Attentional processing and the subjective contour illusion.

Abstract

Leading explanations of the subjective contour illusion can be classified as being either "bottom-up" or "top-down." Bottom-up explanations assert that peripheral, physiological mechanisms often associated with the perception of real contours also account for subjective contour (SC) perception. In contrast, top-down explanations posit a more central locus of SC perception and are formulated on a molar, psychological level. A major aspect of bottom-up perceptual processing is that it is largely automatic. On the other hand, top-down processing implies a greater role for selective attention. In an effort to distinguish between bottom-up and top-down accounts of SC perception, the present investigation used a dual-task paradigm to test the relative attentional demands of real contour perception versus SC perception. In the primary task, subjects made speeded same-different discriminations of either paired SC forms or their real contour analogues. Half the subjects performed this primary task in conjunction with a six-digit short-term memory load secondary task. If subjective forms indeed impose a greater limited-capacity processing load than real forms, then the need to share processing capacity with a secondary task was expected to produce a greater increment in reaction time (RT) for subjective relative to real forms. The results indicated that the expected enhanced RT increment for subjective relative to real forms with the addition of a concurrent memory load was limited to same trials. This result implies that the nature of response indicators must be considered in assessing capacity requirements with the sort of dual-task paradigm used in the present investigation. Nevertheless, the fact that the increment in same RT with the addition of a concurrent memory load was greater for subjective relative to real forms accords with expectations derived from the notion that the perception of SCs is more attention demanding than that of real contours. If the interpretation of the present study is correct, then a comprehensive theory of SC perception will most likely be formulated within the top-down perspective of conceptually driven visual information processing.

Masking with minimal contours: Selective inhibition with low spatial frequencies

“…Adding lines to our illusory contours always increased the masking magnitude. Second, the perception of illusions as illusions takes time (on the order of 100 msec; Reynolds, 1978) and the perception of illusory contours apparently requires effortful attention (Pritchard & Warm, 1983). One way of assessing whether naive subjects are perceiving illusory contours is to establish whether they see depth separationor a brightnesschange (Parks & Prendergrass, 1982;Rock & Anson, 1979).…”

Illusory contours: Toward a neurally based perceptual theory

“…In the context of a texture segmentation task, Meyer and Fish (1987) have reported similar findings. Comparing the times required to discriminate between different shapes of edge-induced illusory forms and between equivalent outlined forms, Pritchard and Warm (1983) found that reaction times increased more for illusory form discrimination than for outlined form discrimination as attentional loads were increased, implying a greater attentional demand for illusory contour perception. The high attentional demand indicated by these experiments has been used to argue for a cognitive theory of illusory contour formation.…”

“…The salience of the illusory contour varied as a function of time, apparently indicating time-varying cognitive hypotheses regarding the relative depths of the inducers, overlayed pattern, and illusory figure. Additional support for this form of cognitive theory comes from the perception of reversible and ambiguous illusory figures (Bradley, 1982(Bradley, , 1987Bradley,Dumais, & Petry, 1976),the effects ofleaming and memory on contour perception (Coren et aI., 1986(Coren et aI., , 1987Gellatly, 1982;Gellatly & Bishop, 1987;Landauer, 1978;Pritchard & Warm, 1983;Wallach& Slaughter, 1988), and other time course studies (Meyer & Fish, 1987;Pomerantz, Goldberg, Golder,& Tetewski, 1981;Takahashi, 1993).…”

Parallel discrimination of subjective contours defined by offset gratings

“…If subjective contours are computed in a bottom-up, or reflexive, fashion, then they should exhibit the characteristics of preattentive processes (Neisser, 1967). Namely, their detectability should not be influenced by concurrent, nonvisual task requirements (Pritchard & Warm, 1983), they should show spontaneous segregation in a texturediscrimination task (Beck, 1982;Julesz, 1984), and they should be detected in parallel in a visual-search task (Treisman & Gelade, 1980). Recent evidence indicates that subjective contour perception demonstrates none of these characteristics (Grabowecky & Treisman, 1989;Meyer & Fish, 1987;Pritchard & Warm, 1983).…”

“…Dual Task Procedures Pritchard and Warm (1983) examined whether form discrimination based on Kaniza-like subjective contours versus real contours was differentially affected by attentionalload. They found that without attentionalload there was no significant difference in the speed with which same-different judgments could be made between forms defined by real or subjective contours.…”