Brain systems for assessing the affective value of faces

Abstract

Cognitive neuroscience research on facial expression recognition and face evaluation has proliferated over the past 15 years. Nevertheless, large questions remain unanswered. In this overview, we discuss the current understanding in the field, and describe what is known and what remains unknown. In §2, we describe three types of behavioural evidence that the perception of traits in neutral faces is related to the perception of facial expressions, and may rely on the same mechanisms. In §3, we discuss cortical systems for the perception of facial expressions, and argue for a partial segregation of function in the superior temporal sulcus and the fusiform gyrus. In §4, we describe the current understanding of how the brain responds to emotionally neutral faces. To resolve some of the inconsistencies in the literature, we perform a large group analysis across three different studies, and argue that one parsimonious explanation of prior findings is that faces are coded in terms of their typicality. In §5, we discuss how these two lines of research--perception of emotional expressions and face evaluation--could be integrated into a common, cognitive neuroscience framework.

Figure 1.

(a) Correlations between trait and emotion judgements of emotionally neutral faces. (b) Correlations between trait judgements and a classifier's probabilities of emotional expressions in these faces. Traits are ordered by their loadings on the first PC derived from a PCA of the traits.

Figure 2.

A plot of emotion judgements and a selected set of trait judgements in a two-dimensional space derived from a PCA on all trait and emotion judgements collectively. A representative subset of the traits is shown to avoid overcrowding.

Figure 3.

Parametric manipulation of face trustworthiness. From left to right: −3, −1, 1 and 3 standard deviations away from the mean face.

Figure 4.

Brain responses to faces parametrically manipulated to vary on perceived trustworthiness. (a–c) Statistical overlay of regions showing a linear response to face trustworthiness in a group analysis of 67 subjects across three studies. Cool colours indicate a negative linear trend with greater responses to untrustworthy faces than trustworthy faces. Uncorrected p < 10⁻⁴. (d–f) Statistical overlay of regions showing a quadratic response to face trustworthiness. Hot colours indicate a positive quadratic term. Cool colours indicate a negative quadratic term. Uncorrected p < 10⁻⁴.

Figure 5.

The response to both the high-social dimension (green; valence) and the low-social dimension (red; control) in the amygdala and the FFA. (a) The bilateral amygdala, defined anatomically by the AFNI Talairach atlas; (b) the bilateral FFA, defined by a face localizer.