title: The role of second-order motion signals in coherence and transparency.
abstract: Second-order or non-Fourier motion was originally demonstrated in the laboratory by the use of contrast-modulated stimuli of various types. As these stimuli seem somewhat artificial, it might be questioned whether they play a significant role in the processing of natural motion. An affirmative answer is provided by the key observation that the non-Fourier motion apparatus analyses the motion of texture boundaries in two-dimensional patterns. Given this, a wide range of motion phenomena can be explained by a neural model that combines both Fourier and non-Fourier motion signals in a neural network that computes the vector sum direction. The existence of a vector sum computation is supported by two observations: patterns composed of two cosine gratings ('plaids') appear to move in the vector sum direction during brief presentations and plaids composed solely of non-Fourier components always move in the vector sum direction. The neural model predicts these results and also agrees with much of area MT physiology. Within this context, many instances of motion transparency result when the angle between Fourier motion directions is large (> 90 degrees) and the non-Fourier motion signal is minimal or absent.
authors.affiliation: Visual Sciences Center, University of Chicago, Illinois 60637.
authors.forename: H R
authors.initials: HR
authors.lastname: Wilson
mesh_terms: D000818:Animals; D005583:Fourier Analysis; D006801:Humans; D008954:Models, Biological; D009039:Motion Perception / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology; D014796:Visual Perception / Q000502:physiology