Primacy and Recency in Snails (Cornu aspersum)

Pavlovian conditioning has been proven to be useful for the study of associative learning and animal cognition. This procedure can be used to observe certain memory phenomena. The appetitive conditioning of several neutral stimuli can result in higher response rates, and therefore a better memory, for the first and last stimuli of the series. This is equivalent to primacy and recency effects. In this work, the tentacle lowering procedure was employed to study these phenomena in the snail (Cornu aspersum). Subjects experienced five odorous conditioned stimuli (CS) paired with food (conditioning) in a specific order followed by the exposure to the CSs alone to measure the conditioned response (CR, conditioning test). For Experiment 1, the serial presentation of the five reinforced odors resulted in a higher CR for the initial and final odors in comparison with the middle ones. In Experiment 2, it was established that a 20-min trial is enough to produce appetitive conditioning in snail. For Experiment 3, the results of Experiment 1 were replicated while controlling for odor presentation order. Finally, in Experiment 4, the serial position effect was obtained when the interval between conditioning and test phases were minimized. The results observed in the present study provided evidence of the serial position effect in terrestrial snails. The theoretical implications of these are debated.