Blocking in rabbit eyeblink conditioning is not due to learned inattention: indirect support for an error correction mechanism of blocking.

Blocking is a classical conditioning task in which prior training to one cue such as a tone reduces learning about a second cue such as a light, when subsequently trained as a tone-light compound. Blocking has been theorized to come about through a US-modulated error correction mechanism by Rescorla & Wagner (1972) as well as through a mechanism of learned inattention as theorized by Mackintosh (1973). In the case of eyeblink conditioning, an error correction mechanism has been hypothesized to take place in the cerebellum while some form of inattention has been hypothesized to take place in the hippocampal region. The hypothesis we are testing is whether the mechanism of learned inattention is involved in blocking in rabbit eyeblink conditioning. If blocking in eyeblink conditioning is produced by a mechanism of learned inattention, then training to a previously blocked cue should be slower than training to that cue in a naïve animal. Rabbits that had received tone training followed by tone-light training exhibited blocking. Rabbits that had been previously blocked to the light acquired conditioned responses to the light at the same rate as naive rabbits. This finding failed to support the hypothesis that blocking in rabbit eyeblink conditioning is due to learned inattention, but does support the Rescorla-Wagner mechanism of error correction. The present finding along with previous work on error correction mechanism in the cerebellar-brainstem circuit (Kim et al., 1998) lend support to the theory that blocking, at least in rabbit eyeblink conditioning, seems to be due to an error correction mechanism rather than a learned inattention mechanism.