Face perception in monkeys reared with no exposure to faces

Abstract

Infant monkeys were reared with no exposure to any faces for 6-24 months. Before being allowed to see a face, the monkeys showed a preference for human and monkey faces in photographs, and they discriminated human faces as well as monkey faces. After the deprivation period, the monkeys were exposed first to either human or monkey faces for a month. Soon after, the monkeys selectively discriminated the exposed species of face and showed a marked difficulty in regaining the ability to discriminate the other nonexposed species of face. These results indicate the existence of an experience-independent ability for face processing as well as an apparent sensitive period during which a broad but flexible face prototype develops into a concrete one for efficient processing of familiar faces.

Fig. 1.

An infant monkey and her living circumstance. An infant monkey and a caregiver with (A) and without (B) a facemask. Both photos were taken after the face-deprivation period. (C) Toys placed in the monkey's home cage. (D) Decorations provided around the home cage.

Fig. 2.

Visual stimuli. (A) Photographs of nonface objects. (B) Featural stimulus set of monkey faces: variation in individual features (eyes and mouth). (C) Spacing stimulus set of monkey faces: variation in spacing of the eyes and between eyes and mouth. (D) Featural stimulus set of human faces. (E) Spacing stimulus set of human faces.

Fig. 3.

Average looking time for the preferential looking task. (A) Results obtained during face-deprivation period. (B) Results from control adult monkeys. (C) Results obtained from the monkeys exposed to human faces for a month. (D) Results obtained from the monkeys exposed to monkey faces for a month. (E and F) Results obtained a year after the deprivation period from the monkeys exposed first to human faces (E) and to monkey faces (F). Error bars represent SE.

Fig. 4.

Average looking time for the VPC task. (A) Results obtained during face-deprivation period. (B) Results of control adult monkeys. (C) Results obtained from the monkeys exposed to human faces for a month. (D) Results obtained from the monkeys exposed to monkey faces for a month. (E and F) Results obtained a year after the deprivation period from the monkeys exposed first to human faces (E) and to monkey faces (F). Error bars represent SE.