Effects of methamphetamine on response rate: A microstructural analysis

Key pecking in pigeons was maintained under a multiple random-interval (RI) 1-min, RI 4-min schedule of food presentation. Several doses (0.3–5.6 mg/kg) of methamphetamine were administered, and effects on overall response rates and on the microstructure of responding were characterized. In three of the four pigeons, methamphetamine dose-dependently decreased overall response rate in both components; in the fourth pigeon, intermediate doses increased response rates. Log-survivor analyses did not produce the clear “broken-stick” pattern previously reported with rats [Shull, R.L., Gaynor, S.T., Grimes, J.A., 2001. Response rate viewed as engagement bouts: effects of relative reinforcement and schedule type. J. Exp. Anal. Behav. 75, 247–274]. A fine-grained analysis of inter-response times (IRTs) revealed clear bands of responding around certain IRT durations. Methamphetamine tended to decrease the frequency of IRTs in the shorter bands and increase the frequency of IRTs across all bins greater than 2 s. These results suggest that (a) survivor analyses may not extend to pigeon key pecking, (b) microstructural analyses can reveal order not evident with overall response rate, and (c) a detailed analysis of responding might prove more useful than summary measures in characterizing drug effects on behavior.