Stuart Anstis

Bio: Stuart Anstis is an academic researcher from University of California, San Diego. The author has contributed to research in topics: Illusion & Motion perception. The author has an hindex of 46, co-authored 188 publications receiving 7707 citations. Previous affiliations of Stuart Anstis include Keele University & University of Bristol.

The perception of apparent movement.

Abstract: When two similar pictures, overlapping but slightly displaced, were projected on a screen in alternation, apparent movement could be seen. How similar must successive pictures be to give apparent movement? This is the 'correspondence problem'. Manipulations of the local and global correspondences between pictures included motion phenomena such as reversed apparent movement; a four-stroke oscillatory cycle which gave an illusion of continuous motion in one direction; edges defined by texture, stereoscopic depth, or flicker, kinetic edges; and wave motion. It was concluded that human motion perception may comprise two separate mechanisms. Local point-by-point correlations between pictures are detected by a relatively peripheral system, probably based on directionally selective neural units. More subtle global correspondences are analysed by a more cognitive system which extracts edges before it processes motion.

The motion aftereffect: A modern perspective.

Abstract: Motion perception lies at the heart of the scientific study of vision. The motion aftereffect (MAE), probably the best known phenomenon in the study of visual illusions, is the appearance of directional movement in a stationary object or scene after the viewer has been exposed to visual motion in the opposite direction. For example, after one has looked at a waterfall for a period of time, the scene beside the waterfall may appear to move upward when ones gaze is transferred to it. Although the phenomenon seems simple, research has revealed surprising complexities in the underlying mechanisms, and offered general lessons about how the brain processes visual information. In the last decade alone, more than 200 papers have been published on MAE, largely inspired by improved techniques for examining brain electrophysiology and by emerging new theories of motion perception. The contributors to this volume are all active researchers who have helped to shape the modern conception of MAE. Contributors: David Alais, Stuart Anstis, Patrick Cavanagh, Jody Culham, John Harris, Michelle Kwas, Timothy Ledgeway, George Mather, Bernard Moulden, Michael Niedeggen, Shin'ya Nishida, Allan Pantle, Robert Patterson, Jane Raymond, Michael Swanston, Peter Thompson, Frans Verstraten, Michael von Grunau, Nicolas Wade, Eugene Wist.

Spatiotemporal energy models for the perception of motion

Abstract: A motion sequence may be represented as a single pattern in x–y–t space; a velocity of motion corresponds to a three-dimensional orientation in this space. Motion sinformation can be extracted by a system that responds to the oriented spatiotemporal energy. We discuss a class of models for human motion mechanisms in which the first stage consists of linear filters that are oriented in space-time and tuned in spatial frequency. The outputs of quadrature pairs of such filters are squared and summed to give a measure of motion energy. These responses are then fed into an opponent stage. Energy models can be built from elements that are consistent with known physiology and psychophysics, and they permit a qualitative understanding of a variety of motion phenomena.

Segregation of form, color, movement, and depth: anatomy, physiology, and perception

Abstract: Anatomical and physiological observations in monkeys indicate that the primate visual system consists of several separate and independent subdivisions that analyze different aspects of the same retinal image: cells in cortical visual areas 1 and 2 and higher visual areas are segregated into three interdigitating subdivisions that differ in their selectivity for color, stereopsis, movement, and orientation. The pathways selective for form and color seem to be derived mainly from the parvocellular geniculate subdivisions, the depth- and movement-selective components from the magnocellular. At lower levels, in the retina and in the geniculate, cells in these two subdivisions differ in their color selectivity, contrast sensitivity, temporal properties, and spatial resolution. These major differences in the properties of cells at lower levels in each of the subdivisions led to the prediction that different visual functions, such as color, depth, movement, and form perception, should exhibit corresponding differences. Human perceptual experiments are remarkably consistent with these predictions. Moreover, perceptual experiments can be designed to ask which subdivisions of the system are responsible for particular visual abilities, such as figure/ground discrimination or perception of depth from perspective or relative movement--functions that might be difficult to deduce from single-cell response properties.

What we can do and what we cannot do with fMRI

Abstract: Functional magnetic resonance imaging (fMRI) is currently the mainstay of neuroimaging in cognitive neuroscience. Advances in scanner technology, image acquisition protocols, experimental design, and analysis methods promise to push forward fMRI from mere cartography to the true study of brain organization. However, fundamental questions concerning the interpretation of fMRI data abound, as the conclusions drawn often ignore the actual limitations of the methodology. Here I give an overview of the current state of fMRI, and draw on neuroimaging and physiological data to present the current understanding of the haemodynamic signals and the constraints they impose on neuroimaging data interpretation.