Hypnosis enhances recall memory: a test of forced and non-forced conditions.

Visual memory recall in hypnosis was investigated. To address criterion shift problems in previous studies, both forced and non-forced recall procedures were used. Previous methodological weaknesses with regard to hypnotizability and hypnotic depth were also addressed. Over 300 volunteers were screened for hypnotizability using the Harvard Group Scale of Hypnotic Susceptibility: Form A (Shor & Orne, 1962). Final high and low hypnotizability groups were selected using the Stanford Hypnotic Susceptibility Scale: Form C (Weitzenhoffer & Hilgard, 1962). Participants in each hypnotizability group were randomly assigned to either forced or non-forced recall conditions and to hypnosis or waking conditions. Participants were shown 60 slides of line drawings and then tested immediately in 3 recall periods. Analysis of variance results showed that those exposed to hypnosis and to a forced recall procedure were significantly more confident of their responses to correct items than those exposed to a non-forced recall procedure or a waking condition. Participants exposed to hypnosis and forced recall procedures recalled more correct items than those exposed to a waking condition. The findings support the hypermnesic effects of hypnosis when participants are required to provide a fixed number of responses.