1/14. Establishing joint visual attention and pointing in autistic children with no functional language.Joint visual attention is defined as looking where someone else is looking. The purpose of this study was to examine the conditions for establishing joint visual attention in autistic children who have no functional speech. An experimenter, sitting facing the child, looked at one of six pictures near the child. Analysis showed that joint visual attention to stimuli behind the child and therefore outside of the visual field occurred at a higher rate when the visual angle between the stimuli was about 60 degrees. Spontaneous pointing at the target object increased with training which included feedback and physical guidance. These results are discussed in terms of the effects of environmental variables and perceptual mechanisms on the emergence of joint visual attention in autistic children. The possibility of using an adult's social cues and expanding the child's visual field as a remedial procedure is also addressed.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
2/14. prosopagnosia: a case study involving problems in processing configural information.An ongoing issue in face recognition research is whether holistic face processing relies on the segregation of local discrete facial parts. Evidence in favor of the holistic-plus-parts view stems from a recent study reported by Arguin and Saumier (1999), who show that the priming effects of individual facial parts (i.e., eyes, nose, mouth, orcontour) depends on the presence of configural information and that the magnitude of priming augments as the number of facial parts serving as primes increase. The present study demonstrates that these global processing effects are absent in a prosopagnosic patient (A.R.), who shows no priming from single face parts and a linear increase in the magnitude of priming as a function of the number of parts presented. These findings indicate that A.R. is incapable of integrating individual facial parts into a global facial configuration ant that this is likely at the root of her prosopagnosia.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
3/14. Conflict and integration of spatial attention between disconnected hemispheres.OBJECTIVES: To clarify how the disconnected hemispheres perceive a line and bisect it with successful or unsuccessful integration of spatial attention. methods: eye movements were recorded when a patient with an extensive callosa infarction bisected horizontal lines. The lesion extended into the left cingulate gyrus. RESULTS: When the patient bisected lines with the right hand, the gaze was initially directed rightward and shifted further to the right side with the execution of manual response, which resulted in rightward errors. Shortly after bisection, rapid ocular searches occurred to the left side, whereas the rightward errors did not decrease throughout the trials. When using the left hand, there was no deviation of the gaze before presentation of lines. In the first few trials, the patient bisected the line with a leftward error and then searched rapidly to the right side. The subsequent bisections were almost accurate, as the subjective midpoint was placed near the point of the initial fixation that fell around the true centre. Ocular searching was mostly absent during and after line bisection. CONCLUSIONS: In callosa disconnection, left unilateral spatial neglect may appear when use of the right hand induces a rightward bias in the attentional control of the left hemisphere and damage to its cingulate gyrus inhibits interhemispheric integration of attention. Resultant rightward errors of line bisection often cause interhemispheric conflict of attention, as the right hemisphere perceives the longer extent on the left side. By contrast, the disconnected but intact right hemisphere may bisect a line accurately by integrating attention to the extents perceived in the left and right visual fields.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
4/14. So near yet so far: neglect in far or near space depends on tool use.The study of unilateral spatial neglect has shown that space can be dissociated on a peripersonal versus extrapersonal basis. We report a novel type of dissociation based on tool use in a patient suffering from left neglect. Line bisection was carried out in near and far space, using a stick and a laser pointer. A rightward bias was always found for the former, but not for the latter. Neglect thus appears to be contingent not only on distance, but also on the motor action required by the task.- - - - - - - - - - ranking = 9keywords = near (Clic here for more details about this article) |
5/14. Expectation-based attentional modulation of visual extinction in spatial neglect.Visual extinction, the failure of patients with unilateral focal brain damage to report the contralesional of two simultaneously presented stimuli, may be modulated by characteristics of the display such as similarity, collinearity, or connectedness. Since these factors affect the perceptual configuration of stimuli, the modulation of extinction is believed to reflect low-level perceptual grouping. In the present study, patient AG did not show any modulation of contralesional detection when the ipsilesional and contralesional stimulus grouped by colour, by form, or both (Experiment 1). In contrast, identification of the contralesional stimulus was facilitated when the stimuli grouped (Experiment 2), suggesting a modulation of extinction by specific task demands. Experiment 3 used a cueing procedure to demonstrate modulation of extinction by expectation biases. Prior to stimulus presentation, AG was cued to attend to a particular feature (e.g. colour). After stimulus exposure he was prompted to identify the expected feature on valid trials and the unexpected feature on invalid trials. AG showed a significant validity effect for contralesional stimuli i.e. he identified the expected feature (e.g. colour) significantly better than the unexpected feature (e.g. form). These results suggest that competition for selection between visual stimuli may not only be influenced by perceptual characteristics of the display, but also by high-level factors such as the response criterion or expectation biases.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
6/14. Multiple reference frames in neglect? An investigation of the object-centred frame and the dissociation between "near" and "far" from the body by use of a mirror.In this single case study of a man (AE) who suffered a right hemisphere stroke we showed the co-existence of neglect within different spatial frames: (a) In left hemispace and (b) in 'far' versus 'near' space, both as defined from the patient's viewpoint, as well as (c) for the left side of an object (as defined from an object-centred view). In the experiment, AE's latencies to name the colour of two cubes, each located in one hemispace, were measured. In some conditions, the cubes were placed on a table but in other conditions each cube was held in one hand of an experimenter who could either face the patient or show the cubes while her back was turned towards him. One prediction was that AE would show longer latencies for cubes in left hemispace; however, if object-centred neglect also occurred, then latencies should be even longer for cubes held in the experimenter's left hand. In order to reveal the presence of neglect for 'far' versus 'near' space, the cubes could also be positioned either near to (i.e. reaching distance) or far from the patient (i.e., several metres out of reach), by moving the table or the experimenter. Finally, in some conditions, AE looked at the cubes into a mirror that was positioned far away from his body. Because external objects seen in a mirror can be 'near' the patient's body, the patient actually looked at a 'far' location (i.e. the surface of the mirror) to see an object that is 'near'. The experiment confirmed the presence of all forms of neglect, since AE not only named the colour of a cube seen in his left hemispace more slowly than in right hemispace, but latencies increased for a cube held by the experimenter in her left hand and in left hemispace (both when the left hand was seen directly or as a mirror reflection). Finally, AE's performance was worse for 'far' than 'near' locations, when the cubes were physically located near his body (i.e., within "grasping" space) but seen in the mirror.- - - - - - - - - - ranking = 11keywords = near (Clic here for more details about this article) |
7/14. Pure imagery hemi-neglect of far space.patients with hemispatial neglect restricted to near (within reaching distance) or to far space (beyond reaching distance) have been described. This constitutes a double-dissociation considered by current neurocognitive thinking as compelling evidence for separate networks. However, a similar double-dissociation exists with respect to perceived as opposed to imagined space. If the organization of represented space was similar to that of perceived space, it should contain a far/near dissociation as well. This paper describes a patient with pure representational neglect restricted to far space.- - - - - - - - - - ranking = 2keywords = near (Clic here for more details about this article) |
8/14. acceleration perception and spatial distortion in a left unilateral neglect patient.To explain relative leftward overextension in a line extension task by left unilateral neglect subjects, Bisiach et al. (1998) suggested that the representation of space is distorted--i.e., dilated towards the left side. If perception of the velocity of a moving stimulus is due to a calculation of the distance covered per unit time in representational space, then a stimulus with uniform linear motion should be perceived as decelerating when moving leftwards in the visual field of a subject with left unilateral neglect. We investigated the perception of acceleration in a patient with left unilateral neglect and spatial distortion (revealed as relative left overextension in a line extension task) using a task in which the stimuli were right and left moving targets with variable acceleration. The patient's ability to perceive acceleration was much lower (higher acceleration threshold) for leftward movements than rightward movements. Fourteen months later unilateral neglect had improved, and the relative left overextension and decreasing acceleration threshold for leftward movements were reduced. By contrast, alterations in the perception of acceleration for leftward movements were not found in a patient with left unilateral neglect and left underextension and in a patient with right brain damage and left hemianopia. These findings in one patient with left spatial unilateral neglect and a relative left overextension in a line extension task are consistent with the hypothesis that representational space is distorted, with a disproportionate leftward expansion, that affects perception of movement.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
9/14. Clinical application of the multifocal visual evoked potential.BACKGROUND: Measures of visual function thresholds such as visual acuity and visual fields are generally dependent on subjective responses and assume maintenance of fixation, attention and motivation. In the young, elderly, cognitively impaired or malingering populations, such measures may be inaccurate or difficult to obtain. The Visual Evoked Response Imaging System (VERIS) has been claimed to give more objective topographic recordings of retinal and cortical function. This paper aims to explore the adequacy of this technique in four unusual, unrelated, clinically difficult cases. methods: Multifocal visual evoked potentials (mfVEPs) recorded on the VERIS System 3.01 are used to assess visual function in four cases with contradictory clinical findings or unreliable subjective responses. RESULTS: Patient 1 had sustained a head injury and had normal ocular and pupil examination but light perception in the right eye and 6/5 acuity in the left. Multifocal VEPs showed a marked depression of the right visual field with little macular response. Patient 2 had sustained a head injury, had a left field hemianopia, possible macular sparing and loss of much of the right field, reduced but variable visual acuities, good near vision and normal ocular fundi. Multifocal VEPs showed a severe depression in both visual fields (L more than R) with little macular response. Patient 3 had a left optic nerve meningioma and experienced great difficulty with visual field assessment. mfVEPs showed a bilateral depression in the superior field particularly the left field, with a larger deficit in the left eye. Patient 4 had unexplained visual acuity and peripheral field deficits. mfVEP results were inconclusive in this case. DISCUSSION: Where there is difficulty performing traditional techniques or conflicting clinical findings, mfVEPs may provide additional objective information to aid in the assessment of patients.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
10/14. The space of senses: impaired crossmodal interactions in a patient with Balint syndrome after bilateral parietal damage.Balint syndrome after bilateral parietal damage involves a severe disturbance of space representation including impaired oculomotor behaviour, optic ataxia, and simultanagnosia. Binding of object features into a unique spatial representation can also be impaired. We report a patient with bilateral parietal lesions and Balint syndrome, showing severe spatial deficits in several visual tasks predominantly affecting the left hemispace. In particular, we tested whether a loss of spatial representation would affect crossmodal interactions between simultaneous visual and tactile events occurring at the same versus different locations. A tactile discrimination task, where spatially congruent or incongruent visual cues were delivered near the patient's hands, was used. Following stimulation of the left hand in the left side of space, we observed visuo-tactile interactions that were not modulated by spatially congruent conditions. In contrast, performance following stimulation of the right hand in the right side of space was affected in a spatially selective manner--facilitated for congruent stimuli and slowed for incongruent stimuli. To dissociate effects on somatotopic and spatiotopic coordinates, we crossed the patient's hands during unimodal tactile discriminations. Tactile performance of the left hand improved when it was positioned in the right hemispace, whereas placing the right hand in left space produced no significant changes, suggesting that left-sided tactile inputs are coded with respect to a combination of limb- and trunk-centred coordinates. These data converge with recent findings in animals and healthy humans to indicate a critical role of the posterior parietal cortex in multimodal spatial integration, and in the fusion of different coordinates into a unified representation of space.- - - - - - - - - - ranking = 1keywords = near (Clic here for more details about this article) |
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