Motion in response to the hypnotic suggestion of arm rigidity: a window on underlying mechanisms.

Among hypnotized subjects passing a challenge suggestion of arm rigidity, how might patterns of motor activity (strategies) contribute to the illusion that the elbow cannot be bent? Kinematic analyses of upper limb and trunk were performed. Nonhypnotized subjects carefully enacted a set of prescribed strategies typifying responses possibly adopted by a hypnotized subject. Profile analysis showed striking heterogeneity of response in hypnotic subjects. Half of participants showed no perceivable strategy consistent with the hypothesis that subjects hallucinate the suggestion and so do not engage the motor periphery. Equally common were subtle oscillations or trembling of the arm implying that motion resembling difficulty in bending was initiated. This can be misperceived as unintentional and thus evidence of inability to bend. The lack of a motor strategy is more consistent with dissociated-control theory, whereas the trembling response is more consistent with social-cognitive and dissociated-experience theories.