The Effect of Differential Post-Weaning Environment on the Rigidity of an Animal's Behavior

Seventy-two first, second and third grade boys and girls were administered seriation problems involving different combinations of shape and color variation. Success rates and latency scores were influenced by shape variation, but not by color variation or grade level. The failure to obtain predicted interactions between the effects of grade level and stimulus variation was attributed to the clarity of the relevant stimulus dimension.     

The Semantics of Secrecy: Young Children's Classification of Secret Content

The authors explored whether young children can distinguish potential secrets from nonsecrets by their content, as can older children, adolescents, and adults. Ninety children, 4, 5, and 6 years old, rated the secrecy of items from an adult-validated list of personal information about an age- and gender-appropriate puppet. Two factors of the children's data corresponded to the adult categories of nonsecrets and secrets, and a third factor corresponded to surprises. All ages rated surprises as significantly more secret than nonsecret items; however, the surprise items contained linguistic cues to secrecy. A tendency to rate nonsecrets as secret decreased with age, but only the 6-year-olds rated secrets other than surprises as significantly more secret than nonsecrets. Thus, children acquire the implicit rules defining secret content from a somewhat later age than that reported for the cognitive or behavioral capacities for secrecy.     

Moral Virtue and Practical Wisdom: Theme Comprehension in Children,Youth, and Adults

The authors tested 3 hypotheses about the relation of moral comprehension to prudential comprehension by contrasting comprehension of themes in moral stories with comprehension of themes in prudential stories among third-grade, fifth-grade, and college students (n = 168) in Study 1, and among college students, young and middle-aged adults, and older adults (n = 96) in Study 2. In both studies, all groups were statistically significantly better at moral theme comprehension than prudential theme comprehension, suggesting that moral comprehension may develop prior to prudential comprehension. In Study 2, all groups performed equally on moral theme generation whereas both adult groups were significantly better than college students on prudential theme generation. Overall, the findings of these studies provide modest evidence that moral and prudential comprehension each develop separately, and that the latter may develop more slowly.     

Development of Postural Adjustment During Gait Initiation: Kinematic and EMG Analysis

The authors studied the development of postural adjustments associated with the initiation of gait in children by using kinematic and electromyographic (EMG) analysis. Participants (N = 28) included infants with 1-4 and 9-17 months of walking experience, children 4-5 years of age, and adults. Anticipatory postural adjustments (APA) were present in the youngest age groups, including a clear anticipatory lateral tilt of the pelvis and the stance leg, which enabled the child to unload the opposite leg shortly before its swing phase. An anticipatory activation of the hip abductor of the leg in stance phase prior to heel-off was found, suggesting pelvis stabilization. APA did not appear consistently until 4-5 years of age. A decrease in segmental oscillations occurred across the ages, indicating better control of intersegmental coordination in the frontal and sagittal planes during the postural phase of gait initiation. Young walkers presented APA involving movements of both the upper and the lower parts of the body, whereas, like adults, 4- to 5-year-olds were able to laterally shift only the pelvis and the stance leg. The oldest children and the adults also showed lower activation levels of hip and knee muscles but higher activation at the ankle level. Those kinematic and EMG results taken together suggest a clear developmental sequence from an en bloc operation of the body through an articulated operation with maturation, walking experience, or both.     

Form and Variability During Sit-to-Stand Transitions: Children Versus Adults

In performing the sit-to-stand transition, young children (6- to 7-year-olds) were expected to display a movement form similar to that of adults. However, movement consistency was predicted to be poorer in children than in adults because they lack refinement of motor control processes. Kinematic analysis of 10 repetitions of the sit-to-stand movement was carried out for 6 typically developing children and 6 adults. Supporting the authors' prediction of comparable form, no differences were evident between age groups for sequence of joint onsets, proportional duration of segmental motion, or in angle-angle plots of displacement at 2 segments. In contrast, within-participant variability was found to be higher for children: Coefficients of variation for most kinematic measures were twice those seen for adults. The authors interpret the children's lack of movement consistency as a reflection of inadequate stabilization of an internal model of intersegmental dynamics. Whereas adults have attained a skill level associated with refinement of that model, children have not. Children have an additional control problem because changes in body morphology throughout childhood require ongoing updating of the internal model that controls intrinsic dynamics.     

Postural Requirements and Progression Velocity in Young Walkers

This article describes developmental changes in gait velocity and relates these changes to gait parameters that index postural stability (step width and lateral acceleration) and two components of velocity (cadence and step length).

Five children were observed longitudinally over a 2-year period after onset of independent walking. Their range of speed increased threefold in the first 6 months of independent walking and then remained constant. In contrast, step width decreased approximately twofold. Whereas in adults, cadence and step length contribute approximately equally to speed, when infants first begin to walk independently, increase in velocity is due mostly to increased step length. After 5 months of independent walking, the pattern reverses, and increase in velocity is due primarly to increased cadence. The pattern remains constant over the next 18 months. From a developmental point of view, the data lead us to interpret early walking (the first 5 months) as a process of integration of postural constraints into the dynamic necessities of gait movement. A second phase, beginning after 4 to 5 months of independent walking, is considered to be a tuning phase characterized by a more precise adjustment of the gait parameters.     

Repetition and Lag Effects in Movement Recognition

Whether repetition and lag improve the recognition of movement patterns was investigated. Recognition memory was tested for one repetition, two-repetitions massed, and two-repetitions distributed with movement patterns repeated at lags of 3, 5, 7, and 13. Recognition performance was examined both immediately afterwards and following a 48 hour delay. Both repetition and lag effects failed to be demonstrated, providing some support for the claim that memory is unaffected by repetition at a constant level of processing (Craik & Lockhart, 1972). There was, as expected, a significant decrease in recognition memory following the retention interval, but this appeared unrelated to repetition or lag.     

Effect of Short-Term Training on Reaching Behavior in Infants: A Randomized Controlled Clinical Trial

The purpose of this study was to test the effect of short-term training on reaching behavior in infants at the onset of reaching. The study was a single-blind, parallel group design, randomized controlled clinical trial. Thirty healthy infants were randomly assigned to a social control group (n = 15) or a reaching training group (n = 15). Infants began the study up to 3 days after the onset of reaching and were assessed three times across 2 days: pretraining (before training), posttraining 1 (after 1 session of training), and posttraining 2 (after 3 sessions of training). The reaching training group received 3 sessions of training by a physical therapist while the control group received a similar amount of time sitting in the therapist's lap. The data were analyzed using repeated-measures analyses of variance, and independent-samples tests with Bonferroni adjustments. Short-term training resulted in increased frequency of object contacts, shorter and smoother reaches, and improved hand positioning. The few short training sessions likely provided opportunities for infants to explore and learn to select movements from their existing movement repertoire. These results demonstrate that adaptive changes in infants' novel behaviors can emerge rapidly, and highlight the need for increased understanding of how to most effectively time early interventions.     

Communal Versus Individual Learning of a Math-Estimation Task: African American Children and the Culture of Learning Contexts

The authors compared the performance of 78 African American 5th-grade students who studied a math-estimation task in one of two learning contexts. Learning contexts differed in the degree to which they afforded the expression of communalism. ANCOVA confirmed that posttest performance was best for students who studied in the high communal-learning context. The findings support A. W. Boykin's (1994) contention that the cultural context of learning can be a critical mediator of children's performance.     

Kinesthetic Aftereffect and Augmenting/Reducing: A Two-Session Procedure,and Hence Identification of Stimulus-Governed Subjects,is Contraindicated

A few of the recent researchers of kinesthetic aftereffect (KAE) as an index of augmenting/reducing have continued to employ a two-session procedure. Findings that have accrued in the past decade indicate (a) The first administration of KAE is a reliable (internally consistent) and valid index of augmenting-reducing; (b) there are carry-over effects from the first to the second administration that bias the second session's preinduction scores; (c) KAE scores from sessions after the first do not relate to first-session scores (low retest reliability) and do not measure augmenting/reducing; and (d) unless special procedures are undertaken to avoid using the biased second- (or later-) session preinduction scores, a KAE procedure involving more than one session is contraindicated. When we reached a similar conclusion earlier (Baker et al., 1974), Petrie (1974) disagreed, arguing that a two-session procedure was needed to identify and eliminate an atypical subgroup, the “stimulus governed.” The case for determining which subjects are stimulus-governed is assessed and found wanting. Except in special circumstances, a one-session KAE procedure, in which all preinduction trials precede the first exposure to aftereffect induction, is indicated.