ABSTRACTExtent of habituation was manipulated by the number of presentations of a short burst of moderate intensity white noise: 4, 8. 15. 22. or 30 times. Skin conductance response (SCR) magnitude to subsequent lest noise pulses of markedly less intensity increased with the extent of habituation. However, response magnitude to tests after 4 or 8 pulses was less than that to the immediately preceding louder pulse, and response to the less intense probe noises after 15, 22, or 30 habituation pulses was greater than that to the immediately preceding pulse. These changes in intensity of stimulation had two effects. They directly determined SCR magnitude, and they provided a stimulation discrepancy yielding an orienting reaction. The experimental problem was introduced using both conditioning/learning and neuronal modeling concepts.