Removal of visual feedback lowers structural variability of inter-digit force coordination during sustained precision pinch

This study examined the effects of visual feedback on inter-digit force coordination during a precision pinch. Sixteen healthy, right-handed subjects were instructed to pinch an instrumented apparatus for 1 min with a stable force output. Visual feedback was provided for the first 30 s and withdrawn for the second 30 s. Detrended fluctuation analysis (DFA) and detrended cross-correlation analysis (DCCA) methods were used to quantify the time-dependent structures of each digit's force and of the force correlation between the digits. After removing visual feedback, the DFA scaling exponent, αDFA, increased from 1.10 ± 0.12 to 1.29 ± 0.13 for the thumb and from 0.95 ± 0.08 to 1.33 ± 0.13 for the index finger (F1,95 = 372.47, p < 0.001); the DCCA scaling exponent, αDCCA, increased from 1.00 ± 0.08 to 1.33 ± 0.13 (t95 = 20.33, p < 0.001). Structural changes were observed beginning with the first 5 s epoch after the removal of visual feedback. The results provide evidence that removing visual feedback lowers the structural variability of inter-digit force coordination. This change is reflected in the high-level control strategy, resulting in the two digits being more tightly coupled under somatosensory feedback without visual inputs.