Neural correlates of contextually modulated depth perception

Abstract

The neural mechanisms underlying the perception of depth from disparity information are not well understood. In previous work (Wong & Chang, 2018 JOV 18(1): 994), we have shown that behavioural sensitivities to depth position are affected by object context, defined in terms of the conformity of the stimulus with natural physical laws (i.e., physically plausible versus implausible geometric shapes).Here, we asked how the plausibility of complex 3D objects affects neural responses to disparity information. Stimuli were disparity-defined geometric objects rendered as random dot stereograms (RDS), presented in plausible and implausible variations (e.g. a normal versus a physically implausible Penrose triangle). Observers were asked to complete a signal-in-noise task (SNR task), judging whether the object was in front or behind of a reference plane, while BOLD responses were measured using fMRI (3T, 2 mm3 iso voxels). Task difficulty was manipulated adaptively via the QUEST staircase procedure, varying the percentage of signal dots that defined the target. Comparisons of the multivariate fMRI response patterns indicated that contextual modulations of depth sensitivity are reflected in both dorsal and ventral areas. Specifically, areas V3a, V7 and LO can distinguish between response patterns of plausible and implausible triangles. In subsequent functional connectivity analyses (Granger causality), we observed context-driven (plausibility-based) modulations of connections along the dorsal and ventral stream for the implausible triangle only, signalled by stronger feedforward connections from V3a to higher-order dorsal areas as compared to the ventral areas. Our data suggest substantial modulation of disparity responses along cortex based on object context, indicating an intrinsic relationship between object perception and depth-related mechanisms.