Marijuana effects on visual imagery in a paired-associate task

Marijuana effects on visual imagery, examined using a paired-associate learning task, differed from expectations based on previous subjective reports that marijuana enhances visual imagery. Subjects (48 men, mean age 22.4 yr.) were assigned to four groups (12 subjects per group) differing in (a) whether or not they received specific instructions to use imagery to facilitate learning and (b) whether they received marijuana or placebo. Imagery instructions improved recall, but marijuana did not influence the amount of this improvement. After the memory tests, subjects instructed to use imagery described their images. Marijuana decreased the rated vividness of these imagery descriptions.