Kinematic strategies of upper limbs lowering during suggestions of heaviness: a real-simulator design

Abstract The aim of the experiment was to study possible differences between the kinematic strategies for the “involuntary” arm lowering of hypnotized highly susceptible subjects (H-Highs) and for the voluntary movement of non-hypnotizable simulators (Sims) during suggestions of arm heaviness (Part I). In addition, a comparison between awake susceptible subjects (W- Highs) and H-Highs was carried out to clarify the specific role of the hypnotic state and hypnotizability (Part II) Subjects’ absorption and attentional/imagery capabilities were evaluated through neuropsychological tests. Their arm movements were monitored three-dimensionally at hand, wrist and elbow level through a Polhemus Fastrack system. A final interview collected self-reports concerning the perception of movement involuntariness. Neuropsy- chological tests showed better “absorption” and imagery capabilities in Highs. In the interview, H-Highs perceived a higher involvement in the task and greater involuntari- ness and difficulties in contrasting the arm lowering than the Sims. Kinematic analysis showed significant differ- ences between H-Highs and Sims for arm displacements along the vertical axis and on the horizontal plane. In fact the former lowered the left arm earlier and to a greater degree than the right arm; on the horizontal plane, a forearm flexion was observed for H-Highs on the right side. On comparing W-Highs and H-Highs, hypnosis appeared to magnify the waking motor strategies, but also to induce specific changes, mainly concerning the horizontal plane. These results cannot be interpreted on the basis of “role playing” and socio-cognitive factors