Proprioceptive judgements made with the hand and the jaw: two distinct but functionally related body parts.

We compared proprioceptive judgements made within a single frame of reference (e.g., grasp → grasp; i.e., low-level) and those made between frames of reference (e.g., grasp → vision; i.e., high-level) at the hand and jaw in 30 healthy participants. Participants judged the size of grasped or bitten objects of different sizes. Compared to high-level judgements, low-level judgements were more accurate (hand: mean difference in mean absolute error: 0.20 mm [95% CI 0.12 to 0.27]; jaw: (0.15 mm [0.09 to 0.20]) and precise (hand: mean difference in RMSE: 3.94 [2.73 to 5.15]; jaw: 1.67 [1.19 to 2.14]). A regression line was fit to a participant’s high-level proprioception responses to reflect the central transformation used to make these judgements. Comparing the regression lines for the hand and jaw conditions indicates the brain does not appear to apply a similar calibration to make high-level proprioceptive judgements with these distinct yet functionally related body parts.