Memory formation processes in weakly reinforced learning.

Day-old chicks trained on a single-trail passive avoidance learning task, with varying concentrations of the aversive stimulus (methyl anthranilate), truncated retention functions for low concentrations. The retention function for a 20% v/v dilution of methyl anthranilate in absolute ethanol yielded high retention levels until approximately 40 to 45 minutes following learning. This retention function appears to consist of only the short-term and intermediate (phase A) memory stages of Gibbs and Ng's three-stage model of memory formation, with the short-term stage susceptible to inhibition by monosodium glutamate, and the intermediate stage by ouabain and dinitrophenol. The results suggest that processing of memory into the relatively permanent long-term stage may depend on the strength of the reinforcer in aversive learning.