Differential effects of progesterone and medroxyprogesterone on delay eyeblink conditioning in ovariectomized rats

Ovarian hormones modulate acquisition processes involved in classical conditioning. Although progesterone has been indirectly implicated, its role in classical conditioning of the eyeblink response has not been directly investigated. We assessed the effects of daily dosing of progesterone or medroxyprogesterone (MPA), a non-metabolized synthetic progestin, upon the acquisition of a classically conditioned eyeblink response in ovariectomized (OVX) female rats. Rats were dosed 4h prior to each training session with 0.1 or 1.5 mg/kg of either of these hormones or sesame oil. A delay conditioning paradigm was employed using a 500 ms conditioned stimulus coterminating with a 10 ms 10 V unconditioned stimulus. At the low dose, progesterone and MPA rats did differ from each other, with MPA-treated rats learning slower, but neither group differed from OVX-oil or Sham-oil controls. No group differences in acquisition were observed at the higher dose. During extinction trials, high-dose MPA-treatment and OVX-oil groups extinguished quicker than the high-dose progesterone-treated group. In addition, unconditional response (UR) amplitudes were lower in all OVX groups, regardless of hormone or oil treatment, compared to the sham-oil group. Since MPA did not affect extinction, it is likely the slower extinction in the progesterone-treated rats is due to a metabolite of progesterone. Corticosterone is discussed as a likely candidate for such a role. In addition, we found chronic absence of ovarian hormones decreased UR amplitudes, although differences in UR amplitudes were not associated with changes in the acquisition process. These results are discussed with respect to differences in the hormonal effects upon acquisition versus extinction processes and how these data may explain reports of learning differences in women based on oral contraceptive usage.     

How special is sameness for pigeons and people?

Because of the importance of the sense of sameness for psychological science and because of the tenuous support for this notion in pigeons' matching-to-sample behavior, we experimentally explored the possibly special status of sameness for pigeons. Using photographs from three different natural categories (dogs, fish, and flowers) in a three-alternative matching-to-sample design, we obtained a reliable sameness advantage for pigeons only when the number of correct sample-comparison combinations could have contributed to a sameness advantage; otherwise, no sameness advantage emerged. However, human participants exhibited an immediate and dramatic sameness advantage under essentially the same training and testing conditions as had been given to pigeons. At least under these experimental circumstances, humans exhibit a sameness advantage that far eclipses that of pigeons.     

Control-related beliefs and sleep characteristics of posttraumatic stress disorder patients

To examine correlations among chronic Posttraumatic Stress Disorder (PTSD), control-related beliefs, and sleep difficulties 7 PTSD casualities and 7 non-PTSD matched subjects were compared in their laboratory sleep patterns as well as in their beliefs about personal control over external and internal events in general and over sleep-related events in particular. Analyses indicated that PTSD casualties had poorer sleep and reported more doubts regarding their ability to control external and internal events than control subjects. Further, we found a significant association between perceived control and sleep difficulties. Results were discussed in terms of Horowitz's conception of intrapsychic processes related to PTSD.     

Response-outcome contingency: Behavioral and judgmental effects of appetitive and aversive outcomes with college students

In two experiments, positive, negative, and zero response-outcome contingencies were responded to and rated by college students under a free-operant procedure. In Experiment 1, outcomes were either neutral or were associated with point gain. In Experiment 2, subjects were administered different outcome treatments: neutral outcomes, outcomes associated with money gain, or outcomes associated with money loss. In both experiments, subjects' judgments of response-outcome contingency and their operant responses were each strong linear functions of ΔP, the difference between the probability of an outcome given a response and the probability of an outcome given no response. Appetitive and aversive outcomes produced opposite and symmetrical response patterns. In Experiment 1, no differences in ratings occurred with neutral or appetitive outcomes; however, in Experiment 2, more potent appetitve outcomes led to somewhat more extreme ratings than either neutral or aversive outcomes. Increasing outcome probability produced only a slight bias in ratings of noncontingent problems in Experiment 1 and no bias in Experiment 2. Contrary to predictions derived from an analysis of superstitious behavior, increasing outcome probability in noncontingent problems decreased operant responding when outcomes were appetitive and increased operant responding when outcomes were aversive. Trend analyses revealed that Δ P was superior to several other metrics in predicting subjects' estimates of contingency and the behavioral effects of contingency. Operant responding was in closer accord with matching predictions than with maximizing predictions.     

Conformity of two sociometric relations

The problem of comparing two sociometric relations or measurements (A andB) recorded in distinct sociomatrices was originally discussed by Katz and Powell in the early 1950's and Hubert and Baker in the late 1970's. The problem is considered again using a probabilistic model designed specifically for discrete-valued network measurements. The model allows for the presence of various structural tendencies, such as reciprocity and differential popularity. A parameter that isolates the tendency for actors to choose other actors on both relations simultaneously is introduced, and estimated conditional on the presence of other parameters that reflect additional important network properties. The parameter is presented as a symmetric index but is also generalized to the predictive (A onB orB onA) situation. This approach to the problem is illustrated with the same data used by the earlier solutions, and the unique nature of the two relations in the data set (A = received choices,B = perceived choices), as it affects the modeling, is discussed. Significance tests for the parameter and related parameters are described, as well as an extension to more than two relations.Research support provided by National Science Grant #SES84-08626 to the University of Illinois at Urbana-Champaign. I am grateful to Dawn Iacobucci and Sheila Weaver for assistance with the research reported here, and to Carolyn Anderson, James Green, David Holtgrave, and four anonymous referees for comments on the paper.     

The role of the magazine-response contingency on signal-directed responding in pigeons

Three experiments used a procedure for directly delivering water into the thirsty pigeon's mouth to explore the role that the instrumental magazine contingency plays in autoshaped responding. Magazine training was accomplished by requiring birds to contact a “magazine” key when it was illuminated, in order to obtain intraoral injections of water. Other subjects received water injections independent of a magazine-response contingency. Subsequently, magazine-trained subjects showed a transient enhancement in responding to the illumination of another “signal” key, whether that stimulus was presented alone or paired with water delivery. The overall level of maintained autoshaped responding was little influenced by the instrumental magazine contingency, although the within-trial time course of signal-directed responding was affected. When illumination of the signal key preceded access to water only when the signal was not contacted, pigeons directed many responses toward the signal key. However, there was no evidence that the instrumental magazine contingency enhanced responding on this omission schedule of reinforcement. These results thus confirm a small, but measurable contribution of the magazine-response contingency to signal-directed responding; they fail to support the conclusion that the instrumental magazine contingency greatly affects the outcomes of autoshaping studies.     

Conditioning of within-trial patterns of key pecking in pigeons

The possibility of conditioning systematic patterns of responding during brief discrete trials was studied by requiring hungry pigeons to key peck and then pause or to pause and then key peck in order to gain access to food. These schedules were highly effective in promoting decelerated and accelerated rates of responding, respectively, within individual trials; indeed, performance was quite similar to that observed when explicit external stimuli were correlated with “peck” and “pause” portions of the daily trials. Finally, schedules of reinforcement that did not selectively reinforce peck-pause or pause-peck patterns neither generated these patterns nor maintained them at the previous high levels. The results, therefore, confirm Shimp's (1976) proposal that organized groupings of discrete responses may function as operants—even in the absence of strict response-reinforcer contiguity.     

Trace autoshaping: Acquisition, maintenance, and path dependence at long trace intervals

The pigeon's tendency to acquire and maintain signal-directed key pecking under a trace conditioning procedure was parametrically examined. In Experiment 1, the percentage of CS trials with a key peck response was a decreasing function of the trace interval for separate groups of pigeons. The majority of subjects acquired signal-directed key pecking with trace intervals as long as 36 sec. In Experiment 2, differential maintenance of key pecking occurred across trace intervals in a within-subject procedure. Maintenance of key pecking at 36- and 60-sec trace intervals was path dependent in that responding depended on the subject's performance under the preceding trace interval.