Tactile masking within and between hands: Insights for spatial coding of touch at the fingers

A tactile stimulus at the fingers can be encoded according to multiple reference frames (hand-, body- or space-specific). We examined the relative importance of these reference frames by adapting a tactile masking paradigm for stimuli at the index or middle fingers of either hand (unseen). In Exp.1, participants performed a go-no-go task to detect a vibrotactile target at a pre-specified finger (e.g., right index), when this was presented alone or with a concurrent distractor either on the same hand (right middle finger), or on the opposite hand (at homologous or non-homologous locations with respect to the target finger; e.g., left index or left middle finger, respectively). Tactile masking emerged under double stimulation, both for a distractor within the target-hand and for distractors at the non-homologous location on the opposite hand. This suggests use of hand-specific (than body- or space-specific) reference frames when solving this task. In Exp.2, one hand rotated by 180° around the wrist in half of the trials. Masking effects changed only between-hands. Intriguingly, masking from the non-homologous finger reduced only when the hand that changed posture contained the target. This suggests that spatial coding for touches at the fingers depend upon the behavioural relevance of tactile stimuli.