Within mode quality and intensity changes of habituated stimuli.

Habituation of skin conductance response (SCR) magnitude was established by a number of presentations of a short burst of moderate intensity white noise. The 6th, 11th, or 21st stimulus event was either a pure tone of unchanged loudness or another noise pulse of greatly reduced loudness. Mean SCR magnitude to the reduced intensity noise pulses was consistently smaller than that to the tones, but the difference of each of these response from the habituation curve varied with the number of prior habituation trials. The qualitative changes in the stimulus produced a consistent increase in SCR magnitude; the greater the number of prior habituation trials, the larger the difference from the habituation curve. The reduced intensity noise stimulus reduced SCR magnitude below that of the habituation curve at the 6th trial, equalled the curve at the 11th trial, and yielded a greater response than the habituation curve at the 21st trial test position. The response to the tone was superior to that to the reduced intensity noise by a constant amount over the three habituation curve test points.