Blocking of the response-reinforcer association: Additional evidence

Response rates maintained by free-operant schedules are sometimes reduced when a brief signal is interposed between the response and reinforcer. Early interpretations of this rate reduction were in terms of associative competition between the response and signal, analogous to blocking and overshadowing effects obtained in Pavlovian conditioning. But subsequent evidence has disputed this interpretation by showing that the signal enhances response rate in several circumstances. The present study attempted to define the conditions determining the different effects by investigating the role of signal location in the delay-of-reinforcement interval. When it occurred immediately after a response, response rate was enhanced. When it occurred at the end of the delay interval, immediately preceding the reinforcer, the signal decreased response rate. A similar decremental effect occurred when the signal occurred in the middle of the delay interval, contiguous with neither the response nor the reinforcer. Similar blocking effects occurred with a response acquisition procedure. The results demonstrate that blocking effects do indeed occur in instrumental conditioning but that the usual procedure of using signals immediately contingent on responding confounds such blocking effects with the competing effects of conditioned reinforcement/marking.     

Gender and ethnic differences in psychosocial stress and generalized distress among Hispanics

This study examined the relationship between gender, ethnicity, psychosocial stress and generalized distress in 593 Hispanic immigrants, Mexican Americans, and Anglo Americans using the Hispanic Stress Inventory (HSI) and the Center for Epidemiologic Studies Depression Scale (CES-D). Findings revealed that immigrant females had higher scores on the Cultural/Family Conflict sub-scale of the HSI and on the CES-D than immigrant males. Also, higher levels of generalized distress and psychosocial stress associated with the immigration process were found among immigrants from Central America when compared with Mexican immigrants. Central Americans' stress appraisal ratings on specific HSI items related to pre-migration trauma were significantly higher than the ratings of Mexican immigrants. Our findings indicate that research and clinical service delivery models must be sensitive to the vast heterogeneity within the Hispanic population with respect to differences in the experiences of psychosocial stress as related to gender and ethnicity.This project was partially supported by Grant USPHS MH24854 to the third author from the National Institute of Mental Health, Division of Biometry and Applied Science, Minority Research Resources Branch.     

Effects of post-trial administration of naloxone and beta-endorphin on shock-induced fighting in rats

To study the involvement of endogenous opioid peptides in the development of shock-induced fighting, naloxone (2 mg/kg) or beta-endorphin (10 micrograms/kg) was administered subcutaneously immediately after the session and during nine consecutive daily sessions to rats repeatedly exposed to electric shocks. beta-Endorphin blocked the development of shock-induced fighting while naloxone facilitated it but only when shock-induced fighting occurred at a low rate. The effects of beta-endorphin were time dependent since when beta-endorphin was injected 90 min after the shock session instead of immediately after, its impairing effect disappeared. In addition, naloxone blocked the impairment produced by beta-endorphin. Differential postsession treatment of each member of pairs of rats with naloxone and beta-endorphin resulted in a higher probability of rats treated with naloxone to be dominant over rats treated with beta-endorphin in the test situation. These results are discussed in relation with the possible involvement of endogenous opioids in the modulation of the physiological consequences of defensive behavioral responses to shock.     

Choice, experience, and the generalized matching law

Five pigeons were exposed to different pairs of concurrent variable-interval, variable-interval schedules on nine experimental conditions of 30 sessions each. For every session, the parameters of the generalized matching equation were computed for the first five, six, seven, eight, and nine experimental conditions. The exponent a, both for response and time distribution, tended to decrease with increases in number of experimental conditions and to increase with number of sessions per condition, but values of k (bias) varied unsystematically. When the subjects were exposed to five new pairs of schedules, with 55 sessions per condition, the findings were confirmed. Data from the literature on the generalized matching law suggest that the variability of exponent values may be explained in part by the use of naive or experienced subjects in different investigations and by the variability in number of experimental conditions and in number of sessions per condition.     

Mixed models,random utilities,and the triangle inequality

A new probabilistic binary choice model, which we call the mixed model is proposed. This model is used to give an interpretation of probabilistic choice behavior in terms of complete and partial orders. The model is used as a guide to disprove Jacob Marschak's conjecture that the binary random utility model is equivalent to the triangle inequality. Another result is presented concerning the relation between moderate stochastic transitivity and the triangle inequality.     

Key pecking as a function of response-shock and shock-shock intervals in unsignalled avoidance

Five pigeons were exposed to an unsignalled avoidance procedure where key pecks were maintained through shock postponement. Functions obtained showed an inverse relationship between rate of responding and length of the response-shock interval, while changes in the shock-shock interval had no systematic effect on response rates. The rate of shocks delivered generally decreased with increases in length of both response-shock and shock-shock intervals. Results show that key pecking in pigeons, maintained through an unsignalled avoidance procedure, was affected by changes in response-shock and shock-shock intervals in the same manner as other responses in pigeons and in rats.     

Additive structure in qualitative data: An alternating least squares method with optimal scaling features

A method is developed to investigate the additive structure of data that (a) may be measured at the nominal, ordinal or cardinal levels, (b) may be obtained from either a discrete or continuous source, (c) may have known degrees of imprecision, or (d) may be obtained in unbalanced designs. The method also permits experimental variables to be measured at the ordinal level. It is shown that the method is convergent, and includes several previously proposed methods as special cases. Both Monte Carlo and empirical evaluations indicate that the method is robust.This research was supported in part by grant MH-10006 from the National Institute of Mental Health to the Psychometric Laboratory of the University of North Carolina. We wish to thank Thomas S. Wallsten for comments on an earlier draft of this paper. Copies of the paper and of ADDALS, a program to perform the analyses discussed herein, may be obtained from the second author.