Cognitive sequelae of repeated head injury in a population of intravenous drug users

The relationship between closed head injury and performance on neuropsychological (NP) tests was investigated in a group of intravenous drug users (IVDUs). Subjects with repeated head traumas involving loss of consciousness (LOC) performed worse than both a control group without LOC and reference group with only a single episode of LOC. There were no significant differences between the last two groups. Performance on tests of memory, attention, and motor performance was significantly worse in the group with repeated head injury. The average time since the last episode of LOC was more than 11 years. We conclude from these findings that a single episode of LOC does not result in significant cognitive impairment in this population. Two or more episodes, however, are more likely to produce chronic cognitive impairment.     

Effects of cocaine and d-amphetamine on the repeated acquisition and performance of conditional discriminations.

The acute and chronic effects of cocaine and d-amphetamine on food-reinforced behavior were investigated in pigeons responding on a two-component multiple schedule. In one component, the behavioral task consisted of the same chain of conditional discriminations each session (performance). In the other component, the chain of conditional discriminations was changed from session to session (learning). In comparison to control sessions, both acute cocaine and d-amphetamine increased errors in each component of the multiple schedule. Responding in the learning component, however, was generally disrupted at lower doses than those that affected responding in the performance component. At high doses, both drugs produced pauses in responding in each component in three of the four subjects. Pausing engendered by d-amphetamine was approximately twice as long as that under cocaine. Upon chronic administration, both the pausing and error-increasing effects of each drug diminished. Drug-induced changes in timeout responding, however, did not decrease during chronic administration. Redeterminations of the d-amphetamine dose-effect curves following chronic cocaine administration suggested the existence of cross-tolerance between cocaine and d-amphetamine. Both the acute and chronic data are consistent with the view that conditions of stimulus control may modulate the behavioral effects of drugs.     

Experimental effects of receiving negative weight-related feedback: a weight guessing study

The effects of receiving negative verbal weight-related feedback on the mood, self-esteem, and body image of restrained and unrestrained eaters were investigated. Female undergraduate students either reported their current weight (no feedback) or had their weight guessed as 15 lb higher than their actual weight (negative feedback) by an experimenter who presented herself as either an undergraduate (peer) or graduate student (non-peer). Participants overall had higher anxiety and felt “fatter” in the negative feedback condition. When this feedback came from a peer they felt fatter, more dissatisfied with their bodies, and, for restrained eaters, more depressed, as compared to when it came from a non-peer. These results provide empirical evidence that negative weight-related feedback produces adverse psychological consequences for young women, especially restrained eaters, and suggest the importance of peers’ perceptions of weight.     

Estimation of the Nonlinear Random Coefficient Model when Some Random Effects Are Separable

A method is presented for marginal maximum likelihood estimation of the nonlinear random coefficient model when the response function has some linear parameters. This is done by writing the marginal distribution of the repeated measures as a conditional distribution of the response given the nonlinear random effects. The resulting distribution then requires an integral equation that is of dimension equal to the number of nonlinear terms. For nonlinear functions that have linear coefficients, the improvement in computational speed and accuracy using the new algorithm can be dramatic. An illustration of the method with repeated measures data from a learning experiment is presented.     

"Just looking at food makes me gain weight": experimental induction of thought-shape fusion in eating-disordered and non-eating-disordered women

Thought-shape fusion (TSF) is a cognitive distortion that can be induced experimentally and is associated with eating pathology. The current study was conducted in order to elucidate the effects of TSF induction in females with eating disorders (n=35), as well as in restrained eaters (n=38) and unrestrained eaters (n=39). It was hypothesized that TSF induction would result in anxiety, guilt, increased feelings of fatness, perceived weight gain and feelings of moral wrong-doing relative to an anxiety and control induction. It was further hypothesized that restrained eaters and individuals with eating disorders would exhibit a stronger reaction to a TSF induction than would unrestrained eaters. The results indicated that, as predicted, TSF can be induced in individuals both with and without eating disorders, and individuals with eating disorders reported the highest levels of "state" TSF after the induction relative to the non-clinical controls. However, contrary to expectations, restrained eaters reported higher levels of perceived weight gain and moral wrong-doing after the anxiety induction (but not the TSF induction) relative to the control induction. Potential mechanisms for this pattern of results are discussed, and the clinical implications of research on TSF are also considered.     

An experimental analysis of the effects of d-amphetamine and cocaine on the acquisition and performance of response chains in monkeys.

In one component of a multiple schedule of food presentation, monkeys acquired a different four-response chain each session by responding sequentially on three keys in the presence of four geometric forms (learning). In the other component, the four-response chain was the same each session (performance). Both d-amphetamine and cocaine, at the higher doses, disrupted the behavior in the learning component; the overall response rate decreased, the overall accuracy was impaired (i.e., percent errors increased), and there was less within-session error reduction. The performance component was generally less sensitive than the learning component to the disruptive effects of both drugs on rate and accuracy. After pre-feeding or during an extended session, the response rate decreased in both components, but accuracy was generally unaffected. When the four discriminative stimuli in both components were removed, the behavior was disrupted to a greater extent in the performance component. The disruptive effects of both drugs on behavior in the learning component were attenuated when the drugs were administered during the session after the response chain had been acquired. It was concluded that the greater sensitivity of the learning component to disruptive drug effects is related to the relatively weak stimulus control and/or the lower rate of reinforcement associated with that component.     

The Prediction of Negative Events Associated with Anxiety and Dietary Restraint: A Test of the Content Specificity Hypothesis

The prediction of future negative events was studied in a sample of undergraduate students varying on measures of anxiety and dietary restraint. Cognitive theories of psychopathology hypothesize that the emotional concerns of an individual determine which types of information are most often cognitively processed with a biased interpretation. This prediction has generally been called the content specificity hypothesis. Based upon this aspect of cognitive theory, we hypothesized that a high level of trait anxiety would be associated with higher ratings of the probability of future physically threatening events. In addition, it was hypothesized that a high level of dietary restraint would be associated with lower ratings of the probability of future occurrences of overeating. The results of the study supported these hypotheses. These prediction biases were found to be more pronounced in women, as compared to men. The findings were interpreted as supportive of the content specificity hypothesis.