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Dorita H F Chang, Carmel Mevorach, Zoe Kourtzi, Andrew E Welchman; Learning reorganizes the cortical circuits involved in depth perception: evidence from human TMS. Journal of Vision 2012;12(9):1201. doi: 10.1167/12.9.1201.
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© ARVO (1962-2015); The Authors (2016-present)
Judging the position of objects embedded in noise (coarse task), or fine differences in the depth position between objects (fine task) is thought to rely on dorsal and ventral processing, respectively. However, neurophysiological studies suggest that training on fine depth discriminations alters the processing of coarse depth in dorsal brain areas (Chowdhury & DeAngelis, doi: 10.1016/j.neuron.2008.08.023). Here we use online repetitive transcranial magnetic stimulation (rTMS) to test whether training reorganizes depth processing in the human brain. In particular, we ask whether parietal cortex is critical for judging depth position in noise before but not after training on a fine depth discrimination task. We tested observers’ (n =12) ability to judge whether a central plane was in front or behind the surround before and after training on the fine task. Task difficulty was manipulated by altering signal-to-noise ratio (coarse task) or the disparity difference between the center and surround (fine task) using the QUEST staircase procedure. rTMS (5 pulses at 10Hz; 60% intensity) was applied over the left (P3) or right (P4) posterior parietal cortex (PPC) as well as a control site (Cz). Stimulation sites were tested on separate days (counterbalanced for order across participants) during pre- and post-training tests of the coarse task. Before training, performance on the coarse task was significantly worse during P3 stimulation compared to other sites, suggesting critical involvement of left parietal cortex in coarse depth judgments. In contrast, after training performance on the coarse task did not differ among stimulation sites, suggesting that training reduces the involvement of parietal cortex in coarse depth judgments. These findings suggest that learning reshapes the cortical network engaged in depth perception. In particular, training on fine judgments may enhance the representation of target features that in turn facilitate target detection from noise in the context of a coarse task.
Meeting abstract presented at VSS 2012
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