Programming Of Eye Movements Research Articles

Distractor-evoked deviation in saccade direction suggests an asymmetric representation of the upper and lower visual fields on oculomotor maps.

The programming of rapid eye movements or "saccades" involves a large collection of neural substrates. The subcortical oculomotor center - the superior colliculus (SC) - contains a topographical motor map that encodes saccade vectors. Using a visual distractor task, the present study examined a classic model of the SC motor map, which assumes a symmetrical representation of the upper visual field (UVF) and lower visual field (LVF). Visual distractors are known to attract or repel the saccade trajectory, depending on their angular distance from the target. In the present study, the distractor (if presented) was placed at a location that mirrored the target in the opposite visual field (upper or lower). The symmetrical SC model predicts equivalent directional deviations for saccades into the UVF and LVF. The results, however, showed that the directional deviations evoked by visual distractors were much stronger for saccades directed to the LVF. We argue that this observation is consistent with the recent neurophysiological finding that the LVF is relatively under-represented, as compared to the UVF, in the SC and possibly in other oculomotor centers. We conclude the paper with a suggested revision to the SC model.

Shifting attention in visuospatial short-term memory does not require oculomotor planning: Insight from congenital gaze paralysis

Attention allows pieces of information stored in visuospatial short-term memory (VSSTM) to be selectively processed. Previous studies showed that shifts of attention in VSSTM in response to a retro-cue are accompanied by eye movements in the direction of the position of the memorized item although there is nothing left to look at. This finding raises the possibility that shifts of attention in VSSTM are underpinned by mechanisms originally involved in the planning and control of eye movements. To explore this possibility, we investigated the ability of an individual with congenital horizontal gaze paralysis (HGP2) to shift her attention horizontally or vertically toward a memorized item within VSSTM using a retro-cue paradigm. As efficient oculomotor programming is not innate but requires some trial and error learning and adaptation to develop, congenital paralysis prevents this development. Consequently, if shifts of attention in VSSTM rely on the same mechanisms as those supporting the programming of eye movements, then horizontal congenital gaze paralysis should necessarily prevent typical retro-cueing effect in the paralyzed axis. At odds with this prediction, HGP2 showed a typical retro-cueing effect in her paralyzed axis. This original finding indicates that selecting an item within VSSTM does not depend on the ability to program a saccade.

Isolated face features are sufficient to elicit ultra-rapid and involuntary orienting responses toward faces.

Previous studies have shown that face stimuli influence the programming of eye movements by eliciting involuntary and extremely fast saccades toward them. The present study examined whether holistic processing of faces mediates these effects. We used a saccadic choice task in which participants were presented simultaneously with two images and had to perform a saccade toward the one containing a target stimulus (e.g., a face). Across three experiments, stimuli were altered via upside-down inversion (Experiment 1) or scrambling of thumbnails within the images (Experiments 2 and 3) in order to disrupt holistic processing. We found that disruption of holistic processing only had a limited impact on the latency of saccades toward face targets, which remained extremely short (minimum saccadic reaction times of only ∼120–130 ms), and did not affect the proportion of error saccades toward face distractors that captured attention more than other distractor categories. It, however, resulted in increasing error rate of saccades toward face targets. These results suggest that the processing of isolated face features is sufficient to elicit extremely fast and involuntary saccadic responses toward them. Holistic representations of faces may, however, be used as a search template to accurately detect faces.

Face perception influences the programming of eye movements

Face perception influences the programming of eye movements

Visual Perception and Oculomotor Activity during Reading Tasks of Varying Complexity in Children Aged Seven to Ten Years

The paper presents the results of comparative analysis of visual perception (VP) and oculomotor activity in reading tasks of varying complexity in children aged seven to ten years with different levels of reading skills. We observed higher VP variables in children with good reading skills compared with poor readers. The formation of the VP system underlying the basic mechanism of reading, especially at the initial stage of learning, can be assessed by the following key parameters: noise tolerance, spatial relationships, and visual analysis/synthesis affording recognition of the graphic configuration of words, spelling (letter order), and semantics (word meaning). The speed of lexical access and eye movement programming, the accuracy of fixation point positioning, the amount of perceived symbolic information and lexemes and general context stored in the working memory are much higher in children with better qualification and reading experience. When a highly complex text beyond the current educational program is read, discrepancy in the oculomotor activity parameters (duration of progressive and adjustable fixations and the reading speed and time) between groups of children with different reading skills decreases.

The role of fixation disengagement in the parallel programming of sequences of saccades

One of the core mechanisms involved in the control of saccade responses to selected target stimuli is the disengagement from the current fixation location, so that the next saccade can be executed. To carry out everyday visual tasks, we make multiple eye movements that can be programmed in parallel. However, the role of disengagement in the parallel programming of saccades has not been examined. It is well established that the need for disengagement slows down saccadic response time. This may be important in allowing the system to program accurate eye movements and have a role to play in the control of multiple eye movements but as yet this remains untested. Here, we report two experiments that seek to examine whether fixation disengagement reduces saccade latencies when the task completion demands multiple saccade responses. A saccade contingent paradigm was employed and participants were asked to execute saccadic eye movements to a series of seven targets while manipulating when these targets were shown. This both promotes fixation disengagement and controls the extent that parallel programming can occur. We found that trial duration decreased as more targets were made available prior to fixation: this was a result both of a reduction in the number of saccades being executed and in their saccade latencies. This supports the view that even when fixation disengagement is not required, parallel programming of multiple sequential saccadic eye movements is still present. By comparison with previous published data, we demonstrate a substantial speeded of response times in these condition (“a gap effect”) and that parallel programming is attenuated in these conditions.

Face perception influences the programming of eye movements

Previous studies have shown that face stimuli elicit extremely fast and involuntary saccadic responses toward them, relative to other categories of visual stimuli. In the present study, we further investigated to what extent face stimuli influence the programming and execution of saccades examining their amplitude. We performed two experiments using a saccadic choice task: two images (one with a face, one with a vehicle) were simultaneously displayed in the left and right visual fields of participants who had to initiate a saccade toward the image (Experiment 1) or toward a cross in the image (Experiment 2) containing a target stimulus (a face or a vehicle). Results revealed shorter saccades toward vehicle than face targets, even if participants were explicitly asked to perform their saccades toward a specific location (Experiment 2). Furthermore, error saccades had smaller amplitude than correct saccades. Further analyses showed that error saccades were interrupted in mid-flight to initiate a concurrently-programmed corrective saccade. Overall, these data suggest that the content of visual stimuli can influence the programming of saccade amplitude, and that efficient online correction of saccades can be performed during the saccadic choice task.

The Relationship Between Spatial Attention and Eye Movements.

The nature of the relationship between spatial attention and eye movements has been the subject of intense debate for more than 40years. Two ideas have dominated this debate. First is the idea that spatial attention shares common neural mechanisms with eye movement programming, characterizing attention as an eye movement that has been prepared but not executed. Second, based on the observation that attention shifts to saccade targets, several theories have proposed that saccade programming necessarily recruits attentional resources. In this chapter, we review the evidence for each of these ideas and discuss some of the limitations and challenges in confirming their predictions. Although they are clearly dependent under some circumstances, dissociations between spatial attention and eye movements, and clear differences in their basic functions, point to the existence of two interconnected, but separate, systems.

Eye movement programming and reading accuracy.

Eye movements were measured during the silent reading of sentences to extract several oculomotor measures. Rather than each measure being examined independently, oculomotor responses were grouped into two types, the assumption being that the grouping would project onto underlying constructs. Properties of forward-directed movements were assumed to reflect the success with which linguistic information was acquired (acquisition), and corrective responses were assumed to reveal readers' responding to difficulties (correction). These two types of oculomotor responses were linked to indexes of reading accuracy (accuracy), which were obtained from separate materials so that eye movements with one set of materials could be used to predict reading accuracy for another set of materials. Path analyses indicated that correction, but not acquisition, was linked to accuracy. The additional clustering of acquisition, correction, and accuracy scores identified a group of readers with relatively low accuracy scores. These readers were typical in their acquisition of linguistic information but under-used corrective responding.

Feature-based attention across saccades and immediate postsaccadic selection.

Before each eye movement, attentional resources are drawn to the saccade goal. This saccade-related attention is known to be spatial in nature, and in this study we asked whether it also evokes any feature selectivity that is maintained across the saccade. After a saccade toward a colored target, participants performed a postsaccadic feature search on an array displayed at landing. The saccade target either had the same color as the search target in the postsaccadic array (congruent trials) or a different color (incongruent or neutral trials). Our results show that the color of the saccade target did not prime the subsequent feature search. This suggests that "landmark search", the process of searching for the saccade target once the eye lands (Deubel in Visual Cognition, 11, 173-202, 2004), may not involve the attentional mechanisms that underlie feature search. We also analyzed intertrial effects and observed priming of pop-out (Maljkovic & Nakayama in Memory & Cognition, 22, 657-672, 1994) for the postsaccadic feature search: the detection of the color singleton became faster when its color was repeated on successive trials. However, search performance revealed no effect of congruency between the saccade and search targets, either within or across trials, suggesting that the priming of pop-out is specific to target repetitions within the same task and is not seen for repetitions across tasks. Our results support a dissociation between feature-based attention and the attentional mechanisms associated with eye movement programming.

Discrete versus multiple word displays: a re-analysis of studies comparing dyslexic and typically developing children.

The study examines whether impairments in reading a text can be explained by a deficit in word decoding or an additional deficit in the processes governing the integration of reading subcomponents (including eye movement programming and pronunciation) should also be postulated. We report a re-analysis of data from eleven previous experiments conducted in our lab where the reading performance on single, discrete word displays as well multiple displays (texts, and in few cases also word lists) was investigated in groups of dyslexic children and typically developing readers. The analysis focuses on measures of time and not accuracy. Across experiments, dyslexic children are slower and more variable than typically developing readers in reading texts as well as vocal reaction time (RTs) to singly presented words; the dis-homogeneity in variability between groups points to the inappropriateness of standard measures of size effect (such as Cohen’s d), and suggests the use of the ratio between groups’ performance. The mean ratio for text reading is 1.95 across experiments. Mean ratio for vocal RTs for singly presented words is considerably smaller (1.52). Furthermore, this latter value is probably an overestimation as considering total reading times (i.e., a measure including also the pronunciation component) considerably reduces the group difference in vocal RTs (1.19 according to Martelli et al., 2014). The ratio difference between single and multiple displays does not depend upon the presence of a semantic context in the case of texts as large ratios are also observed with lists of unrelated words (though studies testing this aspect were few). We conclude that, if care is taken in using appropriate comparisons, the deficit in reading texts or lists of words is appreciably greater than that revealed with discrete word presentations. Thus, reading multiple stimuli present a specific, additional challenge to dyslexic children indicating that models of reading should incorporate this aspect.

Visual Attention and Saccadic Oculomotor Control in Parkinson's Disease

Background: In patients with Parkinson's disease (PD) we aimed at differentiating the relation between selective visual attention, deficits of programming and dynamics of saccadic eye movements while searching for a target and hand-reaction time as well as hand-movement time. Visual attention is crucial for concentrating selectively on one aspect of the visual field while ignoring other aspects. Eye movements are anatomically and functionally related to mechanisms of visual attention. Saccadic dysfunction might confound selective visual attention in PD. Methods: We studied visual selective attention in 22 medicated PD patients (clinical ON status, mild to moderate disease severity) and 22 age matched controls. We looked for possible interferences through oculomotor deficits. Two tasks were compared: free viewing of photographs and time optimal visual search of a hidden target. Visual search times (VST), task related dynamics of saccades, and hand-reaction and hand-movement times were analyzed. Results: In the free viewing task mild to moderately affected PD patients did not differ statistically from healthy subjects with respect to saccade dynamics. However, patients differed significantly from healthy subjects in the time optimal visual search task with 25% lower rates of successful searches. Hand movement reaction time did not differ in both groups, whereas hand movement execution time was significantly prolonged in PD patients. Conclusion: Saccadic oculomotor control and hand movement reaction times were intact, whereas in our less severely affected treated PD patients, visual selective attention was not. The highly reduced successful search rate might be related to disturbed programming and delayed execution of saccades during time optimal visual search due to decreased execution of serial-order sequential generation of saccades.

Lack of multisensory integration in hemianopia: no influence of visual stimuli on aurally guided saccades to the blind hemifield.

In patients with visual hemifield defects residual visual functions may be present, a phenomenon called blindsight. The superior colliculus (SC) is part of the spared pathway that is considered to be responsible for this phenomenon. Given that the SC processes input from different modalities and is involved in the programming of saccadic eye movements, the aim of the present study was to examine whether multimodal integration can modulate oculomotor competition in the damaged hemifield. We conducted two experiments with eight patients who had visual field defects due to lesions that affected the retinogeniculate pathway but spared the retinotectal direct SC pathway. They had to make saccades to an auditory target that was presented alone or in combination with a visual stimulus. The visual stimulus could either be spatially coincident with the auditory target (possibly enhancing the auditory target signal), or spatially disparate to the auditory target (possibly competing with the auditory tar-get signal). For each patient we compared the saccade endpoint deviation in these two bi-modal conditions with the endpoint deviation in the unimodal condition (auditory target alone). In all seven hemianopic patients, saccade accuracy was affected only by visual stimuli in the intact, but not in the blind visual field. In one patient with a more limited quadrantano-pia, a facilitation effect of the spatially coincident visual stimulus was observed. We conclude that our results show that multisensory integration is infrequent in the blind field of patients with hemianopia.

Positive Association of Video Game Playing with Left Frontal Cortical Thickness in Adolescents

Playing video games is a common recreational activity of adolescents. Recent research associated frequent video game playing with improvements in cognitive functions. Improvements in cognition have been related to grey matter changes in prefrontal cortex. However, a fine-grained analysis of human brain structure in relation to video gaming is lacking. In magnetic resonance imaging scans of 152 14-year old adolescents, FreeSurfer was used to estimate cortical thickness. Cortical thickness across the whole cortical surface was correlated with self-reported duration of video gaming (hours per week). A robust positive association between cortical thickness and video gaming duration was observed in left dorsolateral prefrontal cortex (DLPFC) and left frontal eye fields (FEFs). No regions showed cortical thinning in association with video gaming frequency. DLPFC is the core correlate of executive control and strategic planning which in turn are essential cognitive domains for successful video gaming. The FEFs are a key region involved in visuo-motor integration important for programming and execution of eye movements and allocation of visuo-spatial attention, processes engaged extensively in video games. The results may represent the biological basis of previously reported cognitive improvements due to video game play. Whether or not these results represent a-priori characteristics or consequences of video gaming should be studied in future longitudinal investigations.

It's not what you see: it's the language you say it in

In an eye-tracking experiment, we investigated the interplay between visual and linguistic information processing during time-telling, and how this is affected by speaking in a non-native language. We compared time-telling in Greek and English, which differ in time-telling word order (hour vs. minute mentioned first), by contrasting Greek-English bilinguals speaking in their L1-Greek or their L2-English, and English monolingual speakers. All three groups were faster when telling the time for digital than for analogue clocks, and when telling the time for the first half-hour than the second half-hour. Critically, first fixation and gaze duration analyses for the hour and minute regions showed a different pattern for Greek-English bilinguals when speaking in their L1 versus L2, with the latter resembling that of English monolinguals. Our results suggest that bilingual speakers' eye-movement programming was influenced by the type of time-telling utterance specific to the language of production currently in use.

The time course of perception of coarticulation

The perception of coarticulated speech as it unfolds over time was investigated by monitoring eye movements of participants as they listened to words with oral vowels or with late or early onset of anticipatory vowel nasalization. When listeners heard [CṼNC] and had visual choices of images of CVNC (e.g., send) and CVC (said) words, they fixated more quickly and more often on the CVNC image when onset of nasalization began early in the vowel compared to when the coarticulatory information occurred later. Moreover, when a standard eye movement programming delay is factored in, fixations on the CVNC image began to occur before listeners heard the nasal consonant. Listeners' attention to coarticulatory cues for velum lowering was selective in two respects: (a) listeners assigned greater perceptual weight to coarticulatory information in phonetic contexts in which [Ṽ] but not N is an especially robust property, and (b) individual listeners differed in their perceptual weights. Overall, the time course of perception of velum lowering in American English indicates that the dynamics of perception parallel the dynamics of the gestural information encoded in the acoustic signal. In real-time processing, listeners closely track unfolding coarticulatory information in ways that speed lexical activation.

Deficits of cortical oculomotor mechanisms in cerebellar atrophy patients

Commonly, the cerebellum is not associated with cortical components of saccadic eye movement programming. The present study investigates cerebellar effects on visually guided saccades in reflexive tasks (step, gap, overlap) and on internally driven saccades in intentional tasks (anti, memory, short memory sequences of four targets) in five patients with isolated cerebellar atrophy. The cerebellar dysfunction led to impairments in both reflexive and intentional saccades. Cerebellar atrophy patients showed an increase in the gain variability and an increase in the saccade latency. Furthermore, in the memory and anti task, suppression and pro-saccade errors were more frequent in the atrophy group compared to the control group. In the sequence task, patients had difficulties reproducing all four target locations in the order of the displayed sequence. The high variability of the saccade gain is a common observation in cerebellar atrophy patients and can be explained by the general variability present in the saccadic system. The increase in the saccade latency could be due to a cerebellar contribution to cortical processes related to fixation and target selection preceding the initiation of a saccade. Furthermore, the frequent occurrence of saccade errors in the memory and anti task suggests a cerebellar involvement in frontal inhibition of unwanted reflexive saccades. The impaired reproduction of saccade sequences in atrophy patients points to a deficit in short-term memory processes. Thus, this study provides further evidence that the cerebellum is involved in different cortical mechanisms related to the control of saccadic eye movements.

Effects of cerebellar infarcts on cortical processing of saccades

The objective of the present study was to investigate cerebellar influences on cortical components of saccadic eye movement programming in human subjects. In 24 patients with a localized cerebellar lesion, saccadic eye movements were recorded in different reflexive (step, gap, overlap) and intentional (anti, memory, short memory sequences) tasks and compared to 23 healthy controls. The cerebellar lesions led to impairments in different saccade parameters. Cerebellar patients tended to show hypermetria and increased latencies compared to the control group. In particular, they executed significantly more erroneous saccades specifically in the memory task (suppression errors) but not in the anti task (pro-saccade errors). Moreover, while reproducing short sequences of saccades from memory, patients with cerebellar infarcts made more errors with regard to the sequence order than controls. The influence of cerebellar hemispheric lesions on the saccade latency, the task-specific lesion effects on the frequency of suppression errors, and the effects on the number of order errors suggest that the cerebellum is involved in cortical processes such as target selection and sequence reproduction.

Overlapping neural circuits for visuospatial attention and eye movements in human cerebellum.

Previous research in patients with cerebellar damage suggests that the cerebellum may play a role in visual attention. One limitation of some of these studies is that they examined patients with heterogeneous cerebellar damage. As a result, the patterns of reported deficits have been inconsistent. In the current study we used functional neuroimaging (fMRI) in healthy adults (n=14) to examine whether the cerebellum plays an important role in visual attention. During the fMRI session, subjects performed two covert attention tasks in which they were cued (with peripheral flashes or central directional arrows) to attend to marked locations in the visual periphery without moving their eyes. Using a block design, we compared BOLD activation in these covert attention conditions to a number of control conditions including: the same attention tasks with eye movements, a target detection task with no cuing, and a self paced button-press task in order to rule out the possibility that any activation observed in the cerebellum during the covert attention tasks might be due to motor output associated with task performance. Results indicated that, in addition to the usual fronto-parietal networks commonly engaged by this visual attention task, two regions of the cerebellum (lobule 6 in the left posterior quadrangular lobe and the culmen) were active when subjects performed the attention task with peripheral cues with or without concomitant eye movements. The same regions of the cerebellum were not active, however, when subjects performed the covert attention task using central arrow cues. This suggests that the cerebellum may play a critical role in both shifting attention and generating eye movements towards stimuli that suddenly appear in the periphery. These results are consistent with the pre-motor theory of attention which posits that shifts of attention are generated through the programming of eye movements that are not executed. Meeting abstract presented at VSS 2012

A combined method for the programming of saccadic eye movements

A saccade is a quick spasmodic movement of an eye formed by the central nervous system before the beginning of the movement and is realized by the oculomotor muscles as a programmed movement. These muscles are modeled as viscoelastic contractile elements. The programmed control is defined as a time function and is considered as a sum of four components (tonic, static, kinematic, and dynamic) under the following assumption: when a muscle contracts, the corresponding antagonist muscle becomes elongated.