How category learning affects object representations: Not all morphspaces stretch alike.

Abstract

How does learning to categorize objects affect how we visually perceive them? Behavioral, neurophysiological, and neuroimaging studies have tested the degree to which category learning influences object representations, with conflicting results. Some studies find that objects become more visually discriminable along dimensions relevant to previously learned categories, while others find no such effect. One critical factor we explore here lies in the structure of the morphspaces used in different studies. Studies finding no increase in discriminability often use “blended” morphspaces, with morphparents lying at corners of the space. By contrast, studies finding increases in discriminability use “factorial” morphspaces, defined by separate morphlines forming axes of the space. Using the same four morphparents, we created both factorial and blended morphspaces matched in pairwise discriminability. Category learning caused a selective increase in discriminability along the relevant dimension of the factorial space, but not in the blended space, and led to the creation of functional dimensions in the factorial space, but not in the blended space. These findings demonstrate that not all morphspaces stretch alike: Only some morphspaces support enhanced discriminability to relevant object dimensions following category learning. Our results have important implications for interpreting neuroimaging studies reporting little or no effect of category learning on object representations in the visual system: Those studies may have been limited by their use of blended morphspaces.

Task- and Experience-dependent Cortical Selectivity to Features Informative for Categorization

“…Having said that, the current morph method does follow Folsteinʼs morph model of a factorial morph space. Such a morph space has been shown to increase discriminability along the relevant dimensions (Folstein et al, 2012). In this study, we manipulated the features of the fish independent of each other.…”

“…Recently, Folstein, Gauthier, and Palmeri (2012) proposed two different methods of morphing stimuli to create different category members, the blended and factorial models. In both cases, the morph space between the prototypes is shaped as a tetrahedral volume.…”

The Effects of Categorization on Perceptual Judgment are Robust across Different Assessment Tasks

“…Several studies have demonstrated that whether CP is observed at all depends on various factors including (1) the availability of verbal labels during perceptual testing [9], (2) the particular kind of perceptual assessment used to determine whether CP is present [10], and (3) how stimulus morphspaces are created [11]. However, few studies have reported differences in the kind of CP effect observed based on experimental manipulations, though there are exceptions.…”

Introduction to the Special Section on theory and data in categorization: Integrating computational, behavioral, and cognitive neuroscience approaches.

“…According to some theories of object recognition, object representations in visual cortex are not systematically influenced by the way those objects have been categorized (e.g., Riesenhuber & Poggio, 1999), with fMRI modulation according to learned category appearing in frontal areas but not in visual areas (e.g., Jiang et al, 2007). By contrast, Folstein et al (2012) appeal to the theories of categorization that place significant emphasis on the role of selective attention (e.g., Kruschke, 1992;Nosofsky, 1984) or perceptual stretching (e.g., Goldstone, 1994) of object dimensions relevant to learned categories (see Gauthier & Palmeri, 2002). Many experiments studying object categorization use morphing techniques to create continuous spaces of complex objects.…”

“…Many experiments studying object categorization use morphing techniques to create continuous spaces of complex objects. Folstein et al (2012) show that the details of how those morphspaces are created matter a lot. When morphspaces are created by factorially combining morphlines (Goldstone & Steyvers, 2001), perceptual stretching along category-relevant object dimensions is observed.…”