Stereoscopic perception with brief exposures

Abstract

In this report we describe the results of an experiment in which we demonstrated that a powerful and compelling stereoscopic experience is elicited with very brief (< 1 msec) stimulus durations. The observers were highly successful in recognizing briefly flashed, stereoscopic, random-dot surfaces in the absence of monocular contours. The results are shown to be closely related to the range of depths for any stimulus form; however, the recognition thresholds were nonmonotonic as a function of disparity. Previous investigators have disagreed about the existence of a temporal threshold for stereopsis. We believe that prior findings suggesting that stereopsis cannot occur at short exposure durations are probably due to inadequate control of fixation disparity. Therefore, there is poor dichoptic image registration when a stereoscopic stimulus is presented. The present results also raise difficulties for any theory of stereopsis that requires eye movements.How long must a stimulus last for stereoscopic perception to occur when there are no monocular cues? There is some dispute over this question in the literature. Lehmkuhle and Fox (1980), who studied the effect of stereoscopic depth on metacontrast masking (produced by random-dot stereograms), demonstrated perceived depths at stimulus durations as low as 50 msec. On the other hand, Richards (1977) reported that depth in briefly presented random-dot stereograms cannot be perceived (unless monocular cues are present) when stimulus durations are less than 200 msec. Richards asserted that eye movements are necessary for many subjects to see random-dot stereograms.In this paper, we demonstrate that brevity of exposure is not an obstacle to high-quality stereoscopic depth perception even when there are no monocular cues, provided that the dichoptic display is properly registered on corresponding retinal points at the moment the dichoptic stimulus is presented. That is, the retinal disparity at the fixation point should be close to zero, and the line of sight should not have to be adjusted to achieve zero fixation disparity. We proved this point by presenting a dichoptic, random-dot stereogram for a total duration of less than 1 msec in an experimental situation in which subjects' eyes were appropriately preconverged. In pilot studies, it was shown that stimuli ofthis kind did not lead to any measurable stereoscopic shape recognition if the eyes were not converged at the necessary small fixation

Evidence for patchwork approximation of shape primitives

“…Uttal, Davis, and Welke's (1994) work shows that observers can detect structure in stereo displays with presentations of less than 1 msec. Our brief stimulus presentation allowed us to test whether observers rely on global properties of the stereo display, such as the implicit surface, or on local cues, such as disparity discontinuities of neighboring texture elements.…”

“…On each trial, the observers first saw a prestimulus display consisting of a square in each monocular image (with zero disparity). They fused the square to converge their eyes appropriately in preparation for the subsequently brief presentation of the stimulus proper (e.g., Uttal et al, 1994). After fusing the square, the observers initiated the stimulus presentation by pressing the middle mouse button.…”

A stereo advantage in generalizing over changes in viewpoint on object recognition tasks

“…It is also possible that stereo information would not have yielded an advantage under brief presentations, which may hinder the building up of more fully integrated representations containing depth and 3-D structure information (and possibly also hinder their transformation in the matching process). However, Uttal, Davis, and Welke (1994) showed that compelling stereo depth can be recovered from very brief stimulus presentations ( 1 msec). In any case, our results show that there is a stereo advantage in generalizing to new orientations …”

Perceptual latencies to discriminate surface orientation in stereopsis

“…A similar mask has been employed previously (Bradshaw, Rogers, & DeBruyn, 1995) and served the important function of disrupting further processing of stimulus disparity. It was important to ensure that the time available to the observers to process disparity information was of a definite duration, since Uttal, Davis, and Welke (1994) have shown that stereopsis may proceed on the basis of images presented for as little as 1 msec when no mask is used. The mask was a randomdot stereogram, similar to the test stimuli, except that each dot was randomly assigned a crossed or uncrossed disparity of between 0 and 10 arc min.…”