Interactions of different body parts in peripersonal space: how vision of the foot influences tactile perception at the hand.

The body schema, a constantly updated representation of the body and its parts, has been suggested to emerge from body part-specific representations which integrate tactile, visual, and proprioceptive information about the identity and posture of the body. Studies using different approaches have provided evidence for a distinct representation of the visual space approximately 30 cm around the upper body, and predominantly the hands, termed the peripersonal space. In humans, peripersonal space representations have often been investigated with a visual-tactile crossmodal congruency task. We used this task to test if a representation of peripersonal space exists also around the feet, and to explore possible interactions of peripersonal space representations of different body parts. In Experiment 1, tactile stimuli to the hands and feet were judged according to their elevation while visual distractors presented near the same limbs had to be ignored. Crossmodal congruency effects did not differ between the two types of limbs, suggesting a representation of peripersonal space also around the feet. In Experiment 2, tactile stimuli were presented to the hands, and visual distractors were flashed either near the participant's foot, near a fake foot, or in distant space. Crossmodal congruency effects were larger in the real foot condition than in the two other conditions, indicating interactions between the peripersonal space representations of foot and hand. Furthermore, results of all three conditions showed that vision of the stimulated body part, compared to only proprioceptive input about its location, strongly influences crossmodal interactions for tactile perception, affirming the central role of vision in the construction of the body schema.