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Olivia Tomeo, Ning Liu, Leslie Ungerleider; The face inversion effect in rhesus macaques. Journal of Vision 2016;16(12):741. doi: 10.1167/16.12.741.
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© 2017 Association for Research in Vision and Ophthalmology.
Face perception plays a critical role in social communications and interactions. Given the similarities between monkeys and humans in the neural circuitry underlying social cognition, the rhesus macaque could provide an ideal animal model to study face processing. Although human and monkey neuroimaging studies have demonstrated similar face patch systems, behavioral studies exploring face processing in monkeys have yielded inconsistent results. Here, we sought to clarify face-processing mechanisms by re-examining in macaques the face inversion effect, which refers to difficulty in recognizing inverted faces compared to inverted non-face objects. Head-fixed rhesus macaques were trained to perform an oculomotor delayed match-to-sample (DMS) task. Stimuli were from six categories (faces: macaque, chimpanzee, human and sheep; objects: shoes and cars). Faces were forward facing and emotionless. All stimuli were contrast-normalized and grayscale. Faces were cropped with an oval mask to isolate central face information and exclude peripheral features. Subjects were first trained on the DMS task with simple shapes until achieving 85% accuracy, and then performed the test for each category. Reaction time (RT), accuracy, and eye movement pattern were recorded; the efficiency score (RT/accuracy) was used to account for the trade-off between RT and accuracy. We found that scan patterns were similar when viewing macaque, chimpanzee and human faces but not sheep faces. However, better efficiency scores for recognizing upright stimuli than the inverted ones were only found for macaque and chimpanzee faces but not for human faces, sheep faces or non-face objects. These results revealed a face inversion effect for conspecific (macaque) and heterospecific (chimpanzee) faces, implying that macaques process macaque and chimpanzee faces holistically. Our data support the idea that the effect is specific for stimuli for which the individual has developed expertise. We speculate that the subjects generalized their expertise of monkey faces to chimpanzee faces due to similarity.
Meeting abstract presented at VSS 2016
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