Serial learning by rhesus monkeys: II. Learning four-item lists by trial and error.

Three rhesus macaque monkeys were trained to produce novel 4-item lists (A-->B-->C-->D) on which all items were displayed from the start of training. Subjects were previously trained to produce 4-item lists by adding one item at a time (A, A-->B, A-->B-->C, and A-->B-->C-->D; lists K. B. Swartz et al., 1991). Those lists could be mastered by responding to each new item last. To learn lists on which all items were displayed from the start of training, subjects had to recall the consequences of errors and correct responses to each item. Errors ended the trial; correct responses to A, B, or C allowed the trial to continue. A correct response to D produced food reward. Although the probability of executing a 4-item list correctly by chance was .04, each subject mastered 4 novel 4-item lists by trial and error. The ability of monkeys to use a trial-and-error strategy to learn novel lists provides a basis for studying the development of serial expertise in animals.

Social preferences by and for pigtailed macaques (Macaca nemestrina) with trisomy 18.

Social choices of trisomic macaques (macaca nemestrina) were compared with those of age-matched controls and of infants and adult females without handicaps. All groups chose social over nonsocial stimuli and showed few differences in their preferences for stimulus animals with and without handicaps. On initial encounter, the trisomic monkeys were socially interesting to age-matched controls and to younger animals and adult females. Thus, avoidance of individuals with handicaps probably is not a general primate trait. Even though the trisomic monkeys showed inappropriate social and motor behavior in play groups, their preference for social stimuli demonstrates that the presence of mental retardation and physical handicaps need not reduce positive social motivation even when prior social experiences have been largely negative.

Serial learning by rhesus monkeys: I. Acquisition and retention of multiple four-item lists.

Two rhesus monkeys were trained to learn eight 4-item lists, each composed of 4 different photographs. Lists were trained in successive phases: A, A----B, A----B----C, and A----B----C----D. After List 4, retention, as measured by the method of savings, was, on average, 66% (range: 44-84%). Indeed, all 4 lists could be recalled reliably during a single session with neither a decrement in accuracy nor an increase in the latency of responding to each item. Response latencies on a subset test employing all possible 2- and 3-item subsets of each 4-item list support the hypothesis that monkeys form linear representations of a list. Latencies to Item 1 of a subset varied directly with the position of that item in the original list. On List 1, latencies to Item 2 varied directly with the number of intervening items between Item 1 and Item 2 in the original list. During the acquisition of Lists 5-8, both Ss mastered the A----B and A----B----C phases of training in the minimum number of trials possible.

Species discrimination in infant pigtail macaques with pictorial stimuli.

Two experiments used a visual fixation habituation-dishabituation paradigm to study the ability of young, socially restricted pigtail macaques to discriminate among adults of 3 macaque species (pigtail, cynomolgus, and stumptail) with pictures as stimuli. The results of the 1st study demonstrated that 3-month-old pigtail infants could discriminate among faces of adult females of all 3 species. The 2nd study was methodologically similar to the 1st, which the exception that the face stimuli were presented upside-down. The results of Experiment II demonstrated no species discrimination, suggesting that the socially relevant discrimination demonstrated in Experiment I was a function of cues unique to the upright face and not a function of abstract cues available in both upright and upside-down facial stimuli.

Responses of juvenile bonnet macaques to social stimuli presented through color videotapes.

Twelve juvenile bonnet macaques (Macaca radiata), 6 males and 6 females, were presented with color videotape recordings of 3 types of social stimuli. The stimulus animals, all unfamiliar adult conspecifics, consisted of a passive female, a passive male, and a threatening male. Subjects were observed in the presence of their mother and 1 other juvenile-mother dyad. The juveniles showed the highest scores for contact with mother when presented with the threatening male stimulus. Similarly, subjects lipsmacked significantly more to the male threatening male stimulus than to either the passive male or female. The female stimulus was approached significantly more than either the passive or threatening male. Results suggest that juvenile macaques will respond to social stimuli presented through color video recordings in a socially appropriate manner. This technique provides a new tool in the investigation of social perception in nonhuman primates.