Blocking and unconditioned response diminution in human classical autonomic conditioning.

Four experiments examined blocking and UR diminution in human SCR conditioning. In Experiment 1, CSX was conditioned in compound with previously conditioned CSA, in one group, or in a compound with another novel stimulus, CSN, in additional group. UR diminution occurred, but there was no post-compound difference in CRs in the two groups and no difference in responding to CSX and CSA following equal training on each, i.e., no blocking. The correlation between blocking and UR diminution was not significant. In Experiment 2, two groups received a blocking procedure, but one was tested on CSX and one on CSA. UR diminution occurred, but there were no post-compound CR or UR differences. There was again no within-subjects blocking effect. The correlation between blocking and UR diminution was not significant, but this correlation was significant when data from Experiments 1 and 2 were combined. In Experiment 3, a differential conditioning procedure was used, followed by reinforcement of two compounds, one with CSA+ and one with CSA-. One subgroup was tested on CSA+ and CSA- with reinforcement; another was tested without reinforcement. UR diminution occurred, and there was significant blocking, but only after two nonreinforced tests. Blocking and UR diminution were significantly correlated. In Experiment 4, four groups received compound conditioning after initial training with CSA. The compound contained CSX and CSA for three groups and two novel CSs for the fourth. Ten nonreinforced test trials were run. The three blocking groups received two CSAs plus eight CSXs four CSAs plus six CSXs, or all CSXs. The fourth group received ten nonblocked CSXs. CR magnitude to blocked CSX was significantly smaller than to nonblocked CSX during the last six test trials, but not initially. Blocking and UR diminution were not correlated, in disagreement with the first three studies. The results indicated that repeated nonreinforced test trails are needed for blocking to be observed in this preparation. The proposition that blocking and UR diminution are both due to reduced processing of the US received only partial support.

Blocking and unconditioned response diminution in human classical autonomic conditioning.

This paper summarizes the results of three experiments on blocking and unconditioned response diminution in human SCR conditioning. Recent theories of conditioning propose that reduced processing of the unconditioned stimulus due to conditioning results in reduced unconditioned response magnitude and in blocking of conditioning of a second conditioned stimulus when it is in compound with the previously conditioned stimulus. In these experiments, clear evidence of diminution of the unconditioned response was obtained in all three studies, but blocking was found only in the third study, which employed a within-subject design and in which the blocking was observed only after at least one extinction trial on both the blocked and nonblocked stimuli. Order of testing was not a factor in this delayed blocking effect. These results do not support the view that blocking occurs because of reduced processing of the unconditioned stimulus in the unconditioned response diminution sense.