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Liam Norman, Lore Thaler; The representation of acoustic space in the calcarine cortex of a blind human echolocator. Journal of Vision 2017;17(10):1359. doi: 10.1167/17.10.1359.
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Echolocation is the perception of objects through sound echoes. Previous work has shown that activity in calcarine cortex correlates with echo-acoustic perception of objects in an early blind expert echolocator, and that the pattern of this activity might possibly resemble retinotopic organization for vision in sighted people (Milne, Goodale & Thaler (2013) JOV, 13(9): 1334). Here we tested if we could replicate this result in another early-blind expert echolocator. During fMRI a blind expert echolocator listened to binaural recordings of clicks and click echoes reflected from objects located at one of eight positions along the horizontal meridian (i.e. 5°, 10°, 20° or 40° to the right or left). We used cross-correlation to map neural representations of these echo-acoustic positions. We applied the same method to fMRI data acquired while the echolocator listened to source-sounds, that could also be at 5°, 10°, 20° or 40° to the right or left. For echo-acoustic locations, results showed a mapping of L10°, R5°, R20° and R40° along the left calcarine sulcus, and mapping of L10° and L40° along the right calcarine sulcus, in both HS with more peripheral locations being mapped more anteriorly. For source sound locations, results showed a mapping of R20° and R40° and along the left calcarine sulcus, and mapping of L40 and R20° along the right calcarine sulcus. We were able to confirm the validity of our analysis by also mapping representation of fingers along the central sulcus (fingers were used to press response keys during fMRI). The evidence is consistent with the idea that there is a contralateral neural representation of acoustic space in calcarine cortex of this blind echo expert, and that this representation is more pronounced for echo-acoustic than source sound locations. Furthermore, this representation might possibly resemble retinotopic organization for vision in sighted people.
Meeting abstract presented at VSS 2017
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