The role of propulsive muscles of the shoulder during quadrupedalism in vervet monkeys (Cercopithecus aethiops): implications for neural control of locomotion in primates

In comparative anatomical studies of the shoulder, the humeral retractors are often grouped together as propulsive muscles, which are important in the propulsive stroke of the forelimb during quadrupedal locomotion. Electromyographic (EMG) analyses of these muscles in opossums, cats, and dogs in general have confirmed such conclusions. An EMG study of chimpanzee shoulder muscles during knuckle-walking found, however, that the humeral retractors are either inactive or perform a function unrelated to propulsion (Larson & Stern, 1987). This contrast in muscle recruitment patterns between chimpanzees and more "typical" mammalian quadrupeds was attributed to the derived morphology of the chimpanzee shoulder. The present study examines the activity patterns of the humeral retractors in the vervet monkey, a primate more closely resembling nonprimate mammals in its shoulder morphology. The results of this EMG analysis show that despite the significant differences in anatomy between chimpanzees and vervets, the two species display very similar muscle recruitment patterns during quadrupedalism, and there is evidence for this same pattern in other species of primates. These differences in muscle activity patterns between primates and nonprimate mammals may be related to changes in the neurological control of locomotion in primates due to the evolutionary development of manipulative abilities in the primate forelimb.     

Is dependence on phonological information in children's reading a product of instructional approach?

Eight-year-old British children were found to be less accurate at rejecting pseudohomophones than ordinary nonwords in a lexical decision task, but 8-year-old New Zealand children did not show this effect. A subsequent homophone decision task showed that this difference was not due to the New Zealand children being unable to distinguish pseudohomophones from other nonwords. The New Zealand children, however, were less accurate than the British children in pronouncing the pseudohomophones they had identified. It was argued that the British children tended to sound out the items before making a choice in the lexical decision task, which gave salience to phonological rather than visual information, resulting in increased errors to the pseudohomophones. It was concluded that where the British children showed this dependency on use of phonological information it was a product of the teaching approach they had experienced.     

Developmental trends in the understanding of perceptual adaptation

In the first of three studies, kindergartners, third graders, and sixth graders were questioned to determine whether they comprehend five types of perceptual adaptation or contrast effects. The results indicated little consistency among kindergartners, but there were strong improvements by the third-grade level, and at the sixth-grade level almost all of the children were showing perfect performance, demonstrating comprehension of the five forms of perceptual adaptation. In the second and third studies, children and adults were placed in a situation in which adaptation to temperature and weight could occur, and they were asked to predict subsequent perceptions. Correct performance in these studies generally occurred at later ages than in Study 1 with even college students showing incorrect performance in some cases. However, the age trends shifted quite markedly depending upon the nature and structure of the task. The results were consistent with a theory stressing the relation of early formed schemas in the form of memory traces of experiences to later appearing and more abstract schemas. The results show the importance of studying older children when considering developing theories of mind.     

The development of structural complexity in the child's concept of family: the effect of cognitive stage, sex, and intactness of family

Twenty-eight boys and 28 girls at each of the Piagetian preoperational, concrete operational, and formal operational cognitive stages were given an interview focusing on their concepts of family. Half of each group were from intact families, and half were from divorced families. Interviews were scored for two structural aspects of the concept of family: conceptual level, and use of dimensions that structure the concept. The complexity of children's concepts was strongly related to cognitive stage and, to a lesser degree, to sex. Frequency of use of concept dimensions was strongly affected by general developmental level, though not specifically cognitive stage, and by intactness of family, but to a lesser degree by sex. Specific information is provided on the effect of these factors on perceptions of family composition, parental roles, and breadth of family activities.     

Altering contingencies to facilitate compliance with traffic light systems

The effects of altering light pattern sequences on driver compliance at a busy, urban intersection were explored. The baseline light timing sequences resulted in only 46.8% of drivers stopping at the yellow or red lights. Using an A-B-C design, we altered light pattern sequences that increased the probability of drivers stopping at the signals to 88.8% and 98.8%. These findings indicate that traffic light contingencies have potent effects in influencing driver behaviors at busy intersections. Following completion of the study, the traffic engineer approved the permanence of the light timing pattern that increased traffic rule compliance. Accident data collected before and after the light timing changes indicated a reduction in automobile accidents.     

The effects of social motives on behavior in social dilemmas in two cultures

Subjects in Santa Barbara, California, and Groningen, The Netherlands, participated in a seven-person social dilemma game, presented in terms of a conservation of resources problem. Prior to their decision making in the social dilemma game, subject's social motive (altruistic, cooperative, individualistic, competitive) was assessed by means of two different classification procedures. On the basis of previous research findings American subjects were expected to display relatively more competitive social motives, and Dutch subjects relatively more cooperative ones. However, no indications of crosscultural differences were found neither with regard to the distribution of social motives nor with regard to the amount of resources taken for self in the social dilemma game. In both locations, competitive subjects took most resources for self, individualistic subjects took next most, cooperative subjects took less than individualists, and altruistic subjects took the least. In addition to predictive validity, indices of the convergent validity of two social motive assessment procedures were described.