Stimulus novelty and significance as determinants of electrodermal responsivity: the serial position effect

Three experiments examined the effects of stimulus novelty and significance on the skin conductance component of the orienting response. The test stimuli used in the different experiments involved either a neutral change in stimulation (i.e., adding or deleting components to the standard stimuli), or an introduction of a significant element to the standard stimulus. The serial position of the test stimulus was manipulated in all three experiments. In Experiment 1, nonsignificant test stimuli were introduced at the second, fourth, sixth, or eighth trial of the complex sequence of eight stimuli (i.e., a sequence comprised of varying standard stimuli). None of the test stimuli produced enhanced skin conductance responses under these conditions. Experiment 2 utilized the same design with only one difference: the test stimuli were presented following a simple stimulus sequence (i.e., repetition of a fixed standard stimulus). In this design enhanced skin conductance responses to the test stimuli were observed in almost all experimental conditions, with an advantage of a late over an early presentation of the test stimulus. Experiment 3 was designed to compare serial position effects of significant and neutral test stimuli. A serial position effect was obtained only for the neutral test stimuli, showing once again an advantage for late presentations. It was suggested that different mechanisms might underlie skin conductance responses to significant stimuli and to novel neutral stimuli.