The relationship between latent inhibition and the partial reinforcement extinction effect

Abstract

When a conditioned stimulus (CS) is presented with no consequences, little conditioned responding is observed to that CS when it is subsequently paired with a US in a second phase. This phenomenon, known as latent inhibition (LI), is often used as a model for some symptoms of schizophrenia. The partial reinforcement extinction effect (PREE), increase persistence of responding during extinction following partial reinforcement conditioning, has been observed to be very similar to LI. Many manipulations that affect LI also affect the PREE. Due to these similarities, it has been proposed that LI and the PREE share the same mechanisms. This LI = PREE hypothesis was tested in four experiments using autoshaping with rats. Experiments 1 and 2 were designed to test whether LI and the PREE were sensitive to changes in the context of conditioning. It was found that neither was disrupted by this manipulation in this situation. Experiment 3 used an individual-difference approach. Rats were given LI treatment followed by the PREE with different stimuli and responding during each phase was correlated. The results showed that LI size was negatively correlated to PREE size, a finding that is opposite of that predicted by the LI = PREE hypothesis. Experiment 4 used the same design as Experiment 3, but tested the effects of chlordiazepoxide (CDP). While CDP did not affect LI, it delayed the onset of the PREE. This provided additional evidence against the LI = PREE hypothesis. Overall, this dissertation provided evidence that LI and the PREE do not share the same mechanisms.