Imagery of different sensory modalities: hypnotizability and body sway

Postural control in subjects with high (Highs) and low (Lows) susceptibility to hypnosis is differentially affected by changes in visual and neck tactile/proprioceptive input. The aim of the present experiment was to investigate whether imagery of the visual and tactile sensory modalities also induces different modulation of postural control in Highs and Lows. Fourteen Highs and 16 Lows were included in the study; they were recorded while standing upright with eyes closed during visual and tactile imagery tasks and during mental computation. Their posture and movement were recorded with an Elite System and their experience was assessed after each task in a structured interview. Visual imagery was judged "easier" than tactile imagery by Lows, while Highs performed both tasks easily and judged the tactile imagery less effortful and more vivid than Lows. No difference was observed for the mental computation. The Highs' body sway was not affected by the cognitive tasks, while Lows showed a task-related modulation of body sway. The results are in line with the hypothesis of lower vulnerability of Highs to the effects of tasks interfering with postural control and of different sensory-motor integration in Highs and Lows.

Department of Physiology, University of Siena, Siena, Italy.