Effects of marihuana on auditory signal detection

23 male subjects were tested for auditory signal detection under a no-treatment condition, and smoke marihuana conditions containing 0, 50, 100 and 200 g ⁹-THC per kg body weight. Signal detection was measured under conditions of concentrated attention, in which the subject reported the presence or absence of a tone in a 3-sec noise burst; and divided attention, where the subject also repeated a series of six digits which were presented simultaneously with the noise burst. No differences were found between the no-treatment and placebo conditions. Significant dose-dependent impairment of signal detection resulted for the marihuana conditions under both concentrated and divided attention. Application of signal detection theory indicated that impaired performance was due to a decline in sensitivity (d), independent of changes in subject criteria (beta). There was also some indication of change in criteria—a greater tendency for erroneous reporting of a signal when it was not present.This work was supported by the National Highway Traffic Safety Administration DOT HS-150-2-236, the National Institute of Mental Health MH-17864 and K05-DA-70182, and the National Institute of Alcohol Abuse and Alcoholism AA-00251.