Date of Award
Doctor of Philosophy in Psychology
Nelson F. Smith
This investigation entailed the first systematic analysis of the extinction of a conditioned taste aversion. The study was undertaken because little is known about the elimination of these prepared responses.
Prepared appear the be characterized by (1) the formation of associations between specific stimuli; (2) the rapidity with which associations are established and (4) the apparent lack of stimulus contiguity generally considered to be necessary to establish classical conditioning.
Throughout the paper an attempt has been made to contrast the acquisition and extinction phases of the conditioned taste aversion, the prepared response, with the body of evidence that has been derived from decades of research on unprepared responses with the ultimate goal of determining if the laws of unprepared learning apply to prepared learning. Unprepared responses are not characterized by the presence of specific associations all neutral stimuli being equally conditionable and are acquired when contiguous stimuli are repeatedly paired. Unprepared learning is thought to reflect trial and error learning whereas prepared learning phenomena seem to suggest the presence of special memory mechanisms that facilitate the acquisition of adaptative responses to important events in the organisms environment e.g. associating gustatory cues with stomach malaise.
The subjects for this study were 72 male albino rats. Eighteen rats were assigned as control subjects and did not acquire the conditioned taste aversion. The remaining 54 rats were subdivided into groups of 18 and were all made ill after consuming saccharine, a novel food. Each of these four groups of 18 rats were further subdivided into three subgroups and received either 1, 5 or 10 sensitization trials (controls) or extinction trials (experimental subjects). One group of experimental rats (N=l8) after being subdivided into the three subgroups (n=6) received either 1, 5 or 10 forced exposures to the saccharine. A second groups of 18 rats after subdivision received 1, 5 or 10 injections of LiCl, the illness inducing agent. The final 18 rate were an illness retention group. The three subgroups of six rats each were merely tested for saccharine aversion after 1, 10 or 20 days.
The effect of the extinction manipulation was measured over a seven day test period. The results show that forced exposure to the saccharine, the conditioned stimulus, was the superior procedure. However, comparing the amount of saccharine consumed by the groups treated by this procedure with the controls indicated that recovery from the aversion was not complete, even for the subgroup having received 10 forced exposures to saccharine.
The subjects having received no treatment evidence no recover from the taste aversion irrespective of the length of the retention interval between the last extinction and the first test day. These results and those observed from the groups that received the forced exposure to saccharine are consistent with the findings from the literature on unprepared learning.
The rats that received the repeated injections of LiCl as an extinction procedure ere not recovered on the first test day but recovered very quickly in the test phase. It appears that repeated non0contingent injections of the illness inducing (LiCl) agent and the resulting stomach malaise followed by the opportunity to drink the saccharine in the test phase facilitates recovery during latter phase. Some investigators have reasoned that a procedure like that described above might contribute to the formation of cognitions which was inconsistent with these formed during the acquisition phase. That is, the illness that was ascribed to the saccharine in the acquisition phase is, during the test phase no longer so ascribed because of the non-saccharine related illness of the extinction period. This cognition would expedite recovery when the saccharine is later presented with no subsequent illness as is the case in the test phase. This latter result was not expected based on the sensitization data from the unprepared area of leaning.
Colby, John J., "The Effect of Extinction on the Delayed Learning of a Conditioned Taste Aversion in the Rat" (1974). Open Access Dissertations. Paper 997.