Are Greebles Special? Or, Why the Fusiform Fish Area Would be Recruited for Sword Expertise (If We had One)
Are Greebles Special? Or, why the Fusiform Fish Area would be recruited for Sword Expertise (If we had one) Matthew H. Tong (mhtong@cs.ucsd.edu) Carrie A. Joyce (cjoyce@cs.ucsd.edu) Garrison W. Cottrell (gary@cs.ucsd.edu) UCSD Department of Computer Science and Engineering, 9500 Gilman Drive, Dept. 0123 La Jolla, CA 92093-0114 USA Abstract The fusiform face area (FFA) has commonly been deemed an area specialized for face processing. Many recent studies have challenged this view by showing that the FFA also responds to stimuli from domains in which the subject is an expert. We have developed neurocomputational models to explore the question of why an area initially devoted to face processing would later be recruited for other domains. Previous studies showed that the FFA could be a fine-level discriminator, spreading apart similar stimuli in its representational space. These characteristics would make it ideal for recruitment to other fine-level discrimination tasks. These initial findings have been challenged on several accounts. Here we introduce new work showing that the expertise effect remains despite additional controls on the type and difficulty of the task presented. Keywords: Perceptual expertise; connectionist models; face recognition; object classification Introduction As its name suggests, the fusiform face area (FFA) has been identified as an area that is specific to processing faces. Imaging scans show increased activity of this area when face stimuli are presented when compared to activation when non- face stimuli are presented (Kanwisher, McDermott & Chun, 1997). Damage to the FFA tends to lead to prosopagnosia (an inability to recognize faces) and similar deficits, further implicating this area in facial recognition (De Renzi et al., 1994). There is also electrophysiological evidence in the form of a maximum amplitude of a negative going wave about 170 ms following a stimulus (the N170) that shows that faces may be handled differently at a neurological level (Eimer, 2000). Based on this evidence and psychological evidence showing that faces are processed differently at a behavioral level, many have concluded that the FFA is a face-specific processing module. The view of the FFA as a module for face processing has been challenged by evidence reporting that the fusiform face area seems to be recruited for other tasks as well. Experts in recognizing cars, birds, dogs, and Greebles (a class of artificial objects developed by Isabel Gauthier) also show increased activation of the fusiform face area (Gauthier et al., 1999; Gauthier et al., 2000). Furthermore, visual experts show an increased amplitude N170 when shown images from their field of expertise when compared to items for which they are not experts (birds for bird experts, versus dogs for dog show judges) (Tanaka & Curran, 2003). In these studies, subjects are defined as being experts when their reaction times are as fast when verifying the category of an object at the subordinate or individual level as they are when verifying the category at the basic level. These findings suggest a different account of the function of the FFA, that the area is actually a subordinate-level, fine- grained visual discrimination area. Humans become face experts at a young age, and later in life they may pick up additional areas of visual expertise as well. Under this account, earlier studies showing the FFA being highly active only in face processing did so because they did not choose non-face stimuli with which the subjects were experts. Recent studies (Grill-Spector, Knouf, & Kanwisher, 2004; Rhodes et al., 2004; Yovel & Kanwisher , 2004) that purport to refute the expertise claim never seem to achieve the stringent reaction time requirement of expertise (defined above) in their work. For example, although Grill-Spector et al. recruited car experts, they then tested their subjects on antique cars, which would presumably not be named quickly by their “experts.” Indeed, this would seem to be an example of an “other race effect” for cars, as it is already known that other race faces also produce a lower response in the FFA (Golby et al., 2001). In any case, if one assumes the expertise hypothesis, this leads to the question of what characteristics do these different expert-level tasks share that would cause one area of the brain to be used for them but not for basic-level tasks. It has been suggested that the FFA implements a process of fine level discrimination (Tarr & Gauthier, 2000). As we have shown elsewhere (Joyce & Cottrell, 2004), and elaborate on here, we believe that the main feature of this process is a transformation that takes similar visual items and magnifies the differences between them. This transformation generalizes to novel domains, and tuning of the transform allows the model FFA to acquire new expertise faster than an area that simply categorizes objects at the basic level (e.g., Lateral Occipital Complex (LOC)). This suggests that in a competition between cortical areas for processing a new task, the FFA would have a distinct advantage, thus explaining why the FFA would become recruited for novel expertise tasks – it simply learns them faster than an area that only