Initial habituation or sensitization of the GSR depends on magnitude of first response.

Habituation and sensitization of the galvanic skin response (GSR) to shock were studied in college males. One would expect that at any given time individuals vary on a continuum in the degree of their initial GSR responsiveness to a stimulus. Here it is shown that those on the higher end of the continuum are more likely to show a response decrement between trials 1 and 2 when this stimulus is presented intermittently (i.e., habituate), while subjects at the lower end of the continuum are more likely to show a response increment between trials 1 and 2 (i.e., sensitize) to the same intermittent stimulus. Following these initial and opposite changes on the first two trials, which bring all subjects to approximately the same level of responsiveness, they all now behave similarly and continue to show habituation. Previous work on subhuman species showed that habituation and sensitization curves had certain characteristic similarities across species. The present work shows that some of these similarities also occur in humans. One may speculate, that as with other characteristics that are similar across species, they have survival value.