Categorical perception effects induced by category learning.

Abstract

The authors report a series of studies designed to determine whether effects similar to those observed in the innate categorical perception of color and phonemes are induced during the learning of simple unidimensional categories and more complex multidimensional ones. In Experiment 1 no evidence was found for such effects when stimuli varied on 1 dimension. Experiments 2 and 3 demonstrated a within-category compression effect but no betweencategory expansion effect for stimuli varying in 2 dimensions. Compression only was also shown in Experiment 4, which used pictures of actual objects. Multidimensional scaling analyses illustrate how within-category compression without expansion was sut~cient to produce categorical clustering of items in the similarity space. These analyses also show that learning changed the dimensional structure of similarity space. Results are compared with those from other studies exploring similar phenomena and with neural network simulations.Most contemporary models of category learning rely to some degree on relative similarities between category members and nonmembers (

Altering object representations through category learning

“…The difference between the former Strategic Judgment Bias account and this Altered Object Description account is that in the former account, the object descriptions themselves are not in¯uenced by categorization; only the similarity judgments, acting on unchanged object representations, are in¯uenced by categorization. The difference between these positions is important because several researchers have argued that learned categorical perception shows that object representations are in¯uenced by concept learning (Goldstone and Steyvers, in press;Livingston et al, 1998). However, we would only have con®dence in this position if the Altered Object Description account can be unambiguously supported.…”

“…One of the most troubling is: do learned categories merely in¯uence strategic judgments (the Strategic Judgment Bias account) made about objects, or do they affect the psychologically encoded descriptions of the objects (the Altered Object Description account)? This issue is clearly apparent with the results of Livingston et al (1998). Imagine participating in their experiment.…”

“…Whereas some researchers have found the primary impact of category learning to be decreasing people's confusions when making discriminations involving perceptual dimensions relevant to the categorization (Goldstone, 1994a;Levin & Beale, 2000), other researchers have found category learning to primarily increase similarity ratings between objects belonging to the same category (Kurtz, 1996;Livingston et al, 1998). One possible reason for this may be that psychophysical measures of discriminability seem to promote expansion whereas similarity ratings promote compression (Levin & Beale, 2000).…”

“…One possible reason for this may be that psychophysical measures of discriminability seem to promote expansion whereas similarity ratings promote compression (Levin & Beale, 2000). Another proposed resolution is that if the categorized objects are extremely similar, then expansion is found; otherwise, compression is found (Livingston et al, 1998). In the current experiment, we systematically altered the between-and within-category similarities, such that objects belonging to different categories were either similar or dissimilar, as were objects belonging to the same category.…”

“…Particularly strong categorical perception effects have been found when researchers have used similarity ratings rather than psychophysical measures of discriminability. For example, Livingston, Andrews, and Harnad (1998) found that when participants learned to classify objects (animal body parts or arti®cial cells) into a single category, then these objects received far higher similarity ratings than objects that belonged to different categories, or than objects that were not categorized at all (see also Kurtz, 1996). Their ®nding of greater similarity associated with objects grouped together in a category is consistent with results that very young infants (2 months old) show sensitivity to differences between speech sounds that they lose by the age of 10 months (Werker & Tees, 1984).…”