Habituation and rehabituation of the electrodermal orienting reflex in Macaca fascicularis monkeys as a function of stimulus variability

Abstract

Two groups of six adult female Macaca fascicularis monkeys received repeated presentations of either a fixed pure tone or a tone that varied in frequency from trial to trial, until their skin conductance response habituated. The monkeys were then rehabituated with a new, unchanging stimulus. The monkeys showed a small but insignificant tendency towards retention of habituation, but no savings in either SCR magnitude or latency scores. The habituation-retardation effect, seen in humans’ trials-to-criterion data and to some extent in SCR magnitude and latency measures in Cebus monkeys, was suggested in the macaques’ trials data but not in their magnitude or latency data. A significant accelerative change in heart rate was elicited by the tones, unlike the decelerative response seen in humans, Macaca arctoides, and Cebus monkeys. The Macaca fascicularis monkeys showed a change toward HR deceleration with repeated, unchanging stimulation, but not with varying stimulation. Also, a shift in auditory frequency following habituation resulted in a HR increase following initial habituation to a fixed stimulus, but not following habituation to variable stimuli. It could not be determined whether the difference in HR response between the present macaques and previously studied Cebus monkeys was due to species or sex, since the macaques in this study were all female, while the Cebus monkeys in our earlier study were all male. Both species appear to provide some support for the matching model of habituation.