Judgements of hand location and hand spacing show minimal proprioceptive drift

Abstract

With a visual memory of where our hands are, their perceived location drifts. We investigated whether the perceived location of one hand or the spacing between two hands drifts in the absence of visual memories or cues. In 30 participants (17 females, mean age 27 years, range 20–45 years), perceived location of the right index finger was assessed when it was 10 cm to the right or left of the midline. Perceived spacing between the index fingers was assessed when they were spaced 20 cm apart, centred on the midline. Testing included two conditions, one with ten measures at 30 s intervals and another where a 3 min delay was introduced after the fifth measure. Participants responded by selecting a point on a ruler or a line from a series of lines of different lengths. Overall, participants mislocalised their hands closer to the midline. However, there was little to no drift in perceived index finger location when measures were taken at regular intervals (ipsilateral slope: 0.073 cm/measure [$-0.014$ to 0.160], mean [99% CI]; contralateral slope: 0.045 cm/measure [$-0.033$ to 0.120]), or across a 3 min delay (ipsilateral: ($-0.47$ cm [$-1.11$ to 0.17]; contralateral: $-0.44$ cm [$-1.12$ to 0.24]). There was a slight drift in perceived spacing when measures were taken at regular intervals (slope: $-0.15$ cm/measure [$-0.29$ to $-0.01$]), but none across a 3 min delay (0.08 cm [$-1.08$ to 1.24]). Thus, proprioceptive-based perceptions of where our hands are located or how they are spaced drift minimally or not at all, indicating these perceptions are stable.