In this paper, we summarize a series of studies on the developmental changes in social cognition in mother-raised infant chimpanzees from birth to around 2 years old. The infants preferentially tracked a photograph of their mother's face at 1 month but showed indifferent preferences to faces at 2 months old. This change in facial recognition was correlated with a decrease in neonatal spontaneous smiling, increase in social smiling and a decline in neonatal imitation of facial expressions. Also at around 2 months, the infants began to show preferences for directed-gaze faces over averted gazes, and the amount of

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An infant chimpanzee's joint visual attention to objects behind him was investigated. A recent study has shown that a 13-month-old infant chimpanzee can follow human social cues including glancing (Okamoto, Tomonaga, Ishii, Kawai, Tanaka, & Matsuzawa, 2002a). In humans, 12-month-olds do not follow gaze to objects behind them but 18-month-olds do (Butterworth & Jarrett, 1991). In the present study, from 13 months old, the infant chimpanzee had been tested to look at one of two identical objects, which an experimenter indicated by pointing or head turning. The objects were set in front of or behind the subject. In our series of experiments, we used moving or stationary objects as targets. Moreover, the experimenter manipulated a computer at the onset of each block of trials. The results show that by the age of 20 months, the infant reliably followed the experimenter's cues and looked back to the target behind him. Moving targets elicited more responses than stationary targets, and the subject showed more follow responses after having seen the experimenter manipulating the computer.

We investigated the behavioural and cognitive development of a captive male infant chimpanzee, Ayumu, raised by his mother, Ai. Here we report Ayumu's achievements up to the age of 2 years and 3 months, in the context of complex computer-controlled tasks. From soon after birth, Ayumu had been present during an experiment performed by his mother. The task consisted of two phases, a matching-to-sample task in which she received token rewards, and the insertion of these tokens into a vending machine to obtain food rewards. Ayumu himself received no reward or encouragement from humans for any of the actions he exhibited during the experiment. At the age of 9 months and 3 weeks, Ayumu performed his first matching-to-sample trial. At around 1 year and 3 months, he began to perform them consistently. Also during this period, he frequently stole food rewards from his mother. At 2 years and 3 months, Ayumu succeeded for the first time in inserting a token into the vending machine. Once he had succeeded in using a token, he performed both phases of the task in sequence 20 times consecutively. The infant's behaviour was not shaped by food rewards but by a strong motivation to copy his mother's behaviour. Our observations of Ayumu thus mirror the learning processes shown by wild chimpanzees.