Auditory Masked Detection during Marihuana Intoxication

Abstract

The most commonly reported effect of marihuana is an auditory one: “I can hear more subtle changes in “”sounds,” and I can understand the words of songs which are not clear when straight [C. T. Tart, On Being Stoned (Science and Behavior Books, Palo Alto, Calif., 1971)]. These observations have been interpreted as an improvement in auditory acuity during intoxication. To test this idea a simple auditory masked detection experiment was conducted using a single-interval YES-NO paradigm. The signal was a monaural 500-Hz tone, 100 msec in duration, presented in monaural continuous noise (45-dB spectrum level). Psychometric functions were generated in no-drug and drug conditions. For the drug conditions the six observers, all experienced marihuana users, smoked natural marihuana containing 5 mg of Δ9-THC supplied by NIMH. There were only slight differences between conditions in the slopes and locations of the resulting psychometric functions. However, there was a significant shift in the observers' response criterion; during intoxication observers were less strict in reporting the presence of a signal. The results suggest that the changes in auditory perception so often reported by marihuana users are due primarily to modifications in cognitive, not sensory, processes. Data for response latencies are also reported. [Supported by a Grant-in-Aid from Oberlin College.]