Extinction of conditioned taste aversions: Effects of concentration and overshadowing

Extinction of conditioned taste aversions was examined as a function of taste concentration and of the presence of an additional taste. The results of Experiment 1 were consistent with previous evidence in that a conditioned aversion to high concentration saline was more persistent in extinction than an aversion to a low concentration. However, when floor effects were avoided the rate of extinction was faster for the higher (1%) concentration than for 0.2% saline (Experiment 2), a result consistent with accounts of extinction in other preparations. Three further experiments examined extinction of a conditioned sucrose aversion. The addition of 1% saline, but not of 0.2% saline, to sucrose during extinction produced overshadowing (“protection from extinction”; Experiment 3). Such overshadowing by saline was detected after two, but not after a single extinction trial (Experiment 4). This last finding suggests that under the conditions of the present experiments sweet and salty tastes function as elemental stimuli competing for loss of associative strength. No overshadowing was found when almond (an aqueous odour) was used in place of saline as the added stimulus, even when high concentrations of almond were used that produced observable neophobia (Experiments 5A and 5B).

Effect of Chlordiazepoxide Administered Early in Extinction on Subsequent Extinction of a Conditioned Emotional Response in Rats: Implications for Human Clinical Use

Two groups of albino rats ( n = 32), in which a conditioned emotional response (CER) to a tone had previously been established, were given two extinction trials: one group received chlordiazepoxide on the first extinction trial and the other group received saline. No drug was administered to either group on the second extinction trial. A standard extinction decrement was shown by the saline animals. The chlordiazepoxide animals not only failed to extinguish but showed a slight increment that was interpreted as being due to a “dissociation” of learning effect. These results suggest caution in the use of chlordiazepoxide in human clinical situations when the fear stimuli are delineated and the hope is for anxiety reduction that continues after withdrawal of the drug.