The dimensionality of texture-defined motion: a single channel theory

Abstract

We examine apparent motion carried by textural properties. The texture stimuli consist of a sequence of grating patches of various spatial frequencies and amplitudes. Phases are randomized between frames to insure that first-order motion mechanisms direct@ applied to stimulus luminance are not systematically engaged. We use ambiguous apparent motion displays in which a heterogeneous motion path defined by alternating patches of texture s (standard) and texture v (variable) competes with a homogeneous motion path defined solely by patches of texture s. Our results support a one-dimensional (single-channel) model of motion-from-texture in which motion strength is computed from a single spatial transformation of the stimulus--an ucfiuity transformation. The value assigned to a point in space-time by this activity transformation is directly proportional to the modulation amplitude of the local texture and inversely proportional to local spatial frequency (within the range of spatial frequencies examined). The activity transformation is modeled as the rectified output of a low-pass spatial filter applied to stimulus contrast. Our data further suggest that the strength of texture-defined motion between a patch of texture s and a patch of texture v is proportional to the product of the activities of s and v. A strongly counterintuitive prediction of this model borne out in our data is that motion between patches of different texture can be stronger than motion between patches of similar texture (e.g. motion between patches of a low contrast, low frequency texture 1 and patches of high contrast, high frequency texture h can be stronger than motion between patches of similar texture h). Second-order motion Motion metamers Motion energy Motion correspondence INTRODUCTION First -order motion extractionDrifting spatiotemporal modulations of various sorts of optical stuff (such as luminance, contrast, texture, binocular disparity, etc.) can induce vivid motion percepts; in each case "something" appears to move from one place to another. This introspective description, however, does not necessarily reflect the underlying processes in human visual motion processing.The study of visual motion extraction mechanisms has traditionally focused on rigidly moving objects, projecting drifting modulations of luminance. Several physiologically plausible computational models have been proposed to extract motion information from drifting luminance modulations. Examples are the gradient detector (see Moulden & Begg, 1986) and the Reichardt or correlator detector (see Reichardt, 1961). These detectors are designed to detect drifting luminance modulations (or their linear transformations) and are therefore called Jirst-order motion extraction mechanisms (Cavanagh & Mather, 1989) Psychophysical experiments (e.g. van Santen & Sperling, 1984; Werkhoven, Snippe dz Koenderink, 1990b) have shown that motion perception of drifting modulations of luminance is well explained by a first-order computation called motion energy extraction. Indeed, most...

The duration of 3-D form analysis in transformational apparent motion

“…Several authors have argued that second-order motion processing requires a stage of texture extraction Stoner & Albright, 1993;Werkhoven, Sperling, & Chubb, 1993). This stage of texture extraction (presumably carried out in V2, V3, and/or V4; compare Smith, Greenlee, Singh, Kraemer, & Hennig, 1998) may correspond to the stage of form analysis that we argue must precede the assignment of motion paths in TAM.…”

Second-order reversed phi

“…In Figure 6b, the spatial frequency of the texture of the remaining rectangles alternately increases and decreases (relative to the background) in successive frames. In second-order motion, decreasing spatial frequency is equivalent to increasing texture contrast (Werkhoven, Sperling, & Chubb, 1993, 1994, so these stimuli, too, become reversed-phi stimuli for the second-order system. Second-order flicker stimulus.…”

Gaze-Contingent Multiresolutional Displays: An Integrative Review

“…This may involve both texture and motion perception, and therefore studies on 'texture-defined motion' (e.g., Werkhoven, Sperling, & Chubb, 1993) may be informative for developers of live video or animated GCMRDs .…”