How children with autism look at events

Patterns of eye movements were studied in a group of 10 preschool children with Autism Spectrum Disorder (ASD) and in two reference groups with typically developing (TD) children, 12 3-year-olds and 12 1-year-olds. Three hypotheses were tested regarding the origins of problems experienced by children with ASD in dynamic situations. The first one stated that the children with ASD have deficient motion perception. The second one stated that children with ASD are deficient in predicting events, and the third one that the roots are to be found in deficient social perception. The results show that the children with ASD tracked moving objects with smooth pursuit and predicted the reappearance of temporarily occluded moving object in the same way as the TD children. Their eye movements, however, revealed deficient social perception. They looked at a video-taped conversation much less than the TD children, they did not predict the onset of the next turn in the conversation, and the fixations on the speakers were shorter. These effects did not appear in a control video with objects taking turns and making sounds in a similar alternating way to the two participants in the conversation.     

And yet it moves: perceptual illusions and neural mechanisms of pursuit compensation during smooth pursuit eye movements

Pursuit eye movements are smooth rotations of the eye aimed at tracking moving objects. During pursuit, the visual system “compensates” for the eye movements, and transforms image movements captured by the eye from retinal to extra-retinal coordinates, for world-centered perception and action. When this function is impaired such as in schizophrenia, subjects misattribute retinal movements generated by their own eye movements to external sources. Surprisingly, even in healthy subjects pursuit compensation is incomplete, and results in illusory perception of motion. Neurophysiological, psychophysical and imaging studies elucidated many aspects of the neural substrates of visual processing during pursuit, including where and how in the cortex visual and non-visual signals interact to produce extra-retinal perception of motion. Here we review current understanding of motion processing in the visual cortex during pursuit and its relation to perception, from a broad perspective drawing from electrophysiology, fMRI, psychophysics and computational modeling. We discuss the experimental findings in the context of theories of pursuit compensation, and review some of the open questions in the field.     

Coherent motion pops out during smooth pursuit

Stimulus motion is a prominent feature that is used by the visual system to segment figure from ground and perceptually bind widely separated objects. Pursuit eye movements can be influenced by such perceptual grouping processes. We have examined the subjects' ability to detect small amounts of coherent motion in random dot kinematograms during pursuit. We compared performance on tests of coherent motion perception while subjects fixated a stationary spot or while they tracked a moving target. The results indicate that smooth pursuit can improve subjects' ability to detect the presence of coherent motion. We tentatively propose that an efference copy of the eye movement signal can enhance the ability of the visual system to detect correlations between sparsely placed targets among noisy distractors.     

FMRI of response to nicotine during a smooth pursuit eye movement task in schizophrenia

OBJECTIVE: Nicotine temporarily normalizes smooth pursuit eye movement deficits in schizophrenia. This study used functional magnetic resonance imaging (fMRI) to examine changes in brain hemodynamic response associated with nicotine administration during a smooth pursuit eye movement task in subjects with schizophrenia. METHOD: Nine subjects with schizophrenia performed the eye movement task while undergoing fMRI. Subjects then were given nicotine or placebo and repeated the task while being scanned. Subjects repeated the procedure the following week, receiving the counterbalanced condition. RESULTS: Compared with placebo, nicotine was associated with greater activity in the anterior and posterior cingulate gyri, precuneus, and area MT/MST and less activity in the hippocampus and parietal eye fields. CONCLUSIONS: Changes in area MT/MST and the cingulate gyrus are consistent with an improvement in perception and attention to moving stimuli. The most important observed difference between nicotine and placebo--less activation of the hippocampus after nicotine than after placebo administration--is consistent with nicotinic receptor mediation of inhibitory neuronal dysfunction in schizophrenia.     

fMRI of optokinetic eye movements with and without a contribution of smooth pursuit.

BACKGROUND AND PURPOSE: Optokinetic eye movements are elicited when tracking a moving pattern. It can be argued that a moving pattern of stripes invokes both the optokinetic and the smooth pursuit eye movement system, which may confound the observed brain activation patterns using functional magnetic resonance imaging (fMRI). A moving pattern of limited-lifetime-dot stimulation does not target the smooth pursuit eye movement system. METHODS: fMRI was used to compare the cortical activity elicited by an optokinetic eye movement response evoked by a moving pattern of stripes and a moving pattern of limited lifetime dots. RESULTS: The eye movement behavior showed that both types of stimuli evoked an adequate and similar optokinetic eye movement response, but stimulation with stripes evoked more activation in the frontal and parietal eye fields, MT/V5, and in the cerebellar area VI than stimulation with limited-lifetime dots. CONCLUSIONS: These brain areas are implicated in smooth pursuit eye movements. Our results suggest that indeed both the optokinetic and the smooth pursuit eye movement system are involved in tracking a moving pattern of stripes.     

fMRI evidence for sensorimotor transformations in human cortex during smooth pursuit eye movements

Smooth pursuit eye movements (SP) are driven by moving objects. The pursuit system processes the visual input signals and transforms this information into an oculomotor output signal. Despite the object's movement on the retina and the eyes' movement in the head, we are able to locate the object in space implying coordinate transformations from retinal to head and space coordinates. To test for the visual and oculomotor components of SP and the possible transformation sites, we investigated three experimental conditions: (I) fixation of a stationary target with a second target moving across the retina (visual), (II) pursuit of the moving target with the second target moving in phase (oculomotor), (III) pursuit of the moving target with the second target remaining stationary (visuo-oculomotor). Precise eye movement data were simultaneously measured with the fMRI data. Visual components of activation during SP were located in the motion-sensitive, temporo-parieto-occipital region MT+ and the right posterior parietal cortex (PPC). Motor components comprised more widespread activation in these regions and additional activations in the frontal and supplementary eye fields (FEF, SEF), the cingulate gyrus and precuneus. The combined visuo-oculomotor stimulus revealed additional activation in the putamen. Possible transformation sites were found in MT+ and PPC. The MT+ activation evoked by the motion of a single visual dot was very localized, while the activation of the same single dot motion driving the eye was rather extended across MT+. The eye movement information appeared to be dispersed across the visual map of MT+. This could be interpreted as a transfer of the one-dimensional eye movement information into the two-dimensional visual map. Potentially, the dispersed information could be used to remap MT+ to space coordinates rather than retinal coordinates and to provide the basis for a motor output control. A similar interpretation holds for our results in the PPC region.     

Rhesus monkeys behave as if they perceive the Duncker Illusion

The visual system uses the pattern of motion on the retina to analyze the motion of objects in the world, and the motion of the observer him/herself. Distinguishing between retinal motion evoked by movement of the retina in space and retinal motion evoked by movement of objects in the environment is computationally difficult, and the human visual system frequently misinterprets the meaning of retinal motion. In this study, we demonstrate that the visual system of the Rhesus monkey also misinterprets retinal motion. We show that monkeys erroneously report the trajectories of pursuit targets or their own pursuit eye movements during an epoch of smooth pursuit across an orthogonally moving background. Furthermore, when they make saccades to the spatial location of stimuli that flashed early in an epoch of smooth pursuit or fixation, they make large errors that appear to take into account the erroneous smooth eye movement that they report in the first experiment, and not the eye movement that they actually make.     

Coordination of eye and head movements during smooth pursuit in patients with vestibular failure.

During pursuit of smoothly moving targets with combined eye and head movements in normal subjects, accurate gaze control depends on successful interaction of the vestibular and head movement signals with the ocular pursuit mechanisms. To investigate compensation for loss of the vestibulo-ocular reflex during head-free pursuit in labyrinthine-deficient patients, pursuit performance was assessed and compared under head-fixed and head-free conditions in five patients with isolated bilateral loss of vestibular function. Target motion consisted of predictable and unpredictable pseudo-random waveforms containing the sum of three or four sinusoids. Comparison of slow-phase gaze velocity gains under head-free and head-fixed conditions revealed no significant differences during pursuit of any of the three pseudo-random waveforms. The finding of significant compensatory eye movement during active head movements in darkness in labyrinthine-deficient patients, which were comparable in character and gain to the vestibular eye movement elicited in normal subjects, probably explains the similarity of the head-fixed and head-free responses. In two additional patients with cerebellar degeneration and vestibular failure, no compensatory eye movement response was observed, implying that the cerebellum is necessary for the generation of such responses in labyrinthine-deficient patients.     

Dissociable frontal controls during visible and memory‐guided eye‐tracking of moving targets

When tracking visible or occluded moving targets, several frontal regions including the frontal eye fields (FEF), dorsal‐lateral prefrontal cortex (DLPFC), and anterior cingulate cortex (ACC) are involved in smooth pursuit eye movements (SPEM). To investigate how these areas play different roles in predicting future locations of moving targets, 12 healthy college students participated in a smooth pursuit task of visual and occluded targets. Their eye movements and brain responses measured by event‐related functional MRI were simultaneously recorded. Our results show that different visual cues resulted in time discrepancies between physical and estimated pursuit time only when the moving dot was occluded. Visible phase velocity gain was higher that that of occlusion phase. We found bilateral FEF association with eye‐movement whether moving targets are visible or occluded. However, the DLPFC and ACC showed increased activity when tracking and predicting locations of occluded moving targets, and were suppressed during smooth pursuit of visible targets. When visual cues were increasingly available, less activation in the DLPFC and the ACC was observed. In addition, there was a significant hemisphere effect in DLPFC, where right DLPFC showed significantly increased responses over left when pursuing occluded moving targets. Correlation results revealed that DLPFC, the right DLPFC in particular, communicates more with FEF during tracking of occluded moving targets (from memory). The ACC modulates FEF more during tracking of visible targets (likely related to visual attention). Our results suggest that DLPFC and ACC modulate FEF and cortical networks differentially during visible and memory‐guided eye tracking of moving targets. Hum Brain Mapp, 2009. © 2009 Wiley‐Liss, Inc.     

Target selection for pursuit and saccadic eye movements in humans

Eye movements were recorded from three subjects as they initiated tracking of a small circle ("target") moving leftward or rightward, above or below the horizontal meridian, either alone or in the presence of a small square ("distractor") moving leftward or rightward on the other side of the horizontal meridian. At the start of each trial, subjects were provided with either a "form" cue (always centrally positioned and having the circular shape and color of the upcoming moving target) or a "location" cue (a small white square positioned where the upcoming target would appear). The latency of pursuit increased in the presence of an oppositely moving distractor when subjects were provided the form cues but not when they were provided the location cues. The latency of saccades showed similar, but smaller, increases when subjects were given the form cues. On many trials with the form cues, pursuit started in the direction of the distractor and then reversed to follow the target. On these trials, the initial saccade often, but not always, also followed the distractor. These results indicate that the mechanisms of target selection for pursuit and saccades are tightly coordinated but not strictly yoked. The shared effects of the distractor on the latencies of pursuit and saccades probably reflect the common role of visual attention in filtering the inputs that guide these two types of eye movements. The differences in the details of the effects on pursuit and saccades suggest that the neural mechanisms that trigger these two movements can be independently regulated.     

Responses of Visual-Tracking Neurons from Cortical Area MST-I to Visual,Eye and Head Motion

Thirty-one neurons which exhibited ocular pursuit-related activity [visual-tracking (VT) neurons] were found clustered within area MST-I (the lateral part of area MST) of two rhesus monkeys. Their responses were studied to determine whether this activity was correlated only with pursuit eye movement or with head movement as well. The latter hypothesis appeared to be preferable since visual, eye movement and head movement inputs were found to be mapped in register onto most of these cells. First, in each cell tested ( n =19) the pursuit response persisted even in the absence of retinal image motion, offering clear evidence for non-visual input. Second, 22 of the 31 cells were directionally responsive to moving visual stimuli and in 20 of these the preferred directions for the visual motion and pursuit responses agreed closely. Responses were also obtained from many of the same cells during suppression of both the horizontal and the vertical vestibulo-ocular reflex (VOR). In each case, where directional visual, pursuit and VOR suppression responses were each obtained, vector addition of responses during suppression of the horizontal and vertical VOR resulted in an estimated preferred direction for head rotation which was closely aligned with the preferred direction previously obtained for eye motion or visual motion. In addition, the preferred direction of head movement was conserved even when the VOR was elicited by passive head rotation in complete darkness, although the responses in this instance were, on average, only 62% of those obtained during VOR suppression. Our interpretation is that, at present, MST-I VT neurons are best described as encoding the direction of target motion in space-centred coordinates by integrating inputs reflecting retinal image motion plus eye and head movement.     

Functional MRI of lateral occipitotemporal cortex during pursuit and motion perception

We performed functional imaging with a conventional 1.5-T magnetic resonance scanner in 9 normal subjects. We used a gradient-echo technique to examine changes in signal between periods when subjects viewed a stationary black-and-white grating, a moving grating, and when they followed a moving spot. We located image pixels with significant differences between the viewing conditions. In 7 subjects, these occurred in the lateral occipitotemporal cortex, a region previously identified as a putative human homologue of the motion-sensitive middle temporal area (MT, or V5) of monkeys. Signal intensity was greater during pursuit of the moving dot than durin viewing of the moving grating with the eyes still, despite the fact that the moving grating generated more retinal image motion. In contrast, signal intensity in striate cortex was least during pursuit of the moving dot. These findings suggest that the lateral occipitotemporal cortex has extraretinal signals during pursuit. Such signals may include attentional input, corollary eye movement information, or even a pursuit command. Extraretinal signals suggest that the lateral occipitotemporal cortex may contain a human homologue not only of MT but also of other components of monkey V5 complex, such as the medical superior temporal area.     

The coordination of eye and head movement during smooth pursuit

Eye and head movements during tracking of a smoothly moving visual target were recorded in trained monkeys. The head movement clearly followed the target, although with considerable variability from cycle to cycle. The eye stayed relatively near the primary position and moved in an apparently irregular fashion; however, the sum of eye and head, or gaze, remained accurately on target despite the irregularity of the individual eye and head movements. When compared with tracking with head fixed, head free tracking was not measurably different in accuracy. Further experiments were performed which demonstrated a role for the vestibular system in coordinating eye and head during smooth pursuit. The results of these experiments can be best explained by postulating an internal smooth pursuit command driving both eye and head movements. In the case of the eye movement, this smooth pursuit command is combined with vestibular feedback from head movement before being forwarded to eye movement centers.     

Properties of visual inputs that initiate horizontal smooth pursuit eye movements in monkeys

Smooth pursuit eye movements allow primates to fixate and track small, slowly moving objects. Pursuit usually requires visual targets; our aim was to determine the properties of the visual signals transmitted to the pursuit motor system. Rhesus monkeys were rewarded for tracking spots of light that underwent discreet changes in velocity under a variety of visual conditions. We measured the resulting smooth eye acceleration in a 100-msec interval that began with the initiation of pursuit and ended before there had been time for visual feedback. This approach allowed us to vary the parameters of visual stimulation and measure eye movement responses in a way that provides estimates of the properties of signals transmitted by visual pathways. The initiation of pursuit showed different properties early and late in the interval we studied. In the first 20 msec of pursuit, eye acceleration was in the correct direction, but was independent of the initial position of the moving images, the velocity of the stimulus, or the presence or absence of background illumination. Thereafter, the initiation of pursuit depended strongly on all of the above parameters. Eye acceleration was highest when the moving images fell close to the fovea and decreased sharply as eccentricity was increased up to 21 degrees. When the background was diffusely illuminated, eye acceleration showed velocity selectivity; it was highest for a middle range of velocities (30 to 60 degrees/sec) and decreased for higher velocities. When the background was dark, eye acceleration increased as a function of target velocity up to 150 degrees/sec. We conclude that the initiation of pursuit has at least 2 visual components. The two components have different latencies and show quite different relationships to the visual properties of the stimulus, suggesting two cell populations that could provide the visual inputs for pursuit.     

Tracking with the mind’s eye

The two components of voluntary tracking eye-movements in primates, pursuit and saccades, are generally viewed as relatively independent oculomotor subsystems that move the eyes in different ways using independent visual information. Although saccades have long been known to be guided by visual processes related to perception and cognition, only recently have psychophysical and physiological studies provided compelling evidence that pursuit is also guided by such higher-order visual processes, rather than by the raw retinal stimulus. Pursuit and saccades also do not appear to be entirely independent anatomical systems, but involve overlapping neural mechanisms that might be important for coordinating these two types of eye movement during the tracking of a selected visual object. Given that the recovery of objects from real-world images is inherently ambiguous, guiding both pursuit and saccades with perception could represent an explicit strategy for ensuring that these two motor actions are driven by a single visual interpretation.     

Nonambulatory persons with profound mental retardation: Physical, developmental, and behavioral characteristics

Although profound mental retardation is generally associated with various organic etiologies that result in substantial cognitive and behavioral deficits, little is known about specific subgroups of persons with profound mental retardation. This study presents data on the physical, developmental, and behavioral characteristics of a group of 203 nonambulatory persons with profound mental retardation residing within a specialized service setting. The results indicate that nonambulatory persons with profound mental retardation have a high prevalence of physical and medical problems along with high rates of self-injurious, stereotypic, and aggressive behavior. Assessment results from the Stanford-Binet (L-M), Bayley Scales of Infant Development-Mental Scale, and Vineland Adaptive Behavior Scale reveal a high degree of variability in cognitive and adaptive functioning. However, developmental age-equivalent scores of cognitive ability, communication, daily living, socialization, and motor skills for the group fell below the 1-year level. The data illustrate the complexity of needs in providing habilitative services to nonambulatory persons with profound mental retardation.     

Smooth-pursuit eye movements: alterations in Alzheimer's disease.

Smooth-pursuit eye movements induced by targets moving at constant velocities (from 5 to 100 deg/sec) were recorded from 13 patients with Alzheimer's disease (AD) and from 11 healthy subjects. Four variables were evaluated to quantify the patients' response to the eye movement tests: (1) average peak velocity of smooth-pursuit; (2) percent target matching index after saccade removal (percent ratio between the area of the velocity curve of smooth-pursuit eye movement after saccade removal and the area of target velocity) which is related to the eye performance for each value of target velocity; (3) total amplitude of anticipatory saccades; (4) total number of anticipatory saccades. Compared to the controls, AD patients were found to have significantly lower values of average peak velocity of smooth pursuit and of percent target matching index and a significantly increased number and amplitude of anticipatory saccades. A discriminant stepwise analysis indicated that 5 oculographic variables were significantly associated with the patient's clinical condition (healthy volunteer or AD patient). These statistics yielded an equation for predicting the patient's status according to which the percentage of cases classified correctly was 82.6% in the overall group (n = 23). The predictive performance was similar between the healthy volunteers subgroup (81.8%, n = 11) and the AD subgroup (83.3%, n = 12). The discriminant score was significantly correlated with the score resulting from the MiniMental test (r = 0.67). A significant correlation was also found between the MiniMental score and the number of anticipatory saccades (r = -0.61). No significant correlation was present between the gain of smooth pursuit and the patients' cognitive decline.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sleep in subjects with autistic disorder: a neurophysiological and psychological study

Polysomnography (EOG, EEG, EMG) was carried out in 17 male children and adolescents with autistic disorder, in seven patients with mental retardation and fragile X syndrome, and in five age- and sex-matched normal male subjects. Density of rapid eye movements was not significantly different in the three groups of subjects; however, some sleep parameters such as time in bed, sleep period time, and total sleep time were significantly lower in subjects with autistic disorder than in normal controls; moreover, patients with autistic disorder showed values of sleep period time, first REM latency and percent (%) sleep stage 1 lower than those of patients with fragile X syndrome with mental retardation. Density of muscle twitches was significantly higher in patients with autistic disorder than in normal controls. In contrast only minor differences were observed between patients with autistic disorder and those with fragile X syndrome with mental retardation. Furthermore, some psychoeducational profile-revised items such as perception and eye-hand coordination, showed significant correlation with some sleep parameters (time in bed, sleep latency, stage shifts, first REM latency and wakefulness after sleep onset). Childhood Autism Rating Scale (CARS) scores to visual response and non-verbal communication showed significant correlation with some tonic sleep parameters, such as sleep period time, wakefulness after sleep onset, and total sleep time. Relating to people and activity level items were found to be significantly correlated with rapid eye movement density. Our results suggest the existence of a sleep pattern in autistic patients different from that observed in subjects with mental retardation and from that of normal controls. In addition, these findings indicate that sleep parameters in these patients are correlated with some psychological indices generally used for the diagnosis of autistic disorder; for this reason, polysomnographies might be useful in the comprehension of the neurophysiological mechanisms underlying this condition.     

Horizontal and vertical pursuit eye movements,the oculocephalic reflex,and the functional psychoses

Sixteen schizophrenic patients, 16 manic-depressive patients, and 14 nonpatient control subjects were tested for horizontal and vertical smooth pursuit eye movements (SPEM) and the oculocephalic reflex. All patients with impaired horizontal pursuit also displayed disrupted vertical pursuit, suggesting that a common mechanism underlies these abnormalities. The oculocephalic reflex was intact in 96% of the subjects whether or not pursuit was disrupted, suggesting that the locus of the eye movement disorder in psychosis may be cortical. For horizontal pursuit, there were significant differences between schizophrenics and nonpatient controls, and between manic depressives and nonpatient controls, but not between schizophrenics and manic depressives, suggesting that the SPEM disruption occurs with significant prevalence in major functional psychoses and not only in schizophrenia.     

Parkinsonian patients show impaired predictive smooth pursuit

To determine if patients with Parkinson's disease (PD) are able to use a visual contextual cue to induce a predictive change in smooth pursuit direction and if this ability depends on the state of the dopaminergic system, we measured predictive smooth pursuit in nine patients with mild to moderate PD during OFF and ON medication. These values were compared with those of nine age-matched and sex-matched healthy controls.Our focus was on the horizontal smooth pursuit when subjects pursued a downward moving target entering a+/-90 deg curve. The target moved on a homogeneous background or on a static "street" that indicated the future trajectory of the target. Our main result is that PD patients were impaired in eliciting predictive smooth pursuit using the context information of the street compared to healthy subjects. The control group elicited predictive pursuit 250 ms before target onset. In contrast, PD patients showed significantly longer latency (100-120 ms) and reduced maximal pursuit velocity. However, without the street guiding pursuit, a delay of about 250 ms was seen in both groups. There was no significant difference in the smooth pursuit performance between OFF and ON medication in the patient group.These results show that early stage PD patients are impaired in the use of static visual information as a cue for predictive pursuit compared to controls and that this deficit does not depend on dopaminergic medication. In the context of predictive eye movement, the involvement of the striatal-frontal pathway and the spatial working memory is discussed.