Binocular Eye Movements Are Adapted to the Natural Environment.

Humans and many animals make frequent saccades requiring coordinated movements of the eyes. When landing on the new fixation point, the eyes must converge accurately or double images will be perceived. We asked whether the visual system uses statistical regularities in the natural environment to aid eye alignment at the end of saccades. We measured the distribution of naturally occurring disparities in different parts of the visual field. The central tendency of the distributions was crossed (nearer than fixation) in the lower field and uncrossed (farther) in the upper field in male and female participants. It was uncrossed in the left and right fields. We also measured horizontal vergence after completion of vertical, horizontal, and oblique saccades. When the eyes first landed near the eccentric target, vergence was quite consistent with the natural-disparity distribution. For example, when making an upward saccade, the eyes diverged to be aligned with the most probable uncrossed disparity in that part of the visual field. Likewise, when making a downward saccade, the eyes converged to enable alignment with crossed disparity in that part of the field. Our results show that rapid binocular eye movements are adapted to the statistics of the 3D environment, minimizing the need for large corrective vergence movements at the end of saccades. The results are relevant to the debate about whether eye movements are derived from separate saccadic and vergence neural commands that control both eyes or from separate monocular commands that control the eyes independently.SIGNIFICANCE STATEMENT We show that the human visual system incorporates statistical regularities in the visual environment to enable efficient binocular eye movements. We define the oculomotor horopter: the surface of 3D positions to which the eyes initially move when stimulated by eccentric targets. The observed movements maximize the probability of accurate fixation as the eyes move from one position to another. This is the first study to show quantitatively that binocular eye movements conform to 3D scene statistics, thereby enabling efficient processing. The results provide greater insight into the neural mechanisms underlying the planning and execution of saccadic eye movements

The antisaccade task as a research tool in psychopathology: A critical review

The antisaccade task is a measure of volitional control of behavior sensitive to fronto-striatal dysfunction. Here we outline important issues concerning antisaccade methodology, consider recent evidence of the cognitive processes and neural mechanisms involved in task performance, and review how the task has been applied to study psychopathology. We conclude that the task yields reliable and sensitive measures of the processes involved in resolving the conflict between volitional and reflexive behavioral responses, a key cognitive deficit relevant to a number of neuropsychiatric conditions. Additionally, antisaccade deficits may reflect genetic liability for schizophrenia. Finally, the ease and accuracy with which the task can be administered, combined with its sensitivity to fronto-striatal dysfunction and the availability of suitable control conditions, may make it a useful benchmark tool for studies of potential cognitive enhancers

Suppression of displacement in severely slowed saccades

Severely slowed saccades in <I>spinocerebellar ataxia</I> have previously been shown to be at least partially closed-loop in nature: their long duration means that they can be modified in-flight in response to intrasaccadic target movements. In this study, a woman with these pathologically slowed saccades could modify them in-flight in response to target movements, even when saccadic suppression of displacement prevented conscious awareness of those movements. Thus saccadic suppression of displacement is not complete, in that it provides perceptual information that is sub-threshold to consciousness but which can still be effectively utilised by the oculomotor system

The Measurement of Eye Movements in Mild Traumatic Brain Injury: A Structured Review of an Emerging Area

Mild traumatic brain injury (mTBI), or concussion, occurs following a direct or indirect force to the head that causes a change in brain function. Many neurological signs and symptoms of mTBI can be subtle and transient, and some can persist beyond the usual recovery timeframe, such as balance, cognitive or sensory disturbance that may pre-dispose to further injury in the future. There is currently no accepted definition or diagnostic criteria for mTBI and therefore no single assessment has been developed or accepted as being able to identify those with an mTBI. Eye-movement assessment may be useful, as specific eye-movements and their metrics can be attributed to specific brain regions or functions, and eye-movement involves a multitude of brain regions. Recently, research has focused on quantitative eye-movement assessments using eye-tracking technology for diagnosis and monitoring symptoms of an mTBI. However, the approaches taken to objectively measure eye-movements varies with respect to instrumentation, protocols and recognition of factors that may influence results, such as cognitive function or basic visual function. This review aimed to examine previous work that has measured eye-movements within those with mTBI to inform the development of robust or standardized testing protocols. Medline/PubMed, CINAHL, PsychInfo and Scopus databases were searched. Twenty-two articles met inclusion/exclusion criteria and were reviewed, which examined saccades, smooth pursuits, fixations and nystagmus in mTBI compared to controls. Current methodologies for data collection, analysis and interpretation from eye-tracking technology in individuals following an mTBI are discussed. In brief, a wide range of eye-movement instruments and outcome measures were reported, but validity and reliability of devices and metrics were insufficiently reported across studies. Interpretation of outcomes was complicated by poor study reporting of demographics, mTBI-related features (e.g., time since injury), and few studies considered the influence that cognitive or visual functions may have on eye-movements. The reviewed evidence suggests that eye-movements are impaired in mTBI, but future research is required to accurately and robustly establish findings. Standardization and reporting of eye-movement instruments, data collection procedures, processing algorithms and analysis methods are required. Recommendations also include comprehensive reporting of demographics, mTBI-related features, and confounding variables

Abnormal negative feedback processing in first episode schizophrenia: evidence from an oculomotor rule switching task

Background. Previous studies have shown that patients with schizophrenia are impaired on executive tasks, where positive and negative feedbacks are used to update task rules or switch attention. However, research to date using saccadic tasks has not revealed clear deficits in task switching in these patients. The present study used an oculomotor ‘ rule switching ’ task to investigate the use of negative feedback when switching between task rules in people with schizophrenia. Method. A total of 50 patients with first episode schizophrenia and 25 healthy controls performed a task in which the association between a centrally presented visual cue and the direction of a saccade could change from trial to trial. Rule changes were heralded by an unexpected negative feedback, indicating that the cue-response mapping had reversed. Results. Schizophrenia patients were found to make increased errors following a rule switch, but these were almost entirely the result of executing saccades away from the location at which the negative feedback had been presented on the preceding trial. This impairment in negative feedback processing was independent of IQ. Conclusions. The results not only confirm the existence of a basic deficit in stimulus–response rule switching in schizophrenia, but also suggest that this arises from aberrant processing of response outcomes, resulting in a failure to appropriately update rules. The findings are discussed in the context of neurological and pharmacological abnormalities in the conditions that may disrupt prediction error signalling in schizophrenia

Frontal Eye Field Neurons Assess Visual Stability Across Saccades

The image on the retina may move because the eyes move, or because something in the visual scene moves. The brain is not fooled by this ambiguity. Even as we make saccades, we are able to detect whether visual objects remain stable or move. Here we test whether this ability to assess visual stability across saccades is present at the single-neuron level in the frontal eye field (FEF), an area that receives both visual input and information about imminent saccades. Our hypothesis was that neurons in the FEF report whether a visual stimulus remains stable or moves as a saccade is made. Monkeys made saccades in the presence of a visual stimulus outside of the receptive field. In some trials, the stimulus remained stable, but in other trials, it moved during the saccade. In every trial, the stimulus occupied the center of the receptive field after the saccade, thus evoking a reafferent visual response. We found that many FEF neurons signaled, in the strength and timing of their reafferent response, whether the stimulus had remained stable or moved. Reafferent responses were tuned for the amount of stimulus translation, and, in accordance with human psychophysics, tuning was better (more prevalent, stronger, and quicker) for stimuli that moved perpendicular, rather than parallel, to the saccade. Tuning was sometimes present as well for nonspatial transaccadic changes (in color, size, or both). Our results indicate that FEF neurons evaluate visual stability during saccades and may be general purpose detectors of transaccadic visual change

Involuntary saccades and binocular coordination during visual pursuit in Parkinson's disease

Prior studies of oculomotor function in Parkinson's disease (PD) have either focused on saccades while smooth pursuit eye movements were not involved, or tested smooth pursuit without considering the effect of any involuntary saccades. The present study investigated whether these involuntary saccades could serve as a useful biomarker for PD. Ten observers with PD participated in the study along with 10 age-matched normal control (NC) and 10 young control participants (YC). Observers fixated on a central cross while a disk (target) moved toward it from either side of the screen. Once the target reached the fixation cross, observers began to pursue the moving target until the target reached to the other side. To vary the difficulty of fixation and pursuit, the moving target was presented on a blank or a moving background. The moving background consisted of uniformly distributed dots moved in either the same or the opposite direction of the target once the target reached the central fixation cross. To investigate binocular coordination, each background condition was presented under a binocular condition, in which both eyes saw the same stimulus, and under a dichoptic condition, in which one eye saw only the target and the other eye only saw the background. The results showed that in both background conditions, observers with PD made more involuntary saccades than NC and YC during both fixation and pursuit periods while YC and NC showed no difference. Moreover, the difference between left and right eye positions increased over time during the pursuit period for PD group but not for the other two groups. This suggests that individuals with PD may be impaired not only in saccade inhibition, but also in binocular coordination during pursuit. [Meeting abstract presented at VSS 2016.]Accepted manuscrip

Representation, space and Hollywood Squares: Looking at things that aren't there anymore

It has been argued that the human cognitive system is capable of using spatial indexes or oculomotor coordinates to relieve working memory load (Ballard, Hayhoe, Pook & Rao, 1997) track multiple moving items through occlusion (Scholl & Pylyshyn, 1999) or link incompatible cognitive and sensorimotor codes (Bridgeman and Huemer, 1998). Here we examine the use of such spatial information in memory for semantic information. Previous research has often focused on the role of task demands and the level of automaticity in the encoding of spatial location in memory tasks. We present five experiments where location is irrelevant to the task, and participants' encoding of spatial information is measured implicitly by their looking behavior during recall. In a paradigm developed from Spivey and Geng (submitted), participants were presented with pieces of auditory, semantic information as part of an event occurring in one of four regions of a computer screen. In front of a blank grid, they were asked a question relating to one of those facts. Under certain conditions it was found that during the question period participants made significantly more saccades to the empty region of space where the semantic information had been previously presented. Our findings are discussed in relation to previous research on memory and spatial location, the dorsal and ventral streams of the visual system, and the notion of a cognitive-perceptual system using spatial indexes to exploit the stability of the external world

Eye movement control during visual pursuit in Parkinson's disease

BACKGROUND: Prior studies of oculomotor function in Parkinson’s disease (PD) have either focused on saccades without considering smooth pursuit, or tested smooth pursuit while excluding saccades. The present study investigated the control of saccadic eye movements during pursuit tasksand assessed the quality of binocular coordinationas potential sensitive markers of PD. METHODS: Observers fixated on a central cross while a target moved toward it. Once the target reached the fixation cross, observers began to pursue the moving target. To further investigate binocular coordination, the moving target was presented on both eyes (binocular condition), or on one eye only (dichoptic condition). RESULTS: The PD group made more saccades than age-matched normal control adults (NC) both during fixation and pursuit. The difference between left and right gaze positions increased over time during the pursuit period for PD but not for NC. The findings were not related to age, as NC and young-adult control group (YC) performed similarly on most of the eye movement measures, and were not correlated with classical measures of PD severity (e.g., Unified Parkinson’s Disease Rating Scale (UPDRS) score). DISCUSSION: Our results suggest that PD may be associated with impairment not only in saccade inhibition, but also in binocular coordination during pursuit, and these aspects of dysfunction may be useful in PD diagnosis or tracking of disease course.This work was supported in part by grants from the National Science Foundation (NSF SBE-0354378 to Arash Yazdanbakhsh and Bo Cao) and Office of Naval Research (ONR N00014-11-1-0535 to Bo Cao, Chia-Chien Wu, and Arash Yazdanbakhsh). There was no additional external funding received for this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. (SBE-0354378 - National Science Foundation (NSF); ONR N00014-11-1-0535 - Office of Naval Research)Published versio