Retinal and extraretinal information in movement perception: how to invert the Filehne illusion

During a pursuit eye movement made in darkness across a small stationary stimulus, the stimulus is perceived as moving in the opposite direction to the eyes. This so-called Filehne illusion is usually explained by assuming that during pursuit eye movements the extraretinal signal (which informs the visual system about eye velocity so that retinal image motion can be interpreted) falls short. A study is reported in which the concept of an extraretinal signal is replaced by the concept of a reference signal, which serves to inform the visual system about the velocity of the retinae in space. Reference signals are evoked in response to eye movements, but also in response to any stimulation that may yield a sensation of self-motion, because during self-motion the retinae also move in space. Optokinetic stimulation should therefore affect reference signal size. To test this prediction the Filehne illusion was investigated with stimuli of different optokinetic potentials. As predicted, with briefly presented stimuli (no optokinetic potential) the usual illusion always occurred. With longer stimulus presentation times the magnitude of the illusion was reduced when the spatial frequency of the stimulus was reduced (increased optokinetic potential). At very low spatial frequencies (strongest optokinetic potential) the illusion was inverted. The significance of the conclusion, that reference signal size increases with increasing optokinetic stimulus potential, is discussed. It appears to explain many visual illusions, such as the movement aftereffect and center-surround induced motion, and it may bridge the gap between direct Gibsonian and indirect inferential theories of motion perception.     

Behavioral contrast during multiple avoidance schedules

Changes were observed in the rate of avoidance responding in both components of a multiple schedule of Sidman-avoidance after the shock frequency was changed in only one component. The rate change in each component was positively correlated, in direction and magnitude, with the change in the relative rate of reinforcement (percentage of total shocks) in that component.     

Relationships Among Adolescent Girls' Eating Behaviors and Their Parents' Weight-Related Attitudes and Behaviors

This article examines adolescent girls' weightloss behaviors and possible parent influences related toweight and shape. Questionnaires were completed by 369grade 10 girls and their parents. Findings suggested that parent encouragement to loseweight was a more significant predictor of daughterdietary restraint than parents' own dietary restraintlevels. Mother influence variables added significantly to a regression equation after fatherinfluences had been entered, but the reverse was not thecase. Parents' food abstaining behaviors, such asfasting and skipping meals, predicted food abstaining in daughters. Most findings were replicated whendaughter body size was controlled for. Implications formodels of the transmission of diet and weight-relatedvalues from parent to child are discussed.     

Adrenocortical influences on free-operant avoidance behavior

Rats were conditioned to avoid shock on a free-operant avoidance schedule in which no exteroceptive stimulus signaled impending shock. Injections of adrenocorticotropic hormone (ACTH) or dexamethasone raised blood levels of glucocorticoids. These increases were accompanied by changes in avoidance performance: there was a higher frequency of long-duration interresponse times, a greater stability among them, and fewer short interresponse times, total responses, and shocks.     

Internet-Delivered Targeted Group Intervention for Body Dissatisfaction and Disordered Eating in Adolescent Girls: A randomized controlled trial

This study evaluated a targeted intervention designed to alleviate body image and eating problems in adolescent girls that was delivered over the internet so as to increase access to the program. The program consisted of six, 90-minute weekly small group, synchronous on-line sessions and was facilitated by a therapist and manual. Participants were 73 girls (mean age=14.4 years, SD=1.48) who self-identified as having body image or eating problems and were randomly assigned to an intervention group (n=36) (assessed at baseline, post-intervention and at 2- and 6-months follow-up) or a delayed treatment control group (n=37) (assessed at baseline and 6–7 weeks later). Clinically significant improvements in body dissatisfaction, disordered eating, and depression were observed at post-intervention and maintained at follow-up. Internet delivery was enthusiastically endorsed. The program offers a promising approach to improve body image and eating problems that also addresses geographic access problems.     

Predicting Dieting Behavior by Using, Modifying, and Extending the Theory of Planned Behavior

The theory of planned behavior (TPB) was used, modified, and extended to predict dieting intention and behavior. Female undergraduates ( n = 256) responded to a survey assessing variables from the TPB and additional predictor variables. Seventy-eight of these participants also completed a follow-up questionnaire 3 months later that assessed their subsequent weight-loss behavior. A model was developed for dieting using path analysis to assess the most significant paths to intention to diet and follow-up dieting. In the final predictor model, 77% of the variance in intention to diet and 46% of the variance in follow-up dieting were explained. The strongest predictor of intention to diet was direct attitude, and the strongest predictor of follow-up dieting was prior dieting. This study also included a confirmatory analysis of the dieting model (n=117). Approximately 2/3 of the paths were confirmed, and 72% of the variance in intention was explained.