Concomitant heart rate and eyeblink Pavlovian conditioning in human subjects as a function of interstimulus interval

Pavlovian heart rate and eyeblink conditioning were simultaneously assessed in human subjects. Tone durations of 0.6, 1.1, and 2.1 s were employed in separate groups of subjects as the conditioned stimulus. A 100-ms corneal airpuff, which served as the unconditioned stimulus, overlapped the last 100 ms of the tone in each group, thus producing interstimulus intervals of 0.5, 1.0, and 2.0 s. Other groups of pseudoconditioning subjects received explicitly unpaired tone and airpuff presentations of identical durations but in a pseudorandom sequence so that they never occurred together. The best eyeblink conditioning was observed in the group with the .5-s interstimulus interval, although the 1.0-s group also demonstrated some evidence of eyeblink conditioning. The group with the 2.0-s interstimulus interval showed a lower overall rate of conditioned response occurrence and the highest rate of pseudoconditioned responding. The conditioned heart rate response in all three conditioning groups consisted of cardiac decelerations, but tone-evoked cardiac accelerations were observed in the pseudoconditioning groups. The magnitude of the cardiac deceleration was comparable in all three conditioning groups.