[Temporal stimulus structure, gestalt perception and electrodermal reaction pattern]

The presentation of tones with alternating interstimulus intervals (ISIs) of 10 and 70 s leads to an electrodermal response pattern with an increase in magnitude after long and a decrease after short ISIs. The present study investigated whether there is a relation between the occurrence of the response pattern and the perception of stimuli as a pattern and, furthermore, whether the greater response to the stimulus after the long ISI is due to the greater information content of this stimulus (announcing the occurrence of the pair of tones). Four groups, each consisting of 12 subjects, were subjected to a 1 s, 1000 Hz tone of 90 dB(A) intensity over 21 trials. Group I received the tones in randomized sequences of 10 and 70 s, groups II and III received alternating ISIs of 10 and 70 s. While in group II the regularity of the stimulus pattern was interrupted by the presentation of an extra stimulus, group III was confronted with a stimulus omission. As a control condition, group IV received regularly alternating tones with ISIs of 10 and 70 s. Skin conductance and heart rate were recorded as dependent physiological variables. The perception of the stimulus patterns was measured by means of a questionnaire. The electrodermal response pattern found in earlier studies was replicated, and this pattern even occurred in the random group when 10 and 70 s ISIs appeared directly after each other. The presentation of the extra stimulus and the stimulus omission did not have any effect. For heart rate, a deceleration to tones after long ISIs and an acceleration to tones after short ISIs was found. Subjective pattern perception and electrodermal response patterns did not coincide. In general, the results can be interpreted as showing that the relationship between the ISIs seems to be of importance for the occurrence of the response pattern.