Effects of acute and chronic d-amphetamine on two variations of a temporal discrimination procedure.

This study assessed temporal discrimination using a procedure in which pigeons classified temporal intervals as short or long based on different responses following visually presented stimulus durations. For the Location group, response alternatives were defined by the location of response keys, whereas for the Color group response alternatives were defined by key color. Temporal parameters were derived from psychophysical curves for time, and the impact of d-amphetamine was determined during acute and chronic dosing. Results showed that classification of temporal intervals was disrupted dose dependently during the acute drug assessment, regardless of the procedural variation. During the chronic drug assessment, differences in one of the psychophysical parameters, Range, were found between groups, as well as a significant effect of Dose on Standard Deviation values in the Color group. These data suggest that procedural variation does not lead to differential effects of d-amphetamine when administered in an acute regimen; however, differences found during chronic administration suggest that procedural variations may influence the development of tolerance as evidenced by differing Range values between groups and marked disruption of Standard Deviation values at the low dose in the Color group. The influence exerted on temporal behavior and tolerance by procedural variations during acute and chronic regimens of d-amphetamine should be explored further.