Scopolamine and the sensory conditioning of hallucinations.

By means of a sensory conditioning procedure, auditory 'hallucinations' were produced in a set of subjects by pairing a light and a tone. The effect of two doses of scopolamine on the occurrence of these hallucinations was investigated, and the results showed that they were more likely to occur after scopolamine than when subjects had received a placebo. This change was attributed to the impairment of information processing induced by scopolamine.