The dominance of feedback mechanisms for perception in the central visual field: the flip tilt illusion by backward masking and the Feedforward-Feedback-Verify-reWeight algorithm

Abstract

The flip tilt illusion is the misperception of the orientation of the alignment between a pair of dots by 90 degrees. It occurs when the dot-pair contains one black dot and one white dot, is typically visible only in the peripheral visual field. It is predicted by the central-peripheral dichotomy (CPD) theory. Along the visual pathway from retina to downstream stages, our brain admits only a tiny fraction of visual input information for recognition due to a processing bottleneck that starts from the output of the primary visual cortex (V1) along the visual pathway. Accordingly, perception downstream from V1 relies on impoverished information, selected largely by gaze shifts to center the selected content at fovea and additionally by the capacity of the bottleneck even in the central visual field, likely making perceptual hypotheses about the visual scene ambiguous or illusory. To overcome, downstream areas send feedback to upstream areas such as V1 to query for additional information, thereby re-assessing the weights of the initial hypotheses. This perceptual algorithm is termed Feedforward-Feedback-Verify-reWeight (FFVW). To save resources, the feedback query is limited largely to the central visual field. The peripheral visual field is thus vulnerable to perceptual ambiguities and illusions. The CPD theory further predicts that impairing the feedback renders the flip tilt illusion visible in the central visual field. This paper reports a confirmation of the prediction. The feedback is disrupted by masking the visual inputs after a short viewing duration t. Furthermore, the FFVW algorithm is studied by a computational model of the perceptual data as a function of t. It reveals that the initial feedforward sweep of visual information explains the flip tilt illusion for t shorter than 20 ms, whereas the feedback mechanism dominates perception for longer t.