Preference and response suppression under different correlations between shock and a positive reinforcer in rats

A lever-press response by rats was reinforced by food in two successively presented types of trial signalled by different discriminative stimuli. When responding was punished by a shock in one type of trial, a groups for which the shock always preceded the reinforcer by .5 sec (positive correlation) showed less suppression in those trials than a group which received the shock and food separated in time (negative correlation). When, in a second experiment, rats were given a choice between food alone in one end of a shuttle box and either positively or negatively correlated shock and food in the other on a concurrent schedule, the group receiving the negatively correlated shock showed a greater preference for the food alone end. On the basis of a third experiment in which a tone was substituted for the shock in the choice situation, it was argued that the effect of correlation was not simply due to the stimulus properties of the shock. A final experiment demonstrated that when shock punishment is administered during extinction of the lever-press response, the rate of extinction is slower if the shock has been previously paired with the food reinforcer. Pairing a shock with food seems to attenuate the intrinsic aversiveness of the shock through Pavlovian counterconditioning.