Anticipatory control of postural and task muscles during rapid arm flexion

A multicomponent pattern of premovement (anticipatory) activity in both task and postural muscles was examined for a unilateral rapid arm flexion movement (Belen'kii, Gurflnkel, & Pal'tsev, 1967) performed under simple visual reaction-time conditions. Subjects performed 30 right- and 30 left-side responses on each of four consecutive days. The anticipatory postural muscle activity may be considered a valid component of voluntary unilateral arm flexion. Invariances and variability in the spatial and temporal characteristics of the neuromuscular pattern are described in relationship to behavioral and motor control models of response organization. It is suggested that some temporal patterning among response components may not be preprogrammed centrally.     

Visual control of step length during running over irregular terrain

Running over uneven ground requires visually regulating step length to secure proper footing. To examine how this is achieved, we studied subjects running on a treadmill on a series of irregularly spaced targets. The movements of their lower limbs and coccyx relative to the targets were monitored opto-electronically by a Selspot system. The results indicated that step length was adjusted to strike the targets primarily by varying the vertical component of impulse applied to the ground during the stance phase. In contrast, horizontal impulse was not varied significantly, and changing the reach forward of the foot on landing contributed little to variation in step length. Changing the vertical impulse simply altered the step time proportionately. Thus the data are consistent with a time-based model in which vertical impulse is modulated by the optic variable delta tau (Lee, 1976) specifying the time gap that has to be bridged by the runner between two targets.     

TEACHING SOCIAL LANGUAGE TO MODERATELY HANDICAPPED STUDENTS

Three students with moderate handicaps were taught to initiate and expand on conversational topics. The teaching procedure used stimuli generated from actual conversations with nonhandicapped peers. Generalization was assessed by audiotaping conversations between the handicapped students and their peers in natural school contexts without adult supervision. Results indicated that training generalized to natural contexts. These results were socially validated by undergraduate special education students, who rated tapes of two of the students' conversations during training phases as more socially competent than during baseline. Results are discussed in terms of the evaluation of complex social behavior as multioperant behaviors.     

Evolution and the nonlegal equivalent of aggressive criminal behavior

Within the framework of modern evolutionary theory, arguments are reviewed that the nonlegal equivalent of aggressive criminal behavior may have evolved by natural selection among mammals, particularly primates, as part of their overall approach to reproduction. If so, the commission of aggressive crimes (or their nonlegal equivalent) by humans, and even efforts to prevent fellow social group members from being victimized by aggressive crimes, may also be partially explainable in natural selection terms. The plausibility of this deduction was explored, first, by specifying the three elements that a human act must have to be regarded as an aggressive crime. Summarily, these were that (1) injury to a victim must be a likely result of the act, (2) the act must be intended, and (3) the act must elicit negative responses from those witnessing it. The primate behavior literature was examined for evidence that some behavior of nonhumans met all three conditions. Affirmative results were obtained. Therefore, while further research is in order, human aggressive criminal behavior, as well as human efforts to control it, seem to have close parallels in other primates. This would be consistent with the notion that aggressive criminal behavior (along with its condemnation by fellow group members) is part of a social system produced and sustained by natural selection.     

Victim-Blaming and Society-Blaming Scales for Social Problems

Until now, no general scales have been available for measuring victim or society blaming. This constraint has been an impediment to policymaking with regard to those who are affected by social problems. Four scales were constructed: stable victim-blaming scale, unstable victim-blaming scale, stable society-blaming scale, and unstable society-blaming scale. Based on the results of the preliminary exploratory factor analysis and the reliability coefficients, the unstable society-blaming scale was deleted from further analysis. Then, a confirmatory factor analysis using the LISREL 7 program was conducted to evaluate the parameter estimates of the scale items and examine the construct validity of the 3 scales. The scales were judged to have construct validity with satisfactory reliability.     

Individual and age-related differences in children’s working memory

The purpose of this study was to investigate the degree to which age-related and individual differences in children’s working memory (WM) are due to a general or task-specific capacity system. Experiment 1 correlated children’s (N=146; age range 5–19 years) verbal and visual-spatial working memory performance with various intelligence and achievement measures. The results supporting a general system were that (1) visual-spatial and verbal WM measures were significantly intercorrelated with and without age partialed out and (2) both verbal and visual-spatial WM measures were significantly correlated with diverse achievement and intelligence measures. Experiment 2 compared three age groups (N=192; 7-, 10-, and 13-year-olds) on working-memory performance tasks under initial, enhanced (cued), and maintenance conditions. The results supporting a general capacity system were that (1) age-related performance differences in WM were found on all conditions and not isolated to specific processes, (2) the maintenance measures (high-load condition) predicted the variance better in age-related performance than process measures, and (3) although individual differences in WM performance reflected two independent operations, these operations produced similar correlations to achievement within age groups. Overall, the results support a general capacity explanation of age-related and individual differences in children’s WM performance.     

Estimation for structural equation models with missing data

A direct method in handling incomplete data in general covariance structural models is investigated. Asymptotic statistical properties of the generalized least squares method are developed. It is shown that this approach has very close relationships with the maximum likelihood approach. Iterative procedures for obtaining the generalized least squares estimates, the maximum likelihood estimates, as well as their standard error estimates are derived. Computer programs for the confirmatory factor analysis model are implemented. A longitudinal type data set is used as an example to illustrate the results.This research was supported in part by Research Grant DAD1070 from the U.S. Public Health Service. The author is indebted to anonymous reviewers for some very valuable suggestions. Computer funding is provided by the Computer Services Centre, The Chinese University of Hong Kong.     

A comparison of measures of responding under fixed-interval schedules

Average response rate, post-reinforcement pause, elapsed time to the fourth response, average quarter-life, and running rate were examined to see how they reflected changes in fixed-interval performance. Rats were exposed to a mixed schedule of water presentation comprising fixed-interval schedules of two durations. Changes in responding were produced by varying the duration of the shorter component. The five measures were derived only from the longer schedule component. Post-reinforcement pause, elapsed time to the fourth response in the interval, and quarter-life all showed high, positive inter-correlations (0.78<r<0.99). Running rate and post-reinforcement pause were not as highly correlated. Quarter-life reliably reflected changes in fixed-interval performance but changes in the quarter-life value did not necessarily result from similar changes in fixed-interval response pattern. The two measures that adequately described changes in response patterning were post-reinforcement pause and running rate. These two measures also had the advantage of being simple both computationally and in terms of the instrumentation involved in their recording.     

Detection theory,micromatching, and the constant-ratio rule

The conformance of detection theory and micromatching with the constant-ratio rule (CRR) was determined by calculations for sets of three stimuli and subsets of two stimuli. For an arbitrary selection of sets, the CRR would be expected to hold quite well if either detection theory or micromatching lay behind the responses. For specific stimulus configurations, however, detection theory and micromatching differ considerably from one another and from the CRR. These configurations are found particularly for the univariate distributions, and this corresponds to empirical findings that the CRR holds better for multidimensional than for unidimensional stimuli. It is shown how the differences between the three theories in the implied constancies of ratios can be used in diagnosis of the basis ofempirical confusion matrices.