Abstract
INTRODUCTION: Previous studies have shown that hMT+, well-known for its non-separable spatiotemporal selectivity for visual motion in sighted individuals, responds to auditory motion following early blindness. However, it is not yet known how this recruitment of hMT+ alters auditory motion processing in early blind individuals. METHODS: A psychophysical reverse correlation paradigm was used to estimate the auditory motion filters in 8 sighted and 8 early blind participants. Participants discriminated the direction of signal motion (left/right; 62.5 °/s). The signal was embedded in broadband noise bursts sampled over a 10x10 grid in space (-/+30 °) and time (0-800 ms). Staircases were used to adjust the signal amplitude. We measured the amplitude thresholds for discriminating the signal and estimated the auditory motion filters by characterizing the influence of spatiotemporal noise on performance. RESULTS: In sighted individuals, in contrast to visual motion, auditory motion discrimination was based on separable filters with broad spatial tuning to opposite hemifields. In early blind individuals, auditory motion discrimination similarly relied on separable filters tuned to opposite hemifields – the recruitment of hMT+ did not result in a qualitative shift in auditory motion processing towards non-separable spatiotemporal tuning. Early blind individuals did show significantly lower amplitude thresholds, with filters that were better tuned to signal onsets/offsets. An ideal observer model assuming broad spatial tuning and separable onset/offset filters predicted better performance than the one based on a non-separable spatiotemporal filter, suggesting that early blind individuals were performing close to optimally, given the poor spatial resolution of auditory input. CONCLUSIONS: The computations underlying auditory motion processing in early blind individuals are not qualitatively altered; instead, the recruitment of hMT+ to extract auditory motion involves significant modification of its normal computational operations to make optimal use of the novel auditory input.