Modulation of the postural effects of cognitive load by hypnotizability.

Aim of the experiment was to study whether cognitive load affects postural control more in low (Lows) than in highly hypnotizable (Highs) subjects due to the latter's greater attentional abilities. Standing Highs and Lows underwent an experimental session (closed eyes) consisting of a basal condition and of mental computation in an easy (stable support) and a difficult (unstable support) postural condition. Variability [standard deviation (SD)] and complexity [sample entropy (SampEn)] of the movement of the centre of pressure (CoP), its mean velocity (Velocity), the area swept by the CoP (Area) and the ratio between the CoP trajectory length and area [length for surface (LFS)] were measured. Few hypnotizability-related differences were detected (reduction in the Highs' SD and increases in the Lows' LFS in the difficult postural condition). Thus, the hypnotizability-related postural differences observed in previous studies during sensory alteration could not be accounted mainly by attentional abilities.