Brain Advance Access originally published online on June 23, 2005
Brain 2005 128(9):2134-2145; doi:10.1093/brain/awh573
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Deficits of motion integration and segregation in patients with unilateral extrastriate lesions
Departments of 1 Biomedical Engineering and 2 Neurology, Boston University, Departments of 3 Neurology and 4 Radiology, Harvard Medical School, Boston, MA, USA and 5 Department of Experimental Psychology, University of Oxford, Oxford, UK
Correspondence to: Prof. Lucia M. Vaina, Department of Biomedical Engineering, Boston University, 44 Cummington Street, Boston, MA 02215, USA E-mail: Vaina{at}bu.edu
Functional neuroimaging in human subjects and single cell recordings in monkeys show that several extra-striate visual areas are activated by visual motion. However, the extent to which different types of motion are processed in different regions remains unclear, although neuropsychological studies of patients with circumscribed lesions hint at regional specialization. We, therefore, studied four patients with unilateral damage to different regions of extrastriate visual cortex on a series of visual discrimination tasks that required them, to a different extent, to integrate local motion signals in order to correctly perceive the direction of global motion. Performance was assessed psychophysically and compared with that of control subjects and with the patients' performance with stimuli presented in the visual field ipsilateral to the lesion. The results indicate considerable regional specialization in extra-striate regions for different aspects of motion processing, namely the largest displacement from frame to frame (D-max) that can sustain perception of coherent motion; perception of relative speed; the amount of coherent motion needed to sustain a percept of global motion in a particular direction; the detection of discontinuities within a moving display; the extraction of form from motion. It was also clear that a defect in local motion, i.e. D-max, can be overcome by integrating local motion signals over a longer period of time. Although no patient suffered from only one defect, the overall pattern of results strongly supports the notion of regional specialization for different aspects of motion processing.
Key Words: extra-striate lesions; motion integration; motion segregation
Abbreviations: 2AMCT = two-apertures motion coherence test; CSD = constant direction; MCT = motion coherence test; MDT = motion discontinuity test; RSD = random direction
Received October 8, 2004. Revised May 6, 2005. Accepted May 8, 2005.
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