Multisensory task action strategies affect arm placement

Proprioceptive precision for elbow matching in the dark is typically within ±2°. Mechanical loading (exercise) or tendon vibration can alter this precision by impacting peripheral mechanisms. Are accuracy and precision also impacted by multisensory task action strategies giving us a clue as to which central resources are involved in arm placement? In three experiments, subjects had their forearms affixed to lightweight paddles hinged sagittally at the elbow joint. Subjects positioned their arms sequentially while trying to keep the first arm still. Subjects used three strategies to place their arms: (1) guided by an indirect visual signal (traffic lights), (2) bisecting two visually guided angles, and (3) unimodal proprioceptive matching to the first arm’s position. Subjects had more difficulty positioning the second arm when matching without light cues (>2.6° from the target) and were most precise when bisecting two light-guided angles (<2.2° from target). Surprisingly, the indirect light cue did not improve accuracy, but only improved the precision of arm placement. We conclude that interaction between visual and proprioceptive guidance strategies result in superior performance even when the visually presented information is indirect in nature.