The fundamental purpose of this experiment was to obtain empiric, replicatable, dose-response data from human subjects on the psychological effects of a common psychoactive drug. Six normal humans were first trained for six sessions on a series of tasks involving different aspects of memory and attention. Their individual sensitivity to secobarbital was also determined. After training, they were tested at zero and three levels of drug on a doubleblind basis. The drug levels for a given subject were selected so that the highest level was just under that which would make the subject untestable. The four point dose-response curves were replicated three times for each subject. Some of the tasks performed by the subjects were affected by the drug in the expected manner as related to dose. Some tasks were unaffected by the drug. In no case were there drug effects which did not follow a regular dose-response curve. In all cases the dose-response curves for an individual subject were replicable. The data from the experiment were interpreted as evidence for an effort stress effect inherent in some tasks. When the demand load of the tests was great, even very high doses of secobarbital had no effect. When the demand load of a task was lower, a dose related drug action was obtained. Some questions were raised by the data on the generality of the Mirsky-Kornetsky hypothesis as to the differential effects of barbiturates on the CPT and the DSST at all dose ranges. Finally, additional evidence was added to the position that a common effect of intoxicating chemicals is to produce a less differentiated, i.e., simpler, mental structure. © 1969 Springer-Verlag.
