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Milena Kaestner, Ryan Maloney, Marina Bloj, Julie Harris, Alex Wade; fMRI reveals S-cone and achromatic contributions to motion-in-depth perception. Journal of Vision 2017;17(10):602. doi: https://doi.org/10.1167/17.10.602.
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Motion in depth (MID) can be perceived due to a change in disparity over time (CD) or inter-ocular velocity differences (IOVD). Both cues to MID appear to be processed in extrastriate motion areas but their precise neural substrates are unclear. We used fMRI to investigate how signals carried by the luminance and S-cone pathways contribute to CD and IOVD processing. S-cone isolating and achromatic stimuli driving CD or IOVD mechanisms, as well as monocular-motion-matched controls, were presented in an interleaved, rapid event-related fMRI design. Participants (N=10) performed an attentionally demanding task at fixation throughout all scans. The subjective S-cone isoluminance point was determined in situ prior to scanning using a minimum flicker task. Retinotopic mapping was performed on all subjects to delineate early visual areas (V1, V2 and V3). Areas V3A/B, hMT and hMST were identified in additional localiser scans based on their receptive field sizes and motion selectivity. We used a general linear model to identify the responses within regions of interest (ROI) to each stimulus type. Beta weights for each condition within each ROI were averaged across participants, revealing response profiles at a group level across visual cortex. Responses in early visual areas showed no preference for MID overall, and responses to achromatic stimuli were comparable to those for S-cone stimuli. In comparison, areas hMT and hMST showed selectivity to both types of achromatic MID stimuli. Surprisingly, we also found a selective response to S-cone IOVD in areas V3A/B, hMT and hMST, while the response to S-cone CD and controls in these areas was negligible. These findings provide novel evidence for the role of S-cone signals in MID processing. Specifically, they suggest that dichoptic S-cone motion signals may be combined in an opponent manner in these areas to provide input to an IOVD-based motion-in-depth system.
Meeting abstract presented at VSS 2017
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