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2002 |
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 |
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. |
Maarten A. Frens Scleral search coils influence saccade dynamics Journal Article In: Journal of Neurophysiology, vol. 88, no. 2, pp. 692–698, 2002. @article{Frens2002,The scleral search coil technique is commonly used for recording eye movements. The goal of this paper is to investigate to what extent the placement of scleral search coils onto the eyes influences the kinematics of saccades. To that end saccadic eye movements of human subjects were recorded with an infrared video system, while they wore coils and we compared the main sequence properties with recordings in which no coils were mounted on the eyes. It was found that saccades last longer (by about 8%) and become slower (by about 5%) when both eyes wear coils. This is truly due to the fact that the coils are on the eyes and not due to other factors that are part of this method, such as the scleral anesthesia. The influence of coils in both eyes was also observed when one coil was mounted on one eye only. Therefore the effect that the coils have on the eye movements cannot be attributed to purely mechanical factors, such as inertial load on the eyeball or increased friction. Rather the coils appear to change the oculomotor command signals that drive the saccadic eye movements. |
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 Desmet; Constantijn De Baecke; Marc Brysbaert The influence of referential discourse context on modifier attachment in Dutch Journal Article In: Memory and Cognition, vol. 30, no. 1, pp. 150–157, 2002. @article{Desmet2002,In an eye-tracking experiment we investigated the influence of referential context on the attachment of a relative clause to two possible hosts (as in "Someone shot the servant of the actress who was on the balcony"). The attachment of the relative clause was disambiguated grammatically at the first word after the onset of the ambiguity in order to investigate immediate effects of discourse. The contexts had been verified in a sentence completion study to make sure that they induced a strong bias toward early or late closure. The results of the reading experiment, however, revealed no significant interaction of referential context with the attachment preference of the relative clause. The only robust and consistent effect we found was a preference for early closure, independent of the preceding context. These data favor accounts positing that referential context does not influence the initial attachment decision, but does play a role in later phases of sentence processing. |
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. |
David A. Leopold; Holger K. Plettenberg; Nikos K. Logothetis Visual processing in the ketamine-anesthetized monkey: Optokinetic and blood oxygenation level-dependent responses Journal Article In: Experimental Brain Research, vol. 143, no. 3, pp. 359–372, 2002. @article{Leopold2002,We used optokinetic responses and functional magnetic resonance imaging (fMRI) to examine visual processing in monkeys whose conscious state was modulated by low doses (1-2 mg/kg) of the dissociative anesthetic ketamine. We found that, despite the animal's dissociated state and despite specific influences of ketamine on the oculomotor system, optokinetic nystagmus (OKN) could be reliably elicited with large, moving visual patterns. Responses were horizontally bidirectional for monocular stimulation, indicating that ketamine did not eliminate cortical processing of the motion stimulus. Also, results from fMRI directly demonstrated that the cortical blood oxygenation level-dependent (BOLD) response to visual patterns was preserved at the same ketamine doses used to elicit OKN. Finally, in the ketamine-anesthetized state, perceptually bistable motion stimuli produced patterns of spontaneously alternating OKN that normally would be tightly coupled to perceptual changes. These results, taken together, demonstrate that after ketamine administration cortical circuits continue to processes visual patterns in a dose-dependent manner despite the animal's behavioral dissociation. While perceptual experience is difficult to evaluate under these conditions, oculomotor patterns revealed that the brain not only registers but also acts upon its sensory input, employing it to drive a sensorimotor loop and even responding to a sensory conflict by engaging in spontaneous perception-related state changes. The ketamine-anesthetized monkey preparation thereby offers a safe and viable paradigm for the behavioral and electrophysiological investigation of issues related to conscious perception and anesthesia, as well as neural mechanisms of basic sensory processing. |
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. |
Hyung-Chul O. Li; Eli Brenner; Frans W. Cornelissen; Eun-Soo Kim Systematic distortion of perceived 2D shape during smooth pursuit eye movements Journal Article In: Vision Research, vol. 42, no. 23, pp. 2569–2575, 2002. @article{Li2002b,Even when the retinal image of a static scene is constantly shifting, as occurs when the viewer pursues a small moving object with his or her eyes, the scene is usually correctly perceived to be static. Following early suggestions by von Helmholtz, it is commonly believed that this spatial stability is achieved by combining retinal and extra-retinal signals. Here, we report a perceptually salient 2D shape distortion that can arise during pursuit. We provide evidence that the perceived 2D shape reflects retinal image contents alone, implying that the extra-retinal signal is ignored when judging 2D shape. textcopyright 2002 Elsevier Science Ltd. All rights reserved. |
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{Ludwig2002,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. |
Casimir J. H. Ludwig; Iain D. Gilchrist Measuring saccade curvature: A curve-fitting approach Journal Article In: Behavior Research Methods, Instruments & Computers, vol. 34, no. 4, pp. 618–624, 2002. @article{Ludwig2002a,Saccade curvature is becoming a popular measure for detecting the presence of competing saccadic motor programs. Several different methods of quantifying saccade curvature have been employed. In the present study, we compared these metrics with each other and with novel measures based on curve fitting. Initial deviation metrics were only moderately associated with the more widely used metric of maximum curvature. The latter was strongly related to a recently developed area-based measure and to the novel methods based on second- and third-order polynomial fits. The curve-fitting methods showed that although most saccades curved in only one direction, there was a population of trajectories with both a maximum and a minimum (i.e., double-curved saccades). We argue that a curvature metric based on a quadratic polynomial fit deals effectively with both types of trajectories and, because it is based on all the samples of a saccade, is less susceptible to sampling noise. |
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. |
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. |
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. |
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. |
Frans W. Cornelissen; Enno M. Peters; John Palmer The Eyelink Toolbox: Eye tracking with MATLAB and the Psychophysics Toolbox Journal Article In: Behavior Research Methods, Instruments & Computers, vol. 34, no. 4, pp. 613–617, 2002. @article{Cornelissen2002,The Eyelink Toolbox software supports the measurement of eye movements. The toolbox provides an interface between a high-level interpreted language (MATLAB), a visual display programming tool- box (Psychophysics Toolbox), and a video-based eyetracker (Eyelink). The Eyelink Toolbox enables experimenters to measure eye movements while simultaneously executing the stimulus presentation routines provided by the Psychophysics Toolbox. Example programs are included with the toolbox distribution. Information on the Eyelink Toolbox can be found at http://psychtoolbox.org/. |
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. |
Eyal M. Reingold On the perceptual specificity of memory representations Journal Article In: Memory, vol. 10, no. 5-6, pp. 365–379, 2002. @article{Reingold2002,The present paradigm involved manipulating the congruency of the perceptual processing during the study and test phases of a recognition memory task. During each trial, a gaze-contingent window was used to limit the stimulus display to a region either inside or outside a 10 degrees square centred on the participant's point of gaze, constituting the Central and Peripheral viewing modes respectively. The window position changed in real time in concert with changes in gaze position. Four experiments documented better task performance when viewing modes at encoding and retrieval matched than when they mismatched (i.e., perceptual specificity effects). Viewing mode congruency effects were demonstrated with both verbal and non-verbal stimuli. The present research is motivated and discussed in terms of theoretical views proposed in the 1970s including the levels-of-processing framework and the proceduralist viewpoint. In addition, implications for current processing and multiple systems views of memory are outlined. |
Eyal M. Reingold; Lester C. Loschky Saliency of peripheral targets in gaze-contingent multiresolutional displays Journal Article In: Behavior Research Methods, Instruments & Computers, vol. 34, no. 4, pp. 491–499, 2002. @article{Reingold2002a,Gaze-contingent multiresolutional displays (GCMRDs) have been proposed to solve the processing and bandwidth bottleneck in many single-user displays, by dynamically placing high-resolution in a window at the center of gaze, with lower resolution everywhere else. The three experiments reported here document a slowing of peripheral target acquisition associated with the presence of a gaze-contingent window. This window effect was shown for displays using either moving video or still images. The win- dow effect was similar across a resolution-defined window condition and a luminance-defined window condition, suggesting that peripheral image degradation is not a prerequisite of this effect. The window effect was also unaffected by the type of window boundary used (sharp or blended). These results are interpreted in terms of an attentional bias resulting in a reduced saliency of peripheral targets due to increased competition from items within the window. We discuss the implications of the window effect for the study of natural scene perception and for human factors research related to GCMRDs. |
Eyal M. Reingold; Dave M. Stampe Saccadic inhibition in voluntary and reflexive saccades Journal Article In: Journal of Cognitive Neuroscience, vol. 14, no. 3, pp. 371–388, 2002. @article{Reingold2002b,The present study investigated saccadic inhibition in both voluntary and stimulus-elicited saccades. Two experiments examined saccadic inhibition caused by an irrelevant flash occurring subsequent to target onset. In each trial, participants were required to perform a single saccade following the presentation of a black target on a gray background, 4 degrees to the left or to the right of screen center. In some trials (flash trials), after a variable delay, a 33-msec flash was displayed at the top and bottom third of the monitor (these regions turned white). In all experimental conditions, histograms of flash-to-saccade latencies documented a decrease in saccadic frequency, forming a dip, time-locked to the flash and occurring as early as 60-70 msec following its onset. The fast latency of this effect strongly suggests a low-level, reflex-like, oculomotor effect, which was referred to as saccadic inhibition. A novel procedure was developed to allow comparisons of saccadic inhibition even across conditions, which in the absence of a flash (no-flash trials) produce dissimilar saccadic reaction times (SRTs) distributions. Experiment 1 examined the effects of the fixation stimulus on saccadic inhibition by contrasting three conditions: a gap condition (fixation stimulus disappeared 200 msec prior to target onset), a step condition (offset of the fixation stimulus was simultaneous with target onset), and an overlap condition (the fixation stimulus remained on for the duration of the trial). The overlap condition produced substantially stronger saccadic inhibition, relative to the gap and the step conditions. Experiment 2 contrasted the saccadic inhibition effect obtained for prosaccades (saccades aimed at the target) with the effect obtained for antisaccades (i.e., saccades aimed away from the same target). The onset of saccadic inhibition was earlier, and its magnitude was stronger, for antisaccades, relative to prosaccades. The plausibility that the superior colliculus is the neurophysiological locus of the saccadic inhibition effect was explored. |
Paola Ricciardelli; Emanuela Bricolo; Salvatore M. Aglioti; Leonardo Chelazzi My eyes want to look where your eyes are looking: Exploring the tendency to imitate another individual's gaze Journal Article In: NeuroReport, vol. 13, no. 17, pp. 2259–2264, 2002. @article{Ricciardelli2002,In this studyweinvestigated the tendencyofhumans toimitate the gaze direction of other individuals.Distracting gaze stimuli or non biological directional cues (arrows) were presented to observers performing an instructed saccadic eyemovement task. Eyemove- mentrecordings showed thatobserversperformedless accurately when the distracting gaze and the instructed saccade had opposite directions,with a substantial number of saccadesmatching the di- rection of the distracting gaze. Static (Experiment1) and dynamic (Experiment 2) gaze distracters, but not pointing arrows (Experiment 3), produced the e¡ect.Results showa strong predisposition of humans to imitate somebody else's oculomotor behaviour, even when detrimental to task performance. This is likely linked to a strong tendency to share attentional states of other individuals, known as joint attention. |
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. |
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. |
Amelia R. Hunt; Raymond M. Klein Eliminating the cost of task set reconfiguration Journal Article In: Memory and 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. |
Jukka Hyönä; Robert F. Lorch; Johanna K. Kaakinen Individual differences in reading to summarize expository text: Evidence from eye fixation patterns. Journal Article In: Journal of Educational Psychology, vol. 94, no. 1, pp. 44–55, 2002. @article{Hyoenae2002,Eye fixation patterns were used to identify reading strategies of adults as they read multiple-topic expository texts. A clustering technique distinguished 4 strategies that differed with respect to the ways in which readers reprocessed text. The processing of fast linear readers was characterized by the absence of fixations returning to previous text. Slow linear readers made lots of forward fixations and reinspected each sentence before moving to the next. The reading of nonselective reviewers was characterized by look backs to previous sentences. The distinctive feature of topic structure processors was that they paid close attention to headings. They also had the largest working-memory capacity and wrote the most accurate text summaries. Thus, qualitatively distinct reading strategies are observable among competent, adult readers. |
Jukka Hyönä; Seppo Vainio; Matti Laine A morphological effect obtains for isolated words but not for words in sentence context Journal Article In: European Journal of Cognitive Psychology, vol. 14, no. 4, pp. 417–433, 2002. @article{Hyoenae2002a,The effect of morphological complexity on word identification was studied in three experiments conducted in Finnish, employing the same set of target nouns. In Experiment 1, the target nouns were presented in isolation, and lexical decision times were employed as lexical access measures. In Experiments 2 and 3, the same wordsnwere embedded in sentence contexts, where both the inflected and non-inflected forms were equally plausible, and eye fixation patterns (Exp. 2) and lexical decision latencies (Exp. 3) were recorded. The experiment with isolated words replicated previous lexical decision studies by showing more effortful processing for inflected than monomorphemic nouns. However, this morphological complexity effect did not generalise to the context experiments; fixation durations and response latencies were highly similar for inflected and monomorphemic words. It is suggested that, at least for the type of inflected nouns studied,nthe morphological effect observed for isolated words may derive from the syntactic and/or semantic level and not necessarily from the lexical level, as previously assumed. |
Albrecht W. Inhoff; Cynthia M. Connine; Ralph Radach A contingent speech technique in eye movement research on reading Journal Article In: Behavior Research Methods, Instruments & Computers, vol. 34, no. 4, pp. 471–480, 2002. @article{Inhoff2002,A novel eye-movement-contingent method is presented. It builds on and extends established eye-movement-contingent visual display change methods in that it uses movements of the eyes to control the presentation of acoustic information during sentence reading. In one implementation, an irrelevant spoken word is presented when the eyes cross a predetermined spatial boundary before they move on to a selected visual target word. The relationship between the spoken word and the visual target is manipulated, and the pattern of interference, caused by the presentation of the spoken word, is used to determine the nature and time course of activated representations. Results from three recently completed experiments in which the technique was used show that a word's phonological code remains active after it has been read and that the activated code has speech-like properties. |
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. |
Johanna K. Kaakinen; Jukka Hyönä; Janice M. Keenan Perspective effects on online text processing Journal Article In: Discourse Processes, vol. 33, no. 2, pp. 159–173, 2002. @article{Kaakinen2002,The effect of a reading perspective on online text processing was studied by recording readers' eye movements during reading. Participants read an expository text about 4 countries with the goal of deciding whether one of the countries, designated by the experimenter as the reading perspective, would be a good new place of residence. The results showed better memory for perspective-relevant information and longer fixation times on perspective-relevant information. Individual differences in working memory were assessed with the reading span test. Results showed that the time course of the perspective effect varied with memory span: High-span readers showed a perspective relevance effect on initial reading of the target segments, whereas low-span readers showed the effect only in the later look backs. |
Boris M. Velichkovsky; Sascha M. Dornhoefer; Mathias Kopf; Jens R. Helmert; Markus Joos Change detection and occlusion modes in road-traffic scenarios Journal Article In: Transportation Research Part F: Traffic Psychology and Behaviour, vol. 5, no. 2, pp. 99–109, 2002. @article{Velichkovsky2002,Change blindness phenomena are widely known in cognitive science, but their relation to driving is not quite clear. We report a study where subjects viewed colour video stills of natural traffic while eye movements were recorded. A change could occur randomly in three different occlusion modes-blinks, blanks and saccades-or during a fixation (as control condition). These changes could be either relevant or irrelevant with respect to the traffic safety. We used deletions as well as insertions of objects. All occlusion modes were equivalent concerning detection rate and reaction time, deviating from the control condition only. The detection of relevant changes was both more likely and faster than that of irrelevant ones, particularly for relevant insertions, which approached the base line level. Even in this case, it took about 180 ms longer to react to changes when they occurred during a saccade, blink or blank. In a second study, relevant insertions and the blank occlusion were used in a driving simulator environment. We found a surprising effect in the dynamic setting: an advantage in change detection rate and time with blanks compared to the control condition. Change detection was also good during blinks, but not in saccades. Possible explanation of these effects and their practical implications are discussed. |
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. |
Scott D. Slotnick; Joseph B. Hopfinger; Stanley A. Klein; Erich E. Sutter Darkness beyond the light: Attentional inhibition surrounding the classic spotlight Journal Article In: NeuroReport, vol. 13, no. 6, pp. 773–778, 2002. @article{Slotnick2002,The aim of the present investigation was to determine the nature and spatial distribution of selective visual attention. Using cortical source localization of ERP data corresponding to 60 task-irrelevant stimuli across the visual field, we assessed attention effects on visual processing. Consistent with previous findings, visual processing was enhanced at the attended spatial location. In addition, this facilitation of processing extended from the attended location to the point of fixation resulting in a region of facilitation. Furthermore, a large region of inhibition was found surrounding this region of facilitation. The latter result is inconsistent with a simple facilitative spotlight model of attention and indicates that attention effects can be both facilitatory and inhibitory. |
Sonja Stork; Sebastiaan F. W. Neggers; Jochen Müsseler Intentionally-evoked modulations of smooth pursuit eye movements Journal Article In: Human Movement Science, vol. 21, no. 3, pp. 335–348, 2002. @article{Stork2002,When observers pursue a moving target with their eyes, they use predictions of future target positions in order to keep the target within the fovea. It was suggested that these predictions of smooth pursuit (SP) eye movements are computed only from the visual feedback of the target characteristics. As a consequence, if the target vanishes unexpectedly, the eye movements do not stop immediately, but they overshoot the vanishing point. We compared the spatial and temporal features of such predictive eye movements in a task with or without intentional control over the target vanishing point. If the observers stopped the target with a button press, the overshoot of the eyes was reduced compared to a condition where the offset was computer generated. Accordingly, the eyes started to decelerate well before the target offset and lagged further behind the target when it disappeared. The involvement of intentionally-generated expectancies in eye movement control was also obvious in the spatial trajectories of the eyes, which showed a clear flexion in anticipation of the circular motion path we used. These findings are discussed together with neurophysiological mechanisms underlying the SP eye movements. |
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. |
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. textcopyright 2002 Elsevier Science Ltd. All rights reserved. |
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. |
F. Møller; M. L. Laursen; J. Tygesen; A. K. Sjølie Binocular quantification and characterization of microsaccades Journal Article In: Graefe's Archive for Clinical and Experimental Ophthalmology, vol. 240, no. 9, pp. 765–770, 2002. @article{Moeller2002,BACKGROUND: The significance of microsaccades in the visual process has been discussed for more than 50 years. However, only a few studies have measured microsaccades binocularly, and detailed quantification and characterization of these small movements are needed in order to further understand their nature. METHOD: The amplitude, velocity, acceleration and direction of microsaccades were quantified binocularly in 10 normal test persons during a 40-s fixation task, using an infrared recording technique. RESULTS: All microsaccades for all test persons were performed simultaneously and individually with an almost identical amplitude in the right and left eye (a range of 0.003-0.042 deg between right and left eye mean values). The mean microsaccadic amplitude for the test persons was within a range of 0.223-1.079 deg. The directional difference between simultaneously-performed right and left eye microsaccades was less than 22.5 deg for 84.8% of the saccades, indicating that the majority of microsaccades are conjugated. Three different fixation patterns were identified and characterized: (1) a classic interplay between easily identified drifts and medium-sized microsaccades (mean amplitude range 0.328-0.413 deg); (2) long intersaccadic intervals (4-5 s) with almost absent drifts, followed by three or four large microsaccades (mean amplitude range 0.755-1.079 deg); and (3) low-amplitude drift movements interrupted by low-amplitude microsaccades (mean amplitude range 0.231-0.265 deg). CONCLUSION: Microsaccades are involuntary, predominantly conjugated, simultaneously performed, and of almost identical amplitude in the right and left eye, suggesting a central control mechanism for microsaccades at subcortical level. |
Bob McMurray; Michael K. Tanenhaus; Richard N. Aslin Gradient effects of within-category phonetic variation on lexical access Journal Article In: Cognition, vol. 86, no. 2, pp. B33–B42, 2002. @article{McMurray2002,In order to determine whether small within-category differences in voice onset time (VOT) affect lexical access, eye movements were monitored as participants indicated which of four pictures was named by spoken stimuli that varied along a 0-40 ms VOT continuum. Within-category differences in VOT resulted in gradient increases in fixations to cross-boundary lexical competitors as VOT approached the category boundary. Thus, fine-grained acoustic/phonetic differences are preserved in patterns of lexical activation for competing lexical candidates and could be used to maximize the efficiency of on-line word recognition. |
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. |
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. |
Dale J. Barr; Boaz Keysar Anchoring comprehension in linguistic precedents Journal Article In: Journal of Memory and Language, vol. 46, no. 2, pp. 391–418, 2002. @article{Barr2002,Past research has shown that when speakers refer to the same referent multiple times, they tend to standardize their descriptions by establishing linguistic precedents. In three experiments, we show that listeners reduce uncertainty in comprehension by taking advantage of these precedents. We tracked listeners' eye movements in a referential communication task and found that listeners identified referents more quickly when specific precedents existed than when there were none. Furthermore, we found that listeners expected speakers to adhere to precedents even in contexts where it would lead to referential overspecification. Finally, we provide evidence that the benefits of linguistic precedents are independent of mutual knowledge - listeners were not more likely to benefit from precedents when they were mutually known than when they were not. We conclude that listeners use precedents simply because they are available, not because they are mutually known. |
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. |
2001 |
Ch. Klein; P. Berg In: Psychophysiology, vol. 38, no. 4, pp. 704–711, 2001. @article{Klein2001,The aim of the present study was the comparative assessment of the 4-week test-retest stabilities of the saccadic CNV (sCNV) and saccadic reaction times (SRT) during the execution of pro- and antisaccades, as well as the stability of RT during execution of two neuropsychological tests of alertness and S-R incompatibility. Prosaccades were elicited under the 200-ms gap and overlap conditions, antisaccades under the overlap condition (64 trials each). The EEG was recorded from 25 channels with a DC amplifier (MES, Munich). Data of 20 healthy participants were statistically analyzed. We found high test-retest correlations for all SRT (.76 < or = r(tt) < or = .88) and neuropsychological (.62 < or = r(tt) < or = .88) measures. For the sCNV, coefficients ranging between .58 (pro/gap) and .77 (anti/overlap) were obtained. Whereas SRT were significantly faster during the second than during the first session, group means for the saccadic CNV were stable across the sessions. Our results suggest high 4-week stability of individual differences in SRT, and moderate to good stabilities of saccadic CNV amplitudes. Our results recommend these "traitlike" measures to be used in individual differences research. |
Masud Husain; Sabira K. Mannan; Timothy L. Hodgson; Ewa Wojciulik; Jon Driver; Christopher Kennard Impaired spatial working memory across saccades contributes to abnormal search in parietal neglect Journal Article In: Brain, vol. 124, no. 5, pp. 941–952, 2001. @article{Husain2001,Visual neglect of left space following right parietal damage in humans involves a lateral bias in attention, apparent in many search tasks. We hypothesized that parietal neglect may also involve a failure to remember which locations have already been examined during visual search: an impairment in retaining searched locations across saccades. Using a new paradigm, we monitored gaze during search, while simultaneously probing whether observers judged they had found a new target, or judged instead that they were re-fixating a previously examined target. A patient with left neglect following focal right parietal infarction repeatedly re-fixated right locations. Critically, he often failed to remember that these locations had already been searched, treating old targets as new discoveries at an abnormal rate. In comparison, healthy age-matched control subjects rarely re-fixated targets, and mistook old targets as new targets even more rarely. The frequency of such mistakes in the parietal patient, for different conditions, correlated with the severity of his neglect. Control experiments indicated no perceptual localization deficit in non-search tasks. These results suggest a deficit in retaining searched locations across saccades in parietal neglect, in addition to the lateral spatial bias. Moreover, the former deficit exacerbates the latter, such that patients do not realize that the rightward locations favoured by their bias have already been examined during previous fixations and, for this reason, they saccade back to them repeatedly. The combination of the two deficits (a lateral bias plus a deficit in retaining locations already searched) may thus explain the pathological pattern of search that characterizes parietal neglect: why stimuli on the right are re-examined recursively, as if being searched for the first time, and hence why stimuli on the left continue to be ignored even with unlimited viewing time. These proposals accord with recent electrophysiological and functional imaging data, demonstrating posterior parietal involvement in the retention of target locations across saccades. |
Jukka Hyönä; Seppo Vainio Reading morphologically complex clause structures in Finnish. Journal Article In: European Journal of Cognitive Psychology, vol. 13, no. 4, pp. 451–474, 2001. @article{Hyoenae2001,The study examined how morphologically complex clause constructions were processed during reading Finnish. Readers' eye fixation patterns were recorded when they read two alternative versions of the same linguistic construction, a morphologically complex converb construction and its less complex subclause counterpart. The complexity of the converb construction is apparent in the construction being marked by less perceivable bound morphemes, which make the clause subject and predicate morphologically more complex and more dense in information. Experiment 1 showed that more complex converb constructions produced longer gaze durations than the length- and frequency-matched subclause constructions. Experiment 2 showed that the complexity effect is reversed when the more complex clause form was clearly more common in the language than its less complex counterpart. It is concluded that both structural complexity and structural frequency influence the ease with which linguistic expressions are processed during reading. |
Arthur F. Kramer; Nicholas D. Cassavaugh; David E. Irwin; Matthew S. Peterson; Sowon Hahn Influence of single and multiple onset distractors on visual search for singleton targets Journal Article In: Perception and Psychophysics, vol. 63, no. 6, pp. 952–968, 2001. @article{Kramer2001,In three experiments, we examined attentional and oculomotor capture by single and multiple abrupt onsets in a singleton search paradigm. Subjects were instructed to move their eyes as quickly as possible to a color singleton target and to identify a small letter located inside of it. In Experiment 1, task-irrelevant sudden onsets appeared simultaneously on half the trials with the presentation of the color singleton target. Response times (RTs) were longer when onsets appeared in the display regardless of the number of onsets. Eye-scan strategies were also disrupted by the appearance of the onset distractors, although the proportion of trials on which the eyes were directed to the onsets was the same regardless of the number of onsets. In Experiment 2, we manipulated the time of presentation of two task-irrelevant onsets in order to further examine whether multiple onsets would be attended and fixated prior to attending a color singleton target. Again, subjects made a saccade to a task-irrelevant onset on a substantial proportion of trials prior to fixating the target. However, saccades to the second onset were rare. Experiment 3 served as a replication of Experiment 1 but without the requirement for subjects to move their eyes to detect and identify the singleton target. The RT results were consistent with those in Experiment 1; dual onsets had no larger an effect on response speed than single onset distractors. These data are discussed in terms of the interaction between top-down and bottom-up control of attention and the eyes. |
Nomdo M. Jansonius; Ton (A) M. Vliet; Frans W. Cornelissen; Jan Willem R. Pott; Aart C. Kooijman In: Journal of Neuro-Ophthalmology, vol. 21, no. 1, pp. 26–29, 2001. @article{Jansonius2001,An otherwise healthy 15-year-old girl with a congenital nystagmus was evaluated at our department using visual evoked potential recording and magnetic resonance imaging. She appears to have the unique isolated inborn absence of the optic chiasm, described only once before in two unrelated girls. Unlike these previously described cases, our patient does not seem to display a see-saw nystagmus. |
S. -N. Yang; George W. McConkie Eye movements during reading: A theory of saccade initiation times Journal Article In: Vision Research, vol. 41, no. 25–26, pp. 3567–3585, 2001. @article{Yang2001,As people read continuous text, on occasional single eye fixations the text was replaced by one of six alternate stimulus patterns. Frequency distributions of the durations of these fixations were used to test predictions from four types of theories of saccadic eye movement control. Contrary to current cognitive theories, cognitive influences appeared to delay saccades rather than trigger them. Two saccade disruption times were identified, suggesting the existence of three distributions of saccades, labeled early, normal and late. The Competition–inhibition theory, an enhanced version of Findlay and Walker's (1999) theory, is proposed to account for eye movement control during reading. |
Diane E. Williams; Eyal M. Reingold Preattentive guidance of eye movements during triple conjunction search tasks: The effects of feature discriminability and saccadic amplitude Journal Article In: Psychonomic Bulletin & Review, vol. 8, no. 3, pp. 476–488, 2001. @article{Williams2001,Eye movements were monitored during the performance of triple conjunction search tasks. Stimuli varied in color, shape, and orientation. Across trials, the target was either present or absent, and displays consisted of 6, 12, or 24 stimuli. Stimulus discriminability was manipulated for the shape dimension, with half of the participants seeing displays of Es and Fs (low-discriminability [LD] condition) and half seeing displays of Cs and Ts (high-discriminability [HD] condition). Participants in both conditions performed two search tasks. In the single-feature (SF) task, the target stimulus shared one feature with each of the distractors, whereas in the two-feature (TF) task, it shared two features with each distractor. An examination of saccadic endpoints revealed that participants were more likely to fixate on distractor stimuli sharing color (SF task) or color and shape (TF task) with the target. This was a robust finding, being observed across participants, saccades of different amplitudes and sequential position, and following short and long latencies to move. The extent to which participants made use of shape information increased with discriminability. |
Uri Hasson; Talma Hendler; Dafna Ben Bashat; Rafael Malach Vase or face? A neural correlate of shape-selective grouping processes in the human brain Journal Article In: Journal of Cognitive Neuroscience, vol. 13, no. 6, pp. 744–753, 2001. @article{Hasson2001,Recent neuroimaging studies have described a differential activation pattern associated with specific object images (e.g., face-related and building-related activation) in human occipito-temporal cortex. However, it is as yet unclear to what extent this selectivity is due to differences in the statistics of local object features present in the different object categories, and to what extent it reflects holistic grouping processes operating across the entire object image. To resolve this question it is essential to use images in which identical sets of local features elicit the perception of different object categories. The classic Rubin vase-face illusion provides an excellent experimental set to test this question. In the illusion, the same local contours lead to the perception of different objects (vase or face). Here we employed a modified Rubin vase-face illusion to explore to what extent the activation in face-related regions is attributable to the presence of local face features, or is due to a more holistic grouping process that involves the entire face figure. Biasing cues (gratings and color) were used to control the perceptual state of the observer. We found enhanced activation in face-related regions during the "face profile" perceptual state compared to the "vase" perceptual state. Control images ruled out the involvement of the biasing cues in the effect. Thus, object-selective activation in human face-related regions entails global grouping processes that go beyond the local processing of stimulus features. |
Diane C. Gooding; Kathleen A. Tallent The association between antisaccade task and working memory task performance in schizophrenia and bipolar disorder Journal Article In: Journal of Nervous and Mental Disease, vol. 189, no. 1, pp. 8–16, 2001. @article{Gooding2001,To date, the research literature has yielded conflicting reports regarding the specificity of antisaccade deficits to schizophrenia. We sought to examine antisaccade and working memory task performance in schizophrenia patients and bipolar patients, as well as to examine the relationship between the two tasks in both patient populations. Thirty-four schizophrenia patients, 20 bipolar patients, and 30 nonpatient controls were administered saccadic inhibition (antisaccade), working memory, and sensorimotor tasks. Compared with the controls, the schizophrenia patients displayed both antisaccade deficits and working memory deficits. In contrast, the bipolar patients produced significantly more errors on the antisaccade task than the controls, though the bipolar group performed similarly to the control group on the working memory task. Mediational analyses demonstrated that working memory partially mediates the relationship between patients' diagnostic group status and antisaccade task performance; working memory performance contributed uniquely to the prediction of antisaccade task performance in the two patient groups. Antisaccade deficits do not appear specific to schizophrenia. The results suggest that in schizophrenia, working memory and antisaccade tasks are tapping similar cognitive processes, whereas in bipolar patients the processes underlying antisaccade and working memory performance are disparate. |
Harold H. Greene; Keith Rayner Eye-movement control in direction-coded visual search Journal Article In: Perception, vol. 30, no. 2, pp. 147–157, 2001. @article{Greene2001,Subjects searched for a target among distractors which were arranged randomly or such that each distractor provided information about the relative position of a target. Trials were presented either in a blocked design (so that the subjects knew a priori the contextual information in the display) or in a mixed design. When the distractors provided information about target position, there were (i) shorter manual RTs, (ii) fewer fixations made in search of the target, (iii) longer mean fixation durations, (iv) shorter initial fixation durations, (v) shorter mean gaze shifts, (vi) a smaller area of fixation dispersion, and (vii) a greater percentage of optimally directed saccades. Except for gaze shifts, the results were uninfluenced by whether or not there was a blocked or a mixed presentation. The results of the study suggest that despite noise in the search mechanism, fixation durations were adjusted to process directly the currently fixated element(s). |
Harold H. Greene; Keith Rayner Eye movements and familiarity effects in visual search Journal Article In: Vision Research, vol. 41, no. 27, pp. 3763–3773, 2001. @article{Greene2001a,Familiarity with the distractors around an unfamiliar target facilitates visual search. Three Experiments examined whether the effect occurs because fixations are (a) shorter and fewer, (b) shorter, but more abundant, (c) equally long, but fewer, or (d) longer, but fewer when distractors are familiar. Results indicated comparably long, but fewer fixations when distractors are familiar. Hence, the theory that unfamiliar distractors need longer processing is discounted. In a fourth Experiment, a gaze-contingent moving window paradigm was used to control peripheral processing. Results revealed a wider span of effective processing for familiar distractors. A hypothesis based on low-level physiological processes is introduced to account for the familiarity effect. |
Avital Deutsch; Shlomo Bentin Syntactic and semantic factors in processing gender agreement in Hebrew: Evidence from ERPs and eye movements Journal Article In: Journal of Memory and Language, vol. 45, no. 2, pp. 200–224, 2001. @article{Deutsch2001,The interrelation between syntactic analysis of agreement and semantic processing was examined by recording eye movements and event-related potentials. Subject-predicate gender agreement was manipulated within Hebrew sentences. The subject was either animate or inanimate, with conceptual gender denoted by the subject's morphological structure. First-pass reading time was found to be longer for incongruent predicates than of congruent predicates but only if the predicate's gender was morphologically marked. Furthermore, this effect was larger in the animate than in the inanimate condition. Second-pass reading time was also prolonged by gender incongruity but this effect was not affected by either markedness or animacy. Gender incongruity enhanced the amplitude of an early negative potential (ostensibly ELAN), of a later negative potential (N400), and of a positive potential (P600). Like first-pass reading time, the congruity effect on the syntactically modulated P600 was significant only for marked predicates, but it did not interact with animacy. In contrast, the congruity effect on the semantically modulated N400 was significant only in the animate condition. The N400 was not affected by markedness. The congruity effect on the early negativity did not interact with either animacy or markedness. The interaction between semantic and syntactic processing and its time course are discussed within the framework set by interactive, constraint-based models for online sentence processing. |
Elliot M. Frohman; Teresa C. Frohman; J. Fleckenstein; M. K. Racke; K. Hawker; Phillip D. Kramer Ocular contrapulsion in multiple sclerosis: Clinical features and pathophysiological mechanisms Journal Article In: Journal of Neurology, Neurosurgery and Psychiatry, vol. 70, no. 5, pp. 688–692, 2001. @article{Frohman2001,The objective was to describe in multiple sclerosis, a cerebellar eye movement syndrome that resulted from an acute episode of inflammatory demyelination. Contrapulsion is an ocular motor disturbance characterised by a triad of (1) hypermetric saccadic eye movements in a direction opposite from a precisely localised lesion within a specific white matter pathway, the uncinate fasciculus, at the level of the superior cerebellar peduncle (SCP); (2) hypometric saccades towards the side of the lesion; (3) oblique saccades directed away from the side of the lesion on attempted vertical saccades. Infrared oculography was used to demonstrate the characteristic features of contrapulsion in two patients with multiple sclerosis. Brain MRI showed lesions within the region of the uncinate fasciculus and superior cerebellar peduncle in both patients. Eye movement recordings showed saccadic hypermetria away from the side of the lesion and saccadic hypometria towards the side of the lesion. The hypometria decomposed into a series of stepwise movements as the eye approached the target. Oblique saccades directed away from the side of the lesion were seen on attempted vertical saccades. In conclusion, ocular contrapulsion can be seen in patients with multiple sclerosis and results from a lesion in the region of the SCP, involving the uncinate fasciculus. |
Elliot M. Frohman; H. Zhang; Phillip D. Kramer; J. Fleckenstein; K. Hawker; M. K. Racke; Teresa C. Frohman MRI characteristics of the MLF in MS patients with chronic internuclear ophthalmoparesis Journal Article In: Neurology, vol. 57, no. 5, pp. 762–768, 2001. @article{Frohman2001a,OBJECTIVE: The authors imaged the medial longitudinal fasciculus (MLF) in 58 patients with MS and chronic internuclear ophthalmoparesis (INO) to determine which MRI technique best shows the characteristic lesion associated with this ocular motor syndrome. METHODS: Using quantitative infrared oculography, the authors determined the ratios of abduction to adduction for velocity and acceleration, to confirm the presence of INO and to determine the severity of MLF dysfunction in 58 patients with MS and INO. Conventional MRI techniques, including proton density imaging (PDI), T2-weighted imaging, and fluid-attenuated inversion recovery (FLAIR) imaging, were used to ascertain which technique best shows MLF lesions within the brainstem tegmentum. T1-weighted imaging was performed to determine the frequency of brainstem tegmentum hypointensities. RESULTS: All patients studied had evidence of an MLF lesion hyperintensity on PDI, whereas T2-weighted imaging and FLAIR imaging showed these lesions in 88% and 48% of patients, respectively. With PDI, dorsomedial tegmentum lesions were seen in the pons in 93% of patients and in the midbrain of 66% of patients. Lesions were observed at both locations in 59% of patients. One patient had an MLF lesion with a corresponding T1 hypointensity. CONCLUSIONS: PDI best shows the MLF lesion in patients with MS and INO. |
Gary Feng; Kevin Miller; Hua Shu; Houcan Zhang Rowed to recovery: The use of phonological and orthographic information in reading Chinese and English Journal Article In: Journal of Experimental Psychology: Learning, Memory, and Cognition, vol. 27, no. 4, pp. 1079–1100, 2001. @article{Feng2001,To examine how readers of Chinese and English take advantage of orthographic and phonological features in reading, the authors investigated the effects of spelling errors on reading text in Chinese and English using the error disruption paradigm of M. Daneman and E. Reingold (1993). Skilled readers in China and the United States read passages in their native language that contained occasional spelling errors. Results showed that under some circumstances very early phonological activation can be identified in English, but no evidence for early phonology was found in Chinese. In both languages, homophone errors showed a benefit in measures of later processing, suggesting that phonology helps readers recover from the disruptive effects of errors. These results suggest that skilled readers take advantage of the special features of particular orthographies but that these orthographic effects may be most pronounced in the early stages of lexical access. |
Melanie Doyle; Robin Walker Curved saccade trajectories: Voluntary and reflexive saccades curve away from irrelevant distractors Journal Article In: Experimental Brain Research, vol. 139, no. 3, pp. 333–344, 2001. @article{Doyle2001,In this study we examined the impact of irrelevant distractors upon trajectories of reflexive and voluntary saccades. Observers made saccades to visual targets above and below fixation as directed by target appearance (reflexive) or by a central directional cue (voluntary) in the presence of an irrelevant distractor stimulus (a cross) whose appearance was simultaneous with target onset. We recorded saccade latency, amplitude and the magnitude of saccade curvature relative to the direct route from the start-to-end of the saccade. Previous studies of saccades curvature have used distractors to provide information about the saccade task and, as a result, have only examined trajectories of voluntary saccades. However, we have shown that both reflexive and voluntary saccades curved away from irrelevant distractors. The effect of irrelevant distractors indicates that observers do not need to attend to distractors in a voluntary fashion for distractors to modify saccade trajectories. Furthermore, it highlights an important parallel in curvature of saccades and reach trajectories, namely that both curve away from irrelevant distractors. The second important observation was that reflexive, as well as voluntary, saccades curved away from distractors. This suggests that curvature is not solely a consequence of voluntary control. These results have been considered within the context of inhibition-based theories of curvature derived from studies of saccade and manual reach trajectories. |
Matthew S. Peterson; Arthur F. Kramer Attentional guidance of the eyes by contextual information and abrupt onsets Journal Article In: Perception and Psychophysics, vol. 63, no. 7, pp. 1239–1249, 2001. @article{Peterson2001a,Contextual cuing is a memory-based phenomenon in which previously encountered global pattern information in a display can automatically guide attention to the location of a target (Chun & Jiang, 1998), leading to rapid and accurate responses. What is not clear is how contextual cuing works. By monitoring eye movements, we investigated the roles that recognition and guidance play in contextual cuing. Recognition does not appear to occur on every trial and sometimes does not have its effects until later in the search process. When recognition does occur, attention is guided straight to the target rather than in the general direction. In Experiment 2, we investigated the interaction between memory-driven search (contextual cuing) and stimulus-driven attentional capture by abrupt onsets. Contextual cuing was able to override capture by abrupt onsets. In contrast, onsets had almost no effect on the degree of contextual cuing. These data are discussed in terms of the role of top-down and bottom-up factors in the guidance of attention in visual search. |
Matthew S. Peterson; Arthur F. Kramer; Ranxiao Frances Wang; David E. Irwin; Jason S. McCarley Visual search has memory Journal Article In: Psychological Science, vol. 12, no. 4, pp. 287–292, 2001. @article{Peterson2001,By monitoring subjects' eye movements during a visual search task, we examined the possibility that the mechanism responsi- ble for guiding attention during visual search has no memory for which locations have already been examined. Subjects did reexamine some items during their search, but the pattern of revisitations did not fit the predictions of the memoryless search model. In addition, a large pro- portion of the refixations were directed at the target, suggesting that the revisitations were due to subjects' remembering which items had not been adequately identified. We also examined the patterns of fixations and compared them with the predictions of a memoryless search model. Subjects' fixation patterns showed an increasing hazard function, whereas the memoryless model predicts a flat function. Lastly, we found no evidence suggesting that fixations were guided by amnesic co- vert scans that scouted the environment for new items during fixations. Results do not support the claims of the memoryless search model, and instead suggest that visual search does have memory. |
Jean Saint-Aubin; Raymond M. Klein Influence of parafoveal processing on the missing letter effect Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 27, no. 2, pp. 318–334, 2001. @article{SaintAubin2001,According to the parafoveal-processing hypothesis, letters are more often missed in function words than in content words because the former are more likely to be identified in the parafovea, where letter processing is not available. Contrary to previous demonstrations, more omissions occurred in function words than in content words when parafoveal processing was not available because words were displayed in column format, text was read through a 5-letter window, or words were presented 1 at a time on a computer screen. In all experiments, impeding parafoveal processing decreased omission rates for function but not for content words. In the last experiment, direct monitoring of eye movements revealed that, for both fixated and skipped words, letters in function words are missed more often than content words. These results are best interpreted within a model including the structural precedence hypothesis and stressing the importance of visual factors. |
Marc Pomplun; Eyal M. Reingold; Jiye Shen The effects of peripheral and parafoveal cueing and masking on saccadic selectivity in a gaze-contingent window paradigm Journal Article In: Vision Research, vol. 41, no. 21, pp. 2757–2769, 2001. @article{Pomplun2001,The present study employed the gaze-contingent window paradigm to investigate parafoveal and peripheral cueing and masking effects on saccadic selectivity in a triple-conjunction visual search task. In the cueing conditions, the information shown outside the gaze-contingent window was restricted to the feature or feature pair shared between the target and a particular distractor type. In the masking conditions, no stimulus features were shown outside the window. Significant cueing and masking effects on saccadic selectivity were observed for saccades directed at items within the window, where all features were visible across experimental conditions. Cueing a particular feature or feature pair biased saccadic selectivity towards this feature or feature pair, while masking generally reduced saccadic selectivity. These findings support the concept of visual guidance being a preattentive process that operates in parallel across the display. |
Marc Pomplun; Eyal M. Reingold; Jiye Shen Investigating the visual span in comparative search: The effects of task difficulty and divided attention Journal Article In: Cognition, vol. 81, no. 2, pp. B57–B67, 2001. @article{Pomplun2001a,In three experiments, participants' visual span was measured in a comparative visual search task in which they had to detect a local match or mismatch between two displays presented side by side. Experiment 1 manipulated the difficulty of the comparative visual search task by contrasting a mismatch detection task with a substantially more difficult match detection task. In Experiment 2, participants were tested in a single-task condition involving only the visual task and a dual-task condition in which they concurrently performed an auditory task. Finally, in Experiment 3, participants performed two dual-task conditions, which differed in the difficulty of the concurrent auditory task. Both the comparative search task difficulty (Experiment 1) and the divided attention manipulation (Experiments 2 and 3) produced strong effects on visual span size. |
Keith Rayner; Caren M. Rotello; Andrew J. Stewart; Jessica Keir; Susan A. Duffy Integrating text and pictorial information: Eye movements when looking at print advertisements Journal Article In: Journal of Experimental Psychology: Applied, vol. 7, no. 3, pp. 219–226, 2001. @article{Rayner2001,Viewers looked at print advertisements as their eye movements were recorded. Half of them were told to pay special attention to car ads, and the other half were told to pay special attention to skin-care ads. Viewers tended to spend more time looking at the text than the picture part of the ad, though they did spend more time looking at the type of ad they were instructed to pay attention to. Fixation durations and saccade lengths were both longer on the picture part of the ad than the text, but more fixations were made on the text regions. Viewers did not alternate fixations between the text and picture part of the ad, but they tended to read the large print, then the smaller print, and then they looked at the picture (although some viewers did an initial cursory scan of the picture). Implications for (a) how viewers integrate pictorial and textual information and (b) applied research and advertisement development are discussed. |
Eyal M. Reingold; Neil Charness; Marc Pomplun; Dave M. Stampe Visual span in expert chess players: Evidence from eye movements Journal Article In: Psychological Science, vol. 12, no. 1, pp. 48–55, 2001. @article{Reingold2001,The reported research extends classic findings that after briefly viewing structured, but not random, chess positions, chess masters reproduce these positions much more accurately than lessskilled players. Using a combination of the gaze-contingent window paradigm and the change blindness flicker paradigm, we documented dramatically larger visual spans for experts while processing structured, but not random, chess positions. In addition, in a checkdetection task, a minimized 3 × 3 chessboard containing a King and potentially checking pieces was displayed. In this task, experts made fewer fixations per trial than less-skilled players, and had a greater proportion of fixations between individual pieces, rather than on pieces. Our results provide strong evidence for a perceptual encoding advantage for experts attributable to chess experience, rather than to a general perceptual or memory superiority. |
David A. Leopold; Alice J. O. Toole; Thomas Vetter; Volker Blanz Prototype-referenced shape encoding revealed by high-level aftereffects Journal Article In: Nature Neuroscience, vol. 4, no. 1, pp. 89–94, 2001. @article{Leopold2001,We used high-level configural aftereffects induced by adaptation to realistic faces to investigate visual representations underlying complex pattern perception. We found that exposure to an individual face for a few seconds generated a significant and precise bias in the subsequent perception of face identity. In the context of a computationally derived 'face space,' adaptation specifically shifted perception along a trajectory passing through the adapting and average faces, selectively facilitating recognition of a test face lying on this trajectory and impairing recognition of other faces. The results suggest that the encoding of faces and other complex patterns draws upon contrastive neural mechanisms that reference the central tendency of the stimulus category. |
Adrienne L. LeVasseur; J. Randall Flanagan; Richard J. Riopelle; Douglas P. Munoz Control of volitional and reflexive saccades in Tourette's syndrome Journal Article In: Brain, vol. 124, pp. 2045–2058, 2001. @article{LeVasseur2001,Tourette's syndrome is characterized by involuntary tics and, although the underlying pathogenesis and patho- physiology of Tourette's syndrome remains unclear, it is suspected that basal ganglia structures are involved. The basal ganglia also play an important role in the control of saccadic eye movements and we therefore hypothesize that Tourette's syndrome patients have abnormal control of saccadic eye movements. In this study, 10 subjects with Tourette's syndrome and 10 age- and sex-matched controls performed four different oculomotor paradigms requiring the execution and/or suppression of reflexive and/or voluntary saccades. In the immediate saccade tasks, sub- jects were required to look either toward (pro-saccade task) or away from (anti-saccade task) a peripheral target as soon as it appeared. In the delayed saccade tasks, subjects were instructed to wait for a central fixation point to disappear before initiating eye movements. Among Tourette's syndrome subjects, saccadic reaction times were longer in all tasks. Saccadic amplitudes were smaller in Tourette's syndrome subjects, and they made more saccades to reach the eccentric target. The occurrence of direction errors (i.e. reflexive pro-saccades on anti-saccade trials) was normal in the immediate anti-saccade task, suggesting that the ability to inhibit reflexive saccades towards novel stimuli was not impaired in Tourette's syndrome. Timing errors (i.e. eye movements made prior to disappearance of the central fixation point in delayed saccade tasks) were significantly greater among Tourette's syndrome subjects. Moreover, these errors were predominantly made towards the first target of the remembered sequence in a delayed memory-guided sequential saccade task. These results indicate that the ability to inhibit or delay planned motor programmes is significantly impaired in Tourette's syndrome. We hypothesize that altered cortical–basal ganglia circuitry leads to reduced cortical inhibition making it harder for Tourette's syndrome subjects to withhold the execution of planned motor programmes. |
Neil Charness; Eyal M. Reingold; Marc Pomplun; Dave M. Stampe The perceptual aspect of skilled performance in chess: Evidence from eye movements Journal Article In: Memory and Cognition, vol. 29, no. 8, pp. 1146–1152, 2001. @article{Charness2001,Expert and intermediate chess players attempted to choose the best move in five chess positions while their eye movements were monitored. Experts were faster and more accurate than intermediates in choosing the best move. Experts made fewer fixations per trial and greater amplitude saccades than did intermediates, but there was no difference in fixation duration across skill groups. Examining the spatial distribution of the first five fixations for each position by skill group revealed that experts produced more fixations on empty squares than did intermediates. When fixating pieces, experts produced a greater proportion of fixations on relevant pieces than did intermediates. It is argued that expert chess players perceptually encode chess configurations, rather than individual pieces, and, consequently, parafoveal or peripheral processing guides their eye movements, producing a pattern of saccadic selectivity by piece saliency. |
Risto Näsänen; Jan Karlsson; Helena Ojanpää Display quality and the speed of visual letter search Journal Article In: Displays, vol. 22, no. 4, pp. 107–113, 2001. @article{Naesaenen2001,Previously it has been suggested that visual search tasks can be used to evaluate the perceptual quality of display devices with respect to their ability to convey alphanumeric information. The purpose of the present study was to examine how character size and contrast used in a visual search test affects its sensitivity to differences in the quality of display devices. The task of the observer was to search for, and identify, an uppercase letter from a rectangular array of characters in which the other items were numerals. Threshold search time, that is, the duration of stimulus presentation required for search that is successful with a given probability, was determined by using a multiple-alternative staircase method. Eye movements were recorded simultaneously by using a fast video eye tracker. Threshold search times were measured as a function of character size at two contrast levels using a CRT and an LCD display. For all experimental conditions, threshold search time decreased with increasing letter size. This was accompanied with a decrease in the number of eye fixations per search as well as a decrease of fixation duration. At high contrast (CMichelson≈ 1), no statistically significant difference was found between the two displays. However, at the lower contrast used (CMichelson≈ 0.2) and at small character sizes, threshold search times for the CRT display were clearly longer and the number of fixations per search was higher than for the LCD display. In conclusion, visual letter search is a more sensitive method for display evaluation at small contrasts and with small character sizes. |
Risto Näsänen; Helena Ojanpää; Ilpo Kojo Effect of stimulus contrast on performance and eye movements in visual search Journal Article In: Vision Research, vol. 41, no. 14, pp. 1817–1824, 2001. @article{Naesaenen2001a,According to the visual span control hypothesis, eye movements are controlled in relation to the size of visual span. In reading, the decrease of contrast reduces visual span, saccade sizes, and reading speed. The purpose of the present study is to determine how stimulus contrast affects the speed of two-dimensional visual search and how changes in eye movements and visual span could explain changes in performance. The task of the observer was to search for, and identify, an uppercase letter from a rectangular array of characters in which the other items were numerals. Threshold search time, i.e. the duration of stimulus presentation required for search that is successful with a given probability, was determined by using a multiple-alternative staircase method. Eye movements were recorded simultaneously by using a video eye tracker. Four different set sizes (the sizes of stimulus array) (3 × 3-10 × 10), and five different contrasts (0.0186 - 0.412) were used. At all set sizes, threshold search time decreased with increasing contrast. Also the average number of fixations per search decreased with increasing contrast. At the smallest set size (3 × 3), only one fixation was needed except at the lowest contrast. Average fixation duration decreased and saccade amplitudes increased slightly with increasing contrast. The reduction of the number of fixations with increasing contrast suggests that visual span, i.e. the area from which information can be collected at one fixation, increases with increasing contrast. The reduction of the number of fixations together with reduced fixation duration result in reduced search times when contrast increases. |
Sebastiaan F. W. Neggers; Harold Bekkering Gaze anchoring to a pointing target is present during the entire pointing movement and Is driven by a non-visual signal Journal Article In: Journal of Neurophysiology, vol. 86, no. 2, pp. 961–970, 2001. @article{Neggers2001,A well-coordinated pattern of eye and hand movements can be observed during goal-directed arm movements. Typically, a saccadic eye movement precedes the arm movement, and its occurrence is temporally correlated with the start of the arm movement. Furthermore, the coupling of gaze and aiming movements is also observable after pointing initiation. It has recently been observed that saccades cannot be directed to new target stimuli, away from a pointing target stimulus. Saccades directed to targets presented during the final phase of a pointing movement were delayed until after pointing movement offset (“gaze anchoring”). The present study investigated whether ocular gaze is anchored to a pointing target during the entire pointing movement. In experiment 1, new targets were presented at various times during the duration of a pointing movement, triggered by the kinematics arm moment itself (movement onset, peak acceleration/velocity/deceleration, and offset). Subjects had to make a saccade to the new target as fast as possible while maintaining the pointing movement to the initial target. Saccadic latencies were increased by an amount of time that approximately equaled the remaining pointing time after saccadic target presentation, with the majority of saccades executed after pointing movement offset. The nature of the signal driving gaze stabilization during pointing was investigated in exper- iment 2. In previous experiments where ocular gaze was anchored to a pointing target, subjects could always see their moving arm, thus it was unknown whether a visual image of the moving arm, an afferent (proprioceptive) signal or an efferent (motor control related) signal produced gaze anchoring. In experiment 2 subjects had to point with or without vision of the moving arm to test whether a visual signal is used to anchor gaze to a pointing target. Results indicate that gaze anchoring was also observed without vision of the moving arm. The findings support the existence of a mechanism enforcing ocular gaze anchoring during the entire duration of a pointing movement. Moreover, such a mechanism uses an internally generated, or proprioceptive, nonvisual signal. Possible neural substrates underlying these processes are discussed, as well as the role of selective attention. |
Sebastian Pannasch; Sascha M. Dornhoefer; Pieter J. A. Unema; Boris M. Velichkovsky The omnipresent prolongation of visual fixations: Saccades are inhibited by changes in situation and in subject's activity Journal Article In: Vision Research, vol. 41, no. 25-26, pp. 3345–3351, 2001. @article{Pannasch2001,Presenting a distractor prolongs not only saccadic reaction times in paced tasks but also fixation durations in unpaced tasks. To investigate whether the effect of a distractor is a pure optomotor reflex, we used both visual and auditory distractors in an unpaced picture-viewing paradigm. Results show a distractor effect for both modalities. Analysis of data from previous studies showed similar effects, even in amodal shifts of attention. These findings challenge the hypothesis that the effect is modality-specific and suggest that the distractor effect may be another expression of the orienting reflex. |
Albert V. Berg; J. A. Beintema; Maarten A. Frens Heading and path percepts from visual flow and eye pursuit signals Journal Article In: Vision Research, vol. 41, no. 25-26, pp. 3467–3486, 2001. @article{Berg2001,The percept of self-motion through the environment is supported by visual motion signals and eye movement signals. The interaction between these signals by decoupling of the eye movement and the pattern of retinal motion during brief simulated ego-movement on straight or circular trajectories was studied. A new response method enabled subjects to report perceived destination and perceived curvature of their future path simultaneously. Various combinations of simulated gaze rotation in the retinal flow and eye pursuit were investigated. Simulated gaze rotation ranged from consistent and larger than, to opponent and larger than eye pursuit. It was found that the perceived destination shifts non-linearly with the mismatch between simulated gaze rotation and eye pursuit. The non-linearity is also revealed in the perceived tangent heading direction and perceived path curvature, although to different extent in different subjects. For the same retinal flow, eye pursuit that is consistent with the simulated gaze rotation reduces heading error and the perceived path straightens out. In contrast, perceived path and/or heading do not become more curved or more biased in the direction opposite to pursuit when the eye -in-head rotation is opposite to the simulated gaze rotation. These observations point to modulation of the effect of the extra-retinal pursuit signal by the visual evidence for eye rotation. In a second experiment, one presented to a stationary eye the sum of a component of simulated gaze rotation and radial flow. It was found that the bi-circular flow component, that characterizes the change in pattern of flow directions by the gaze rotation, induces a shift of perceived heading without appreciable perceived path curvature. Conversely, the complementary component of simulated gaze rotation (bi-radial flow) evokes a percept of motion on a curved path with a small tangent heading error. It was suggested that bi-circular and bi-radial flow components contribute primarily to percepts of heading and path curvature, respectively. |
Femke Meulen; Antje S. Meyer; Willem J. M. Levelt Eye movements during the production of nouns and pronouns Journal Article In: Memory and Cognition, vol. 29, no. 3, pp. 512–521, 2001. @article{Meulen2001,Earlier research has established that speakers usually fixate the objects they name and that the viewing time for an object depends on the time necessary for object recognition and for the retrieval of its name. In three experiments, speakers produced pronouns and noun phrases to refer to new objects and to objects already known. Speakers looked less frequently and for shorter periods at the objects to be named when they had very recently seen or heard of these objects than when the objects were new. Looking rates were higher and viewing times longer in preparation of noun phrases than in preparation of pronouns. If it is assumed that there is a close relationship between eye gaze and visual attention, these results reveal (1) that speakers allocate less visual attention to given objects than to new ones and (2) that they allocate visual attention both less often and for shorter periods to objects they will refer to by a pronoun than to objects they will name in a full noun phrase. The experiments suggest that linguistic processing benefits, directly or indirectly, from allocation of visual attention to the referent object. |
Jie-Li Tsai A multichannel PC tachistoscope with high resolution and fast display change capability Journal Article In: Behavior Research Methods, Instruments & Computers, vol. 33, no. 4, pp. 524–531, 2001. @article{Tsai2001,The number of channels that PC tachistoscopes can have has increased recently (Bokhorst, 1995; Myors, 1998); however, neither the quality of display nor speed of image switching has been improved. This article shows the capability of VESA's VBE 3.0 standard (1998) for increasing the number of channels of high-quality images. And the refresh rate can be set to the fastest cathode ray tube (CRT) scanning rate the monitor can tolerate in order to reduce the timing delay of changing display. A PCTSCOPE library was written in C to provide these capabilities, which is compatible with conventional DOS real mode. The PC tachistoscope can have numbers of channels with various resolutions and colors and different refresh rates. For example, 25 images with the resolution of 640 x 480 pixels and 256 colors can be loaded to video memory, and vertical refresh rate can be set to 180 Hz. It takes less than 6 msec to change the display among 25 channels in synchronizing with the start of the video scanning frame. In this library, the number of channels, the resolution of the images, and the speed of changing display all are improved. The multichannel PC tachistoscope with this technique is especially suitable for research requiring high-quality images and rapid successive presentation of stimuli. |
John F. Soechting; Kevin C. Engel; Martha Flanders The Duncker Illusion and eye–hand coordination Journal Article In: Journal of Neurophysiology, vol. 85, no. 2, pp. 843–854, 2001. @article{Soechting2001,A moving background alters the perceived direction of target motion (the Duncker illusion). To test whether this illusion also affects pointing movements to remembered/extrapolated target locations, we constructed a display in which a target moved in a straight line and disappeared behind a band of moving random dots. Subjects were required to touch the spot where the target would emerge from the occlusion. The four directions of random-dot motion induced pointing errors that were predictable from the Duncker illusion. Because it has been previously established that saccadic direction is influenced by this illusion, gaze was subsequently recorded in a second series of experiments while subjects performed the pointing task and a similar task with eye-tracking only. In the pointing task, subjects typically saccaded to the lower border of the occlusion zone as soon as the target disappeared and then tried to maintain fixation at that spot. However, it was particularly obvious in the eye-tracking-only condition that horizontally moving random dots generally evoked an appreciable ocular following response, altering the gaze direction. Hand-pointing errors were related to the saccadic gaze error but were more highly correlated with final gaze errors (resulting from the initial saccade and the subsequent ocular following response). The results suggest a model of limb control in which gaze position can provide the target signal for limb movement. |
2000 |
John Schlag; Rick H. Cai; Andrews Dorfman; Ali Mohempour; Madeleine Schlag-Rey Extrapolating movement without retinal motion Journal Article In: Nature, vol. 403, pp. 38–39, 2000. @article{Schlag2000,In contrast to the perception of a stationary object that is briefly flashed in the dark, a continuously visible moving object is seen as being ahead of its actual position at the time of the flash. An explanation for this simple effect, in which a stimulus moving on the retina is seen as being further along its path and not where it was in space when its signal impinged on the retina, is keenly debated. We show here that this illusion is not just limited to retinal motion, and that perceptual mislocalization occurs even when stimulus motion is inferred entirely from extra-retinal information, for example by movement of the observer's head or whole body, without retinal motion. The phenomenon may therefore rely on a much more general mechanism. |
William C. Schmidt Endogenous attention and illusory line motion reexamined Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 26, no. 3, pp. 980–996, 2000. @article{Schmidt2000,P. Downing and A. Treisman's (1997) failure to replicate an effect of endogenous attention on the direction of illusory line motion (ILM) was reexamined. Four experiments with slightly modified stimulus presentation methods based on gradient theories of ILM found that endogenous attention directed to 1 of 2 similar priming objects is capable of influencing experienced motion direction within a subsequently presented line. The endogenous effect on ILM was consistent with a concomitant response-time discrimination task, was robust across naive and informed participants, occurred whether eye fixation was monitored or not, and occurred under conditions where multiple motion response categories were available to participants. The endogenous effect disappeared when participants moved their eyes to the attended item, when there was no motivation to endogenously attend, and when the presentation methods of P. Downing and A. Treisman (1997) were used. |
Jiye Shen; Eyal M. Reingold; Marc Pomplun Distractor ratio influences patterns of eye movements during visual search Journal Article In: Perception, vol. 29, no. 2, pp. 241–250, 2000. @article{Shen2000,We examined the flexibility of guidance in a conjunctive search task by manipulating the ratios between different types of distractors. Participants were asked to decide whether a target was present or absent among distractors sharing either colour or shape. Results indicated a strong effect of distractor ratio on search performance. Shorter latency to move, faster manual response, and fewer fixations per trial were observed at extreme distractor ratios. The distribution of saccadic endpoints also varied flexibly as a function of distractor ratio. When there were very few same-colour distractors, the saccadic selectivity was biased towards the colour dimension. In contrast, when most of the distractors shared colour with the target, the saccadic selectivity was biased towards the shape dimension. Results are discussed within the framework of the guided search model. |
Avital Deutsch; Ram Frost; Alexander Pollatsek; Keith Rayner Early morphological effects in word recognition in Hebrew: Evidence from parafoveal preview benefit Journal Article In: Language and Cognitive Processes, vol. 15, no. 4-5, pp. 487–506, 2000. @article{Deutsch2000,Hebrew words are composed of two interwoven morphemes: a triconso- nantal root and a word pattern. Two experiments examined the effect of the root morpheme on word identi?cation by assessing parafoveal preview bene?t effects.Although the information of the previewwas not consciously perceived, preview of the root's letters facilitated both naming and lexical decisions of target words derived from these roots. These results converge with previous results in Hebrew using the masked priming paradigm, suggesting that morphological units mediate early stages of word identification in Hebrew. |
Alexander P. Leff; Sophie K. Scott; H. Crewes; Timothy L. Hodgson; A. Cowey; D. Howard; Richard J. S. Wise Impaired reading in patients with right hemianopia Journal Article In: Annals of Neurology, vol. 47, no. 2, pp. 171–178, 2000. @article{Leff2000,A left occipital stroke may result in alexia for two reasons, which may coexist depending on the distribution of the lesion. A lesion of the left lateroventral prestriate cortex or its afferents impairs word recognition ("pure" alexia). If the left primary visual cortex or its afferents are destroyed, resulting in a complete right homonymous hemianopia, rightward saccades during text reading are disrupted ("hemianopic" alexia). By using functional imaging, we showed two separate but interdependent systems involved in reading. The first, subserving word recognition, involved the representation of foveal vision in the left and right primary visual cortex and the ventral prestriate cortex. The second system, responsible for the planning and execution of reading saccades, consisted of the representation of right parafoveal vision in the left visual cortex, the bilateral posterior parietal cortex (left > right), and the frontal eye fields (right > left). Disruption of this distributed neural system was demonstrated in patients with severe right homonymous hemianopia, commensurate with their inability to perform normal reading eye movements. Text reading, before processes involved in comprehension, requires the integration of perceptual and motor processes. We have demonstrated these distributed neural systems in normal readers and have shown how a right homonymous hemianopia disrupts the motor preparation of reading saccades during text reading. |
Chiang-Shan Ray Li; Mon-Chu Chen; Yong-Yi Yang; Hsueh-Ling Chang; Chia-Yih Liu; Seng Shen; Ching-Yen Chen Perceptual alternation in obsessive compulsive disorder - implications for a role of the cortico-striatal circuitry in mediating awareness Journal Article In: Behavioural Brain Research, vol. 111, no. 1-2, pp. 61–69, 2000. @article{Li2000,Mounting evidence suggests that obsessive compulsive disorder (OCD) results from functional aberrations of the fronto-striatal circuitry. However, empirical studies of the behavioral manifestations of OCD have been relatively lacking. The present study employs a behavioral task that allows a quantitative measure of how alternative percepts are formed from one moment to another, a process mimicking the brain state in which different thoughts and imageries compete for access to awareness. Eighteen patients with OCD, 12 with generalized anxiety disorder, and 18 normal subjects participated in the experiment, in which they viewed one of the three Schroder staircases and responded by pressing a key to each perceptual reversal. The results demonstrate that the patients with OCD have a higher perceptual alternation rate than the normal controls. Moreover, the frequency of perceptual alternation is significantly correlated with the Yale-Brown obsessive compulsive and the Hamilton anxiety scores. The increase in the frequency of perceptual reversals cannot easily be accounted for by learning or by different patterns of eye fixations on the task. These results provide further evidence that an impairment of the inhibitory function of the cortico-striatal circuitry might underlie the etiology of OCD. The implications of the results for a general role of the cortico-striatal circuitry in mediating awareness are discussed. |
Diane C. Gooding; Jeffrey A. Grabowski; Christian S. Hendershot Fixation stability in schizophrenia, bipolar, and control subjects Journal Article In: Psychiatry Research, vol. 97, no. 2-3, pp. 119–128, 2000. @article{Gooding2000,A few investigators have suggested that visual fixation abnormalities may serve as an endophenotype of liability for schizophrenia. However, the data are equivocal. Conflicting reports regarding the specificity of fixation deficits to schizophrenia may be attributable to methodological differences. Thirty-four schizophrenia patients, 20 bipolar patients, and 30 non-patient controls were presented targets for central fixation. Fixation was scored in terms of frequency of saccades as well as qualitative ratings. Analysis of variance on the number of saccades produced during fixation revealed that the three groups did not differ. Similarly, we observed that the schizophrenia patients did not differ from either bipolar patients or controls in terms of ratings of fixation quality. It appears that schizophrenia patients are not characterized by poor visual fixation. The findings are discussed in terms of the viability of visual fixation as a marker of schizophrenic diathesis, as well as possible implications for the analysis of schizophrenia patients' visual search performance. |
Diane C. Gooding; Meghan D. Miller; Thomas R. Kwapil Smooth pursuit eye tracking and visual fixation in psychosis-prone individuals Journal Article In: Psychiatry Research, vol. 93, no. 1, pp. 41–54, 2000. @article{Gooding2000a,Subjects identified by Perceptual Aberration-Magical Ideation (Per-Mag) scores (n = 97), Social Anhedonia (SocAnh) scores (n = 45), and Physical Anhedonia (PhysAnh) scores (n = 31) as well as normal controls (n = 94), underwent psychophysiological and clinical assessment. This is the first published investigation of pursuit system functioning in three groups of questionnaire-identified at-risk individuals. Pursuit during a simple non- monitor tracking task was measured using root-mean-square error (RMSE) scores and pursuit gain scores. Fixation performance was measured in terms of number of saccades away from the central fixation point. The at-risk subjects were more likely to display aberrant smooth pursuit tracking than controls, though there were no significant differences between the at-risk subjects endorsing items relevant to positive-symptom schizotypy and those endorsing items pertaining to negative-symptom schizotypy. The groups did not differ significantly in their visual fixation performance. Participants were also evaluated for the presence of Axis I symptomatology and psychotic-like experiences. Neither the experimental subjects nor the control subjects displayed a significant association between ocular motor performance and psychotic-like experiences. These findings are consistent with prior evidence that pursuit tracking is a trait characteristic, independent of clinical status. |
Zenzi M. Griffin; Kathryn Bock What the eyes say about speaking Journal Article In: Psychological Science, vol. 11, no. 4, pp. 274–279, 2000. @article{Griffin2000,To study the time course of sentence formulation, we monitored the eye movements of speakers as they described simple events. The similarity between speakers' initial eye movements and those ofobservers performing a nonverbal event-comprehension task suggested that response-relevant information was rapidly extracted from scenes, allowing speakers to select grammatical subjects based on comprehended events rather than salience. When speaking extem- poraneously, speakers began fixating pictured elements less than a second before naming them within their descriptions, a finding con- sistent with incremental lexical encoding. Eye movements anticipated the order of mention despite changes in picture orientation, in who- did-what-to-whom, and in sentence structure. The results support Wundt's theory of sentence production. From |
Kalanit Grill-Spector; Tammar Kushnir; Talma Hendler; Rafael Malach The dynamics of object-selective activation correlate with recognition performance in humans Journal Article In: Nature Neuroscience, vol. 3, no. 8, pp. 837–893, 2000. @article{GrillSpector2000,To investigate the relationship between perceptual awareness and brain activity, we measured both recogni-tion performance and fMRI signal from object-related areas in human cortex while images were presented briefly using a masking protocol. Our results suggest that recognition performance is correlated with selective activation in object areas. Selective activation was correlated to object naming when exposure duration was varied from 20 to 500 milliseconds. Subjects' recognition during identical visual stimulation could be enhanced by training, which also increased the fMRI signal. Overall, the correlation between recognition per- formance and fMRI signal was highest in occipitotemporal object areas (the lateral occipital complex). |
Timothy L. Hodgson; Adnan Bajwa; Adrian M. Owen; Christopher Kennard The strategic control of gaze direction in the tower of London task Journal Article In: Journal of Cognitive Neuroscience, vol. 12, no. 5, pp. 894–907, 2000. @article{Hodgson2000,In this paper, we describe 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 (TOL) task. We showed subjects a series of pictures depicting two arrangements of colored balls in pockets within the upper and lower halves of a computer display. The task was to plan (but not to 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 minimum number of moves required for problem solution. We report that subjects are more likely to look towards the Goalspace in the initial period after picture presentation, but bias gaze towards the Workspace during the middle of trials. Towards the end of a trial, subjects are once again more likely to fixate the Goalspace. This pattern is found regardless of whether the subjects solve problems by rearranging the balls in the lower or upper visual fields, demonstrating that this strategy correlates with discrete phases in problem solving. A second experiment showed that efficient planners direct their gaze selectively towards the problem critical balls in the Workspace. In contrast, individuals who make errors spend more time looking at irrelevant items and are strongly influenced by the movement strategy needed to solve the preceding problem. We conclude that efficient solution of the TOL requires the capacity to generate and flexibly shift between control sets, including those underlying ocular scanning. The role of working memory and the prefrontal cerebral cortex in the task are discussed. |
Iain D. Gilchrist; Monika Harvey Refixation frequency and memory mechanisms in visual search Journal Article In: Current Biology, vol. 10, no. 19, pp. 1209–1212, 2000. @article{Gilchrist2000,Visual search - looking for a target object in the presence of a number of distractor items - is an everyday activity for humans (for example, finding the car in a busy car park) and animals (for example, foraging for food). Our understanding of visual search has been enriched by an interdisciplinary effort using a wide range of research techniques including behavioural studies in humans [1], single-cell electrophysiology [2], transcranial magnetic stimulation [3], event-related potentials [4] and studies of patients with focal brain injury [5]. A central question is what kind of information controls the search process. Visual search is typically accompanied by a series of eye movements, and investigating the nature and location of fixations helps to identify the kind of information that might control the search process. It has already been demonstrated that objects are fixated if they are visually similar to the target [6]. Also, if an item has been fixated, it is less likely to be returned to on the subsequent saccade. This automatic process is referred to as inhibition of return (IOR [7,8]). Here, we investigated the role of memory for which items had been fixated previously. We found that, during search, subjects often refixated items that had been previously fixated. Although there were fewer return saccades than would be expected by chance, the number of refixations indicated limited functional memory, indeed the memory effects that were present may primarily be a result of IOR. |
Laurence R. Harris; Andrew T. Smith Interactions between first- and second-order motion revealed by optokinetic nystagmus Journal Article In: Experimental Brain Research, vol. 130, no. 1, pp. 67–72, 2000. @article{Harris2000,A previous study has suggested that second-order motion is ineffective at driving optokinetic nystagmus (OKN) when presented alone. First- and second-order motion cues interact in creating the perception of motion. Is there an interaction between first- and second-order cues in the control of eye movements? We presented combinations of first- and second-order cues moving in the same or opposite directions and measured the eye movements evoked, to look for a modification of the oculomotor response to first-order motion by simultaneously presented second-order cues. Dynamic random noise was used as a carrier for first- and second-order drifting gratings (13.4 degrees/s; 0.25 cycles/degree; 64 x 48 degrees screen viewed at 28.5 cm). Second-order gratings were defined by spatial modulation of the luminance flicker frequency of noise pixels of constant contrast (50%). A first-order, luminance-defined grating (13.4 degrees/s; 0.25 cycles/degree; variable contrast from 4-50%) was moved in either the same or the opposite direction. Eye movements were recorded by video-oculography from six subjects as they looked straight ahead. The gain (eye velocity/stimulus velocity) of first-order-evoked OKN increased with contrast. The presence of flicker-defined second-order motion in the opposite direction attenuated this OKN below a first-order contrast of 15%, although it had little effect at higher contrasts. When first- and second-order motion were in the same direction, there was an enhancement of the OKN response. We conclude that second-order motion can modify the optokinetic response to simultaneously presented first-order motion. |
Raymond Bertram; Jukka Hyönä; Matti Laine The role of context in morphological processing: Evidence from Finnish Journal Article In: Language and Cognitive Processes, vol. 15, no. 4/5, pp. 367–388, 2000. @article{Bertram2000,This paper is concernedwith the role of context on the processing of in?ected nouns inFinnish. Identi?cation of partitive plurals with the homonymic suf?x -jA was studied by presenting the target nouns in a sentence context and by recording durations of readers' eye ?xations and self-paced reading times for these targets. A recent visual lexical decision study indicated that the same in?ected words with -jA were sensitive to surface frequency manipulations, but not to base frequency manipulations. The authors interpreted these results to suggest that these in?ectional forms are stored and processed by means of their whole-word representations. In contrast, the present context study shows both a surface frequency effect and a lagged base frequency effect. We argue that syntactic cues prior to the target word prime the in?ectional reading of the -jA suf?x, and as a consequence the base is reinstated as an effective unit in processing these nouns with a homonymic suf?x. INTRODUCTION |
David E. Irwin; Angela M. Colcombe; Arthur F. Kramer; Sowon Hahn Attentional and oculomotor capture by onset, luminance and color singletons Journal Article In: Vision Research, vol. 40, no. 10-12, pp. 1443–1458, 2000. @article{Irwin2000,In three experiments we investigated whether attentional and oculomotor capture occur only when object-defining abrupt onsets are used as distractors in a visual search task, or whether other salient stimuli also capture attention and the eyes even when they do not constitute new objects. The results showed that abrupt onsets (new objects) are especially effective in capturing attention and the eyes, but that luminance increments that do not accompany the appearance of new objects capture attention as well. Color singletons do not capture attention unless subjects have experienced the color singleton as a search target in a previous experimental session. Both abrupt onsets and luminance increments elicit reflexive, involuntary saccades whereas transient color changes do not. Implications for theories of attentional capture are discussed. |
Arthur F. Kramer; Sowon Hahn; David E. Irwin; Jan Theeuwes Age differences in the control of looking behavior: Do you know where your eyes have been? Book 11, 2000. @book{Kramer2000,Previous research has shown that during visual search young and old adults' eye movements are equivalently influenced by the appearance of task-irrelevant abrupt onsets. The finding of age-equivalent oculomotor capture is quite surprising in light of the abundant research suggesting that older adults exhibit poorer inhibitory control than young adults on a variety of different tasks. In the present study, we examined the hypothesis that oculomotor capture is age invariant when subjects' awareness of the appearance of task-irrelevant onsets is low, but that older adults will have more difficulty than young adults in inhibiting reflexive eye movements to task-irrelevant onsets when awareness of these objects is high. Our results were consistent with the level-of-awareness hypothesis. Young and old adults showed equivalent patterns of oculomotor capture with equiluminant onsets, but older adults misdirected their eyes to bright onsets more often than young adults did. |
Alexander Pollatsek; Jukka Hyönä; Raymond Bertram The role of morphological constituents in Reading finnish compound words Journal Article In: Journal of Experimental Psychology: Human Perception and Performance, vol. 26, no. 2, pp. 820–833, 2000. @article{Pollatsek2000,The processing of transparent Finnish compound words was investigated in 2 experiments in which eye movements were recorded while sentences were read silently. The frequency of the second constituent had a large influence (95 ms) on gaze duration on the target words, but its influence was relatively late in processing: A clear effect only occurred on the probability of a third fixation. The frequency of the whole compound word had a similar influence on gaze duration (82 ms) and influenced eye movements at least as rapidly as did the frequency of the second constituent. These results, together with an earlier finding that the frequency of the first constituent affected the first fixation duration, indicate that the identification of these compound words involves parallel processing of both morphological constituents and whole-word representations. |
Josef N. Geest; Maarten A. Frens Video-oculography and scleral search coils: a direct comparison of two methods for recording the movements of the eye Journal Article In: Vision Research, vol. 114, pp. 185–195, 2000. @article{Geest2000,A video-based 2D eye-tracking system (EyeLink version 2.04, SR Research Ltd/SMI) was compared with the scleral search coil technique for its performance on recording the properties of fixations and saccadic eye movements. Fixation positions and saccadic properties (amplitude, duration, and peak velocity) were calculated independently from the data of the two systems that recorded eye positions simultaneously. Fixation positions were well correlated between the video and the coil output with an average discrepancy of B 1° over a tested range of 40 by 40° of visual angle. With respect to the saccade analysis, the values measured by the video system were fitted as a linear function of the values measured by the coil system. Highly correlated linear fits with slopes near one were obtained for all the saccadic parameters. Main sequence relationships (amplitudes– duration and amplitude–peak velocity) were also similar for both systems. A disadvantage of the video method is its low sample rate of 250 Hz. The relatively noisier estimate of all parameters of small saccades could be attributed to this low sampling frequency. |
D. W. J. Cabel; I. T. Armstrong; Eyal M. Reingold; D. P. Munoz Control of saccade initiation in a countermanding task using visual and auditory stop signals Journal Article In: Experimental Brain Research, vol. 133, no. 4, pp. 431–441, 2000. @article{Cabel2000,We examined inhibitory control in an oculomotor countermanding task, where the primary task required a saccadic eye movement be made to a target and a less-frequent secondary task required that the movement be halted. Previous studies have used a visual stimulus presented centrally on the fovea as the signal to stop or countermand a saccade. In these previous studies, there are at least two possible sources of saccadic inhibition: (1) sensory stimulation at the fovea can elicit a bottom-up mechanism, where a visual transient signal can delay or inhibit the developing saccade command; and (2) information based on the task instruction can be used to initiate a top-down mechanism to halt the movement. In the present study, we used both visual and auditory stop signals to test the hypothesis that the bottom-up mechanism is activated only after presentation of a foveal visual stop signal. Subjects were instructed first to look at a central spot and then to look to an eccentric visual target that appeared randomly to the left or right of center. On about one-third of the trials, a stop signal was presented. Three types of stop signals were used with equal probability: a broad-band noise burst (auditory), a central fixation spot (visual), and a combination of the auditory and visual stimuli (combined). Saccadic reaction time and stop-signal accuracy were used to calculate stop signal reaction time (SSRT), an estimate of the time required to inhibit the eye movement. Mean SSRT was longer for the auditory stop signals (201 ms) than for the signals with a foveal visual component (visual 113 ms; combined 91 ms). We conclude that a foveal visual stop signal in an oculomotor countermanding task changes the measure of inhibitory control to reflect not only inhibitory processes but also the sensory information afforded by stimulation at the fovea. |
Eli Brenner; Frans W. Cornelissen Separate simultaneous processing of egocentric and relative positions Journal Article In: Vision Research, vol. 40, no. 19, pp. 2557–2563, 2000. @article{Brenner2000,It is well established that all kinds of visual attributes are processed separately within the brain. This separation is related to differences in the information that is relevant for the different attributes. When attributes differ greatly (such as colour and motion) it is obvious that they must rely on different information. However, separating the processing of different attributes could also allow highly related attributes to evolve independently, so that they end up being judged on the basis of different types of information. Here, we examine the case of egocentric and relative localisation. For judging egocentric positions, the orientation of the eyes has to be taken into account. This is not so for judging relative positions. We demonstrate that these two attributes can be processed separately by showing that simultaneous judgements of relative and egocentric position differ in their dependency on eye orientation. Subjects pursued a moving dot. We flashed either single targets, or pairs of targets with a 67 ms interval between them, directly below the subjects' gaze. As the eyes were moving during the 67 ms interval, the retinal separation between pairs of targets was different from their actual separation. Subjects indicated the position at which they saw the targets with reasonable reproducibility, with a consistent bias in the direction of the eye movement. However, when two targets were flashed, the indicated separation between them usually coincided with their retinal separation, rather than with their actual separation. We conclude that egocentric and relative spatial positions can be estimated separately and simultaneously, on the basis of different types of information. |
Gillian A. OʼDriscoll; Anne-Lise V. G. Wolff; Chawki Benkelfat; Patrik S. Florencio; Samarthji Lal; Alan C. Evans Functional neuroanatomy of smooth pursuit and predictive saccades Journal Article In: NeuroReport, vol. 11, no. 6, pp. 1335–1340, 2000. @article{OʼDriscoll2000,We used PET to study differences in cerebral blood flow (CBF) in smooth pursuit, predictive saccades and fixation. Eye movements were monitored in the scanner. Compared with fixation, pursuit and predictive saccades activated a network of highly similar areas, including frontal eye fields, supplementary eye fields, V5 and medial cuneus. Our findings are consistent with non-human primate studies that suggest that pursuit and saccades are controlled by similar and adjacent neural areas. Pursuit was associated with greater activation of caudate than saccades, suggesting a role for basal ganglia in pursuit that is consistent with studies of neurological populations. Saccades were associated with greater activation of cerebellum and frontal eye fields. A frontal-cerebellar loop may be important in coordinating the preparation and timing of saccades in predictive tracking. |