Modulation of the Effective Salience of a Stimulus by Direct and Associative Activation of Its Representation.

Abstract

In 2 experiments, rats received exposure to presentations of a footshock preceded by a given cue. In the PRf (partial reinforcement) condition, this cue also occurred in the absence of the shock; in the CRf (continuous reinforcement) condition, it did not. Subsequent testing in which a new stimulus was used to signal the shock (Experiment 1) showed that the shock was more effective as a reinforcer for the PRf than for the CRf group. In Experiment 2, the shock was used as a conditioned stimulus signaling food delivery, and it was found that conditioning occurred more readily in the PRf than in the CRf group. These results accord with the hypothesis that preexposure to the shock results in a decline in its effective salience but that experience of a cue that signals shock in the absence of the shock itself attenuates this effect and helps maintain stimulus salience.

Partial reinforcement effects on learning and extinction of place preferences in the water maze

“…Greater similarity between the two phases of the experiment would lead us to expect less generalization decrement in the group that was always given continuous reinforcement, resulting in better learning of the second task in Group Continuous than in Group Partial. This, however, was not the result found in the present Experiment 2-nor in the original experiments reported by Hall et al (2005) using a Pavlovian preparation.…”

“…By the same token, animals trained according to a continuous reinforcement schedule should show more generalization when trained in a novel task using continuous reinforcement than would animals previously trained according to a partial reinforcement schedule. In a series of experiments using a conditioned emotional response procedure, Hall, Prados, and Sansa (2005) found a pattern of results that seems to challenge this prediction. In their experiments, a group of rats was given conditioning trials in which a given cue, A, was consistently paired with a shock unconditioned stimulus (US; A , a continuous reinforcement procedure, where "A" represents the signal, either a light or a tone, and " " represents the shock).…”

“…That is, associative activation of a stimulus (in the absence of the stimulus itself ) will act to restore its salience. Hall et al (2005) argued that, in the continuous reinforcement condition of their experiments, presentations of the shock consistently signaled by Cue A would result in a loss of effective salience by the shock US. On the contrary, in the partial reinforcement condition, presentations of Cue A alone would result in associative activation of the shock representation and would, thus, alleviate the loss of effective salience produced by shock presentations in A trials.…”

“…As suggested above, this result is the opposite of what could be expected from a generalization decrement view of partial reinforcement effects. Hall et al (2005) suggested an alternative explanation based on salience modulation processes.…”

“…In Experiment 2, we replicated the design employed by Hall et al (2005) described above but used the Morris swimming pool navigation task instead of a standard Pavlovian preparation. Two groups of rats were trained to locate an invisible goal, whose position was defined by several landmarks.…”