Implicit Distinction of the Race Underlying the Perception of Faces by Event-Related fMRI

A few studies have shown that the function of the fusiform face area is selectively involved in the perception of faces, including the perception of racial difference. We investigated the neural substrates of the face-selective region called fusiform face area and the superiority of the same-race memory in the fusiform face area by employing event-related fMRI. In our fMRI study, twelve healthy subjects (Oriental-Korean) performed the implicit distinction of race while they consciously made familiarity judgments, regardless of whether they considered a face as Oriental-Korean or Caucasian-American. For race distinction as an implicit task, the fusiform face areas (FFA) and the right parahippocampal gyrus had a greater response to the presentation of Oriental-Korean faces than for the Caucasian-American faces, but in the conscious race distinction between Oriental-Korean and Caucasian-American faces, there was no significant difference observed in the FFA. These results suggest that different activation in the fusiform regions and right parahippocampal gyrus resulting from superiority of same-race memory could have implicitly taken place by the physiological processes of face recognition. INTRODUCTION People are better at recognizing faces of their own than faces of other races. The same-race advantage has been demonstrated with behavioral studies involving a wide variety of protocols, face stimuli, participants and cultural settings. Golby et. al (1) have shown differential responses in the fusiform region to the same-race faces and other-race faces using conventional block paradigm fMRI with gray photographs of Caucasian-Americans and Afro-Americans. The contrastpolarity-specific structure (2) showed that the bilateral fusiform areas responded much stronger for faces with positive than negative contrast polarity. In our case, gray photographs of Oriental-Koreans and Caucasians-Americans are a more similar in the contrast of faces compared to those of Caucasian-Americans and AfroAmerican. In this study, we present our findings, which are called same-race memory superiority, from the bilateral fusiform gyri and the right parahippocampal gyrus, and we employed event-related functional magnetic resonance imaging (fMRI) study. MATERIALS AND METHODS Twelve right-handed normal, healthy volunteer adults participated in the experiment. The stimuli consisted of gray photographs of 100 Oriental-Korean and 100 Caucasian-American and each 100 were split into 50 familiar and 50 unfamiliar groups. The faces were presented for 1000 ms, replacing a baseline of an oval checquerboard present throughout the interstimulus interval, with minimal SOA of 4.5 s and 100 randomly intermixed null events. Each subject were scanned during one session, In the session named the fame-judgment (implicit task), the subjects were instructed to press one of two possible buttons with either the index or middle finger of their right hand to indicate whether a face was familiar or not, regardless of whether they considered it as Oriental-Korean or CaucasianAmerican. Incorrect answers were ignored. A 1.5T VISION system (Siemens Corps., Iselin, NJ) was used to acquired T2* weighted transverse EPI images (TR/TE/FA = 3000ms/60ms/90, FOV=240 x 240mm, 24 axial slices, 5mm slice thickness with no gap). The acquired data were applied to SPM99 for the preprocessing such as realignment, normalization, spatial smoothing, and then the individual contrast images for the effect of interest were entered into one-sample ttests to determine the group-level activation. The resulting statistical parametric maps of t-statistics at the each voxel were thresholded at P < 0.001; they were uncorrected for multiple comparisons. Statistical comparisons were made by one-way ANOVA between the Oriental-Korean and Caucasian-American faces.