Decoding sound content in early visual cortex of aphantasic individuals

The retinotopic visual cortex of blindfolded and congenitally blind participants responds with decodable activity patterns to the sound of natural scenes (Vetter et al., 2014, 2020). Decoding accuracies increase from foveal to far peripheral retinotopic regions in V1 and V2, with stronger effects in the blind (V1, V2 & V3). There are direct projections from the auditory cortex to the peripheral visual cortex in non-human primates (Falchier et al., 2002) and we assume that in humans these projections are also more predominant in the periphery. In congenitally blind participants, visual feedforward processing is absent and top-down projections to the visual cortex might proliferate. In contrast, in aphantasia top-down projections might be less effective, leading to a loss of visual imagery experience. How about other forms of top-down projections? Is auditory top-down influence reduced in aphantasia? We presented auditory stimuli to 22 blindfolded aphantasic participants. We found that sound could only be decoded in foveal V3, reporting reduced decoding in V1 and V2 in aphantasics compared to controls and blind participants. When fitting a linear mixed effect model on data from the control, blind and aphantasic groups, we found a significant interaction effect between group and eccentricity and between area and eccentricity: in V1, the relative increase of decoding with eccentricity was strong only in the blind participants. The differences between groups increased in V2 and V3, with the largest differences being reported in V3, where decoding increased by eccentricity for the blind, did not change for controls, and decreased for aphantasic participants. Contrary to the enhanced feedback observed in blind participants, our findings suggest that the feedback of auditory content to the early visual cortex may be reduced in aphantasic participants. Reduced top-down projections might lead to both less decoding of sounds and reduced subjective experience of visual imagery.