Lateral skin stretch influences direction judgments of motion across the skin

Background: Sliding of surfaces across the skin changes the position of edges and texture elements relative to the receptive fields of somatosensory neurons. This 'successive positions' cue is sufficient to elicit motion sensation. Surfaces also create lateral skin stretch due to friction and we ask whether this potential cue influences perceived direction. Method: A 4-pin array was applied to the forearm to manipulate the two motion cues independently. It indicated distal or proximal direction by pin activation in the order 1-2-3-4 or 4-3-2-1. Crucially, each pin also stretched the skin by moving 3.5 mm laterally in the same (Congruent cues) or opposite direction (Incongruent cues). Results: 90% of motion direction judgments accurately reflected succession of positions with a Congruent skin stretch cue but only 79% with an Incongruent skin stretch cue (F1,7 = 6.80, p =.035).Conclusion: The skin stretch cue contributes to neural coding of motion direction.