Analysis of Instinctive Drift, II: The Development and Control of Species-Specific Responses in Appetitive Conditioning

Abstract

In the first experiment, albino rats were studied under gradually increasing and decreasing fixed-ratio schedules of food reinforcement. All of the rats maintained either a one- or two-pawed lever press throughout the experiment, and they all showed a direct relationship between ratio size and the duration of the postreinforcement pause. In Experiment 2, Mongolian gerbils were studied under relatively prolonged and unchanging fixed ratio requirements. Almost all of the gerbils showed changes in response topography from the two-pawed press, which had been shaped initially, to species-specific responses in the form of scratching and biting of the lever and scratching of the test chamber wall. The changes in response topography were unrelated to changes in schedule requirement. Experiment 3 studied the development of response topographies in gerbils under increasing fixed-ratio schedules, when no shaping technique was employed. All of the gerbils developed consistent responding within several sessions, and scratching and biting of the lever quickly emerged as the predominant response topography. Experiment 4 studied responding in gerbils with changes from fixed ratio to differential reinforcement at low rate (DRL) schedules. Again, scratching and biting of the lever was displayed by all of the gerbils, but the distribution of these responses in time was effectively controlled by the DRL schedule. The major effect noted was that under the fixed-ratio schedules the gerbils scratched and bit the lever, which produced high rates of response, while under the DRL schedules, they scratched and bit the chamber wall and floor grids adjacent to the lever, which resulted in low rates of response. These findings are evaluated in the context of instinctive behaviors which com-pete with, and sometimes replace, conditioned responses.