Chemosensory conditioning in molluscs: I. Failure of contextual conditioning in Hermissenda.

Aversive chemosensory conditioning alters Hermissenda's feeding behavior. But opposite behavioral changes have been reported, depending on whether discrete-trial or context-conditioning paradigms were used, raising questions about the roles of associative and nonassociative processes. We attempted to produce chemosensory contextual conditioning but failed to do so across a wide range of conditions. In Experiments 1-3, we observed large, nonspecific bite latency increases to shellfish extracts, regardless of whether they had signaled the presence or absence of shaking. In Experiment 4, we found that mere exposure to shellfish extract produced latency increases; vestibular stimulation was unnecessary. In a final experiment, using Y-maze choice tests, we failed to observe selective reductions in animals' preference for shellfish paired with shaking. Nonassociative processes stemming from prolonged exposure to concentrated shellfish extracts appear to be major factors in our failure to demonstrate associative chemosensory contextual conditioning.