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Figures 1 and 2. The tactile stimulus device consisted of a hand layer (6), a palmar wall (3) with a U-shaped slot (4) in which a plastic pointer (2) can be moved on the palm of the left or right hand and a dorsal wall (5). One hand was put on the hand layer (6) and fixed tightly with a screw fixation (1) between the palmar wall (3) and the padded dorsal wall (5). The other hand (for self-stimulation) or the experimenter (for external stimulation) could move a plastic rod with the pointer (2) at its end, following the U-shaped slot in the palmar wall (3). The pointer (2) had a spherical tip of 1-mm diameter and was counterweighted with a spring in the plastic rod to maintain a constant pressure of approximately 17 g on the palm during its movement. To obtain a maximum of convenience for the subjects during the procedure, the angle of the hand layer (6) was adjustable at its joint (7). The whole apparatus was movable but stable as a result of its firm basis (8).
