Attending to attention: Reverse correlation reveals subtle cues to attentiveness in others' faces.

Some of the most foundational properties we can perceive from others' faces involve cognitive states, such as how attentive (vs. distracted) they seem - an important ability, since the likelihood of someone in our local environment affecting our fitness is enhanced when they are attentive. But how can we tell whether another person is attentive? This study reveals that the way in which we perceive attentiveness in others' faces is straightforward in some ways, but deeply counterintuitive in others. We explored this using reverse correlation, a data-driven approach that can reveal the nature of internal representations without prior assumptions. In two online studies (n = 200 each), observers viewed pairs of faces created by adding randomly generated noise (across many spatial frequencies) to a constant base face, and had to select which appeared to be most attentive. Analyses of automatically extracted facial landmarks from the resulting "classification images" revealed the determinants of perceived attentiveness. Some cues were straightforward: attentive faces indeed had more direct eye gaze, and larger pupils. But other novel and equally robust cues were subtle and surprising; for example, attentive faces reliably had darker (as if more flared, or retroussé) nostrils. These powerful and subtle effects of facial cues on impressions of attentiveness highlight the importance of attention not just as a perceptual process, but as an object of perception itself.