Academic journal article Attention, Perception and Psychophysics

Limits of Generalization between Categories and Implications for Theories of Category Specificity

Academic journal article Attention, Perception and Psychophysics

Limits of Generalization between Categories and Implications for Theories of Category Specificity

Article excerpt

Both domain-specific and expertise accounts of category specialization assume that generalization occurs within a domain but not between domains. Yet it is often difficult to define the boundaries and critical features of object domains. Differences in how categories are defined make it difficult to adjudicate between accounts of category specificity and may lead to contradictory results. For example, evidence for whether car experts recruit the fusiform face area is mixed, and this inconsistency may be due to the inclusion of antique cars in one of those previous studies (e.g., Grill-Spector, Knouf, & Kanwisher, 2004). The present study tested the generalization of expertise from modern to antique cars and found that modern-car experts showed expert discrimination and holistic processing of modern cars but not of antique cars. These findings suggest that the neural specialization underlying perceptual expertise is highly specific and may not generalize to distinct subclasses, even when they share some degree of perceptual and conceptual features.

By definition, expertise is domain specific. We would not expect a sommelier (wine expert) to know much about perfumery. We would not be surprised if a sommelier who can detect a taste of vanilla in a Chardonnay could not detect the same fragrance in a complex perfume like Shalimar, which, according to Guerlain, includes notes of lemon, bergamot, jasmine, may rose, iris, incense, opoponax, tonka bean, and vanilla. In this case, it may be intuitive that wines and perfumes form two separate domains, in great part as a result of functional differences. A sommelier may fail to engage wine-related expert strategies in the context of perfume identification. Yet perceptual expertise is also defined in part by generalization of expert skills to novel exemplars within a domain. For example, we would expect a sommelier trained with Australian wines to be able to apply his or her skills to a new Australian wine never before encountered. Indeed, empirical studies of expertise have demonstrated that an expert in a given domain can learn new items in his or her domain faster than can novices (Gauthier, Williams, Tarr, & Tanaka, 1998) and can outperform novices even on tasks that were not part of the training experience (Gauthier & Tarr, 2002).

Because expertise is characterized by both specificity between domains and generalization within a domain, understanding limits of generalization is particularly important for developing an account of how the brain becomes specialized for recognizing particular classes of objects. Specialization within the visual recognition system has been demonstrated for many homogeneous categories, including faces, cars, birds, and novel objects (Diamond & Carey, 1986; Gauthier, Anderson, Tarr, Skudlarski, & Gore, 1997; Gauthier, Behrmann, & Tarr, 1999; Gauthier, Skudlarski, Gore, & Anderson, 2000; Gauthier & Tarr, 1997; Wong, Palmeri, Rogers, Gore, & Gauthier, 2009). Differences between theoretical accounts for the development of such category specificity have centered on the relationship between recognition of faces and objects and the role of experience in the development of specialization within the visual recognition system. On the one hand, a domain-specificity account focuses on the idea that face recognition is carried out by a modular system that is dedicated to faces and is separate from a more generalized object-recognition system (Kanwisher, 2000). On the other hand, a perceptual-expertise account suggests that specialization for visual recognition of any homogeneous class of objects, including faces, is the result of an interaction between experience, task demands, and neural biases (Bukach, Gauthier, & Tarr, 2006; Gauthier & Tarr, 2002). Understanding domain boundaries and the limits of generalization between object categories is critical to both approaches. Differences in how categories are defined make it difficult to weigh the evidence in favor of one or the other theory of category specificity and may lead to contradictory results. …

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