Measuring Generalization of Visuomotor Perturbations in Wrist Movements Using Mobile Phones

Recent studies in motor control have shown that visuomotor rotations for reaching have narrow generalization functions: what we learn during movements in one direction only affects subsequent movements into close directions. Here we wanted to measure the generalization functions for wrist movement. To do so we had 7 subjects performing an experiment holding a mobile phone in their dominant hand. The mobile phone's built in acceleration sensor provided a convenient way to measure wrist movements and to run the behavioral protocol. Subjects moved a cursor on the screen by tilting the phone. Movements on the screen toward the training target were rotated and we then measured how learning of the rotation in the training direction affected subsequent movements in other directions. We find that generalization is local and similar to generalization patterns of visuomotor rotation for reaching

Generalization patterns.

<p><b>A</b>) Baseline (black) and generalization (red) of the rotation across multiple directions (±SEM). <b>B</b>) Percent adaptation (±SEM) in the generalizing directions relative to the learning direction. <b>C</b>) Percent adaptation (±SEM) for a visuomotor rotation in a center-out reaching task <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020290#pone.0020290-Krakauer2" target="_blank">[16]</a> (black) overlapped with data from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0020290#pone-0020290-g003" target="_blank">Fig. 3b</a> (red). Data from targets at the same absolute distance from the learning direction were combined.</p

Experimental setup and validation.

<p><b>A</b>) Subjects hold an android mobile phone with their dominant hand. They control the position of a cursor on the screen of the mobile phone by tilting it. During perturbed trials the cursor position is rotated 30° degrees relative to the true direction of tilt. <b>B</b>) Comparing the measured angle of tilt around the proximal-distal and medial-lateral axis using the optotrack versus using the mobile phone. Red line is the y = x axis.</p