Human Factors and Behavioral Science: Textons, The Fundamental Elements in Preattentive Vision and Perception of Textures

Abstract

Recent research in texture discrimination has revealed the existence of a separate “preattentive visual system” that cannot process complex forms, yet can, almost instantaneously, without effort or scrutiny, detect differences in a few local conspicuous features, regardless of where they occur. These features, called “textons”, are elongated blobs (e.g., rectangles, ellipses, or line segments) with specific properties, including color, angular orientation, width, length, binocular and movement disparity, and flicker rate. The ends-of-lines (terminators) and crossings of line segments are also textons. Only differences in the textons or in their density (or number) can be preattentively detected while the positional relationship between neighboring textons passes unnoticed. This kind of positional information is the essence of form perception, and can be extracted only by a time-consuming and spatially restricted process that we call “focal attention”. The aperture of focal attention can be very narrow, even restricted to a minute portion of the fovea, and shifting its locus requires about 50 ms. Thus preattentive vision serves as an “early warning system” by pointing out those loci of texton differences that should be attended to. According to this theory, at any given instant the visual information intake is relatively modest.