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Samantha Strong, Edward Silson, Andr� Gouws, Antony Morland, Declan McKeefry; Dissociable processing of radial motion direction and focus of expansion in human cortical areas V3A and V5/MT+. Journal of Vision 2016;16(12):890. doi: 10.1167/16.12.890.
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Neuropsychological studies (Beardsley and Vaina, 2005) have shown that patients with damage to V5/MT+ are unable to identify the direction of radially moving stimuli, but maintain their ability to identify the focus of the expansion (FOE). This suggests that FOE position is signalled by neural activity outside V5/MT+ and another motion area, V3A, has been identified as a possible cortical locus for this analysis (Koyama et al., 2005). The purpose of this study was to investigate the roles played by V5/MT+ and V3A in the perception of radial motion stimuli. We tested the hypothesis that human V5/MT+ (or more specifically its anterior sub-division, TO-2) is important for the perception of the direction of radial motion, whilst V3A, is crucial for FOE analysis. To this end we used repetitive Transcranial Magnetic Stimulation (TMS) to transiently disrupt areas TO-2 and V3A whilst participants performed psychophysical tasks involving the detection of changes in direction and changes in the position of the FOE of radial motion stimuli. Locations of all cortical areas were identified in preliminary fMRI experiments and TMS was delivered to these experimental areas (TO-1, TO-2, V3A) as well as a control site (LO-1) in participants whilst they performed the tasks (n=6). The results showed that application of TMS to area V3A disrupts performance on the FOE task, but not the direction discrimination task, whilst TMS to TO-2 generates the reverse effects. This double dissociation demonstrates that for radial motion stimuli, area V3A is necessary for analysis of the FOE, but not direction discrimination, whilst TO-2 is responsible for processing radial directions, but not the FOE.
Meeting abstract presented at VSS 2016
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