Accuracy of hand localization is subject-specific and improved without performance feedback

Abstract

Accumulating evidence indicates that the spatial error of human's hand localization appears subject-specific. However, whether the idiosyncratic pattern persists across time with good within-subject consistency has not been adequately examined. Here we measured the hand localization map by a Visual-matching task in multiple sessions over 2 days. Interestingly, we found that participants improved their hand localization accuracy when tested repetitively without performance feedback. Importantly, despite the reduction of average error, the spatial pattern of hand localization errors remained idiosyncratic. Based on individuals' hand localization performance, a standard convolutional neural network classifier could identify participants with good accuracy. Moreover, we did not find supporting evidence that participants' baseline hand localization performance could predict their motor performance in a visual Trajectory-matching task even though both tasks require accurate mapping of hand position to visual targets in the same workspace. Using a separate experiment, we not only replicated these findings but also ruled out the possibility that performance feedback during a few familiarization trials caused the observed improvement in hand localization. We conclude that the conventional hand localization test itself, even without feedback, can improve hand localization but leave the idiosyncrasy of hand localization map unchanged.

The Origin of Movement Biases During Reaching

“…Fig 1h (top) shows the recovered visual-proprioceptive bias map based on the parameters of the Transformation Bias model when fit to the reaching data in Exp 1b. The simulated results are very similar to the map measured empirically in the previous study 20 (Fig 1e). In contrast, the Visual Bias and Proprioceptive Bias models provide poor fits (all R 2 <0.18, Fig 3a right).…”

“…While the overall pattern of biases in the visuo-proprioceptive map are similar across individuals, there are subtle individual differences 18,20 . As such, we would anticipate that the motor bias function would also exhibit stable individual differences due to idiosyncrasies in the visuo-proprioceptive map.…”

“…15.585272 doi: bioRxiv preprint Another perceptual cause of motor biases stems from proprioception (Fig 1c). Systematic distortions in the perceived position of the hand [18][19][20] and/or joint position 21,22 can infleunce motor planning. For example, if the perceived starting position of the hand is leftwards of its true location, a reaching movement to a forward visual target would exhibit a rightward bias and a reaching movement to a rightward visual target would fall short 7 .…”

“…Motor biases may arise from a transformation error between coordinate systems. Two prominent features stand out when this transformation error is empirically measured [18][19][20]27 . First, the direction of the transformation error is similar across the workspace (e.g., a leftward and downward matching error for right-handers).…”

“…For the lab-based study (Exp 1, 2), 206 undergraduate students (age: 18-24) were recruited from University of California, Berkeley. For the online study (Exp 3), 183 young adult participants (age: [18][19][20][21][22][23][24][25][26][27][28][29][30] were recruited via Prolific, a website designed to recruit participants for online behavioral testing. All participants were right-handed as assessed by the Edinburgh handedness test 53 Experiments 1a, 1b, and 2 were conducted in the lab.…”