Time estimation, knowledge of results and drug effects.

1. Knowledge of results can obscure the effects of a drug on time estimation, particularly when 10 s is estimated. The effect of such knowledge on 1 s estimation differs from the effect on 10 s estimation. 2. Secobarbital was the only drug which produced significant directional effects when tested with a nonparametric technique of moderate power. The effects of alcohol were found to be variable. The performance under d-amphetamine could not be discriminated from the performance under placebo. 3. Under the conditions of the present experiment, the one second estimation schedule appears more sensitive to drug effects than the 10 s schedule. 4. Timing responses were found to be sequentially dependent: within limits, successive interresponse times are positively correlated, a finding which warrants further study and elucidation.