Temporal integration in structure from motion.

Abstract

A temporal integration model is proposed that predicts the results reported in 4 psychophysical experiments. The main findings were (a) the initial part of a structure-from-motion (SFM) sequence influences the orientation evoked by the final part of that sequence (an effect lasting for more than 1 s), and (b) for oscillating SFM sequences, perceived slant is affected by the oscillation frequency and by the sign of the final gradient. For contracting optic flows (i.e., rotations away from the image plane), the sequence with the lowest oscillation frequency appeared more slanted; for expanding optic flows (i.e., rotations toward the image plane), the sequence with the highest oscillation frequency appeared more slanted.The continuous change in the retinal projections produced by the relative motion between an observer and the environment is a very important source of information for the 3-D structure of the world. A way to characterize the dynamic properties of retinal projections is to describe them in terms of a pattern of moving features. We refer to this pattern as the optic flow (Gibson, 1950). Several investigations have revealed that perceptual analysis of the optic flow is not instantaneous but, rather, is performed over an extensive temporal window. Treue, Husain, and Andersen (1991) asked observers to discriminate between structured (cylinder) and unstructured (noise) random-dot displays with a limited dot lifetime. They found that performance improved over several dot lifetimes, thus indicating that some form of temporal integration occurs for the detection of a 3-D surface from the optic flow. In particular, they found a relatively constant point lifetime threshold (50 -85 ms) for perceiving structure from motion (SFM) and long reaction times for detecting the structure (approximately 1 s).Atchley, Andersen, and Wuestefeld (1998) showed observers optic-flow displays with an increasing (the displays began with few dots, and the number of dots increased as time went by) or decreasing (the number of dots decreased as time went by) texture density. Observers had to report when a 3-D surface was perceived (increasing condition) or when the surface disappeared (decreasing condition). A hysteresis effect was found: Detection thresholds were lower for the decreasing texture condition. These previous experiments indicate that the recovery of a 3-D surface from the optic flow builds up in time, thus revealing that human SFM is the product of a form of short-term temporal integration: A

Temporal integration of motion and stereo cues to depth

“…This finding is apparently inconsistent with the results of Domini et al (2002), which clearly indicate that perceived 3-D orientation specified by motion information is the result of a process of temporal integration. This apparent inconsistency, however, can be easily explained by noting that two velocity gradients presented in the same spatial location can, in principle, be produced by the same 3-D surface orientation, as the consequence of the acceleration or deceleration of the surface.…”

“…According to this hypothesis, observers should perceive a larger slant when a given velocity gradient follows a large disparity gradient than when it follows a small disparity gradient. We propose, in fact, that perceived 3-D surface orientation builds up in time, by taking into account the orientation perceived in the previous moment of time (Domini et al, 2002). Alternatively, no integration of stereo and motion information occurs over time.…”

“…In one of their experiments, Domini et al presented in succession two opticflow fields in the same spatial location, and observers were asked to judge, at the end of the stimulus sequence, the orientation of the perceived 3-D surface. Domini et al (2002) found an effect of long-term temporal integration for the perceptual interpretation of the optic flow: The 3-D orientation perceived at the end of the stimulus sequence was strongly affected by the properties of the first of the two optic flow fields that had been presented in succession. Such temporal effects were found to last for over 1,200 msec. In the present investigation, our intention was to extend those findings by studying the interactions of different depth cues over time.…”

“…In the present study, the temporal interactions among different depth cues were not investigated by means of an adaptation procedure (as in the experiments described above), but rather, by using a method previously employed by Domini et al (2002). In one of their experiments, Domini et al presented in succession two opticflow fields in the same spatial location, and observers were asked to judge, at the end of the stimulus sequence, the orientation of the perceived 3-D surface.…”

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

“…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).…”