The functional architecture of the object vision pathway in the human brain was investigated using functional magnetic resonance imaging to measure patterns of response in ventral temporal cortex while subjects viewed faces, cats, five categories of man-made objects, and nonsense pictures. A distinct pattern of response was found for each stimulus category. The distinctiveness of the response to a given category was not due simply to the regions that responded maximally to that category, because the category being viewed also could be identified on the basis of the pattern of response when those regions were excluded from the analysis. Patterns of response that discriminated among all categories were found even within cortical regions that responded maximally to only one category. These results indicate that the representations of faces and objects in ventral temporal cortex are widely distributed and overlapping. The ventral object vision pathway in the human brain has the capacity to generate distinct representations for a virtually unlimited variety of individual faces and objects, but the functional architecture that embodies this capacity is a matter of intense debate. Singlecell recording studies in the nonhuman primate have demonstrated differential tuning of individual neurons in temporal cortex to faces, whole objects, and complex object form features (1-3). Although columns containing cells that respond selectively to faces or similar features tend to cluster together, these studies have not revealed any consistent larger scale organization for object representation. Numerous computational models for object recognition have been developed (4), but the correspondence between these models and the neural architecture of the ventral object vision pathway is uncertain. Unlike single-cell studies, functional brain imaging has revealed a large-scale spatial organization for specialization within the ventral object vision pathway, as demonstrated by differential patterns of response, i.e., increases in neural activity indicated by localized increases in blood oxygenation, to faces and other categories of objects in ventral temporal cortex (5-17). Models for this functional architecture fall into three classes. One model proposes that ventral temporal cortex contains a limited number of areas that are specialized for representing specific categories of stimuli (5-8). Thus far, two specialized areas have been described: the fusiform face area (FFA) and the parahippocampal place area (PPA) (Fig. 1) . A second model proposes that different areas in ventral temporal cortex are specialized for different types of perceptual processes (9 -11). In particular, this model proposes that the FFA is specialized for expert visual recognition of individual exemplars from any object category, not just faces. The third model proposes that the representations of faces and different categories of objects are widely distributed and overlapping (12) (13) (14) (15) . According to this model, which we have named "object form topography," ventral temporal cortex has a topographically organized representation of attributes of form that underlie face and object recognition. The representation of a face or object is reflected by a distinct pattern of response across a wide expanse of cortex in which both large-and small-amplitude responses carry information about object appearance. Unlike the other models, object form topography predicts how all categories might evoke distinct patterns of response in ventral temporal cortex and, thereby, provides an explicit account for how this cortex can produce unique representations for a virtually unlimited number of categories. We tested our model by investigating the patterns of response evoked in ventral temporal cortex by faces and multiple categories of objects. Our model predicts that each category elicits a distinct pattern of response in ventral temporal cortex that is also evident in the cortex that responds maximally to other categories. Analysis of patterns of neural response to object categories. Patterns of response were measured with functional magnetic resonance imaging (f MRI) in six subjects while they viewed pictures of faces, cats, five categories of man-made objects (houses, chairs, scissors, shoes, and bottles), and control, nonsense images (18) (Fig. 2) . The data were analyzed to determine whether each stimulus category evoked a pattern of response in the ventral object vision pathway that could be distinguished from the patterns of response evoked by all other individual categories. Patterns of response were examined in ventral temporal object-selective cortex, defined as those voxels with responses that differed significantly by category. The data for each subject were split into two sets, namely even and odd runs. We then determined whether the stimulus category that a subject was viewing could be identified by examining the similarity between the patterns of response evoked by each category on even and odd runs (19). Correlations between patterns of response served as indices of similarity (Fig. 3) . For example, to determine whether the pattern of response to one category, such as chairs, could be distinguished from the pattern of response to a different category, such as shoes, the correlation between the pattern of response to chairs on even runs and the response to chairs on odd runs (within-category correlation) was compared with the correlation between the response to chairs on even runs and the response to shoes on odd runs (between-category correlation). Distinct patterns of neural response for multiple categories of objects. The pattern of response in object-selective ventral temporal cortex correctly identified the category being viewed in 96% of pairwise comparisons (20). The pattern of response indicated when subjects were viewing faces, houses, and scrambled pictures with no errors (Table 1) . Identification accuracy for the small man-made objects (bottles, scissors, shoes, and chairs) was significantly better than chance for each category (21). Category identification based on patterns of nonmaximal responses. Although these results suggest that categoryspecific patterns of response are distributed and overlapping, higher within-category correlations could be due simply to the regions that reliably respond maximally to each category, with no information about a specific category carried by the pattern of response in cortex that responded maximally to other categories. To test whether the patterns of nonmaximal responses carry category-related information, we analyzed whether each stimu-
Haxby et al. employed brain patterns located in Fusiform Face Area (FFA) and Parahippocampal Place Area (PPA) in order to analyze correlations between different categories of visual stimuli, i.e., grayscale images of faces, houses, cats, bottles, scissors, shoes, chairs, and scrambled (nonsense) photos REF .
Distributed and overlapping representations of faces and objects in ventral temporal cortex
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