Area and contrast effects upon perceptual and imagery acuity.

Abstract

We measured the size of visual fields within which actual and imagined circular patterns could be resolved, as the patterns varied in both area and relative contrast. As pattern area increased, imagery fields increased in size at the same rate as perceptual fields. However, as the relative contrast between parts of the patterns was reduced, perceptual fields diminished in size, while imagery fields did not. For all variations of pattern area and contrast, fields in imagery were roughly the same shape as fields in perception. A control experiment provided no support for the possible criticism that these results might be explained on the basis of subjects' expectations for the size and shape of the imagery fields, especially since control subjects falsely believed that reductions in contrast would reduce considerably the size of these fields. Although these findings suggest that images and physical objects are functionally equivalent at pattern-processing levels of the visual system, they demonstrate that images and objects are not functionally equivalent at certain levels of the visual system where information about relative contrast is processed.

Creation of the horizontal-vertical illusion through imagery

“…The substitution of an image for a physical stimulus to create a percept has recently been shown to be a possibility for a variety of phenomena. As examples, such substitution has been reported for perceptual adaptation to displacing prisms (Finke, 1979), letter search and identification (Podgorny & Shepard , 1978), observation of the McCollough effect (Finke & Schmidt , 1977Kunen & May, 1980), perceptual acuity of objects in the peripheral visual field (Finke & Kosslyn, 1980), perception of area and contrast effects (Finke & Kurtzman, 1981), production of the Poggendorff illusion (Goldstein & Weintraub, 1973;Pressey & Wilson, 1974), and creation of the autokinetic effect (Wallace, 1980). Finke (1980) argued that not only can an image substitute for a physical stimulus, but also that the two are equivalent in their effect on perception.…”

Discriminations among perceptual and symbolic stimuli

“…Similarities between processing of perceptually available objects and processing of memories of the same objects are commonly taken as evidence that the purely mental processing uses representations that are close to perception (Banks, 1981;Finke, 1980;Finke & Kurtzman, 1981;Shepard, 1978;Shepard & Podgorny, 1978). Conversely, in cases in which the two sorts of processing give dissimilar results, it should be concluded that the mental processing does not use perceptual representations.…”

Levels of equivalence in imagery and perception.

“…Instead, these subjects imagined that they saw their pointing finger arrive at one side of the target when they pointed at it, in such a way that they imagined making the same average prism-induced errors that subjects in the perceptual feedback condition actually did make and observe. This was done using the following technique: As shown in Figure 5, a set of visual markers was placed to one side of the target, corresponding to the average pointing errors that subjects in the perceptual condition made on their first pointing trial (Y), on Trials 1-5 (1), on Trials 6-10 (2), and on Trials 11-20 (3). The subjects in the imagery condition were instructed, prior to the adaptation procedure, to try to point to where they saw the target, but then to imagine that they saw their pointing finger arrive under each of the markers in that same sequence.…”