Fast Eye Movements Research Articles

Microsaccades: Empirical Research and Methodological Advances - Introduction to Part 1 of the Thematic Special Issue.

Microsaccades: Empirical Research and Methodological Advances - Introduction to Part 1 of the Thematic Special Issue.

Optimal time task in saccadic eye movement

This article is devoted to fast goal-directed human eye movements. Such movements are described in few ways. One of them is the time-optimal problem model. It this work, the saccade – fast single conformable ballistic eye movement, is under consideration. Saccadic eye trajectory is described by time-optimal task solution. Differential equations system are based on pendulum model. It defines control moment applied from extraocular muscles to eye globe and movement of it. Main feature of the system is all values in suggested system have physical meaning and were found in published experimental investigations. Consideration of the moment applied from extraocular muscles to eye glob as control is main difference of the system from other models for eye movement in submitted works. In this case, the open-loop system has two real roots and one zero. The particular case of the ratio of real roots of 1:3 is analyzed in the article. As a result of modelling, trajectory characteristics closed to the saccades observed in experimental studies is obtained. On the basis of the constructed model, the parameters of the synthesized saccades were compared with the parameters obtained on the experimental sample. The obtained models can be used both for problems of physiology and medicine, and for constructing virtual reality environments. For example, when developing 3D interfaces, the use of a mathematical model makes it possible to optimize the elements arrangement using game theory.

A Computational System-Level Model of Oculomotor Pathways Accounting for the Representation of Eye Biomechanics in the Cerebellar Vermis

In this paper a comprehensive system-level computational model of oculomotor pathways is presented. This model shows the necessity of embedding internal models of muscles biomechanics in the cerebellar Vermis to realize fast saccadic eye movements based on predicting the changes in muscles lengths. First, the eye biomechanics are described by nonlinear equations during “slow” and “fast” movements. Afterward, by analyzing these equations, a computational model, is deduced. Furthermore, each part of this model is interpreted as a possible function of an element in the oculomotor pathways based on physiological and anatomical pieces of evidence. In this model, two internal feedback loops compensate two types of error: 1- error between desired and estimated values of eye position, calculated by Superior Colliculus, and 2- error between desired and estimated torque, calculated by Cerebellar pathways. Simulations of this circuit produce signals similar to the actual neuronal activities in the corresponding sites of the oculomotor pathways during saccades. Effects of bilateral lesions of Fastigial nuclei, Vermis, Prepositus Hypoglossi, the stimulation of Omni-Pause Neuron and Superior Colliculus are studied. Furthermore, the model ability in performing smooth pursuit eye movements is investigated. Finally, the “main sequence” is reproduced. This model is the first one to derive both the cerebellar function and the bilateral connectivity of the oculomotor pathways from calculations based on physical hypotheses. The proposed model is useful to better understand computational functions of different parts of the oculomotor pathways, and also using in robotics application for controlling fast movement inspired by the brain.

Fixational eye movement waveforms in amblyopia: Characteristics of fast and slow eye movements

Fixational eye movements comprise of fast microsaccades alternating with slow intersaccadic drifts. These physiologic eye movements play an important role in visual perception. Amblyopic patients are known to have fixation instability, particularly of the amblyopic eye. We examined eye movement abnormalities that contribute to this instability. We found that fixation stability is affected by the presence of fusion maldevelopment nystagmus (FMN). However, some amblyopes can have nystagmus without nasally directed slow phases and reversal in direction of the quick phase on ocular occlusion, features seen in FMN. In patients without nystagmus, we found increased amplitude of fixational saccades and inter-saccadic drifts. We categorized amblyopia patients by type (anisometropic, strabismic, or mixed) and eye movement waveform (no nystagmus, nystagmus without FMN, and FMN). We found specific fast and slow eye movement abnormalities of the fellow and amblyopic eye during fellow, amblyopic and both eyes viewing conditions across eye movement waveforms and types of amblyopia. These eye movement abnormalities can serve as biomarkers that can predict the impact of amblyopia as measured by visual acuity and stereopsis. Evaluation of fixational eye movements in amblyopia could be important to diagnose these common eye diseases and predict treatment effectiveness.

A Stable Visual World in Primate Primary Visual Cortex

Humans and other primates rely on eye movements to explore visual scenes and to track moving objects. As a result, the image that is projected onto the retina-and propagated throughout the visual cortical hierarchy-is almost constantly changing and makes little sense without taking into account the momentary direction of gaze. How is this achieved in the visual system? Here, we show that in primary visual cortex (V1), the earliest stage of cortical vision, neural representations carry an embedded "eye tracker" that signals the direction of gaze associated with each image. Using chronically implanted multi-electrode arrays, we recorded the activity of neurons in area V1 of macaque monkeys during tasks requiring fast (exploratory) and slow (pursuit) eye movements. Neurons were stimulated with flickering, full-field luminance noise at all times. As in previous studies, we observed neurons that were sensitive to gaze direction during fixation, despite comparable stimulation of their receptive fields. We trained a decoder to translate neural activity into metric estimates of gaze direction. This decoded signal tracked the eye accurately not only during fixation but also during fast and slow eye movements. After a fast eye movement, the eye-position signal arrived in V1 at approximately the same time at which the new visual information arrived from the retina. Using simulations, we show that this V1 eye-position signal could be used to take into account the sensory consequences of eye movements and map the fleeting positions of objects on the retina onto their stable position in the world.

Saccadic suppression measured by steady-state visual evoked potentials.

Visual sensitivity is severely impaired during the execution of saccadic eye movements. This phenomenon has been extensively characterized in human psychophysics and nonhuman primate single-neuron studies, but a physiological characterization in humans is less established. Here, we used a method based on steady-state visually evoked potential (SSVEP), an oscillatory brain response to periodic visual stimulation, to examine how saccades affect visual sensitivity. Observers made horizontal saccades back and forth, while horizontal black-and-white gratings flickered at 5-30 Hz in the background. We analyzed EEG epochs with a length of 0.3 s either centered at saccade onset (saccade epochs) or centered at fixations half a second before the saccade (fixation epochs). Compared with fixation epochs, saccade epochs showed a broadband power increase, which most likely resulted from saccade-related EEG activity. The execution of saccades, however, led to an average reduction of 57% in the SSVEP amplitude at the stimulation frequency. This result provides additional evidence for an active saccadic suppression in the early visual cortex in humans. Compared with previous functional MRI and EEG studies, an advantage of this approach lies in its capability to trace the temporal dynamics of neural activity throughout the time course of a saccade. In contrast to previous electrophysiological studies in nonhuman primates, we did not find any evidence for postsaccadic enhancement, even though simulation results show that our method would have been able to detect it. We conclude that SSVEP is a useful technique to investigate the neural correlates of visual perception during saccadic eye movements in humans. NEW & NOTEWORTHY We make fast ballistic saccadic eye movements a few times every second. At the time of saccades, visual sensitivity is severely impaired. The present study uses steady-state visually evoked potentials to reveal a neural correlate of the fine temporal dynamics of these modulations at the time of saccades in humans. We observed a strong reduction (57%) of visually driven neural activity associated with saccades but did not find any evidence for postsaccadic enhancement.

Validation of a velocity-based algorithm to quantify saccades during walking and turning in mild traumatic brain injury and healthy controls

Objective: Saccadic (fast) eye movements are a routine aspect of neurological examination and are a potential biomarker of mild traumatic brain injury (mTBI). Objective measurement of saccades has become a prominent focus of mTBI research, as eye movements may be a useful assessment tool for deficits in neural structures or processes. However, saccadic measurement within mobile infra-red (IR) eye-tracker raw data requires a valid algorithm. The objective of this study was to validate a velocity-based algorithm for saccade detection in IR eye-tracking raw data during walking (straight ahead and while turning) in people with mTBI and healthy controls. Approach: Eye-tracking via a mobile IR Tobii Pro Glasses 2 eye-tracker (100 Hz) was performed in people with mTBI (n = 10) and healthy controls (n = 10). Participants completed two walking tasks: straight walking (walking back and forth for 1 min over a 10 m distance), and walking and turning (turns course included 45°, 90° and 135° turns). Five trials per subject, for one-hundred total trials, were completed. A previously reported velocity-based saccade detection algorithm was adapted and validated by assessing agreement between algorithm saccade detections and the number of correct saccade detections determined from manual video inspection (ground truth reference). Main results: Compared with video inspection, the IR algorithm detected ~97% (n = 4888) and ~95% (n = 3699) of saccades made by people with mTBI and controls, respectively, with excellent agreement to the ground truth (intra-class correlation coefficient2,1 = .979 to .999). Significance: This study provides a simple yet highly robust algorithm for the processing of mobile eye-tracker raw data in mTBI and controls. Future studies may consider validating this algorithm with other IR eye-trackers and populations.

Early anticipation of driver’s maneuver in semiautonomous vehicles using deep learning

Making machines to anticipate human action is a complex research problem. Some of the recent research studies on computer vision and assistive driving have reported that the anticipation of driver’s action few seconds in advance is a challenging problem. These studies are based on the driver’s head movement tracking, eye gaze tracking, and spatiotemporal interest points. The study is aimed to address an important question of how to anticipate a driver’s action while driving and improve the anticipation time. The goal of this study is to review the existing deep learning framework for assistive driving. This paper differs from the existing solutions in two ways. First, it proposes a simplified framework using the driver’s inside video data and develops a driver’s movement tracking (DMT) algorithm. Majority of the existing state of the art is based on inside and outside features of the vehicles. Second, the proposed work tends to improve the image pattern recognition by introducing a fusion of spatiotemporal data points (STIPs) for movement tracking along with eye cuboids and then action anticipation by using deep learning. The proposed DMT algorithm tracks the driver’s movement using STIPs from the input video. Also, a fast eye gaze algorithm tracks eye movements. The features extracted from STIP and eye gaze are fused and analyzed by a deep recurrent neural network to improve the prediction time, thereby giving a few extra seconds to anticipate the driver’s correct action. The performance of the DMT algorithm is compared with the previous algorithms and found that DMT offers 30% improvement with regards to anticipating driver’s action over two recently proposed deep learning algorithms.

Microsaccadic rate and pupil size dynamics in pro-/anti-saccade preparation: the impact of intermixed vs. blocked trial administration.

Prolonged fixation can lead to the generation of tiny and fast eye movements called microsaccades, whose dynamics can be associated with higher cognitive mechanisms. Saccade preparation is also reflected in microsaccadic activity, but the few studies on this topic provided mixed results. For instance, fewer microsaccades have been observed when participants were asked to prepare for an anti-saccade (i.e., a saccade in the opposite direction to the target) as compared to a pro-saccade (i.e., a saccade executed towards a target), but null results have also been reported. In the attempt to shed new light on this topic, two experiments were carried out in which the context of presentation of pro- and anti-saccade trials was manipulated. Pupil size was also recorded, as a further index of cognitive load. In Experiment 1, participants were asked to prepare and perform pro- and anti-saccades in response to a peripheral target, according to a central instruction cue provided at the beginning of each trial (intermixed condition). In Experiment 2, the same task was employed, but pro- and anti-saccade trials were delivered in two distinct blocks (blocked condition). In both experiments, greater saccadic latencies and lower accuracy emerged for anti- than for pro-saccades. However, in the intermixed condition, a lower microsaccadic rate and a greater pupil size emerged when participants prepared for anti- rather than pro-saccades, whereas these differences disappeared in the blocked condition. These results suggest that contextual factors may play a key role in shaping oculomotor dynamics linked to saccade preparation.

Faster eye movements in children with autism spectrum disorder.

Atypical visual exploration of both social and nonsocial scenes is often reported in Autism Spectrum Disorder (ASD) with less precise and longer saccades, potentially reflecting difficulties in oculomotor control. To assess a subset of oculomotor functions in ASD, 20 children with ASD and 21 age-matched typically developing (TD) children (2.6-11.5 years) partook in three tasks of increasing complexity, while no explicit instruction was provided: a prosaccade gap task, a color and a "categorical" visual search tasks (a face among butterflies and vice-versa). In addition to classical saccade metrics, we measured Distance error, (the distance between the target and the closest gaze position) and Time-to-target (the time taken to reach the target). In the prosaccade task, children with ASD were as accurate as TD children, yet faster to reach the stimulus. In the color visual search task, children with ASD were faster but less precise than TD children. In the categorical visual search, while TD children were more precise in orienting their gaze towards the face, children with ASD performed similarly in the two conditions; Time-to-target did not differ. Our results provide contradictory evidence regarding enhanced visual search ability in ASD: when considering response times, enhanced visual search performance was found in one task only, while when considering gaze precision no advantage was found. These three experiments demonstrate that the automatic saccadic system may function more rapidly in children with ASD. Nonetheless, a diminished sensitivity to bottom-up saliency and top-down influence might suppress this advantage in more complex visual environments. Autism Res 2019, 12: 212-224 © 2018 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Three experiments with no instructions were designed to assess oculomotor functions in children with Autism Spectrum Disorder (ASD). In a saccade task, children with ASD were faster than but as accurate as control children. In visual search tasks, accuracy and speed decreased with increasing complexity of visual environment. Children with ASD showed faster automatic visual orientation, but this might hinder exploratory behaviors, leading to difficulties in complex and social situations.

Modeling the Triggering of Saccades, Microsaccades, and Saccadic Intrusions.

When we explore a static visual scene, our eyes move in a sequence of fast eye movements called saccades, which are separated by fixation periods of relative eye stability. Based on uncertain sensory and cognitive inputs, the oculomotor system must decide, at every moment, whether to initiate a saccade or to remain in the fixation state. Even when we attempt to maintain our gaze on a small spot, small saccades, called microsaccades, intrude on fixation once or twice per second. Because microsaccades occur at the boundary of the decision to maintain fixation versus starting a saccade, they offer a unique opportunity to study the mechanisms that control saccadic triggering. Abnormal saccadic intrusions can occur during attempted fixation in patients with neurodegenerative disorders. We have implemented a model of the triggering mechanism of saccades, based on known anatomy and physiology, that successfully simulates the generation of saccades of any size—including microsaccades in healthy observers, and the saccadic intrusions that interrupt attempted fixation in parkinsonian patients. The model suggests that noisy neuronal activity in the superior colliculus controls the state of a mutually inhibitory network in the brain stem formed by burst neurons and omnipause neurons. When the neuronal activity is centered at the rostral pole, the system remains at a state of fixation. When activity is perturbed away from this center, a saccade is triggered. This perturbation can be produced either by the intent to move one’s gaze or by random fluctuations in activity.

Saccades and smooth pursuit eye movements trigger equivalent gaze-cued orienting effects.

Research has established that a perceived eye gaze produces a concomitant shift in a viewer's spatial attention in the direction of that gaze. The two experiments reported here investigate the extent to which the nature of the eye movement made by the gazer contributes to this orienting effect. On each trial in these experiments, participants were asked to make a speeded response to a target that could appear in a location toward which a centrally presented face had just gazed (a cued target) or in a location that was not the recipient of a gaze (an uncued target). The gaze cues consisted of either fast saccadic eye movements or slower smooth pursuit movements. Cued targets were responded to faster than uncued targets, and this gaze-cued orienting effect was found to be equivalent for each type of gaze shift both when the gazes were un-predictive of target location (Experiment 1) and counterpredictive of target location (Experiment 2). The results offer no support for the hypothesis that motion speed modulates gaze-cued orienting. However, they do suggest that motion of the eyes per se, regardless of the type of movement, may be sufficient to trigger an orienting effect.

Heading representations in primates are compressed by saccades

Perceptual illusions help to understand how sensory signals are decoded in the brain. Here we report that the opposite approach is also applicable, i.e., results from decoding neural activity from monkey extrastriate visual cortex correctly predict a hitherto unknown perceptual illusion in humans. We record neural activity from monkey medial superior temporal (MST) and ventral intraparietal (VIP) area during presentation of self-motion stimuli and concurrent reflexive eye movements. A heading-decoder performs veridically during slow eye movements. During fast eye movements (saccades), however, the decoder erroneously reports compression of heading toward straight ahead. Functional equivalents of macaque areas MST and VIP have been identified in humans, implying a perceptual correlate (illusion) of this perisaccadic decoding error. Indeed, a behavioral experiment in humans shows that perceived heading is perisaccadically compressed toward the direction of gaze. Response properties of primate areas MST and VIP are consistent with being the substrate of the newly described visual illusion.

Latency Requirements for Foveated Rendering in Virtual Reality

Foveated rendering is a performance optimization based on the well-known degradation of peripheral visual acuity. It reduces computational costs by showing a high-quality image in the user’s central (foveal) vision and a lower quality image in the periphery. Foveated rendering is a promising optimization for Virtual Reality (VR) graphics, and generally requires accurate and low-latency eye tracking to ensure correctness even when a user makes large, fast eye movements such as saccades. However, due to the phenomenon of saccadic omission, it is possible that these requirements may be relaxed. In this article, we explore the effect of latency for foveated rendering in VR applications. We evaluated the detectability of visual artifacts for three techniques capable of generating foveated images and for three different radii of the high-quality foveal region. Our results show that larger foveal regions allow for more aggressive foveation, but this effect is more pronounced for temporally stable foveation techniques. Added eye tracking latency of 80--150ms causes a significant reduction in acceptable amount of foveation, but a similar decrease in acceptable foveation was not found for shorter eye-tracking latencies of 20--40ms, suggesting that a total system latency of 50--70ms could be tolerated.

Differential responses of neurons in the macaque Lateral Intraparietal area to voluntary and reflexive saccades

The macaque lateral intraparietal area (LIP) is known for its involvement in processing of saccadic eye movements (Barash et al. 1991) as well as higher cognitive concepts like attention (Bisley & Goldberg 2003), value (Sugrue et al. 2004) and numerosity (Roitman 2007). While its contribution to cognitive processes is being heavily investigated, some of its basic visuo-motor functions are not described yet. We investigated the responses of 96 single neurons from area LIP of one macaque monkey to different types of fast eye movements. The neurons were first tested using regular visually guided saccade and delayed saccade paradigms. Neurons that have shown a significant (p< 0.05) peri-saccadic response were further investigated using two other categories of fast eye movements. The first category were saccades interacting with smooth pursuit eye movements (SPEM) such as visually guided saccades to moving targets and catch-up saccades that are used to re-foveate a moving target during SPEM. The second category of eye movements were fast phases of the optokinetic nystagmus (OKN). We found huge differences between the responses to the two categories. While saccades in combination with SPEM revealed similar motor responses like regular visually guided saccades (significant visuo-motor responses were preserved in all neurons), none of the neurons responded significantly during the fast phases of the OKN. However, we found a modulation of activity in OKN that consisted of a significant post-saccadic inhibition in ~50% of the investigated neurons. The inhibition was regularly followed by a brief peak in activity which may be caused by a release from inhibition. We conclude that area LIP is not primarily concerned with generation of motor commands for fast eye movements but with goal directed interaction and target selection in the visual environment (Thomas & Pare 2007). Meeting abstract presented at VSS 2017

Saccadic suppression during voluntary versus reactive saccades.

Saccades are fast eye movements that reorient gaze. They can be performed voluntarily-for example, when viewing a scene-but they can also be triggered in reaction to suddenly appearing targets. The generation of these voluntary and reactive saccades have been shown to involve partially different cortical pathways. However, saccades of either type confront the visual system with a major challenge from massive image motion on the retina. Despite the fact that the whole scene is swept across the retina, a saccade usually does not elicit a percept of motion. This saccadic omission has been linked to a transient decrease of visual sensitivity during the eye movement, a phenomenon called saccadic suppression. A passive origin of saccadic suppression based on temporal masking has been proposed as well as an active central process that inhibits visual processing during the saccade. The latter one would need to include an extraretinal signal, which is generated already during saccade preparation. Since saccade generation differs for voluntary and reactive saccades, timing and nature of this extraretinal signal as well as its impact on visual sensitivity might also differ. We measured detection thresholds for luminance stimuli that were flashed during voluntary and reactive saccades and during fixation. Detection thresholds were higher during voluntary than during reactive saccades such that suppression appeared stronger during voluntary saccades. Stronger suppression in voluntary saccades could arise from a stronger extraretinal signal that activates suppression or could indicate that a suppression underlying process itself partially differs between voluntary and reactive saccades.

12 Apathy in neurological disease

Sanjay examines how reward motivates us, using eye movements and pupillometry. His work focuses on mechanisms of reward processing, and their disruption in focal brain damage and Parkinson’s disease. Motivation is commonly disrupted in neurological and psychiatric disorders leading to clinical apathy. A traditional view is that motivation directs behaviour towards goals. According to this view, apathetic patients fail to select behaviours apposite to their goals. But clinically, these patients describe something more specific: a subjective inability to generate effortful action. An alternative view focuses not on action selection, but on initiation and energisation. This view characterises motivation as driving true performance enhancement. Improving performance is costly, and motivation enables us to pay these costs. Apathy amounts to an inability to overcome costs, such as physical energy or mental concentration. I studied the energisation of action using saccades – simple fast eye movements generated by well-understood circuits in the midbrain. When high rewards are at stake, saccades are earlier, more precise, and more energetic, indicating a higher signal-to-noise ratio in generating movements. Midbrain dopamine depletion in Parkinson’s disease makes eye movements insensitive to reward. Damage to the globus pallidus may also reduce reward sensitivity of eye movements, and responds to dopaminergic therapy. Rewards can even drive improvements when we are unable to influence the outcome, indicating their primitive inflexible nature. Energisation of action may therefore be controlled at a primitive brainstem level by reward expectation. How might rewards influence such low-level mechanisms? One possibility is through autonomic arousal. Pupils dilate when incentives are expected, but this dilatation is attenuated in Parkinson’s disease. Pupil reactivity is restored with medication, and correlates with clinical apathy. These effects in the eyes also generalise to voluntary motor systems, as measured by willingness to exert manual effort in order to obtain rewards. Apathetic individuals needed higher incentives to engage in effort, and this correlated with structural and functional connectivity between preSMA and cingulate cortex. Patients with PD showed a similar behaviour pattern that was reversed with dopaminergic drugs. I conclude that human motivation, viewed in terms of energisation of behaviour, appears to operate at multiple levels in the brain, involving brainstem arousal mechanisms, basal ganglia dopamine, and motor cortex connectivity.

Sampling rate influences saccade detection in mobile eye tracking of a reading task.

The purpose of this study was to compare saccade detection characteristics in two mobile eye trackers with different sampling rates in a natural task. Gaze data of 11 participants were recorded in one 60 Hz and one 120 Hz mobile eye tracker and compared directly to the saccades detected by a 1000 HZ stationary tracker while a reading task was performed. Saccades and fixations were detected using a velocity based algorithm and their properties analyzed. Results showed that there was no significant difference in the number of detected fixations but mean fixation durations differed between the 60 Hz mobile and the stationary eye tracker. The 120 Hz mobile eye tracker showed a significant increase in the detection rate of saccades and an improved estimation of the mean saccade duration, compared to the 60 Hz eye tracker. To conclude, for the detection and analysis of fast eye movements, such as saccades, it is better to use a 120 Hz mobile eye tracker.

Direct and indirect effects of attention and visual function on gait impairment in Parkinson's disease: influence of task and turning.

Gait impairment is a core feature of Parkinson's disease (PD) which has been linked to cognitive and visual deficits, but interactions between these features are poorly understood. Monitoring saccades allows investigation of real-time cognitive and visual processes and their impact on gait when walking. This study explored: (i) saccade frequency when walking under different attentional manipulations of turning and dual-task; and (ii) direct and indirect relationships between saccades, gait impairment, vision and attention. Saccade frequency (number of fast eye movements per-second) was measured during gait in 60 PD and 40 age-matched control participants using a mobile eye-tracker. Saccade frequency was significantly reduced in PD compared to controls during all conditions. However, saccade frequency increased with a turn and decreased under dual-task for both groups. Poorer attention directly related to saccade frequency, visual function and gait impairment in PD, but not controls. Saccade frequency did not directly relate to gait in PD, but did in controls. Instead, saccade frequency and visual function deficit indirectly impacted gait impairment in PD, which was underpinned by their relationship with attention. In conclusion, our results suggest a vital role for attention with direct and indirect influences on gait impairment in PD. Attention directly impacted saccade frequency, visual function and gait impairment in PD, with connotations for falls. It also underpinned indirect impact of visual and saccadic impairment on gait. Attention therefore represents a key therapeutic target that should be considered in future research.

Posterior Parietal Visual Dysfunction: An Explanatory Review

Dysfunction or injury of the posterior parietal lobes impairs 3D mapping of the visual scene and can… (1) Make body movement guided by vision inaccurate (optic ataxia). (2) Limit the number of items seen at a glance, due to simultanagnostic visual dysfunction. (3) Cause inability to move the eyes to a specified target (apraxia of gaze), despite intact pursuit and fast (saccadic) eye movements. (Perhaps because the target cannot be located.) When severe, these features comprise Balint syndrome, but when less marked, the term dorsal stream dysfunction has been used. Associated lower visual field impairment due to the superior optic radiations passing through the parietal lobes being affected as well, can cause the feet not to be seen during locomotion. While accompanying inability to see fast moving targets, or dyskinetopsia is not uncommon. In our experience, a wider inflight gap between the fingers and thumb of a hand reaching in the lower visual field than when reaching in the upper visual field, and disability locating where sounds are coming from, may also be evident. Central and peripheral visual functions can be diminished if the occipital lobes are affected as well, while recognition can be impaired by this and / or associated temporal lobe dysfunction. Those with accompanying intellectual impairment and four-limb cerebral palsy may ‘wake up’ and start to look around, even reaching out for a single object, when surrounded by a monochromatic tent that excludes extraneous visual and auditory distraction. In the authors’ experience, dorsal stream dysfunction is the commonest pattern of cerebral visual impairment seen in children and in many affected (often previously undiagnosed) adults. A series of case history data is presented to illustrate the origin, nature and heterogeneity of this condition, as well as its potential management.