The internal representation of the body can be altered by artificially stimulating arm tendons which distort the body’s idea of where the limbs are. If the limbs are touching another body part, then this can distort the perceived size of that body part (Lackner, 1988). Here we explore whether two-point tactile discrimination and tactile sensitivity are affected by such perceptual distortions. We used tendon vibration to distort the length of an arm and the width of the waist.

Vibrotactile stimuli were delivered with an array of 5 tactors that were spaced by 3 cms on a belt that was either laid on the arm or worn on the stomach. Two-point discrimination and tactile sensitivity detection tasks were performed using two-interval forced choice designs. The arm’s perceptual length was modified by having it held by the other arm while the biceps and triceps tendons were activated by vibration. Perceived waist thickness was modified by holding the arms akimbo and stimulating the extensor or flexor tendons on both arms simultaneously (Ehrsson et al., 2005).

Both two-point discrimination thresholds and sensitivity thresholds were increased when the arm was perceptually lengthened and when the waist was extended. Two-point thresholds and sensitivity thresholds were unaffected when the arm was shortened but were decreased when the waist was made to feel smaller.

We conclude that fundamental sensory properties determining discrimination and sensitivity thresholds are not exclusively determined by cutaneous mechanisms but depend on higher-level representations in the brain that can be distorted.

Body representation; tactile perception; distorted body representation