Intramuscular electrical stimulation of facial muscles in humans and chimpanzees: Duchenne revisited and extended

The pioneering work of Duchenne (1862/1990) was replicated in humans using intramuscular electrical stimulation and extended to another species (Pan troglodytes: chimpanzees) to facilitate comparative facial expression research. Intramuscular electrical stimulation, in contrast to the original surface stimulation, offers the opportunity to activate individual muscles as opposed to groups of muscles. In humans, stimulation resulted in appearance changes in line with Facial Action Coding System (FACS) action units (AUs), and chimpanzee facial musculature displayed functional similarity to human facial musculature. The present results provide objective identification of the muscle substrate of human and chimpanzee facial expressions- data that will be useful in providing a common language to compare the units of human and chimpanzee facial expression.     

Bootstrapping to test for nonzero population correlation coefficients using univariate sampling

This article proposes 2 new approaches to test a nonzero population correlation (rho): the hypothesis-imposed univariate sampling bootstrap (HI) and the observed-imposed univariate sampling bootstrap (OI). The authors simulated correlated populations with various combinations of normal and skewed variates. With alpha set=.05, N> or =10, and rho< or =0.4, empirical Type I error rates of the parametric r and the conventional bivariate sampling bootstrap reached .168 and .081, respectively, whereas the largest error rates of the HI and the OI were .079 and .062. On the basis of these results, the authors suggest that the OI is preferable in alpha control to parametric approaches if the researcher believes the population is nonnormal and wishes to test for nonzero rhos of moderate size.     

Classifying chimpanzee facial expressions using muscle action

The Chimpanzee Facial Action Coding System (ChimpFACS) is an objective, standardized observational tool for measuring facial movement in chimpanzees based on the well-known human Facial Action Coding System (FACS; P. Ekman & W. V. Friesen, 1978). This tool enables direct structural comparisons of facial expressions between humans and chimpanzees in terms of their common underlying musculature. Here the authors provide data on the first application of the ChimpFACS to validate existing categories of chimpanzee facial expressions using discriminant functions analyses. The ChimpFACS validated most existing expression categories (6 of 9) and, where the predicted group memberships were poor, the authors discuss potential problems with ChimpFACS and/or existing categorizations. The authors also report the prototypical movement configurations associated with these 6 expression categories. For all expressions, unique combinations of muscle movements were identified, and these are illustrated as peak intensity prototypical expression configurations. Finally, the authors suggest a potential homology between these prototypical chimpanzee expressions and human expressions based on structural similarities. These results contribute to our understanding of the evolution of emotional communication by suggesting several structural homologies between the facial expressions of chimpanzees and humans and facilitating future research.     

Sibling Influence on Smoking Behavior: A Within-Family Look at Explanations for a Birth-Order Effect

Using a repeated-measures design, we found a significant birth-order relationship suggesting lower ages of smoking onset in later born siblings of a 1979 National Longitudinal Survey of Youth cohort. Two social learning mechanisms, modeling and opportunity, were explored to help illuminate the causes of trends in the within-family means. When empirical patterns were compared to predictions derived from our specifications of how opportunity and modeling processes should work, the results were unsuccessful in explaining the birth-order effect. As a third explanation of the birth-order effect, telescoping did show a significant influence. The effect size was small, however, and had little effect on the group means assessed. Finally, a pattern did emerge that was consistent with a reformulation of the opportunity process in which sisters play a particularly strong role. We develop future research implications of this pattern and speculate on genetic and social conservatism explanations.     

Further findings on assaultiveness and alcohol use in interpersonal disputes

In a previous study uniform observational data were collected regarding family disputes managed by police officers; those data contradicted views commonly held by social scientists and by police about the roles of assaultiveness and alcohol use in these events. In the present study police officers employed systematic naturalistic observation during their interventions as third parties in disputes between nonfamily members as well as those between family members. Tentative conclusions about assaultiveness, based on the data of both studies, are that it: does not usually precede the arrival of police in such disputes; is associated with interpersonal closeness of the disputants; is associated with poverty rather than race; and is as likely in a middle-class small city as in a poor inner-city area. Tentative conclusions about the use of alcohol in police-managed interpersonal disputes are: that these disputes are not usually influenced by alcohol use; and that assaultiveness is not related to alcohol use in such disputes.     

Head orienting contributes to the directional accuracy of aiming at distant targets

The aim of this study was to evaluate the contribution of head orienting to the directional accuracy of aiming at targets of different eccentricities. Six right-handed females were tested in three experimental conditions: (1) aiming at a target with head fixed, (2) aiming with head free to move, (3) aiming with instruction to align head with target. For all conditions, accuracy is reduced when aiming at the more eccentric targets. However, undershooting increases considerably when the head is fixed. The present results support a twofold hypothesis for encoding spatial information of visual origin: an eye (<15° of eccentricity) and a head (>25° of eccentricity) range. It can be concluded that head movements contribute to accuracy of aiming at targets located beyond 20° of eccentricity of the subject's visual field, thus providing the arm program with directional specifications.     

Group differences in the mutual gaze of chimpanzees (Pan troglodytes)

A comparative developmental framework was used to determine whether mutual gaze is unique to humans and, if not, whether common mechanisms support the development of mutual gaze in chimpanzees and humans. Mother-infant chimpanzees engaged in approximately 17 instances of mutual gaze per hour. Mutual gaze occurred in positive, nonagonistic contexts. Mother-infant chimpanzees at a Japanese center exhibited significantly more mutual gaze than those at a center in the United States. Cradling and motor stimulation varied across groups. Time spent cradling infants was inversely related to mutual gaze. It is suggested that in primates, mutual engagement is supported via an interchangeability of tactile and visual modalities. The importance of mutual gaze is best understood within a perspective that embraces both cross-species and cross-cultural data.     

On-line versus off-line control of rapid aiming movements

Recent studies have shown the importance of visual feedback during the rapid initial phase of aiming movements for the control of direction (e.g., Bard, Paillard, Fleury, Hay, & Larue, 1990; Blouin, Teasdale, Bard, & Fleury, in press; Teasdale, Blouin, Bard, & Fleury, 1991). In most of these studies, visual feedback conditions were presented in blocked sessions. Consequently, higher-order processes (e.g., feedforward and/or learning processes), along with on-line processing of visual feedback, might have contributed to the better accuracy found when subjects had visual feedback of only the initial portion of the movements (compared with movements without visual feedback). To test this possibility, we studied subjects' performance of rapid arm movements under different types of presentation (random, precued, and blocked) of the visual feedback conditions of the trajectory (no vision, initial portion only, and vision of the entire trajectory). Directional errors were larger in the no-vision condition than in both conditions with visual feedback. There were no differences among the presentation conditions, suggesting that on-line processing of visual information contributed to the control of the arm movements.