Aftereffects of reinforcement on variable-ratio schedules

On each of variable-ratio 10, 40, and 80 schedules of reinforcement, when rats' lever-pressing rates were stable, the concentration of a liquid reinforcer was varied within sessions. The duration of the postreinforcement pause was an increasing function of the reinforcer concentration, this effect being more marked the higher the schedule parameter. The running rate, calculated by excluding the postreinforcement pause, was unaffected by concentration. The duration of the postreinforcement pause increased with the schedule parameter, but the proportion of the interreinforcement interval taken up by the pause decreased. Consequently, the overall response rate was an increasing function of the schedule parameter; i.e., it was inversely related to reinforcement frequency, contrary to the law of effect. The running rate, however, decreased with the reinforcement frequency, in accord with the law of effect. When 50% of reinforcements were randomly omitted, the postomission pause was shorter than the postreinforcement pause, but the running rate of responses was not affected.     

On a metric,unidimensional unfolding model for attitudinal and developmental data

If stimulus responses are linearly related to squared distances between stimulus scale values and person scores along a latent continuum, (a) the stimulus × stimulus correlation matrix will display a simplex-like pattern, (b) the signs of first-order partial correlations can be specified in an empirically testable manner, and (c) the variables will have a semicircular, two-factor structure. Along the semicircle, variables will be ordered by their positions on the latent dimension. The above results suggest procedures for examining the appropriateness of the model and procedures for ordering the stimuli. Applications to developmental and attitudinal data are discussed. This research was supported by a grant from the Graduate School of the University of Minnesota to the author and by a grant from the U. S. Public Health Service (Grant No. 1-R01-MH27861-01) to Dr. James Rest, Principal Investigator.     

Effects of magnitude of food reinforcement on free-operant response rates

In Experiment 1 rats were trained to press a lever on a variable-ratio schedule of food presentation and were then exposed to progressively increasing magnitudes of food reinforcement. Response running rates (rates exclusive of the postreinforcement pause) were found to increase as a function of increasing reinforcement magnitudes. The effect of reinforcement magnitude on response rates inclusive of the postreinforcement pause, however, was less pronounced. Increases in the magnitude of reinforcement were also found to increase the length of the postreinforcement pause. Rats in Experiment 2 were trained to respond on a chained differential-reinforcement-of-low-rate variable-ratio schedule, and were exposed to increasing magnitudes of reinforcement as in Experiment 1. Response running rates increased in the variable-ratio component but decreased in the other component of the schedule. The results are discussed with reference to incentive accounts of reinforcement and the action of reinforcement on the response units generated by the operative contingencies.     

Items bundles

An item bundle is a small group of multiple choice items that share a common reading passage or graph, or a small group of matching items that share distractors. Item bundles are easily identified by paging through a copy of a test. Bundled items may violate the latent conditional independence assumption of unidimensional item response theory (IRT), but such a violation would not typically suggest the existence of a new fundamental human ability to read one specific reading passage or to interpret one specific graph. It is important, therefore, to have theoretical concepts and empirical checks that distinguish between, on the one hand, anticipated violations of latent conditional independence within item bundles, and, on the other hand, violations that cannot be attributed to idiosyncratic features of test format and instead suggest departures from unidimensionalty. To this end, two theorems on unidimensional IRT are extended to describe observable item response distributions when there is conditional independencebetween but not necessarilywithin item bundles.The author is grateful to Ivo Molenaar and the referees for many helpful suggestions, and to D. Thayer for assistance with computing.     

Maximum likelihood estimation of polyserial correlations

This paper considers a multivariate normal model with one of the component variables observable only in polytomous form. The maximum likelihood approach is used for estimation of the parameters in the model. The Newton-Raphson algorithm is implemented to obtain the solution of the problem. Examples based on real and simulated data are reported.The research of the first author was supported in part by a research grant (DA01070) from the US Public Health Service. We are indebted to the referees and the editor for some very valuable comments and suggestions.     

Pentobarbital and d-amphetamine effects on concurrent performances.

The effects of pentobarbital and d-amphetamine were studied in pigeons responding under several concurrent fixed-ratio variable-interval and concurrent fixed-ratio fixed-interval schedules of food presentation. Drug effects were compared with different fixed ratios, fixed and variable intervals, changeover delays, and with the schedules operating singly. Doses of d-amphetamine that increased or did not affect responding under the interval schedules decreased responding under the fixed-ratio schedule, whereas doses of pentobarbital that increased responding under the fixed-ratio schedule decreased or eliminated responding under the interval schedules. These effects depended both on the schedule of food delivery and the parameters of schedules arranged concurrently. Pentobarbital increased responding under the fixed-ratio schedule with 4-minute and 10-minute interval schedules arranged concurrently, but not with 1.5-minute schedules. d-Amphetamine decreased concurrent ratio and interval responding with the 1.5-minute interval schedules, but either increased or did not affect responding with the longer intervals. Changes in the parameter of one schedule altered responding controlled by that schedule and also other concurrent performances. As a consequence, the effects of drugs on each behavior were altered.     

Effect of variable-interval punishment on the behavior of humans in variable-interval schedules of monetary reinforcement

One male and three female human subjects pressed a button for monetary reinforcement under a range of variable-interval schedules specifying different frequencies of reinforcement. On alternate days, responding was also punished (by subtraction of money) according to a variable-interval 170-second schedule. In the absence of punishment, the rate of responding was an increasing negatively accelerated function of reinforcement frequency, as predicted by Herrnstein's equation. The effect of the punishment schedule was to suppress responding under lower frequencies of reinforcement; responding under higher reinforcement frequencies was much less affected. This was reflected in an increase in the value of K_H (the constant expressing the reinforcement frequency corresponding to the half-maximal response rate), whereas there was no significant change in the value of R_max (the constant expressing the maximum response rate). Previous results had shown that variable-ratio punishment resulted in a change in the values of both constants (Bradshaw, Szabadi, and Bevan, 1977). The results of the present study were consistent with the concept that the suppressive effects of punishment on responding depend on the nature of the punishment schedule.     

Associations between volume of alcohol consumption and social status, intelligence, and personality in a sample of young adult Danes

Relatively few studies have investigated associations between volume of alcohol consumption and psychological characteristics in normal samples. A sub-sample, comprising 363 men and 331 women between 29 and 34 years of age, was selected from the Copenhagen Perinatal Cohort on the basis of perinatal records. The sample was divided into four consumption categories: abstainers (including occasional drinkers), light, moderate, and risk drinkers. ANOVA and relevant contrasts were used to test the significance of differences among consumption categories. Both abstaining and risk drinking were associated with low social status family background, low education and intelligence. Abstaining was associated with low disinhibition and social recognition scores, while risk drinking was associated with high neuroticism and, in males, high disinhibition, low social recognition, and low achievement scores. Compared with light drinkers, a more "carefree" life orientation characterized male moderate drinkers, while relatively high scores on anxiety, dysthymia, and somatoform symptom scales characterized female moderate drinkers.     

Relationship of resilience to personality, coping, and psychiatric symptoms in young adults

Developing a comprehensive understanding of resilience across the lifespan is potentially important for mental health promotion, yet resilience has been vastly understudied compared to disease and vulnerability. The present study investigated the relationship of resilience to personality traits, coping styles, and psychiatric symptoms in a sample of college students. Measures included the Connor-Davidson Resilience Scale, NEO Five Factor Inventory, Coping Inventory for Stressful Situations, and Brief Symptom Inventory. Results supported hypotheses regarding the relationship of resilience to personality dimensions and coping styles. Resilience was negatively associated with neuroticism, and positively related to extraversion and conscientiousness. Coping styles also predicted variance in resilience above and beyond the contributions of these personality traits. Task-oriented coping was positively related to resilience, and mediated the relationship between conscientiousness and resilience. Emotion-oriented coping was associated with low resilience. Finally, resilience was shown to moderate the relationship between a form of childhood maltreatment (emotional neglect) and current psychiatric symptoms. These results augment the literature that seeks to better define resilience and provide evidence for the construct validity of the Connor-Davidson Resilience Scale.     

Two Distinctive Personality Configurations: Understanding the Therapeutic Context with Suicidal Individuals

Recent theory and research have associated different levels and types of suicide risk with particular personality dimensions, focusing particularly on the distinction between introjective and anaclitic personality orientations. This distinction is discussed in relation to our general understanding of the therapeutic context with those who have attempted, or may be at risk for, suicidal behavior. Individuals characterized as predominantly introjective/self-critical or as anaclitic/dependent seem to represent relatively homogenous subgroups of suicidal individuals, with distinct concerns, vulnerabilities, and behaviors. Our conclusion is that persons in these subgroups seem to warrant different intervention and therapeutic strategies. Implications for the psychotherapeutic process are discussed.