A Neural Basis for Expert Object Recognition

Although most adults are considered to be experts in the identification of faces, fewer people specialize in the recognition of other objects, such as birds and dogs. In this research, the neuro- physiological processes associated with expert bird and dog recog- nition were investigated using event-related potentials. An enhanced early negative component (N170, 164 ms) was found when bird and dog experts categorized objects in their domain of expertise relative to when they categorized objects outside their domain of expertise. This finding indicates that objects from well-learned categories are neu- rologically differentiated from objects from lesser-known categories at a relatively early stage of visual processing. The term jizz is used by veteran birdwatchers to describe their flash of instant recognition of a bird based on its color, shape, and move- ment. Similarly, dog-show judges and breeders can discern in a single glance the specific breed and attributes of a canine from its facial structure, gait, and posture. Although the subtle perceptual cues that differentiate species of birds and breeds of dogs frequently go unno- ticed by the novice, detection of these cues seems obvious and auto- matic to the expert. What is the neural basis of this perceptual expertise? Although relatively few people specialize in the recognition of particular objects (e.g., birds, cars, dogs), it has been suggested that virtually all people are experts in the recognition of faces (Carey, 1992; Tanaka & Gauthier, 1997). Electrophysiological studies employing event-related potentials (ERPs) have been informative for understanding the tem- poral aspects of face processing. Results from these experiments in- dicate that the magnitude of an early ERP component, referred to as the N170, is significantly larger when participants view face stimuli than when they view other natural and human-made objects (Bentin & Deouell, 2000; Eimer, 2000). Moreover, patients with prosopagnosia, the inability to recognize faces, either fail to demonstrate an enhanced N170 to faces (Eimer & McCarthy, 1999) or demonstrate a nonselec- tive enhanced N170 to both face and nonface stimuli (Bentin, Deouell, & Soroker, 1999). Thus, the presence of the N170 component during viewing of faces in normal participants and its absence or the presence of a nonselective N170 during viewing of faces in prosopagnosic patients indicate that the N170 is a good neurophysiological index of face perception processes. More generally, this evidence suggests that the visual system can differentially respond to specific and important kinds of visual information at a relatively early stage of processing (Bentin & Deouell, 2000). However, whether the enhanced N170 component is exclusive to faces or whether it can be extended to other important objects in the environment (i.e., objects of expertise) is an open question. In the current study, we investigated the neural basis of object expertise by monitoring brain wave activity of bird and dog experts while they categorized pictures of common birds and dogs. The ex- periment was designed so that participants served as their own ex- perimental controls in that they were expected to perform as experts when categorizing objects in their domain of expertise (e.g., bird experts categorizing birds) and novices when categorizing objects outside their domain of expertise (e.g., bird experts categorizing dogs). We expected that if the increased N170 reflects a general form of expert processing that is not unique to faces, experts would exhibit an enhanced N170 when categorizing objects in their domain of ex- pertise relative to when they categorized objects outside their domain of expertise.