Blocking and pseudoblocking: the reply of Rattus norvegicus to Apis mellifera.

Blaser, Couvillon, and Bitterman (2006) presented data obtained with honeybees that in principle challenged all traditional interpretations of blocking. They administered A + followed by either A + or + alone (where + indicates an unconditioned stimulus) and then tested on X. They observed less responding to X when they administered A + than when + alone was administered, a phenomenon they called "pseudoblocking". Here we examined pseudoblocking in a rat fear-conditioning preparation. In Experiment 1, using a control procedure that was similar to our usual blocking control, we obtained conventional blocking but failed to observe pseudoblocking in our analogue to Blaser et al.'s procedure. In Experiment 2, we used Blaser et al.'s control procedure and again failed to observe the pseudoblocking effect with rats when we used the experimental context as an analogue to the honeybee feeder used by Blaser et al. After reviewing their protocol and previously published studies from their laboratory, we hypothesized that the feeder that they treated as a training context probably served as a punctate cue. We also tested this possibility in Experiment 2, using a punctate cue as a surrogate feeder, and were now able to reproduce their pseudoblocking phenomena. Our results are consistent with a simple overshadowing account of pseudoblocking, within the framework of existing theories of associative learning, which is not applicable to the conventional blocking paradigm. Thus, blocking remains a real phenomenon that must be addressed by models of associative learning.