At the tip of the fingers: The role of orientation and position on the reference frames used to interpret ambiguous stimuli presented to the hand

Abstract

Coding an object or events position in the environment involves recruitment of multiple reference frames or coordinate systems. Generally retino-, head-, trunk-, arm and object-centred representations have been shown to influence how we estimate relative object position. Visual information can primarily be coded in retinotopic or spatiotopic frames while tactile information does not provide such a one-to-one mapping between position in space and receptor activation. The question asked here is how tactile information presented to the hand, which is able to change its orientation in space and body coordinates, influences interpretation of tactile letter stimuli. As letters are generally perceived visually, when interpreting a letter traced on the skin, one might assume that the perceptual system defaultly employs a visual frame of reference, or at least a simple egocentric perspective. However, previous findings suggest that for cutaneous tracing the perspective taken is influenced in a complex manner by factors such as location, as opposed to receptor type, limb orientation, location of stimulation relative to other body parts and object coordinates (Parsons and Shimojo, 1987). In three experiments we explored the initial interpretation of letter stimuli d, b, p, & q when presented to the hand and fingertips. The stimuli are ambiguous along left/right and top/bottom axes and are therefore ideal for inferring reference frame adopted. The current findings suggest that orientation and position of the hand relative to the body, alters the reference frame selected when interpreting tactile letter stimuli. The results are consistent with a multiple reference frame model of information processing and allow us to disentangle the elements involved in perception of cutaneous stimulation at our fingertips.