Functional equivalence of masking and cue reduction in perception of shape at a slant

Abstract

In a backward masking paradigm Epstein, Hatfield, and Muise (1977) found that presentation of a frontoparallel pattern mask caused the perceived shape of elliptical figures which were rotated in depth to conform to a projective shape function. The current study extended the masking function by examining the effect of a mask which was partially or wholly cotemporal with the target. The study also assessed the functional equivalence of the masking treatment and the conventional treatment for minimizing depth information. Reports of perceived shape and perceived orientation were obtained under three conditions: binocular without mask, binocular with mask, monocular without mask. Under the first condition, perceived shape conformed to objective shape and perceived orientation was proportional to objective orientation. Under the latter two conditions, perceived shape was in very close agreement to projective shape and the two functions did not differ. Orientation was underestimated greatly under both conditions. We concluded that the effect of the mask on perceived shape is mediated by its effect on encoding of orientation information, although an additional effect on the subsequent stage of shape-slant integration cannot be excluded.Epstein, Hatfield, and Muise (1977) examined the effect of a frontoparallel pattern mask on perception of the shape and the orientation of a family of projectively equivalent elliptical figures which were rotated in depth about the vertical axis. Epstein et a1. found that the perceived shapes of rotated figures which were presented for durations sufficient to allow at least 80070 shape constancy in the absence of a mask tended to correspond to projective rather than objective shape when presentation of the target figure was followed after an interval of 0-50 msec by a pattern mask. The tendency toward projective shape matches became less pronounced as the interstimulus interval was lengthened. The mask also affected perceived orientation. The orientation of the figures was underestimated considerably, although the effect of the mask on perceived orientation was not as great as the effect on perceived shape. Epstein et a1. (1977) proposed an account of the effects of the mask based on the process of perceiving shape-at-a-slant which is modeled by the shape-slant invariance hypothesis (Beck & Gibson, 1955, Epstein, 1973Epstein & Park, 1963;Kaiser, 1967;King, Meyer, Tangney, & Biederman, 1976;Oyama, 1977;Winnick & Rogoff, 1965). It was assumed that the operations suggested by the shapeslant hypothesis are not instantaneous. Registration of projective shape, encoding of orientation and the integration of projective shape and slant information require time. The mask preempts processing and reduces the time available for processing the target. In particular, Epstein et a1. proposed that the mask arrested processing of information about orientation. The effect of the mask on perceived shape was a byproduct of the primary effect on orientation processing.The present experiment had two objective...

The locus of masking shape-at-a-slant

“…The present results are the first to show the effect for forms rotated in depth. Epstein and Hatfield (1978) and Epstein, Hatfield, and Muise (1977) discussed the effects of masking shape-at-a-slant in terms of the shape-slant invariance hypothesis and an algorithm processing model (Epstein & Hatfield, 1978, Figure 4). The processing stages of this model are (1-3) separate registration, encoding, and transmission to algorithm processor of orientation and projective shape information, and (4) combination of the two kinds of information by application of a shape-slant algorithm.…”

“…Presence of the mask produced projective shape matching and diminished orientation discrimination. It is argued that the site of masking was postchiasmal, and the results are related to previous work with pattern masking of projectively equivalent ellipses.In previous experiments, Epstein and Hatfield (1978) and Epstein, Hatfield, and Muise (1977) reported masking of simple shapes rotated in depth. When followed by a frontoparallel pattern mask at the appropriate interstimulus interval (lSI), objectively different, projectively identical shapes-at-aslant were indistinguishable.…”

“…In previous experiments, Epstein and Hatfield (1978) and Epstein, Hatfield, and Muise (1977) reported masking of simple shapes rotated in depth. When followed by a frontoparallel pattern mask at the appropriate interstimulus interval (lSI), objectively different, projectively identical shapes-at-aslant were indistinguishable.…”

“…Epstein and Hatfield (1978) used projectively equivalent ellipses as stimuli and found that, at exposure durations varying from 25 to 75 msec, binocular viewing yielded nearly perfect constancy and monocular viewing without a mask…”

“…Epstein and Hatfield (1978) used projectively equivalent ellipses as stimuli and found that, at exposure durations varying from 25 to 75 msec, binocular viewing yielded nearly perfect constancy and monocular viewing without a mask yielded projective shape matching. In unreported pilot experiments it was found that, at exposures of up to 500 msec, monocular viewing of ellipses yielded projective shape matching.…”