fMRI investigation of the central-peripheral difference along the human cortical visual pathway for depth perception of correlated and anti-correlated random-dot stereograms

In a random-dot stereogram (RDS), the percept of object surfaces in a three-dimensional scene is generated by images presented to the left and right eyes that comprise interocularly corresponding random black and white dots. The spatial disparities between the corresponding dots determine the depths of object surfaces. If the dots are anti-correlated, such that a black dot in one monocular image corresponds to a white dot in the other, disparity tuned neurons in the primary visual cortex (V1) respond as if their preferred disparities become non-preferred and vice versa, thereby reversing the disparity signs reported to higher visual areas. In central vision fields, humans have great difficulty perceiving the reversed, or any, depth in an anticorrelated RDS. Zhaoping & Ackermann (2018) showed that in peripheral vision, the reversed depth can be perceived, confirming a prediction (Zhaoping 2017) that feedback from higher visual areas to V1, for analysis-by-synthesis to aid recognition, is weaker or absent peripherally for vetoing the feedforward ``fake-news" in anticorrelated RDSs which violate internal knowledges about the visual world. In this study, we use fMRI to measure brain responses to such stereograms across the visual hierarchy to examine the neural correlates of the central-peripheral dichotomy in visual inference