The other-species effect in human perceptions of sexual dimorphism using human and macaque faces

Humans are better able to discriminate among human faces than faces of other species. This difference in perceptual discrimination is known as the "other-species effect". Models of perception have posited that the ultimate functional significance of the other-species effect is a higher discrimination capability within an organism's most familiar and salient stimulus set while attenuating the ability to discriminate amongst unfamiliar stimuli. Here, human participants made masculinity judgements of human and macaque faces manipulated based on either human or macaque sexual dimorphism. Humans were more accurate at identifying masculine/feminine faces in species-congruent than species-incongruent transforms in both human and macaque faces. We observed an other-species effect whereby accuracy (correctly judging masculinized faces as more masculine) was highest for own-species faces. We also found that both men and women were better at judging the sex-typicality of male faces than female faces, regardless of the species of the face or the species of the manipulation. Our findings demonstrate an other-species effect for the perception of sex-typicality among human raters.