Patterns of sedentary behavior among adolescents.

OBJECTIVE: Reducing certain sedentary behaviors (e.g., watching television, using a computer) can be an effective weight loss strategy for youth. Knowledge about whether behaviors cluster together could inform interventions. STUDY DESIGN: Estimates of time spent in 6 sedentary behaviors (watching television, talking on the telephone, using a computer, listening to music, doing homework, reading) were cluster analyzed for a sample of 878 adolescents (52% girls, mean age = 12.7 years, 58% Caucasian). MAIN OUTCOME MEASURES: The clusters were based on the sedentary behaviors listed above and compared on environmental variables (e.g., household rules), psychosocial variables (e.g., self-efficacy, enjoyment), and health behaviors (e.g., physical activity, diet). RESULTS: Four clusters emerged: low sedentary, medium sedentary, selective high sedentary, and high sedentary. Analyses revealed significant cluster differences for gender (p < .002), age (p < .002), body mass index (p < .001), physical activity (p < .01), and fiber intake (p < .01). CONCLUSIONS: Results suggest a limited number of distinct sedentary behavior patterns. Further study is needed to determine how interventions may use cluster membership to target segments of the adolescent population.     

Blocking and sensory preconditioning effects in morphine analgesic tolerance: Support for a pavlovian conditioning model of drug tolerance

Two experiments on rats tested predictions of a Pavlovian conditioning model of drug tolerance which holds that tolerance is the result of compensatory conditioned responses, developed to environmental stimuli accompanying the drug administrations, which attenuate the direct effects of the drug. In Experiment I, the acquisition of tolerance-modulating properties by the tone component of a tone-light compound stimulus which accompanied morphine administrations was reduced by prior light-morphine pairings (blocking). In Experiment II, a tone stimulus acquired tolerance-modulating properties through prior pairings with a light stimulus which later accompanied morphine administrations (sensory preconditioning). These findings are uniquely predicted by the Pavlovian conditioning model of drug tolerance and are incompatible with traditional theories which assign no role to environmental stimuli present at the time of drug administration.     

Contribution of somesthetic cues to the perception of body orientation and subjective visual vertical

Without relevant visual cues, the subjective visual vertical (SVV) is biased in roll-tilted subjects toward the body axis (Aubert or A-effect). This study focused on the role of the somatosensory system with respect to the SVV and on whether somesthetic cues act through the estimated body tilt. The body cast technology was used to obtain a diffuse tactile stimulation. An increased A-effect was expected because of a greater underestimation of the body position in the body cast. Sixteen subjects placed in a tilt chair were rolled sideways from 0 degrees to 105 degrees. They were asked to verbally indicate their subjective body position and then to adjust a luminous line to the vertical under strapped and body cast conditions. Results showed a greater A-effect (p < .001) but an overestimation of the body orientation (p < .01) in the body cast condition for the higher tilt values (beyond 60 degrees). Since the otolith organs produced the same gravity response in both conditions, errors were due to a change in somesthetic cues. Visual and postural errors were not directly related (no correlation). However, the angular distance between the apparent body position and the SW remained stable, suggesting that the change in somatosensory pattern inputs has a similar impact on the cognitive processes involved in assessing the perception of external space and the sense of self-position.     

THE DEVELOPMENT OF CONSERVATION IN ABORIGINAL CHILDREN1

Deux groupes d'enfants aborigènes australiens (âge 8–15 ans) subissent les épreuves mises au point pour L'étude de la conservation de la quantité, du poids, du volume, de la longueur, de la surface et du nombre. Les résultats montrent que les enfants aborigènes réussissent ces problèmes à des âges plus élevés que les enfants européens et que dans certains cas, la notion de conservation n'est pas atteinte. On constate également des différences significatives chez les enfants aborigènes selon qu'ils sont de souche pure ou non. Les résultats confirment dans L'ensemble la théorie des stades de développement, mais on observe que L'ordre des stades dont L'invariance est postulée par Piaget et Inhelder présente quelques variations. L'A. commente ces résultats et évoque les différents facteurs qui peuvent être responsables du retard observé dans le développement des enfants aborigènes.     

Effects of methylphenidate alone and in combination with behavior modification procedures on the behavior and academic performance of hyperactive children

Twenty hyperactive 6- to 9-year-old children of normal intelligence were studied in a half-day laboratory classroom in a 2-week period baseline-treatment-reversal design for behavior modification. Under double-blind conditions half the children were placed on .3 mg/kg of Ritalin and half on placebo for the entire program. The classroom program consisted of a group period with immediate reinforcement possible, and an individual time period without immediate reinforcement possible. Behavior modification caused a significant decrease in nonattending, out-of-seat, inappropriate vocalizing and inappropriate peer interaction behavior in the group period. Fidgeting, a nontargeted behavior, was not significantly decreased during this period but did signficantly decrease as a result of medication. No other drug effects occurred during this period. During the individual period, the results were essentially reversed. There were no significant behavior modification effects observed. Significant reductions resulted from medication in all behaviors except out-of-seat and fidgeting. Behavior modification alone significantly affected the two academic measures. No significant effects were seen on the Conners Abbreviated Teacher Rating Scale. No significant interactions were noted between medication and behavior modification.This study was supported by a grant from the Health Services and Mental Health Administration, Maternal and Child Health Service Project 920. Special thanks are due to Judy Racheleu, Charles Cunningham, Christopher P. S. Williams, Dan Lee, Russell Barkley, Ross Danielson, Sally Gray, Don Slyman, and Linda Shambeck.