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Biomedical subjects

N H Donegan

Publications and source records attributed to N H Donegan.

6 recordsLinked to original sources
PubMed1992

Potentiation or diminution of discrete motor unconditioned responses (rabbit eyeblink) to an aversive pavlovian unconditioned stimulus by two associative processes: conditioned fear and a conditioned diminution of unconditioned stimulus processing.

In two experiments using the rabbit conditioned eyeblink preparation, the conditions under which a Pavlovian conditioned stimulus (CS) potentiates or diminishes the unconditioned response (UR) were examined. The results indicated that, after discrimination training (CS+ vs. CS-), the CS+ diminished UR amplitude at the training interstimulus interval (ISI). When CS+ trials were segregated into trials on which a conditioned response (CR) did or did not occur, the CS+ diminished the UR when it elicited a CR, but not when a CR failed to occur. When the CS-unconditioned stimulus (US) interval was lengthened to 10 s, the CS+ reliably potentiated the eyeblink UR on CR trials but did not potentiate responding on trials on which a CR was absent. The results are discussed in terms of the modulatory effects and temporal properties of conditioned fear and an associatively produced decrement in US processing.

Animals↗
PubMed1981

Priming-produced facilitation or diminution of responding to a Pavlovian unconditioned stimulus.

Two experiments, concerned with signal-produced variation of unconditioned response (UR) amplitude, evaluated the roles of US intensity and response measure in determining when signaling the US results in a conditioned diminution or a conditioned facilitation of responding. In Experiment 1, rabbits received discrimination training, in an eye-blink-conditioning preparation, with a 1-mA, 50-msec shock US. In testing, preceding the US by SC+ facilitated the eye blink response compared with preceding the US by CS- or neither CS. In Experiment 2, subjects received discrimination training with a 5-mA US and were tested with 1-, 2-, and 5-mA US. During testing, subjects' eye blink responses (for which robust CRs were observed) and gross body movement responses (for which no CRs were observed) were simultaneously recorded. for the eye blink response, preceding the US by CS+ facilitated responding to the 1-mA US, produced negligible differences in responding to the 2-mA US, and diminished responding to the 5-mA US, compared with preceding the US by CS- or neither CS. For the movement response, preceding the US by CS+ diminished responding at all three US intensities, with the decremental effects increasing with increases in US intensity. The results of Experiments 1 and 2 are discussed in terms of the dual effects of CS+: the diminution of US processing and the contribution of the conditioned response to the measured response.

Animals↗
PubMed1980

Evaluation of blocking and conditioned inhibition to a CS signaling a decrease in US intensity.

Two experiments employing a conditioned emotional response procedure with rats evaluated the associative tendencies acquired by a target CS when a compound of that stimulus and another CS was reinforced by a low-intensity US whereas the latter CS alone was reinforced by a higher intensity US. Experiment 1 involved a blocking sequence in which the element and compound trials occurred in successive phases, followed by eventual testing of the responding to the target CS alone. Less evidence of excitatory conditioning was observed than in a comparison group which had the element and compound paired with the same low-intensity US. Experiment 2 included contemporaneous differential reinforcement of the element and compound CSs and periodic summation tests in which the target CS was compounded with another independently trained CS. Clear evidence was obtained of the development of inhibitory tendencies by the target CS. The results are consistent with the predictions of the Rescorla-Wagner model and are discussed in relation to the several determining assumptions of the model.

Animals↗
PubMed1977

Posttrial reinstatement of the CS in Pavlovian conditioning: facilitation or impairment of acquisition as a function of individual differences in responsiveness to the CS.

Gray and Appignanesi reported that conditioning to an element of a compound conditioned stimulus (CS) was facilitated when the compound not only preceded the unconditioned stimulus (US) but was briefly reinstated shortly after US termination. The manipulation was embedded in a "blocking" design, and the effect was interpreted as being peculiar to such a situation. The present study reports five experiments, using rats in a conditioned emotional response (CER) paradigm, aimed at further evaluating the effects of CS reinstatement. In a blocking experiment patterned after that of Gray and Appignanesi, reinstatement was observed to have a decremental rather than an incremental effect on conditioned responding. In four experiments involving simple conditioning with unitary CSs, reinstatement was observed to have either an incremental or decremental effect, depending upon the subject's preconditioning responsiveness to the CSs involved. Possible mechanisms for such variable effects are discussed without obvious resolution.

Acoustic Stimulation↗