Effect of haptic feedback from self-touch on limb movement coordination.

Touching one's own body provides haptic feedback about the spatial configuration and movement of body parts. However, the influence of self-touch on movement performance has not been investigated so far. The authors evaluated the contribution of self-touch by asking participants to perform cyclic movement sequences with their feet while touching them with their hands, or vice versa. Hands and feet were either crossed or uncrossed (parallel), manipulating anatomical congruency of haptic feedback. The effects of self-touch (vs. object-touch), active limb (feet vs. hands) and sequence complexity were assessed in three separate experiments. Task performance was strongly and specifically disrupted in one of the anatomically incongruent conditions (hands-parallel/feet-crossed). This disruption occurred only with self-touch (Experiment 1), with the feet active (Experiment 2), and was more pronounced for the more complex movement sequence (Experiment 3). Thus, incongruent self-touch can strongly interfere with motor performance, showing that haptic information is automatically integrated in the online control of movement. The observed asymmetry between hands and feet indicates limb-specific differences regarding the use of spatial frames of reference and/or regarding the weighting of sensory information. The results emphasize the intimate connection between programming of action sequences and the anticipation of somatic feedback from self-touch.