Stereo and motion information are not independently processed by the visual system

Abstract

Many visual tasks are carried out by using multiple sources of sensory information to estimate environmental properties. In this paper, we present a model for how the visual system combines disparity and velocity information. We propose that, in a first stage of processing, the best possible estimate of the affine structure is obtained by computing a composite score from the disparity and velocity signals. In a second stage, a maximum likelihood Euclidean interpretation is assigned to the recovered affine structure. In two experiments, we show that human performance is consistent with the predictions of our model. The present results are also discussed in the framework of another theoretical approach of the depth cue combination process termed Modified Weak Fusion.

Matching perceived depth from disparity and from velocity: Modeling and psychophysics

“…In the present investigation, we showed that a disparity-only stimulus elicits the same amount of depth as a velocity-only stimulus when they both provide the same signal-to-noise ratio, regardless of the distal depth magnitudes that have generated the two images. Such empirical results are consistent with the hypothesis that the apparent depth of a stimulus is determined by the magnitude of the retinal signals relative to the uncertainty (i.e., internal noise) arising from the measurement of those signals (Domini & Caudek, 2009;Domini et al, 2006). …”

“…In the present experiment, in fact, the fixation distance is either 0.5 or 1.0 m, and the visual angle subtended by the stimulus is very small. In these conditions, the horizontal disparities are negligible and, according to our model, they will not affect the perceptual solution recovered from the velocity signals (e.g., Domini et al, 2006). Most importantly, even if binocular vision of the velocity-only stimuli did produce a decrease of the perceived depth extent, such effect could not explain the results obtained in the depth-matching task.…”

“…We chose binocular viewing for the motion stimuli so as to have the same extra-retinal signals for both disparity-only and velocity-only stimuli. According to our hypothesis, in fact, both retinal velocities and binocular disparities are modulated in the same fashion by the extra-retinal signals (Domini & Caudek, 2009;Domini et al, 2006;Tassinari et al, 2008). If the motion stimuli had been seen monocularly, then no vergence angle information would have been provided to scale the optic flow information.…”

“…We provided evidence that this is achieved by a probabilistic process which assigns the most likely 3D interpretation to (ambiguous) local first-order properties of the optic flow. As a consequence, the perceptual interpretation of velocity information is, in general, neither veridical nor internally consistent Caudek & Proffitt, 1993;Caudek & Rubin, 2001;Di Luca, Domini, & Caudek, 2004Domini & Braunstein, 1998;Domini & Caudek, 1999, 2003a, 2003bDomini, Caudek, & Proffitt, 1997;Domini, Caudek, & Richman, 1998;Domini, Caudek, & Skirko, 2003;Domini, Caudek, & Tassinari, 2006;Domini, Caudek, Turner, & Favretto, 1998;Domini, Vuong, & Caudek, 2002;Tassinari, Domini, & Caudek, 2008).…”

“…(4), respectively. Recently, we have advanced a different proposal, according to which the apparent depth of a stimulus is determined by the magnitude of motion and/or disparity differences in a display relative to the uncertainty (i.e., internal noise) arising from the measurement of those signals (Domini et al, 2006;Tassinari et al, 2008). Our proposal is formulated in terms of a normative model of depth-cue integration (the intrinsic constraint model), but it can also be applied to depth recovery from single cues and to depth-matching tasks.…”