Anisotropy of object nonrigidity: High-level perceptual consequences of cortical anisotropy

Abstract

This study presents instances where variations in a complex, higher-level perceptual phenomenon- an anisotropy in object non-rigidity is explained by the distribution of low-level neural properties in the primary visual cortex. Specifically, we examine the visual interpretation of two rigidly connected rotating circular rings. At speeds where observers predominantly perceive rigid rotation of the rings rotating horizontally, observers perceive only non-rigid wobbling when the image is rotated by 90°. Additionally, vertically rotating rings appear narrower and longer compared to their physically identical horizontally rotating counterparts. We show that these perceived shape changes can be decoded from V1 outputs by considering anisotropies in orientation-selective cells. We then empirically demonstrate that even when the vertically rotating ellipses are widened or the horizontally rotating ellipses are elongated so that the shapes match, the perceived difference in non-rigidity is reduced only by a small amount and increased non-rigidity persists in vertical rotations, suggesting that motion mechanisms also play a role. By incorporating cortical anisotropies into optic flow computations, we show that motion gradients for vertical rotations align more with physical non-rigidity, while horizontal rotations align closer to rigidity, indicating that cortical anisotropies contribute to the heightened perception of non-rigidity when orientation shifts from horizontal to vertical. The study underscores the importance of low-level anisotropies in shaping high-level percepts and raises questions about their evolutionary significance, particularly for shape constancy and motion perception.