Differentiation learning as a function of stimulus intensity and previous experience with the CS

Discrimination between 50- and 70-dB white noise was investigated in rats under three training procedures employing a conditioned emotional response (CER) technique. When a CER was initially established to the CS(+) and then the CS(-) was introduced, clear generalization of the CER from CS(+) to CS(-) was observed at the beginning of differentiation learning. When both CSi were simultaneously introduced from the beginning of training, subjects acquired the CER to both intensities. Only then, did differential response to intensities occur as an effect of CER extinction to the CS(-). Habituation of the white noise intensity used during differentiation learning as the CS(+) exerted only a small effect on the course of training. Under all training procedures differentiation of the 50-dB CS(+) and 70-dB CS(-) was more difficult than between the 70-dB CS(+) and 50-dB CS(-). This finding was related to both slower. acquisition of the CER when the less intense CS was paired with shock and to a marked decrease of suppressive properties of the weak CS(+) together with CER extinction to the more intense CS(-). Even by the end of differentiation learning intensity relations between CSi during criterion sessions exerted a strong effect on the magnitudes of suppression ratios.