Ocular pursuit and visual memory of moving shapes

This paper deals with visual memory of moving shapes. During a visual recognition task, shapes moved on a computer screen, at a constant speed, and in a direction that was either similar, orthogonal or opposite to the direction of motion during learning. Results showed that correct response rate varies according to oculomotor factors: (1) the motor skill of ocular pursuit during learning and (2) the compatibility between motor control of ocular pursuits during learning and recognition. These data suggest that recognition of a moving shape is linked to recognition of ocular pursuits that subjects had previously repeated during shape learning. Possible neural substrates underlying this sensorimotor integration are discussed. More generally, these data shed light on the role of eye movements in visual memory organization.     

Sensory factors are insufficient to define the ocular saccade goal in complex visual fields

In most normal visual search situations, the environment is filled with a variety of stimuli, and selection among possible saccade targets is necessary. Current theories of visuomotor mechanisms must take into account not only the classical 'retinal error' input signal, but also perceptual and decisional factors as well as task-specific strategies adopted by the subjects. Experiments are reported in which eye movements are recorded in tasks requiring ocular saccades to be made onto target letters indicated by a peripherally visible mark or embedded within lines of homogeneous background letters. The results show how nonsensory factors interact with visual determinants in the preparation of the exploratory saccades. Expectations concerning the visibility of the sought-for target influence the spatial and temporal parameters of the eye movement which will be executed.     

Eye movements during object recognition in visual agnosia

This paper reports the first ever detailed study about eye movement patterns during single object recognition in visual agnosia. Eye movements were recorded in a patient with an integrative agnosic deficit during two recognition tasks: common object naming and novel object recognition memory. The patient showed normal directional biases in saccades and fixation dwell times in both tasks and was as likely as controls to fixate within object bounding contour regardless of recognition accuracy. In contrast, following initial saccades of similar amplitude to controls, the patient showed a bias for short saccades. In object naming, but not in recognition memory, the similarity of the spatial distributions of patient and control fixations was modulated by recognition accuracy. The study provides new evidence about how eye movements can be used to elucidate the functional impairments underlying object recognition deficits. We argue that the results reflect a breakdown in normal functional processes involved in the integration of shape information across object structure during the visual perception of shape.     

Complementary hemispheric asymmetries in object naming and recognition: A voxel-based correlational study

Cognitive neuroscientific research proposes complementary hemispheric asymmetries in naming and recognising visual objects, with a left temporal lobe advantage for object naming and a right temporal lobe advantage for object recognition. Specifically, it has been proposed that the left inferior temporal lobe plays a mediational role linking conceptual information with word forms and vice versa, while the right inferior temporal lobe supports the retrieval of conceptual knowledge from visual input. To test these hypotheses, we administered four behavioural tasks to fifteen patients with temporal lobe brain damage, and correlated their behavioural scores with voxel-based measures of neuronal integrity (signal intensities) in whole-brain analyses. The behavioural paradigms included four tasks. Two were verbal tasks: (a) picture naming requiring the mapping of conceptual knowledge to word forms, (b) semantic categorisation of words requiring the reverse mapping of word forms to conceptual knowledge, and two were visual object tasks with no verbal component, both of which required the retrieval of conceptual information from visual objects, i.e., (c) visual object categorisation and (d) normal and chimera object decisions. Performance on the verbal tasks correlated with the neural integrity of partially overlapping left inferior and anterior temporal lobe regions, while performance on the object tasks correlated with the neural integrity of overlapping regions in right inferior and anterior temporal lobe. These findings support the notion of complementary hemispheric advantages for object naming and recognition, and further suggest that the classical language model emphasising posterior regions in the mapping between word forms and conceptual knowledge should be extended to include left inferior temporal lobe.     

Modeling orienting behavior and its disorders with "ecological" neural networks

Computational modeling is a useful tool for spelling out hypotheses in cognitive neuroscience and testing their predictions in artificial systems. Here we describe a series of simulations involving neural networks that learned to perform their task by self-organizing their internal connections. The networks controlled artificial agents with an orienting eye and an arm. Agents saw objects with various shapes and locations and learned to press a key appropriate to their shape. The results showed the following: (1) Despite being able to see the entire visual scene without moving their eye, agents learned to orient their eye toward a peripherally presented object. (2) Neural networks whose hidden layers were previously partitioned into units dedicated to eye orienting and units dedicated to arm movements learned the identification task faster and more accurately than did nonmodular networks. (3) Nonetheless, even nonmodular networks developed a similar functional segregation through self-organization of their hidden layer. (4) After partial disconnection of the hidden layer from the input layer, the lesioned agents continued to respond accurately to single stimuli, wherever they occurred, but on double simultaneous stimulation they oriented toward and responded only to the right-sided stimulus, thus simulating extinction/neglect. These results stress the generality of the advantages provided by orienting processes. Hard-wired modularity, reminiscent of the distinct cortical visual streams in the primate brain, provided further evolutionary advantages. Finally, disconnection is likely to be a mechanism of primary importance in the pathogenesis of neglect and extinction symptoms, consistent with recent evidence from animal studies and brain-damaged patients.     

Laterality of cross-modal spatial processing

This study examined the laterality of spatial-form perception in normal adults using a cross-modal matching paradigm involving visual and tactile processing. Randomly generated eight-point and 12-point Vanderplas and Garvin (1959) patterns were used as the stimuli. In a visual-to-tactile task, a lateralized visual pattern was followed immediately by a haptic task requiring subjects to discriminate which of two simultaneously felt shapes matched the visual pattern. In a tactile-to-visual task, subjects decided which of two simultaneously felt shapes matched a lateralized visual pattern presented after haptic manipulation. There were no main effects for laterality or for sex differences. Matching accuracy was better in the visual-to-tactile task and for less complex stimuli. A visual field by feeling hand interaction showed best recognition accuracy when visual-feeling hand combinations on the same side of the body were used in the two matching tasks. These data reflect a stimulus-response compatibility explanation of spatial-form perception that is consistent with a behavioral and not a cerebral asymmetry model.     

The psychological test pattern in progressive supranuclear palsy

Patients diagnosed as having Progressive Supranuclear Palsy were distinguished by an impairment on tasks requiring efficient eye and head movements to find and/or follow visual stimuli. Objectively measured intellectual impairment was unequivocal only on non-verbal tasks which loaded heavily on visual searching or scanning ability. No other distinctive intellectual or memory defects were apparent.     

The sensorimotor transformation of cross-modal spatial information in the anterior intraparietal sulcus as revealed by functional MRI

The parietal cortex in monkeys and humans has been shown to play an important role in the transformation of sensory information to motor commands. However, it is still unclear whether in humans, these areas are divided functionally into subregions based on different combinations of sensory and motor modalities. To identify subregions in the parietal cortex involved in the sensorimotor information transformation between different modalities, functional MRI was used to examine brain areas activated during tasks requiring different sensorimotor transformations--i.e., various combinations of eye (saccade) or finger movements triggered by visual or somatosensory cues. We then compared the activations between cross-modal conditions (eye movements triggered by somatosensory cues and finger movements triggered by visual cues) and intramodal (eye movements triggered by visual cues and finger movements triggered by somatosensory cues) conditions. Although the parietal cortex was involved in all tasks regardless of sensorimotor combinations, the only region activated to a greater degree in the cross-modal conditions compared to the intramodal conditions was the anterior portion of the intraparietal sulcus (a-IPS). The results suggest that the a-IPS plays an important role in the sensorimotor transformation of cross-modal spatial information.     

Lesions affecting the right hippocampal formation differentially impair short‐term memory of spatial and nonspatial associations

Converging evidence from behavioral and imaging studies suggests that within the human medial temporal lobe (MTL) the hippocampal formation may be particularly involved in recognition memory of associative information. However, it is unclear whether the hippocampal formation processes all types of associations or whether there is a specialization for processing of associations involving spatial information. Here, we investigated this issue in six patients with postsurgical lesions of the right MTL affecting the hippocampal formation and in ten healthy controls. Subjects performed a battery of delayed match‐to‐sample tasks with two delays (900/5,000 ms) and three set sizes. Subjects were requested to remember either single features (colors, locations, shapes, letters) or feature associations (color‐location, color‐shape, color‐letter). In the single‐feature conditions, performance of patients did not differ from controls. In the association conditions, a significant delay‐dependent deficit in memory of color‐location associations was found. This deficit was largely independent of set size. By contrast, performance in the color‐shape and color‐letter conditions was normal. These findings support the hypothesis that a region within the right MTL, presumably the hippocampal formation, does not equally support all kinds of visual memory but rather has a bias for processing of associations involving spatial information. Recruitment of this region during memory tasks appears to depend both on processing type (associative/nonassociative) and to‐be‐remembered material (spatial/nonspatial). © 2010 Wiley‐Liss, Inc.     

Hypervigilance-avoidance pattern in spider phobia

Cognitive-motivational theories of phobias propose that patients' behavior is characterized by a hypervigilance-avoidance pattern. This implies that phobics initially direct their attention towards fear-relevant stimuli, followed by avoidance that is thought to prevent objective evaluation and habituation. However, previous experiments with highly anxious individuals confirmed initial hypervigilance and yet failed to show subsequent avoidance. In the present study, we administered a visual task in spider phobics and controls, requiring participants to search for spiders. Analyzing eye movements during visual exploration allowed the examination of spatial as well as temporal aspects of phobic behavior. Confirming the hypervigilance-avoidance hypothesis as a whole, our results showed that, relative to controls, phobics detected spiders faster, fixated closer to spiders during the initial search phase and fixated further from spiders subsequently.     

Human frontal eye fields and target switching

The frontal eye fields (FEF) have typically been predominantly investigated in terms of their role in the generation of eye movements. Lesions to this area, either accidental or experimental, disrupt saccades and electrical stimulation elicits eye movements. Recently there has been increasing interest in the involvement of this area in visual processes, including in tasks where eye movements were either not required or were precluded. In addition to being involved in a range of visual tasks, evidence from visual search paradigms has suggested that this area might be important when the defining quality of the target is unpredictable or that it may be involved in priming. We investigated the role of FEF in a task requiring localisation of a target defined by colour, in which the target colour was either maintained or switched across trials. Disruption of performance was seen on the task when transcranial magnetic stimulation (TMS) was delivered over the left FEF, specifically elevating response times on trials when the target and distracter colours were switched rather than affecting any benefit of repetition of the target attribute (priming). This result is consistent with altered modulation of extrastriate areas, consequently affecting the speed with which a switch of the target colour could be detected. This both offers an explanation for effects seen in unpredictable feature search and is consistent with other TMS and microstimulation studies showing that FEF modulates responses of extrastriate cortex.     

Visual and auditory socio‐cognitive perception in unilateral temporal lobe epilepsy in children and adolescents: a prospective controlled study

Aim. A high rate of abnormal social behavioural traits or perceptual deficits is observed in children with unilateral temporal lobe epilepsy. In the present study, perception of auditory and visual social signals, carried by faces and voices, was evaluated in children or adolescents with temporal lobe epilepsy. Methods. We prospectively investigated a sample of 62 children with focal non‐idiopathic epilepsy early in the course of the disorder. The present analysis included 39 children with a confirmed diagnosis of temporal lobe epilepsy. Control participants (72), distributed across 10 age groups, served as a control group. Our socio‐perceptual evaluation protocol comprised three socio‐visual tasks (face identity, facial emotion and gaze direction recognition), two socio‐auditory tasks (voice identity and emotional prosody recognition), and three control tasks (lip reading, geometrical pattern and linguistic intonation recognition). All 39 patients also benefited from a neuropsychological examination. Results. As a group, children with temporal lobe epilepsy performed at a significantly lower level compared to the control group with regards to recognition of facial identity, direction of eye gaze, and emotional facial expressions. We found no relationship between the type of visual deficit and age at first seizure, duration of epilepsy, or the epilepsy‐affected cerebral hemisphere. Deficits in socio‐perceptual tasks could be found independently of the presence of deficits in visual or auditory episodic memory, visual non‐facial pattern processing (control tasks), or speech perception. A normal FSIQ did not exempt some of the patients from an underlying deficit in some of the socio‐perceptual tasks. Conclusion. Temporal lobe epilepsy not only impairs development of emotion recognition, but can also impair development of perception of other socio‐perceptual signals in children with or without intellectual deficiency. Prospective studies need to be designed to evaluate the results of appropriate re‐education programs in children presenting with deficits in social cue processing.     

The relationship between visual orienting and interlimb synchrony in a patient with a superior parietal infarction: A case study

Much work indicates that parietal cortex mediates the transformation of visual information into the motor commands necessary for successful performance of many unimanual tasks. Accumulating evidence suggests that parietal cortex also mediates the coordination of bimanual movements, during which the natural tendency is to couple the limbs temporally. However, the extent to which parietal oculomotor and/or visual processes contribute to temporal coupling of the limbs during bimanual task performance is unknown. In the current study, we monitored the eye movements of a patient with a left parietal infarction as she performed a series of bimanual visuomotor tasks. We demonstrate the impact of an ipsilesional (leftward) orientation bias on her ability to synchronize the onset of bimanual limb movements; the movements were performed in serial fashion, i.e., left limb before right, when the patient was permitted to freely shift saccades and the visual target cuing the left (ipsilesional) limb movement was presented at greater (leftward) eccentricities. Disruption of interlimb synchrony as such was not, however, evident when the patient was required to fixate or when visual targets were presented at lesser ipsilesional eccentricities. Additionally, despite the disruptive influence of oculomotor and visual factors on interlimb synchrony, the patient appeared capable of using visual feedback to straighten the right (contralesional) limb trajectory, thus improving the spatial component of task performance. Results suggest that parietal cortex plays an important role in the coordination of limb movements during performance of bimanual visuomotor tasks. This role appears to involve orienting gaze or attention to the goals of each limb so that the nervous system can synchronize the activity of both limbs and thereby ensure successful task completion.     

Visual impairment due to a dyskinetic eye movement disorder in children with dyskinetic cerebral palsy

Neurological lesions that cause dyskinetic cerebral palsy (CP) commonly involve ocular movements. This report describes a group of 14 children (nine males, five females) whose CP is associated with severe dyskinetic eye movements. Ages ranged from 4 months to 13 years (mean 6.9 years). Clinical features of this eye movement disorder are discussed and defined. The visual function of these children is slow, variable, and highly inefficient. They are often misdiagnosed as blind, due to cortical visual impairment. Early recognition of dyskinetic eye moment disorder and appropriate developmental and educational management are important.     

Temporal coupling of rapid eye movements and cerebral activities during REM sleep

ObjectivesWe investigated event-related potentials time locked to the onset and offset of rapid eye movements during rapid eye movement (REM) sleep.MethodNine healthy university students participated in this study. Data were collected in a sleep laboratory. Rapid eye movements during REM sleep were recorded during natural nocturnal sleep. Saccades during wakefulness were recorded during a visually triggered task. Event-related potentials were averaged, time-locked to the onset and offset of eye movements.ResultsDuring REM sleep, a lambda-like response occurred over the occipital region, time-locked to the offset of rapid eye movements (similar to what occurs during wakefulness). Moreover, we found that a positive potential (P200r) occurred at about 200 ms, with the maximal amplitude over the central region and time-locked to the onset of rapid eye movements during REM sleep; this potential was not observed during wakefulness.ConclusionsDuring REM sleep, the P200r occurs with the start of rapid eye movements, and then the lambda-like response occurs after termination of the movements.SignificanceWe demonstrated temporal coupling of rapid eye movements and cerebral activities during REM sleep. These activities might provide a useful basis for future investigations of brain functions during REM sleep.     

Eye movements and the perceived location of phosphenes generated by intracranial primary visual cortex stimulation in the blind

BackgroundRestoring sight for the blind using electrical stimulation of the visual pathways is feasible but demands an understanding of the spatial mapping of the visual world at the site of targeted stimulation, whether in the retina, thalamus, or cortex. While a visual cortex stimulator can bypass the eye and create visual percepts, there is an inherent dissociation between this stimulation and eye movements. It is unknown whether and how robustly the brain maintains the oculomotor circuitry in patients with bare- or no-light perception.ObjectiveTo critically and quantitatively evaluate the effect of eye movements have on phosphene locations elicited by cortical stimulation that bypasses the eyes in order to restore sight in blind subjects.MethodsThe NeuroPace Responsive Neurostimulator (RNS) and the Orion visual cortical prosthesis devices were used to electrically stimulate the visual cortex of blind subjects with bare or no light perception. Eye positions were recorded synchronized with stimulation and the location of the percepts were measured using a handheld marker.ResultsThe locations of cortical stimulation-evoked percepts are shifted based on the eye position at the time of stimulation. Measured responses can be remapped based on measured eye positions to determine the retinotopic locations associated with the implanted electrodes, with remapped responses having variance limited by pointing error.ConclusionsEye movements dominate the perceived location of cortical stimulation-evoked phosphenes, even after years of blindness. By accounting for eye positions, we can mimic retinal mapping as in natural sight.     

Voluntary control of saccadic and smooth-pursuit eye movements in children with learning disorders

Eye movement is crucial to humans in allowing them to aim the foveae at objects of interest. We examined the voluntary control of saccadic and smooth-pursuit eye movements in 18 subjects with learning disorders (LDs) (aged 8–16) and 22 normal controls (aged 7–15). The subjects were assigned visually guided, memory-guided, and anti-saccade tasks, and smooth-pursuit eye movements (SPEM). Although, the LD subjects showed normal results in the visually guided saccade task, they showed more errors in the memory-guided saccade task (e.g. they were unable to stop themselves reflexively looking at the cue) and longer latencies, even when they performed correctly. They also showed longer latencies than the controls in the anti-saccade task. These results suggest that they find it difficult to voluntarily suppress reflexive saccades and initiate voluntary saccades when a target is invisible. In SPEM using step-ramp stimuli, the LD subjects showed lower open- and closed-loop gains. These results suggest disturbances of both acceleration of eye movement in the initial state and maintenance of velocity in minimizing retinal slip in the steady state. Recent anatomical studies in LD subjects have suggested abnormalities in the structure of certain brain areas such as the frontal cortex. Frontal eye movement-related areas such as the frontal eye fields and supplementary eye fields may be involved in these disturbances of voluntary control of eye movement in LDs.     

Neuroanatomical correlates of the near response: voluntary modulation of accommodation/vergence in the human visual system

This study identifies brain regions participating in the execution of eye movements for voluntary positive accommodation (VPA) during open-loop vergence conditions. Neuronal activity was estimated by measurement of changes in regional cerebral blood flow (rCBF) with positron emission tomography and 15O-water. Thirteen naive volunteers viewed a checkerboard pattern with their dominant right eye, while a lens interrupted the line of gaze during alternate 1.5 s intervals. Three counterbalanced tasks required central fixation and viewing of a stationary checkerboard pattern: (i) through a 0.0 diopter (D) lens; (ii) through a -5.0-D lens while avoiding volitional accommodation and permitting blur; and (iii) through a -5. 0-D lens while maintaining maximal focus. The latter required large-amplitude, high-frequency VPA. As an additional control, seven of the subjects viewed passively a digitally blurred checkerboard through a 0.0-D lens as above. Optometric measurements confirmed normal visual acuity and ability to perform the focusing task (VPA). Large-amplitude saccadic eye movements, verified absent by electro-oculography, were inhibited by central fixation. Image averaging across subjects demonstrated multifocal changes in rCBF during VPA: striate and extrastriate visual cortices; superior temporal cortices; and cerebellar cortex and vermis. Decreases in rCBF occurred in the lateral intraparietal area, prefrontal and frontal and/or supplementary eye fields. Analysis of regions of interest in the visual cortex showed systematic and appropriate task dependence of rCBF. Activations may reflect sensorimotor processing along the reflex arc of the accommodation system, while deactivations may indicate inhibition of systems participating in visual search.     

Preserved visual recognition memory in an amnesic patient with hippocampal lesions

There is ongoing debate about whether performance on tests of recognition memory can remain preserved after hippocampal damage. In the present study, we report F.R.G., a patient who became severely amnesic following herpes simplex encephalitis. Although F.R.G. failed all tests involving recall and verbal recognition, she obtained normal performance on a wide number of tests evaluating visual recognition memory (14 of 18 different tests). Her performance was independent of various factors, such as test difficulty, duration of exposure to the stimuli, or delay separating encoding and recognition. F.R.G. also achieved normal performance on two tasks requiring that she associate pairs of visual stimuli. In addition, she demonstrated spared feeling of knowing, suggesting that her performance on recognition tests was explicit and likely to rely on familiarity. Brain imaging (MRI) revealed bilateral lesions of the hippocampus and lesions of the left parahippocampal gyrus, while the right parahippocampal gyrus remained relatively spared. The results of this study support the view that recognition memory can be preserved despite severe hippocampal damage and that familiarity is a distinct memory process that can be dissociated from recollection.     

Changes in sensory inattention, directional motor neglect and "release" of the fixation reflex following a unilateral frontal lesion: a case report

We recorded eye movements to and away from visual stimuli from a patient with left-sided neglect following a right frontal infarct in order to determine (a) whether and to what extent his neglect was due to sensory inattention and directional motor neglect and (b) whether he had difficulty suppressing inappropriate eye movements to visual stimuli ("release" of visual grasp) as his sensory inattention declined. In the first testing session, conducted 5 days following his stroke, he often failed to move his eyes when a stimulus on the left required a rightward eye movement, but he consistently moved his eyes to a stimulus on the right. Thus, he showed contralateral but not ipsilateral sensory inattention. Initially, he also was impaired in making leftward eye movements when right stimuli were presented. Thus, he also showed a directional motor neglect. In subsequent tests, his left-sided sensory inattention as defined above decreased, and was no longer present three weeks following his stroke, nor in a follow-up test conducted almost 6 months following this stroke. In contrast, his directional motor neglect, as defined above, was still present in the follow-up test. As his left-sided sensory inattention declined, his tendency to move his eyes incorrectly to stimuli on the left side (the side contralateral to his lesion) when these stimuli required eye movements to the right became stronger ("release" of visual grasp); he continued to show this strong tendency in the test conducted almost 6 months following his stroke.