Proprioception does not quickly drift during visual occlusion

Several perceptual studies have shown that the ability to estimate the loca tion of the arm degrades quickly during visual occlusion. To account for th is effect, it has been suggested that proprioception drifts when not contin uously calibrated by vision. In the present study, we re-evaluated this hyp othesis by isolating the proprioceptive component of position sense (i.e., the subjects were forced to rely exclusively on proprioception to locate th eir hand, which was not the case in earlier studies). Three experiments wer e conducted. In experiment 1, subjects were required to estimate the locati on of their unseen right hand, at rest, using a visual spot controlled by t he left hand through a joystick. Results showed that the mean accuracy was identical whether the localization task was performed immediately after the positioning of the hand or after a 10-s delay. In experiments 2 and 3, sub jects were required to point, without vision of their limb, to visual targe ts. These two experiments relied on the demonstration that biases in the pe rception of the initial hand location induced systematic variations of the movement characteristics (initial direction, final accuracy, end-point vari ability). For these motor tasks, the subjects did not pay attention to the initial hand location, which removed the possible occurrence of confounding cognitive strategies. Results indicated that movement characteristics were , on average, not affected when a 15-s or 20-s delay was introduced between the positioning of the arm at the starting point and the presentation of t he target. When considered together, our resuits suggest that proprioceptio n does not quickly drift in the absence of visual information. The potentia l origin of the discrepancy between our results and earlier studies is disc ussed.