Contingent negative variation (CNV) and reaction time were measured in 12 subjects after they smoked placebo and marihuana cigarettes. Change in CNV amplitude after smoking marihuana was negatively correlated (r =-.83) with subjects' ratings of their "high," and not significantly correlated with change in reaction time. The results suggest that the relationship of CNV amplitude to marihuana dose is probably in the form of an inverted U. The CNV amplitude may reflect attentional effort or level of interest rather than efficiency of attentional performance, as measured by reaction time.
Braden W, Stillman RC, Wyatt RJ. Effects of Marihuana on Contingent Negative Variation and Reaction Time. Arch Gen Psychiatry. 1974;31(4):537–541. doi:10.1001/archpsyc.1974.01760160077016