Cerebral asymmetry and hypnosis: a signal-detection analysis of divided visual field stimulation

Brightness discriminations in a divided-field paradigm were examined with a signal-detection procedure in three sessions, the second with hypnosis. Practiced, hypnotically susceptible Ss were subdivided into high- (n = 6) and medium- (n = 5) susceptible groups on the basis of a susceptibility scale monitored throughout the hypnosis session. High-susceptible Ss showed increases in d' in the left visual field (right hemisphere) with hypnosis, whereas medium-susceptible Ss showed bilateral enhancements. Beta remained invariant in both groups across three sessions but was higher in the left visual field. The results provide evidence of altered brain function with hypnosis and an association of focal right hemispheric changes with high susceptibility and, through the invariance of beta, fail to support the attribution of perceptual changes to attitudinal, nonstate factors.