Perceptual Cues for a Category Representation of Humans

One issue not yet discussed is the information used by infants to form a category representation for humans. A recent study investigated this question and specifically examined the perceptual information that was the basis for the human versus nonhuman animal asymmetry (Quinn, 2004). The experiment followed from the investigation of whether infants formed category representations for nonhuman animal species based on information from the whole animal, head, or body (Quinn & Eimas, 1996a). Three- and 4-month-old infants were familiarized with 12 exemplars of humans or 12 exemplars of cats, and tested with a novel human versus a novel cat. Within the human and cat conditions, the infants were randomly assigned to one of three experimental groups: Whole Animal, Head Only, and Body Only. In the Whole Animal Group, infants were familiarized and tested with entire, intact stimuli (head + body). In the Head Only group, only the heads of the stimuli were visible; the body information had been occluded. In the Body Only group, only the bodies of the stimuli were visible; the head information had been occluded. Examples of the stimuli are presented in Figure 5.8. The particular form of the asymmetry, a category representation for cats that excludes humans and a category representation for humans that includes cats, was observed only with the Whole Animal stimuli. Neither head nor body information alone were sufficient to produce the asymmetry. The results suggest that the incorporation of nonhuman animal species into a broadly inclusive category representation of humans may be based on the overall structure of the stimuli (e.g., a head region adjoining an elongated body axis with skeletal appendages). This finding, that the human representation is based on global Gestalt information, contrasts with the findings that representations for nonhuman animal species may be based on part or attribute (i.e., featural) information—heads in the case of cats versus dogs.

The data correspond well with the notion that young infants may be representing humans at an "expert" level and with recently proposed ideas regarding the representation of expertise that have emerged in the cognitive neuroscience literature (Gauthier & Nelson, 2001; Gauthier & Tarr, 2002). In particular, Gauthier and colleagues have argued that an area of the fusiform gyrus in the brains of adults, once believed to represent faces specifically, actually represents expert knowledge more generally. Moreover, these researchers have demonstrated that expert object recognition by this brain area is characterized by holistic-configural processing. The results described here are consistent with the idea that young infants may already possess an "expert" representation for humans that is based on holistic information.

Figure 5.8 Black and white examples of the nonhuman animals and human exemplars in the Whole Stimulus, Head Only, and Body Only depictions of Quinn (2004).
Figure 5.9 Black and white examples of the human face stimuli (with and without hair) used in Quinn, Yahr, Kuhn, Slater, and Pascalis (2002).
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