The role of face shape and pigmentation in other-race face perception: an electrophysiological study

Abstract

Adult observers generally find it difficult to recognize and distinguish faces that belong to categories with which they have limited visual experience. One aspect of this phenomenon is commonly known as the "Other-Race Effect" (ORE) since this behavior is typically highly evident in the perception of faces belonging to ethnic or racial groups other than that of the observer. This acquired disadvantage in face recognition likely results from highly specific "tuning" of the underlying representation of facial appearance, leading to efficient processing of commonly seen faces at the expense of poor generalization to other face categories. In the current study we used electrophysiological (event-related potentials or ERPs) and behavioral measures of performance to characterize face processing in racial categories defined by dissociable shape and pigmentation information. Our goal was to examine the specificity of the representation of facial appearance in more detail by investigating how race-specific face shape and pigmentation separately modulated neural responses previously implicated in face processing, the N170 and N250 components. We found that both components were modulated by skin color, independent of face shape, but that only the N250 exhibited sensitivity to face shape. Moreover, the N250 appears to only respond differentially to the skin color of upright faces, showing a lack of color sensitivity for inverted faces.

Figure 1

We created four distinct types of faces by combining the 3D shape of White and Black model faces with White and Black skin. The figure depicts how an individual face with White shape and color (top left) could be given Black skin (top right). The bottom row depicts the complementary process by which faces with Black shape and skin color were given White skin color. “Shape” as used in the current study always refers to the real 3D form of the computer-generated head.

Figure 2

Schematic view of our behavioral match-to-sample task. Observers first viewed a sample face for 500ms before viewing two candidate test images, each rendered from a different lighting direction than the sample. The individual depicted in the sample image was always present at test (in this case pictured at left). The change in illumination was employed between sample and test to discourage simple pattern-matching strategies.

Figure 3

The sensor groups used to analyze the N170, and N250 components. Note that previous research has often used the same sensors to measure the N170 and the N250. We did not do so here because our electode selection criteria depended upon identifying sensors where the relevant component was maximal across conditions, leading to non-overlapping sensor groupings for the N170 and N250. We discuss this point in more detail in the main text.

Figure 4

The N170 component observed at left and right hemisphere sensors of interest (numbered in the text). Waveforms for upright and inverted faces are presented in the top and bottom rows, respectively.

Figure 5

The N250 component observed at left and right hemisphere sensors of interest (numbered in the text). Waveforms for upright and inverted faces are presented in the top and bottom rows, respectively.