Effects of vibrotactile feedback on human learning of arm motions

Abstract

Tactile cues generated from lightweight, wearable actuators can help users learn new motions by providing immediate feedback on when and how to correct their movements. We present a vibrotactile motion guidance system that measures arm motions and provides vibration feedback when the user deviates from a desired trajectory. A study was conducted to test the effects of vibrotactile guidance on a subject's ability to learn arm motions. Twenty-six subjects learned motions of varying difficulty with both visual (V), and visual and vibrotactile (VVT) feedback over the course of four days of training. After four days of rest, subjects returned to perform the motions from memory with no feedback. We found that augmenting visual feedback with vibrotactile feedback helped subjects reduce the root mean square (rms) angle error of their limb significantly while they were learning the motions, particularly for 1DOF motions. Analysis of the retention data showed no significant difference in rms angle errors between feedback conditions.

Fig. 1

StrokeSleeve tactile motion guidance system consists of a Microsoft Kinect to track the user’s motions, a computer screen to provide visuals of the measured and desired motions, and a pair of vibrotactile arm bands to indicate motion errors.

Fig. 2

Plastic caps (in white) are used to attach four vibrotactile actuators around the circumference of an arm band with equal spacing.

Fig. 3

(a) Frequency and (b) amplitude of vibration actuators as applied voltage increases.

Fig. 4

Sample schematic illustrating the vectors used to calculate joint angle errors and which actuator is used to guide the user. In this example, to guide the user from their measured forearm orientation ^NP⃗_F,meas, to the desired orientation, ^NP⃗_F,des, the motor represented by the vector ^NP⃗_m,2 would be activated. This motor is colored in white to indicate that it is active.

Fig. 5

Voltage commanded to the vibrotactile actuators as a function of the angle error outside the deadband. When the angle error was within the deadband, zero voltage was applied.

Fig. 6

Annotated screenshot of the visuals provided. User’s own motions were displayed with an avatar. Wireframe arm, whose diameter was proportional to the deadband, indicated a desired trajectory. Users were instructed to stay within this region. Small spheres representing the vibrotactile actuators and a shadow on the virtual floor provided additional cues.

Fig. 7

Average rms angle errors recorded during the learning trials for all subjects, grouped by motion difficulty (1DOF, 2DOF, 3DOF). Red and blue lines represent the visual and vibrotactile (VVT) and visual only (V) conditions respectively. Upper arm and forearm errors are shown separately. Overall, errors recorded under the VVT condition were significantly smaller (p < 0.01) than those recorded with the V condition.

Fig. 8

Plots displaying significant interactions involving feedback condition for the learning trials. Significant interactions (p < 0.05) were found between (a) motion difficulty and feedback condition, (b), arm segment and feedback condition, (c) motion difficulty, arm segment, and feedback condition, and (d) motion difficulty, day of testing, and feedback condition.

Fig. 9

Average rms angle errors recorded during the probe trials for all subjects, grouped by motion difficulties (1DOF, 2DOF, 3DOF). Red and blue lines represent the Visual and Vibrotactile (VVT) and Visual only (V) conditions, respectively. Upper arm and forearm errors are shown separately. Feedback condition did not have a significant effect on the rms angle errors.

Fig. 10

Average rms angle errors recorded during the retention trials for all subjects, grouped by motion difficulties (1DOF, 2DOF, 3DOF). Red and blue lines represent the Visual and Vibrotactile (VVT) and Visual only (V) conditions respectively. Upper arm and forearm errors are shown separately. Feedback condition did not have a significant effect on the rms angle errors.

Fig. 11

Boxplot of reported workload for all subjects across the four days of learning. On average, subjects reported a higher workload with the VVT condition as compared to the V case, although workload decreased over the course of the study. Line indicates the median, the box shows the span of the second and third quartiles, whiskers show the range up to 1.5 times the inter-quartile range, and x’s mark outliers.

Fig. 12

Average duration of vibrotactile stimuli for the different motions for all subjects.