Recent neuroimaging and neuropsychological studies have suggested that the right hemisphere, particularly frontal regions, is important for the perception of the passage of time. We examined the ability to estimate durations of up to 60 sec in a group of eight patients with unilateral neglect. When estimating multisecond intervals, neglect patients grossly underestimated all durations. On average, healthy controls (HC) demonstrated reasonably accurate estimates of all durations tested. Although the right hemisphere lesioned control patients without neglect also tended to underestimate durations, these underestimations were significantly better than the performance of the neglect group. These findings suggest a pivotal role for a right hemisphere fronto-parietal network in the accurate perception of multisecond durations. Furthermore, these findings add to a growing body of literature suggesting that neglect cannot be understood simply in terms of a bias in orienting attention to one side of space. Additional deficits of the kind demonstrated here are likely to be crucial in determining the nature and extent of the loss of conscious awareness for contralesional events.
Neurophysiology and neuroimaging research implicates distinct regions of posterior parietal cortex for reaching versus grasping and for completing these movements in central versus peripheral space. Typically, visuomotor tasks only examine movements made in the frontoparallel plane. We examined a patient with a right superior parietal lesion encompassing the parietal-occipital junction, the intraparietal sulcus and the putative human homologue of V6A on pointing tasks in the sagittal or frontoparallel planes. The patient did not demonstrate a speed-accuracy trade-off, but did show larger times post-peak velocity for all movement directions. Her movements in the sagittal axis were more disordered than movements in the frontoparallel plane. These data indicate a role for superior parietal cortex in fine tuning of visually guided movements and more particularly for movements made back towards the body.
Information processing is more effective within attended regions of the visual field and the size of the attended region is variable. This observation conflicts with the assumption, used in measuring the spatial extent of global integration of coherent local orientations, that optimal sensitivity to texture information is immediately available within an appropriately sized neuronal receptive field. Using extended patterns that require global processing to detect the presence of coherent orientation structure, we found that the size and topology of the region of integration of local visual cues is not fixed. Integration can occur out to a radius of at least 10 degrees, an area (314 square degrees) much larger than previously supposed, and can be constrained to annular in addition to circular apertures. The use of such spatial apertures was found to be mediated by observer expectation. The processing of texture information available in selected areas is optimized through the exclusion of noise outside the regions of interest.
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