Neural adaptation to faces reveals racial outgroup homogeneity effects in early perception

Abstract

A hallmark of intergroup biases is the tendency to individuate members of one's own group but process members of other groups categorically. While the consequences of these biases for stereotyping and discrimination are well-documented, their early perceptual underpinnings remain less understood. Here, we investigated the neural mechanisms of this effect by testing whether high-level visual cortex is differentially tuned in its sensitivity to variation in own-race versus other-race faces. Using a functional MRI adaptation paradigm, we measured White participants' habituation to blocks of White and Black faces that parametrically varied in their groupwise similarity. Participants showed a greater tendency to individuate own-race faces in perception, showing both greater release from adaptation to unique identities and increased sensitivity in the adaptation response to physical difference among faces. These group differences emerge in the tuning of early face-selective cortex and mirror behavioral differences in the memory and perception of own- versus other-race faces. Our results suggest that biases for other-race faces emerge at some of the earliest stages of sensory perception.

Keywords: intergroup perception; neural adaptation; perceptual sensitivity; race.

Fig. 1.

The volume of face-selectivity in high-level visual cortex is modulated by face race. (A) Thresholded parameter maps show voxelwise t values for the contrast of White faces (Top) or Black faces (Bottom) versus all other stimuli. Data are presented on inflated cortical surfaces of 3 participants (dark regions are sulci; lighter regions are gyri). The region shown is the ventral surface of the temporal lobe, known as the VTC. The blue region outlined in dotted-white is the MFS, whose posterior and anterior tips are anatomical anchors predicting the location of face-selective cortex on the lateral fusiform gyrus. (B) Line plots illustrating the volume of above-threshold (t values > 3) activation in each subject’s VTC defined with the contrasts of White or Black faces.

Fig. 2.

(A) Experimental design of the adaptation experiment. In each block, 6 faces were presented at 1 of 5 levels of groupwise dissimilarity. An example of the morphing scheme is presented on the Left, and 2 example morph lines are shown on the Right. (B) Plots mapping the percentage of signal change in right hemisphere face-selective cortex in each participant for White (Left) and Black (Right) faces, normalized to the zero-morph level (full adaptation), along with the summary curve in black.