I |
Monika Harvey; Bettina Olk; Keith Muir; Iain D. Gilchrist Manual responses and saccades in chronic and recovered hemispatial neglect: A study using visual search Journal Article In: Neuropsychologia, vol. 40, no. 7, pp. 705–717, 2002. @article{Harvey2002, Hemispatial neglect affects both the ability to respond to targets on the contralesional side of space and to programme saccades to such targets. In the current study, we looked in detail at saccade programming and manual reaction times (RTs) in a range of visual search tasks, in which task difficulty was systematically increased by changing the nature of the distractors. In condition 1, the target was presented with no distractors. In the other conditions, displays contained three distractors that were changed across conditions to manipulate similarity to the target and so task difficulty. We tested two neglect patients, one chronic, one recovered along with two RCVA control patients and 12 age-matched controls. Both neglect patients studied could successfully execute saccades into the neglected field when the target was presented alone. However, a dissociation emerged between the two patients when the target was presented with distractor items. Patient ERs first saccade to target performance in the three search conditions revealed clear effects of distractor type. In contrast for the recovered patient AF, the left/right difference was present for all search displays and appeared to be constant regardless of distractor type. This differential pattern of behaviour may reflect the different underlying neural causes of the neglect in these patients. In the current study, the measurement of saccades allowed the task to be fractionated, and thus, reveal the action of multiple mechanisms controlling saccades in search. |
Frank A. Proudlock; Irene Gottlob; Cris S. Constantinescu Oscillopsia without nystagmus caused by head titubation in a patient with multiple sclerosis Journal Article In: Journal of Neuro-Ophthalmology, vol. 22, no. 2, pp. 88–91, 2002. @article{Proudlock2002, Oscillopsia in patients who have brain stem disorders but not nystagmus is attributed to a failure of the vestibular-ocular reflex (VOR) to compensate for head movements. We report a patient who had marked head titubation and oscillopsia in aggressive multiple sclerosis but no nystagmus. Her severe head titubation precluded our ability to measure a VOR accurately. Because oscillopsia has also been described after rapid voluntary head oscillations in normal subjects, we queried whether the oscillopsia in our patient could be ascribed to the head movement alone. Six normal control subjects did not experience oscillopsia while shaking their heads at the same frequency as the patient's titubation. We conclude that the oscillopsia in our patient was probably the result of an impaired VOR or an alternative compensatory mechanism. |
M. L. M. Tant; Frans W. Cornelissen; Aart C. Kooijman; Wiebo H. Brouwer Hemianopic visual field defects elicit hemianopic scanning Journal Article In: Vision Research, vol. 42, no. 10, pp. 1339–1348, 2002. @article{Tant2002, Previous explanations for the variability in success of compensating for homonymous hemianopia (HH) has been in terms of extent of the brain injury. In using on-line eye movement registrations, we simulated HH in 16 healthy subjects and compared their scanning performance on a dot counting task to their own "normal" condition and to real HH patients' performance. We evidenced clear parallels between simulated and real HH, suggesting that hemianopic scanning behaviour is primarily visually elicited, namely by the visual field defect, and not by the additional brain damage. We further observed age-related processes in compensating for the HH. |
Tanja R. M. Coeckelbergh; Frans W. Cornelissen; Wiebo H. Brouwer; Aart C. Kooijman The effect of visual field defects on eye movements and practical fitness to drive Journal Article In: Vision Research, vol. 42, no. 5, pp. 669–677, 2002. @article{Coeckelbergh2002, Eye movements of subjects with visual field defects due to ocular pathology were monitored while performing a dot counting task and a visual search task. Subjects with peripheral field defects required more fixations, longer search times, made more errors, and had shorter fixation durations than control subjects. Subjects with central field defects performed less well than control subjects although no specific impairment could be pinpointed. In both groups a monotonous relationship was observed between the visual field impairment and eye movement parameters. The use of eye movement parameters to predict viewing behavior in a complex task (e.g. driving) was limited. |
Charles A. Collin; Avi Chaudhuri Using MATLAB with the Psychophysics Toolbox to present the heterochromatic fusion nystagmus stimulus Journal Article In: Behavior Research Methods, Instruments & Computers, vol. 34, no. 4, pp. 500–508, 2002. @article{Collin2002, We present a program for MATLAB that generates and presents the heterochromatic fusion nystagmus stimulus. This stimulus allows assessment of isoluminant states through recordings of reflexive eye movements (optokinetic nystagmus). The reflexive nature of the subject's response makes this stimulus especially useful with nonverbal subjects, such as children and animals. Unfortunately, the stimulus is complex and difficult to program. By presenting the present program, we hope to help those who wish to use this tool in their research. The code of the function can be downloaded at www. dal.ca/-mcmullen/downloads.html. |
Michael D. Crossland; Gary S. Rubin The use of an infrared eyetracker to measure fixation stability Journal Article In: Optometry and Vision Science, vol. 79, no. 11, pp. 735–739, 2002. @article{Crossland2002, PURPOSE: To assess fixation stability in patients, a scanning laser ophthalmoscope (SLO) has typically been required. Disadvantages of this technique include the need for a fixed viewing distance and rigid head support. Some modern infrared eyetrackers do not have these constraints. The purpose of this study was to compare fixation stability measurements made with these instruments. METHODS: Normal subjects were asked to fixate a 2.5 degrees high cross while fixation was measured with a SLO and an infrared eyetracker. Bivariate contour ellipse areas were calculated. RESULTS: There was a linear relationship between the bivariate contour ellipse areas measured using each instrument. Bivariate contour ellipse areas returned from the eyetracker were larger. There was no difference in test-retest variability between the instruments. CONCLUSIONS: The eyetracker indicates fixation to be less stable than the SLO does, perhaps because of eye movements to compensate for small head movements. Our eyetracker can be used to analyze fixation when viewing images at any distance, without the need for head immobilization. The eyetracker and the SLO complement each other in the investigation of visual behavior. |
Bettina Olk; Monika Harvey; Iain D. Gilchrist First saccades reveal biases in recovered neglect Journal Article In: Neurocase, vol. 8, no. 4, pp. 306–313, 2002. @article{Olk2002, Hemispatial neglect affects the ability to explore space on the side opposite a brain lesion. This deficit is also mirrored in abnormal saccadic eye movement patterns. The present study investigated if the recovery of neglect is also reflected in saccadic eye movements. Patient AF, who displayed strong hemispatial neglect 1 month post-right thalamic stroke, had largely recovered 3 months later when tested on visual exploration tasks of the Behavioural Inattention Test. At this stage, AF was tested on a visual search task while his eye movements (direction, latencies and amplitudes of first saccades) and manual reaction times were recorded. The experimental conditions differed with respect to stimulus number and distracter type and increased in difficulty. AF correctly generated saccades into the neglected field when the target was presented alone. In contrast, a considerable left/right difference was present for all multiple-stimulus search displays. Although recovered from neglect in standardized assessment, AF showed a strong rightward bias resulting in highly asymmetric response times and eye movement behaviour. We conclude that eye movement patterns are far more susceptible to remaining spatial impairments and can thus provide a sensitive means to assess the extent of neglect recovery. |