title: Direction opponency, not quadrature, is key to the 1/4 cycle preference for apparent motion in the motion energy model.
abstract: Sensitivity to visual motion is a fundamental property of neurons in the visual cortex and has received wide attention in terms of mathematical models. A key feature of many popular models for cortical motion sensors is the use of pairs of functions that are related by a 90 degrees phase shift. This phase relationship, known as quadrature, is the hallmark of the motion energy model and played an important role in the development of a class of model dubbed elaborated Reichardt detectors. For decades, the literature has supported a link between quadrature and the observation that motion detectors and human observers often prefer a 1/4 cycle displacement of an apparent motion stimulus that consists of a pair of sinusoidal gratings. We show that there is essentially no link between quadrature and this preference. Quadrature is neither necessary nor sufficient for a motion sensor to prefer 1/4 cycle displacement, and motion energy is not maximized for a 1/4 cycle step. Other properties of motion sensors are the key: the opponent subtraction of two oppositely tuned stages that individually have sinusoidal displacement tuning curves. Thus, psychophysical and neurophysiological data revealing a preference at or near 1/4 cycle displacement do not offer specific support for common quadrature or energy-based motion models. Instead, they point to a broader class of model.
authors.affiliation: Neuroinformatics and Computational Neuroscience Doctoral Training Centre, Institute for Adaptive and Neural Computation, School of Informatics, University of Edinburgh, Edinburgh EH8 9AB, United Kingdom. n.m.o.heess@sms.ed.ac.uk
authors.forename: Nicolas
authors.initials: N
authors.lastname: Heess
authors.forename: Wyeth
authors.initials: W
authors.lastname: Bair
mesh_terms: D001288:Attention / Q000502:physiology; D004735:Energy Transfer / Q000502:physiology; D008954:Models, Biological; D009039:Motion Perception / Q000502:physiology; D010775:Photic Stimulation / Q000379:methods*; D014793:Visual Cortex / Q000502:physiology