The incremental stimulus intensity effect in the habituation of the eyeblink response in humans

Investigation of the eyeblink response of humans to auditory and tactile stimulation focused on the determinants of the so called incremental stimulus intensity effect. In Experiment 1, two groups of participants were exposed to 100 tones from 60 to 87-dB in intensity. In Group Incremental, the tones increased from 60- to 87-dB in 3-dB steps, whereas participants in Group Random received the same intensities in a pseudorandom order. The performance of the two groups was compared to Group Constant that received all 100 tones at 90-dB intensity and to a fourth group, named “Apparatus” that received no stimulation. In a subsequent testing block, the results indicated that there was less responding to a 90-dB tone in the Incremental than in the other three groups, which replicates the incremental stimulus intensity effect. The novel observation was that there was also significantly less responding in the Incremental than in the other three groups to an untrained tactile stimulus, suggesting that the differences between the conditions may have implicated differences in a more general sensitization, in addition to any differences in stimulus-specific habituation. Experiment 2 demonstrated that repetition of tones at a fixed intensity caused a decrease in responding to the tones, but also an increase in responding to a novel tactile stimulus, as compared to an untrained condition. These results are discussed in terms of the interpretation of the incremental stimulus intensity effect suggested by Davis and Wagner (1969) and the AESOP (Wagner & Brandon, 1989) treatment of habituation and sensitization.