Overpressure on fingertips prevents state estimation of the pen grip force and movement accuracy

Abstract

We tested the hypothesis that the inability to move a pen accurately in a graphic task is partly due to a decrease of afferent somatosensory information resulting from overpressure on the tactile receptors of the fingers holding the pen. To disentangle the depressed somatosensory origin from an altered motor command, we compared a condition in which the participant actively produces pressure on the pen (active grip) with a condition in which pressure is passively applied (passive grip, no grip-related motor command). We expected that the response of the somatosensory cortex to electric stimulation of the wrist's tactile nerve (i.e., SEP) would be greater in the natural pen grip (baseline condition) than in the two overpressure conditions (actively or passively induced). Fifteen adults were required to trace a geometrical shape in the three grip conditions. The SEP amplitude was not significantly different between the baseline and both overpressure conditions. However, behavioral results showed that drawing accuracy is impaired when the pressure on the pen is increased (passively or actively).Cortical source analyses revealed that the activity of the superior parietal areas (SPL) increased in both overpressure conditions. Our findings suggest that the SPL is critical for sensorimotor integration, by maintaining an internal representation of pen holding. These cortical changes might witness the impaired updating of the finger-pen interaction force for such drawing actions under visual guidance.

Influence of eye movements on writing pressure during handwriting: A cross-sectional study

“…Writing (pen) pressure is an important factor in writing easy-to-read characters 8 . Writing pressure is the pressure applied to the desk when handwriting 11 . For patients with hemiplegia, we have been searching for a way to obtain stable writing pressure.…”

“…Gatouillat et al reported that the pen tip normal force (writing pressure) was not affected by the experiment in which they were instructed to draw a circle under varying speed and rhythm conditions 17 . Furthermore, Danna et al showed that increasing pressure (either passively or actively) on the pen impaired drawing accuracy 11 .…”