Effects of d-amphetamine and morphine on discrimination: signal detection analysis and assessment of response repetition in the performance deficits.

Signal detection analysis was used to examine the effects of d-amphetamine and of morphine on auditory discrimination in female rats. The probability of response repetition in the discrete trial two-choice discrimination procedure was used as an additional behavioral measure. d-Amphetamine (0.4-3.2 mg/kg) and morphine (1.88-15.0 mg/kg) decreased the sensitivity measures (A' and SI) but did not consistently affect the response bias measures (B" and RI). The probability of response repetition was increased by d-amphetamine and was not affected by morphine. It is concluded that the response bias measure B", derived from signal detection theory, and the empirical response bias measure RI, do not discriminate between the different ways in which d-amphetamine and morphine affect discriminative responding, under the conditions of this study.