Table 2.

Group mean and standard errors of the mean (in parentheses) for response rates and reinforcement rates for the saline and amphetamine conditions for the indicated DRL parameters. The time intervals for calculations of response rate and reinforcement rate were based on the time interval marked by the resumption of responding after amphetamine treatment to the end of the session. Response rates for saline were based on the same length of time but starting at the beginning of the session. See text for rationale.

	Saline		5.0 mg/kg d-Amphetamine
DRL parameter (s)	Response rate (r/hr)	Reinforcement rate (rft/hr)	Response rate (r/hr)	Reinforcement rate (rft/hr)
24	144.0 (12.0)	61.2 (6.0)	174.0 (13.2)	49.2 (4.2)
72	78.0 (15.0)	16.2 (2.4)	138.6 (13.2)	9.6 (0.6)