Effects of stimulus intensity and quality on discrimination of odorant mixtures by spiny lobsters in an associative learning paradigm.

The Florida spiny lobster, Panulirus argus, can behaviorally discriminate between members of a set of four artificial odorant mixture types: crab, mullet, oyster, and shrimp. The present experiments were designed to examine the effects of both intensity and quality on discrimination of odorant mixtures. This was accomplished by conditioning lobsters to only one concentration (0.5 mM) of shrimp mixture and testing them with four concentrations (0.005, 0.05, 0.5 and 5.0 mM) of shrimp mixture and two concentrations (0.05 and 0.5 mM) of oyster mixture. For the two appetitive behaviors examined, lobsters did not discriminate the conditioned mixture (0.5 mM shrimp) from any other of the same-type nonconditioned mixtures. For a third behavior, active avoidance, lobsters discriminated, to a significant degree, the 0.5 mM shrimp mixture from all of the nonconditioned mixtures. However, aversion values for the nonconditioned shrimp mixtures were markedly and consistently higher than those for the nonconditioned oyster mixtures for all three behaviors. Thus, when spiny lobsters are forced to use intensity as a cue (as in an aversive conditioning situation), they have the ability to discriminate between mixtures of the same quality but different intensity. Nevertheless, based on examination of post-conditioning decreases in appetitive behaviors, it is most likely that the intensity of an odorant mixture has a relatively minor effect on the discrimination of the quality of that mixture by these animals, at least over a 1000-fold concentration range.