Visual Expertise is a General Skill
Visual Expertise is a General Skill Maki Sugimoto (mxs@hnc.com) Garrison W. Cottrell (gary@cs.ucsd.edu) HNC Software, Inc. 5935 Cornerstone Court West San Diego, CA 92121-3728 USA UCSD Computer Science and Engineering 9500 Gilman Dr. La Jolla, CA 92093-0114 USA Abstract The fusiform face area (FFA) in the ventral temporal lobe has been shown through fMRI studies to selectively re- spond with high activation to face stimuli, and has been identified as a face specific processing area. Studies of brain-lesioned subjects with face recognition or object recognition deficits also have often been cited as evidence for face specific processing. Recent studies, however, have shown evidence that the FFA also responds with high activation to a wide variety of non-face objects if the level of discrimination and the level of expertise are controlled. Based on these recent results, we hypothe- sized that the features of faces that the FFA respond to can be useful for discriminating other classes of visu- ally homogeneous stimuli with some tuning through ex- perience. To test our hypothesis, we trained two groups of feed-forward neural networks on visual classification tasks. The first group was pretrained on basic level clas- sification of four stimulus classes, including faces. The second group was pretrained on subordinate level clas- sification on one of the stimulus classes and basic level classification on the other three. In two experiments that used different criteria to stop pretraining, we show that networks that fully acquire the skill of subordinate level classification consistently show an advantage in learning the new task. Introduction The functional role of the so-called fusiform face area (FFA) located in the ventral temporal lobe is controver- sial. The FFA has been shown in fMRI studies to respond with high activation to face stimuli but not to other visual object stimuli, and has thus been identified as a face spe- cific processing area (Kanwisher, 2000). Studies of pa- tients with face recognition or object recognition deficits also have often been cited as evidence for face specific processing. Recent studies by Gauthier and colleagues have questioned whether the FFA is really a face-specific area (Gauthier, Behrmann & Tarr, 1999a). They have proposed an alternative theory that the FFA engages in expert level classification of visually similar stimuli from a wide variety of categories not limited to faces. The current study is an attempt to shed light on the de- bate through simulations of computational models. We constructed our hypothesis based on the recent view that the FFA is a domain-general processing area, special- izing in visual expertise of fine level discrimination of homogeneous stimuli. Our experimental results show strong support for the hypothesis, thus providing further evidence for the plausibility of the domain-general view of the FFA. In the following sections, we will describe the evi- dence for and against the FFA’s face specificity, and our refinement of the domain-general hypothesis. The exper- imental methods are then described in detail followed by the results. We conclude by summarizing our findings and suggesting future research. Evidence for the Face Specificity of the FFA Studies of brain-lesioned subjects provide the strongest evidence for localized face specific processing. Pa- tients with associative prosopagnosia reportedly have deficits in individual face identification, but are normal in face detection and object recognition (Farah, Levin- son & Klein, 1995). On the other hand, patients with visual object agnosia are normal in identifying individ- ual faces but have deficits in recognizing non-face ob- jects (Moscovitch, Winocur & Behrmann, 1997). The two groups of patients serve as evidence for a double dis- sociation of visual processing of faces and other objects. Through fMRI studies of normal brains, the FFA has been identified as the area being most selec- tive to faces (Kanwisher, McDermott & Chun, 1997). Prosopagnosia patients usually have a lesion in an area encompassing the FFA (De Renzi et al., 1994), providing consistent evidence for the face specificity of the FFA. Evidence against the Face Specificity of the FFA Gauthier and colleagues argued that the FFA showed high activity in response to various classes of visual stim- uli when the levels of discrimination and expertise were properly controlled (Gauthier et al., 1999a). One study showed significantly high activity of the FFA for car and bird experts when stimuli from their respective expert class were presented (Gauthier et al., 2000). Another study that utilized 3-D artificially rendered models called “Greebles” (Gauthier & Tarr, 1997), showed the FFA in- creasing its activation in response to the rendered mod- els as the subjects were trained to classify them at a fine level (Gauthier et al., 1999b). For the latter study, the use of the Greebles allowed the authors to develop hu- man subject experts of non-face objects while fully con- trolling the subjects’ experience with the stimuli. These results showing high activity of the FFA for non-face objects including completely novel objects,