Abstract
Human adults and infants show a preference for average faces, which could stem from a general processing mechanism and may be shared among primates. However, little is known about preference for facial averageness in monkeys. We used a comparative developmental approach and eye-tracking methodology to assess visual attention in human and macaque infants to faces naturally varying in their distance from a prototypical face. In Experiment 1, we examined the preference for faces relatively close to or far from the prototype in 12-month-old human infants with human adult female faces. Infants preferred faces closer to the average than faces farther from it. In Experiment 2, we measured the looking time of 3-month-old rhesus macaques (Macaca mulatta) viewing macaque faces varying in their distance from the prototype. Like human infants, macaque infants looked longer to faces closer to the average. In Experiments 3 and 4, both species were presented with unfamiliar categories of faces (i.e., macaque infants tested with adult macaque faces; human infants and adults tested with infant macaque faces) and showed no prototype preferences, suggesting that the prototypicality effect is experience-dependent. Overall, the findings suggest a common processing mechanism across species, leading to averageness preferences in primates.
Highlights
Similarities between humans and macaques have been reported for early developmental processes
Macaque infants showed significantly longer total looking time for faces closer to the prototype compared to faces farther from the prototype, t(22) = 4.16, p < 0.001, 95% CI [0.115, 0.343], Cohen’s d = 0.87, (Mclose = 1018 msec, SDclose = 438 msec, and Mfar = 815 msec, SDfar = 291 msec)
Macaque infants showed no significant preference for faces closer to the prototype compared to faces farther from the prototype, looking long to both face types, t(25) = 0.04, p = 0.97, Cohen’s d = 0.01, 95% CI [− 0.220, 0.230], (Mclose = 808 msec, SDclose = 276 msec, and Mfar = 890 msec, SDfar = 530 msec)
Summary
Similarities between humans and macaques have been reported for early developmental processes. Infant macaques present sensitivity for basic face structures (i.e., first-order relations, eyes above the nose, nose above the mouth). They prefer stimuli that respect face-like configuration[19,20,21], and prior work has revealed a similar sensitivity in human neonates[22,23]. Typical faces are judged more attractive than distinctive faces[32,33], and a meta-analysis has shown that the appeal of averageness is not restricted to face race or sex[34], it might be linked with visual experience[35]. Average traits in a face are linked with greater genetic diversity which may result in greater parasitic resistance[37], whereas deviation from average could signal chromosomal disorders[39], at least for lower scores of face prototypicality (i.e., the “bad genes” hypothesis[40])
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