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Zixin Yong, Po-Jang Hsieh, Dan Milea; Seeing sounds after visual loss: a case study of the neural correlates of acquired auditory-visual synesthesia. Journal of Vision 2017;17(10):1363. doi: 10.1167/17.10.1363.
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In a small proportion of patients who suffered from visual loss, certain auditory stimulation automatically triggers visual experience. These acquired auditory-visual synesthesia (AVS) cases are under-reported and the underlying mechanism remains elusive. In this study, we used fMRI to explore brain regions that correlated with sound-induced visual experience in an acquired AVS case, where the patient started to experience phosphenes triggered by unexpected sound after unilateral visual loss due to optic neuropathy. During the fMRI session, 1-s pure tones at various pitches were presented to the patient, who was asked to report occurrence of sound-induced phosphenes by pressing one of two buttons for yes/no response. The brain activation during phosphene-experienced trials was contrasted with non-phosphene trials. Bilateral primary and secondary visual cortex activations were observed, in addition to response-related motor area activation. To control for attention and motor-related brain activations, one healthy participant underwent a similar fMRI protocol. The participant was made to believe that light would be flashed in certain trials together with the 1-s pure tone (no flash was actually presented), and was required to guess by pressing the buttons while his eyes remained closed. In this case, only motor area activation was observed by contrasting the yes/no trials. Our results demonstrate that sound-induced visual experience in acquired AVS was correlated with bilateral primary and secondary visual cortex activation. The activation possibly occurs because of existing auditory-visual connections being unmasked after visual deafferentation.
Meeting abstract presented at VSS 2017
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