Prior experience and current goals affect muscle-spindle and tactile integration

Ely Rabin, Andrew M. Gordon

We previously have shown that reports of illusory elbow extension from biceps vibration can be attenuated by touching a stationary cue-surface with the index fingertip of a vibrated arm. However, this was not the case if the subject had previously felt genuine motion of the cue-surface without biceps vibration. Two potential explanations for this are that the sense of elbow orientation results from tactile and muscle stretch cues that are integrated based on (1) an awareness of the tactile cue's mobility or (2) specific patterns of tactile and muscle spindle activity resembling the elbow motion during previous interactions with the tactile cue. We tested these hypotheses by comparing how touching the cue-surface attenuated the reports of arm movement during biceps vibration after a demonstration of the cue- surface mobility without involving any elbow motion versus simultaneously touching the cue-surface as it moved and extending the elbow to correspond exactly to the elbow extension illusion during vibration. Touching the cue-surface stopped attenuating the reports of elbow extension during biceps vibration only after experiencing actual cue-surface motion while moving the elbow . This supports the second hypothesis that tactile and muscle stretch feedback that are integrated based on specific patterns of tactile and muscle spindle activity recalled from previous interactions with the tactile cue. We also tested the influence of motor set on the sense of elbow position in this paradigm. We found that even after touching the stationary cue-surface had ceased to attenuate illusory elbow motion during biceps vibration, illusory elbow motion during vibration still could be attenuated. This was possible if the subjects intended to actively use their wrists rather than the elbow to maintain fingertip contact. We conclude that muscle stretch and tactile cues are integrated to locate the arm within a highly specific context associated with tactile and proprioceptive feedback from prior experience and current movement goals.