Local and global aspects of biological motion perception in children born at very low birth weight.

Biological motion perception can be assessed using a variety of tasks. In the present study, 8- to 11-year-old children born prematurely at very low birth weight (<1500 g) and matched, full-term controls completed tasks that required the extraction of local motion cues, the ability to perceptually group these cues to extract information about body structure, and the ability to carry out higher order processes required for action recognition and person identification. Preterm children exhibited difficulties in all 4 aspects of biological motion perception. However, intercorrelations between test scores were weak in both full-term and preterm children--a finding that supports the view that these processes are relatively independent. Preterm children also displayed more autistic-like traits than full-term peers. In preterm (but not full-term) children, these traits were negatively correlated with performance in the task requiring structure-from-motion processing, r(30) = -.36, p < .05), but positively correlated with the ability to extract identity, r(30) = .45, p < .05). These findings extend previous reports of vulnerability in systems involved in processing dynamic cues in preterm children and suggest that a core deficit in social perception/cognition may contribute to the development of the social and behavioral difficulties even in members of this population who are functioning within the normal range intellectually. The results could inform the development of screening, diagnostic, and intervention tools.

Differential vulnerability of global motion, global form, and biological motion processing in full-term and preterm children.

Young children born very prematurely show elevated thresholds for global motion and global form [Atkinson, J. & Braddick, O. (2007). Visual and visuocognitive development in children born very prematurely. Progress in Brain Research, 164, 123-149; MacKay, T. L., Jakobson, L. S., Ellemberg, D., Lewis, T. L., Maurer, D., & Casiro, O. (2005). Deficits in the processing of local and global motion in very low birthweight children. Neuropsychologia, 43, 1738-1748]. In adolescence, those with white matter pathology show reduced sensitivity to biological motion [Pavlova, M., Sokolov, A., Staudt, M., Marconato, F., Birbaumer, N., & Krageloh-Mann, I. (2005). Recruitment of periventricular parietal regions in processing cluttered point-light biological motion. Cerebral Cortex, 15, 594-601; Pavlova, M., Staudt, M., Sokolov, A., Birbaumer, N., & Krageloh-Mann, I. (2003). Perception and production of biological movement in patients with early periventricular brain lesions. Brain, 126, 692-701]. Here, we measured sensitivity to global form, global motion, and biological motion in a sample of 23, five- to nine-year-old children born at <32 weeks gestation, and in 20 full-term controls matched to the clinical sample in age, socioeconomic status, and estimated Verbal IQ. As a group, premature children showed reduced sensitivity, relative to controls, on all three tasks (F>4.1, p<0.05). By computing a deficit score for each task (the ratio between a premature child's threshold and the mean threshold for three age-matched controls) we were able to compare performance across tasks directly. Mean deficit scores were significantly greater than 1 (indicating some level of impairment) for biological motion and global motion (ps<0.03). In contrast, the mean deficit score for global form was not significantly different from 1 (indicating no impairment, relative to age-matched control children). Rates of impairment (deficit score>or=2) were four times higher for global motion than for global form (p<0.04); rates of impairment on the biological motion task fell at an intermediate level. In agreement with previous studies, we find impairments in the processing of global motion (Atkinson & Braddick; MacKay et al.) and of biological motion (Pavlova et al.), which are larger than the impairments in the processing of global form (Atkinson & Braddick). In addition, we show that the impairments are not correlated with each other. The differential vulnerability that we observed across tasks could not be accounted for by stereoacuity deficits, amblyopia, or attentional problems. We suspect, instead, that it reflects the fact that these forms of visual processing develop at different rates, and may be differentially vulnerable to early brain injury or atypical neurodevelopment [c.f., Atkinson, J. & Braddick, O. (2007). Visual and visuocognitive development in children born very prematurely. Progress in Brain Research, 164, 123-149; Braddick, O., Atkinson, J., & Wattam-Bell, J. (2003). Normal and anomalous development of visual motion processing: Motion coherence and 'dorsal-stream vulnerability'. Neuropsychologia, 41, 1769-1784].

Visual and fine-motor outcomes in adolescent survivors of high-risk congenital diaphragmatic hernia who did not receive extracorporeal membrane oxygenation.

OBJECTIVE: Although survivors of congenital diaphragmatic hernia (CDH) are at high risk for brain injury, little is known about their neurodevelopment. Studies exploring short-term outcomes in children who received extracorporeal membrane oxygenation (ECMO) therapy suggest an increased risk for abnormalities in tone and/or motor development. This study provides the first detailed examination of visual and fine-motor outcomes in adolescent survivors of high-risk CDH (manifesting within the first 24 h) who did not receive ECMO. STUDY DESIGN: A total of 13 CDH survivors (mean age 12.9 years) and 11 typically developing controls, matched to the CDH sample in terms of age at test, intelligence quotient and socioeconomic status (SES), completed a battery of visual and motor tests. RESULTS: CDH survivors performed normally on motor-free tests of visual-perceptual function and on tests requiring visual discrimination and scanning, but were impaired on tests requiring visual-motor integration and oral-motor programming. CONCLUSION: Survivors of high-risk CDH who did not receive ECMO treatment are at risk for long-term problems with oral motor and visuomotor control.

Hue-specific colour memory impairment in an individual with intact colour perception and colour naming.

Cases of hue-selective dyschomatopsias, together with the results of recent optical imaging studies [Xiao, Y., Casti, A. R. R., Xiao, J., & Kaplan, E. (2006). A spatially organized representation of colour in macaque primary visual cortex. Perception, 35, ECVP Abstract Supplement; Xiao, Y., Wang, Y., & Felleman, D. J. (2003). A spatially organized representation of colour in macaque cortical area V2. Nature, 421, 535-539], have provided support for the idea that different colours are processed in spatially distinct regions of extrastriate cortex. In the present report, we provide evidence suggesting that a similar, but distinct, map may exist for representations of colour in memory. This evidence comes from observations of a young woman (QP) who demonstrates an isolated deficit in colour memory secondary to a concussive episode. Despite having normal colour perception and colour naming skills, and above-average memory skills in other domains, QP's ability to recall visually encoded colour information over short retention intervals is dramatically impaired. Her long-term memory for colour and her colour imagery skills are also abnormal. Surprisingly, however, these impairments are not seen with all hues; specifically, her ability to remember or imagine blue shades is spared. This interesting case contributes to the literature suggesting that colour perception, naming, and memory can be clinically dissociated, and provides insights into the organization of colour information in memory.

Motion-defined form processing in extremely premature children.

Children born extremely prematurely are at risk for a variety of problems with motion analysis, including problems with motion-defined (MD) form recognition [Downie, A. L. S., Jakobson, L. S., Frisk, V., & Ushycky, I. (2003). Periventricular brain injury, visual motion processing, and reading and spelling abilities in children who were extremely-low-birthweight. Journal of the International Neuropsychological Society, 9, 440-449]. The aims of the present study were (1) to examine the impact of retinopathy of prematurity (ROP) and mild periventricular brain injury (PVBI) on MD form processing in this population; (2) to assess relationships between MD form recognition in these children and their performance in several other areas of visual competence. To this end, a battery of visual and visuomotor tests was administered to 43, 5- and 6-year old, extremely premature children, all of whom had escaped severe PVBI. A group of full-term controls was also studied. Relative to controls, premature children displayed clear deficits in MD form recognition and these deficits were related to the presence of ROP and/or mild PVBI, rather than to a history of prematurity per se. Regression analyses revealed significant associations in premature children between MD form processing deficits and problems with visual search, stereopsis, visuoconstructive and graphomotor skills, motor development, and Performance IQ. The results suggest that assessment of sensitivity to MD forms may be useful in the early identification of preterm children at greatest risk for visual problems associated with dorsal stream dysfunction.

Deficits in the processing of local and global motion in very low birthweight children.

This study evaluated the impact of premature birth on the development of local and global motion processing in a group of very low birthweight (<1500 g), 5- to 8-year-old children. Sensitivity to first- and second-order local motion stimuli and coherence thresholds for global motion in random dot kinematograms were measured. Relative to full-term controls, premature children showed deficits on all three aspects of motion processing. These problems could not be accounted for by stereo deficits, amblyopia, or attentional problems. A history of mild retinopathy of prematurity and/or intraventricular hemorrhage increased risk, but deficits were observed in some children with no apparent ocular or cerebral pathology. It is important to note that, despite the observed group differences, individual profiles of performance did vary; the results suggest that these three forms of motion processing may involve separate neural mechanisms. These findings serve to increase our understanding of the organization and functional development of motion-processing subsystems in humans, and of the impact of prematurity and associated complications on visual development.

The relationship between periventricular brain injury and deficits in visual processing among extremely-low-birthweight (< 1000 g) children.

OBJECTIVE: To examine the relationship between neonatal, periventricular brain damage and visuomotor performance in extremely-low-birthweight (ELBW) children of normal intelligence whose birthweights were appropriate for gestational age (AGA). METHODS: Seventy-eight ELBW and 23 control children, all six years of age, completed two "motor-free" tests of visual spatial ability and three tests requiring visuomotor control. RESULTS: Full-term control children outperformed ELBW children with periventricular brain damage on all three tests requiring visuomotor guidance. No group differences were found on two "motor-free" tests of visual spatial ability. ELBW children without periventricular brain damage performed in a manner indistinguishable from controls on all tests included in this study. CONCLUSIONS: The findings indicate that the presence and severity of periventricular brain injury are important factors to consider in predicting visuomotor development in ELBW children.

Dissociations among functional subsystems governing melody recognition after right-hemisphere damage.

This study describes an amateur musician, KB, who became amusic following a right-hemisphere stroke. A series of assessments conducted post-stroke revealed that KB functioned in the normal range for most verbal skills. However, compared with controls matched in age and music training, KB showed severe loss of pitch and rhythmic processing abilities. His ability to recognise and identify familiar instrumental melodies was also lost. Despite these deficits, KB performed remarkably well when asked to recognise and identify familiar song melodies presented without accompanying lyrics. This dissociation between the ability to recognise/identify song vs. instrumental melodies was replicated across different sets of musical materials, including newly learned melodies. Analyses of the acoustical and musical features of song and instrumental melodies discounted an explanation of the dissociation based on these features alone. Rather, the results suggest a functional dissociation resulting from a focal brain lesion. We propose that, in the case of song melodies, there remains sufficient activation in KB's melody analysis system to coactivate an intact representation of both associative information and the lyrics in the speech lexicon, making recognition and identification possible. In the case of instrumental melodies, no such associative processes exist; thus recognition and identification do not occur.

Music training and rate of presentation as mediators of text and song recall.

The present research addresses whether music training acts as a mediator of the recall of spoken and sung lyrics and whether presentation rate is the essential variable, rather than the inclusion of melody. In Experiment 1, 78 undergraduates, half with music training and half without, heard spoken or sung lyrics. Recall for sung lyrics was superior to that for spoken lyrics for both groups. In Experiments 2 and 3, presentation rate was manipulated so that the durations of the spoken and the sung materials were equal. With presentation rate equated, there was no advantage for sung over spoken lyrics. In all the experiments, those participants with music training outperformed those without training in all the conditions. The results suggest that music training leads to enhanced memory for verbal material. Previous findings of melody's aiding text recall may be attributed to presentation rate.

Anticipatory grip adjustments are observed in both goal-directed movements and movement tics in an individual with Tourette's syndrome.

We examined grip force adjustments during movements of a hand-held object in a young man (BF) with Tourette's syndrome. We directly compared BF's voluntary up and down movements with tics in the same directions. Movement tics were elicited by cueing BF to move either up or down on a GO signal which appeared after a variable delay. During the delay period, we observed frequent tics which were almost always in the cued movement direction. BF's voluntary movements were well coordinated and featured precise and appropriate anticipatory grip force adjustments such that grip force was modulated in phase with movement-induced fluctuations in load. Precise anticipatory grip force adjustments were also observed in all of BF's movement tics. These results support the hypothesis that tics in Tourette's syndrome are purposeful voluntary movements that are well organized and coordinated.

Near, far, or in between?-Target edges and the transport component of prehension.

It is well known that during visually guided prehension movements the peak velocity of the arm is scaled for object distance (e.g., Gentilucci et al., 1991; Jakobson & Goodale, 1991; Servos, Goodale, & Jakobson, 1992). Those movements are being directed not to single points in space, however, but rather to objects with extent. Thus, object distance must be computed relative to some particular point on the object. Whether that point corresponds to the location of a particular edge, for example, has not been clearly demonstrated. In the present study, subjects (N = 9) were presented with a series of oblong blocks positioned at different locations. Peak velocity increased with object size for reaches in which different-sized objects had their near edges lined up; in contrast, the peak velocities of reaches directed to objects of different sizes did not differ when the far edges of the objects were lined up. The present study, therefore, provided confirmation that subjects calibrate the peak velocity of their reaches relative to the far edge of a target object.

Time to contact and the control of manual prehension.

In the present study, a kinematic analysis was made of unconstrained, natural prehension movements directed toward an object approaching the observer on a conveyor belt at one of three constant velocities, from one of three different directions (head-on or along the fronto-parallel plane coming either from the subject's left or right). Subjects were required to grasp the object when it reached a target located 20 cm directly in front of the hand's start position. The kinematic analysis revealed that both the transport and grasp components of the movement changed in response to the experimental manipulations, but did so in a manner that guaranteed that, for objects approaching from a given direction, hand closure would begin at a constant time prior to object contact (regardless of the object's approach speed). The kinematic analysis also revealed, however, that the onset of hand closure began earlier with objects approaching from the right than from other directions -- an effect which would not be predicted if time to contact was the key variable controlling the onset of hand closure. These results, then, lend only partial support to the theory that temporal coordination between the transport and grasp components of prehension is ensured through their common dependence on time to contact information.

Visual and visuomotor performance in dyslexic children.

The present study was designed to compare the performance of nine dyslexic boys and nine age- and IQ-matched controls on tasks which presumably tap visual functions dependent on the subcortical magnocellular (M) pathway (flicker sensitivity) and the cortical dorsal stream (stereoacuity, structure-from-motion, visuomotor control). Increasing evidence suggests that dyslexics experience impairments in M-system functioning. In keeping with previous work supporting this conclusion, dyslexic subjects in the present study were found to have reduced sensitivity to flicker relative to controls. Given that the M system provides the predominant input to the dorsal stream, it was expected that reduced functioning of the M system in dyslexics would result in disruptions of functions related to this cortical visual pathway. Indeed, dyslexic subjects in the present study were found to be less efficient at recognizing structure-from-motion and less accurate at grasping objects precisely. They also showed a mild impairment in stereoacuity. These results, then, lend some support to the hypothesis that dyslexic individuals should show deficiencies on tasks dependent on dorsal stream processing of visual information.

Differences in the visual control of pantomimed and natural grasping movements.

In a series of experiments, we studied the differences between natural target-directed grasping movements and 'pantomimed' movements directed towards remembered objects. Although subjects continued to scale their hand opening for object size when pantomiming, grip formation and other kinematic variables differed significantly from those seen in normal target-directed actions. This was true whether the subjects had just seen the target object 2 sec before (Experiments 1 and 2) or whether the target object was still present and they were simply required to pantomime the grasping movement beside it (Experiment 3). We argued that these pantomimed reaches were being driven by stored perceptual information about the object, and were not utilizing the normal visuomotor control systems that direct actions in real time. This interpretation received strong support from observations of a patient with visual form agnosia who was also tested. In an earlier report, we had shown that this patient showed anticipatory scaling of her grasp despite her inability to discriminate between objects perceptually on the basis of size. The present study showed, however, that the requirement to remember an object even briefly, or to pantomime an action beside it, was enough to completely disrupt her visuomotor scaling (Experiments 2 and 3). That this reflected a failure of perception rather than imagery or understanding was supported by the fact that she could convincingly pantomime actions to imagined, familiar objects, the sizes of which were known to her (Experiment 4). All these results suggest that the mechanisms underlying the formation of perceptual representations of objects are quite independent of those mediating on-line visuomotor control.

Control of proximal and distal components of prehension in callosal agenesis.

Classic work with split-brain monkeys suggests that the reaching limb can be controlled by either cerebral hemisphere, but that finger control is largely crossed (Haaxma and Kuypers, 1974). Accordingly, one might predict that acallosal subjects should have little difficulty grasping objects presented in the visual field ipsilateral to the hand used, but should have great difficulty forming their grasp when reaching into crossed space. In the present study, we carried out a kinematic analysis of reaching and grasping movements executed by four acallosal subjects and four matched control subjects. Subjects maintained central fixation while reaching with either hand for objects placed in left, central and right space. Relative to controls, acallosal subjects took longer to complete reaches directed across the body midline, and spent more time decelerating. Moreover, unlike controls, their grip formation appeared to be impaired in all regions of space, although this deficit was most pronounced during reaches into crossed space. These results suggest that congenital absence of the corpus callosum is associated with deficits in the control of both the proximal and distal musculature.

The role of surface information in object recognition: studies of a visual form agnosic and normal subjects.

Three experiments were conducted to explore the role of colour and other surface properties in object recognition. The effects of manipulating the availability of surface-based information on object naming in a patient with visual form agnosia and in two age-matched control subjects were examined in experiment 1. The objects were presented under seven different viewing conditions ranging from a full view of the actual objects to line drawings of those same objects. The presence of colour and other surface properties aided the recognition of natural objects such as fruits and vegetables in both the patient and the control subjects. Experiment 2 was focused on four of the critical viewing conditions used in experiment 1 but with a large sample of normal subjects. As in experiment 1, it was found that surface properties, particularly colour, aided the naming of natural objects. The presence of colour did not facilitate the naming of manufactured objects. Experiment 3 was focused on possible ways by which colour could assist in the recognition of natural objects and it was found that object naming was facilitated only if the objects were presented in their usual colour. The results of the experiments show that colour does improve recognition for some types of objects and that the improvement occurs at a high level of visual analysis.

The nature and limits of orientation and pattern processing supporting visuomotor control in a visual form agnosic.

Abstract We have previously reported that a patient (DF) with visual form agnosia shows accurate guidance of hand and finger movements with respect to the size, orientation, and shape of the objects to which her movements are directed. Despite this, she is unable to indicate any knowledge about these object properties. In the present study, we investigated the extent to which DF is able to use visual shape or pattern to guide her hand movements. In the first experiment, we found that when presented with a stimulus aperture cut in the shape of the letter T, DF was able to guide a T-shaped form into it on about half of the trials, across a range of different stimulus orientations. On the remaining trials, her responses were almost always perpendicular to the correct Orientation. Thus, the visual information guiding the rotation of DF's hand appears to be limited to a single orientation. In other words, the visuomotor transformations mediating her hand rotation appear to be unable to combine the orientations of the stem and the top of the T, although they are sensitive to the orientation of the element(s) that comprise the T. In a second experiment, we examined her ability to use different sources of visual information to guide her hand rotation. In this experiment, DF was required to guide the leading edge of a hand-held card onto a rectangular target positioned at dHerent orientations on a flat surface. Here the orientation of her hand was determined primarily by the predominant orientation of the luminance edge elements present in the stimulus, rather than by information about orientation that was conveyed by nonluminance boundaries. Little evidence was found for an ability to use contour boundaries defined by Gestalt principles of grouping (good continuation or similarity) or "nonaccidental" image properties (colinearity) to guide her movements. We have argued elsewhere that the dorsal visual pathway from occipital to parietal cortex may underlie these preserved visuomotor skills in DF. If so, the limitations in her ability to use different kinds of "pattern" information to guide her hand rotation suggest that such information may need to be transmitted from the ventral visual stream to these parietal areas to enable the full range of prehensive acts in the intact individual.

The role of binocular vision in prehension: a kinematic analysis.

This study examined the contribution of binocular vision to the control of human prehension. Subjects reached out and grasped oblong blocks under conditions of either monocular or binocular vision. Kinematic analyses revealed that prehensile movements made under monocular viewing differed substantially from those performed under binocular conditions. In particular, grasping movements made under monocular viewing conditions showed longer movement times, lower peak velocities, proportionately longer deceleration phases, and smaller grip apertures than movements made under binocular viewing. In short, subjects appeared to be underestimating the distance of objects (and as a consequence, their size) under monocular viewing. It is argued that the differences in performance between the two viewing conditions were largely a reflection of differences in estimates of the target's size and distance obtained prior to movement onset. This study provides the first clear kinematic evidence that binocular vision (stereopsis and possibly vergence) makes a significant contribution to the accurate programming of prehensile movements in humans.