A COMPARISON OF ESCAPE AND AVOIDANCE CONDITIONING IN WILD AND DOMESTICATED RATS¹

Abstract

In the first of two experiments, three cotton rats (Sigmodon hispidus) and three albino rats were exposed to instrumental escape, unsignaled avoidance, and signaled avoidance, in that order. All subjects learned the escape procedure quickly, with the albino rats having generally shorter latencies, higher response rates, and requiring fewer sessions to reach the criterion. When the avoidance contingency was introduced, the cotton rats continued to respond almost entirely in the presence of the shock, whereas the albino rats responded in its absence, thus displaying effective avoidance behavior. Introduction of a pre-aversive stimulus did not improve the performance of the cotton rats. In the second experiment, five cotton rats and four albino rats were exposed to a free-operant (Sidman) avoidance procedure with a shock-shock interval of 3 sec and a response-shock interval of 20 sec. The cotton rats initiated responding at lower shock intensities than the albino rats, but their asymptotic avoidance responding was far less effective. A Gerbrands rat test chamber and GrasosStadler electromechanical crcuits sved as the apparatus. Electric shock was provided by a 110-v ac shock source which included 200,000 ohms in series with the output. The shock was scrambled to the grid floor of the test chamber. Data were recorded by electromechanical counters and a Gerbrands cumulative recorder.The animals were successively exposed to three experimental contingencies: escape, unsignaled avoidance, and signaled avoidance. No shaping procedure of any type was used. The animals were merely placed in the experimental chamber, and after a 15-min period to allow for adaptation, the shock was turned on.Under the escape contingency, each bar press turned the shock off for 18 sec. Responses during the shock-off period had no effect. The avoidance contingency differed in that responses during the shock-off period served to reset a timer, and thus postpone shock for 18 sec. During the unsignaled component, no cue as to shock imminence was given. During the signaled component, a bank of four 28-v dc bulbs came on 3.5 sec before the shock, and remained on until the animal responded. The lights were mounted behind a translucent panel approximately 2 in. above the bar.Each animal was initially exposed to a shock level of 0.5 ma. This level was increased as necessary to establish and maintain effective 473 1968, 11,[473][474][475][476][477][478] NUMBER 4 (JULY)

RUNNING‐WHEEL ACTIVITY AND AVOIDANCE IN THE MONGOLIAN GERBIL1

“…Only a few behavioral comparisons have been made between wild and domesticated animals which are closely related on the phylogenetic scale. Powell and Morris (1968) compared albino rats and cotton rats (Sigmodon hispidus) under several instrumental avoidance procedures. The albino rats displayed somewhat higher response rates, but the major difference observed was that the cotton rats made few responses except to shock presentation.…”

“…The gerbil was selected for this study because it is docile and therefore easy to handle, and it can be maintained under laboratory conditions similar to those suited to rats. The cotton rats studied earlier (Powell and Morris, 1968) were highly excitable, vicious, and thus difficult to handle. They showed only minor adaptation to handling over the several months of the experiment.…”

RESPONSE PATTERNING ON AN AVOIDANCE SCHEDULE AS A FUNCTION OF TIME‐CORRELATED STIMULI1

“…Post-reinforcement pauses shorten and fewer rate irregularities appear when an added counter is correlated with a fixed-ratio schedule (Ferster and Skinner, 1957). Stimuli correlated with schedule parameters facilitate free operant avoidance acquisition (Powell and Morris, 1968). The major effect of schedule-correlated stimuli (or "preshock" stimulus) on stable avoidance responding is to decrease overall rate (Sidman, 1953;Behrend and Bitterman, 1963;Hyman, 1969).…”

Laboratorizing the wild rat (Rattus norvégiens)

“…Indeed, such studies manage to maximize our embarrassment to zoology by comparing rodents across families (e.g., Powell & Morris, 1968;Eimer & Senter, 1968).…”