Perceptual salience of form versus material as a ... - Springer Link

Perception & Psychophysics 1985. 37. 440-446

Perceptual salience of form versus material as a function of variations in spacing and number of elements RAYMOND M. KLEIN and JOHN BARRESI Dalhousie University, Halifax, Nova Scotia, Canada

When do the elements composing a pattern shift in their functional role from integral parts of its overall form to the material out of which its global form is constructed? In a parametric extension of Goldmeier's (1936/1972) initial work on this problem, subjects judged the similarity between, and serially categorized, pairs of lines that were constructed from element dots such that one line was twice the length of the other, and either maintained the same number of elements or the same spacing between elements. For large stimuli composed offew elements, number of elements rather than spacing determined similarity and categorization time. However, as the number of elements was increased, the two tasks dissociated. Similarity judgments became dependent on spacing between elements rather than on number, whereas categorization time became independent of this factor. This suggests that when they are numerous and closely spaced, the elements shift from integral parts of the figure to independently coded material. One of the most enduring dichotomies in the psychology of perception is epitomized in the debate between the Gestalt and Structuralist schools. Woodworth's summary of the debate is still accurate today, as investigators continue to ask "whether the elements of a figure get together and build up the whole, or whether the whole figure emerges and organizes the available elements" (Woodworth & Schlosberg, 1954, p. 403). In current jargon, scholars ask whether processing is "bottom-up" or "topdown," or whether "global" analysis precedes or follows "local" analysis. Historically, phenomenology was the primary tool for answering such questions about the nature of perception. Within this tradition, Goldmeier's (1936/1972) classic studies of perceived similarity, provide a wealth of interesting empirical data and insightful conceptual analysis. In exploring the general proposition that similarity is dependent upon the identity of relations, rather than the identity of elements, Goldmeier found several exceptions, which seemed to depend upon a phenomenal separation of form and material. He proposed that: (Rule 2) the phenomenal separation of material and form arises in the following manner: Characteristics of the design which (a) because of relative smallness are not phenomenally related to the overall measurements of the figure as a whole, and which (b), in the case of discon-

This paper was presented at the annual meeting of the Psychonomic Society, November 1983. The research reported here was supported by Natural Sciencesand Engineering Research Council of Canada Grants A0667 to John Barresi and A9948 to Raymond Klein. Requests for reprints should be sent to R. Klein, Department of Psychology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4JI.

Copyright 1985 Psychonomic Society, Inc.

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tinuity, are not individualized because of their large number, are relegated to the role of material ... (Rule 1) The form is best preserved by proportional enlargement; material properties are best preserved by keeping the measurements of the material elements constant. (p. 46; 43)

Rule 1 applies only to stimuli in which form and material are phenomenally separate (Rule 2); when they are not separate, proportional enlargement should produce the highest similarity. In a typical, and for this paper, basic experiment, Goldmeier's observers selected the comparison stimuli more similar to each standard in Figure la and lb (corresponding to Goldmeier's Figures 24 and 25). As expected from rule 2b, if the number of elements is small the enlargement of the figure must be proportional (25b), while if the elements are numerous an impression of material is created which is better rendered in an unproportionally enlarged comparison stimulus (24c) than in a proportionally enlarged one. (p. 49)

Although Goldmeier concludes that "it is not possible to designate a definite least number of elements necessary for the impression of material," he does conclude that the crossover point, when material emerges, is between 6 and 9 elements. In recent years mental chronometry has gained favor as a tool (e.g., Garner, 1974; Posner, 1978) and has been profitably used, often in conjunction with phenomenology (e.g., Palmer, 1977), to explore perception. Our principal purpose in this study was to explore the generality of Goldmeier's rules regarding "form" and "material" by parametrically extending his observations from Figures 24 and 25, and by supplementing the phenomenological

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or the like. It is not clear a priori that there will be comparable results on both types of measure. Indeed, in earlier work on perceptual structure, Palmer overcame his concern that verbal measures "are subject to the objection that such conscious judgments may have little in common with unconscious perceptual processing" (Palmer, 1977, p. 456) by exploring the convergence between phenomenology and a variety of performance measures. The present study used perceived similarity together with performance on a speeded classification task, at least partly because we share this concern. As we shall see, differences do occur, and these seem to have theoretical significance.

METHOD

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Figure 1. Stimuli and results from Goldmeier's Experiments 24 and 25 (see text for explanation).

data from similarity judgments with performance data (RT and accuracy) from a categorization task. Goldmeier's work on the form/material distinction has also been extended by Kimchi and Palmer (1982). Although our experiment was conducted independently of theirs, it is worth noting the similarities and differences between our two approaches. Theoretically, there is much in common, as will be pointed out in the discussion section. But empirically there are large and important differences. These occur in both stimulus conditions and response measures. Kimchi and Palmer focused their attention on varying the size, form, and number of the elements out of which the global figures were constructed. Hence, a large square might be constructed out of small or large triangles. In the present study, all of our elements were dots of uniform size and all of our figures were straight lines composed of these dots. Although in both studies the effects of number and spacing of elements were investigated, this was not the major thrust of the Kimchi and Palmer study; nor were their results with this manipulation entirely consistent. The present study investigated this single issue thoroughly within a wide range of psychophysical conditions. The two studies also differed in response measures. In four out of five of their experiments, Kimchi and Palmer used the original Goldmeier forced-choice similarity task. In the fifth experiment, they asked subjects to verbally describe their figures. In the present study, we used continuous similarity ratings and a parallel performance measure (speeded classification). Although we see little difference between the use of the forced-choice and ratings procedures (apart from the increased confidence and generalizability that derives from replication), the use of performance measures confers specific advantages. Kimchi and Palmer address most of their theoretical remarks to recent developments in the global/local debate. Yet, nearly all the studies they cite on this issue used performance measures rather than verbal reports of similarity

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Stimuli The stimuli, shown in Figure 2, were lines composed of from 2-17 dots with a constant distance between dots in a given line. Each triplet in this half matrix represents two stimulus conditions experienced by all subjects. The subjects judged the similarity between the standard stimulus (middle member of triplet) and a comparison stimulus, and then performed a speeded classification task with the same pair. Note that the stimulus pairs presented to the subjects always differed by a factor of 2 in total extent, and were either (I) identical in number and different in spacing (above), or (2) identical in spacing and different in number (below). Interdot spacing varied from approximately .05 0 for the smallest spacing used to about .8 0 for the largest spacing. Two groups, differing only in absolute size (see Design), were tested. These stimuli are analogous to Goldmeier's line stimuli (Figures 24 and 25), except that dots have been substituted for lines. When number (or spacing) is the perceptually salient dimension, pairs that do not differ in number (or spacing) will be perceived as more similar than corresponding pairs that do. Goldmeier's experiments suggest that for linear stimuli those with 3fs elements are dominated by form (the proportional enlargement' with different spacing is chosen as more similar than the enlargement with the same spacing), whereas with 7113 elements, material has emerged as perceptually salient (and the opposite selection is made). Subjects Eighteen college students participated for course credit.

Tasks

Similarity. A stimulus pair was presented with the shorter stimulus on the left side of the screen and the longer one on the right together with a horizontal line marked "low" on the left end and "hi" on the right end. By moving a joystick, the subjects could position a marker anywhere on this line. They were instructed that they should determine the perceived similarity between the two stimuli, place the marker at an appropriate position. and then press a microswitch to indicate that their judgment had been made. The subjects were told to pay special attention to the spatial locations of the two stimuli, since this information would be required during the sorting task. . Sorting. Immediately after the subjects made their similarity ratings, the word "ready" was displayed on the screen until a response was made. Then each of the two stimuli was presented 25 times in a serial RT sorting task. In response to each stimulus, the subject had to depress the microswitch corresponding to the side of presentation of that stimulus during the similarity procedure (for all such tests, the left key was used for the smaller stimulus). Immediately after each response, the next stimulus was presented. The identity and position' of the stimuli was varied randomly from triaI to trial. At the end of each set of 50 trials, the subjects received terminal feedback on their RT and accuracy.

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