Structure of visual perception.

The response properties of a class of motion detectors (Reichardt detectors) are investigated extensively here. Since the outputs of the detectors, responding to an image undergoing two-dimensional rigid translation, are dependent on both the image velocity and the image intensity distribution, they are nonuniform across the entire image, even though the object is moving rigidly as a whole. To achieve perceptual "oneness" in the rigid motion, we are led to contend that visual perception must take place in a space that is non-Euclidean in nature. We then derive the affine connection and the metric of this perceptual space. The Riemann curvature tensor is identically zero, which means that the perceptual space is intrinsically flat. A geodesic in this space is composed of points of constant image intensity gradient along a certain direction. The deviation of geodesics (which are perceptually "straight") from physically straight lines may offer an explanation to the perceptual distortion of angular relationships such as the Hering illusion.