Spatial and Temporal Influences on Discrimination of Vibrotactile Stimuli on The Arm

Body-machine interfaces (BMIs) provide a non-invasive way to use and control external devices such as powered wheelchairs. Vibrotactile stimulation has been proposed as a way for BMIs to provide device performance feedback to the user, thereby reducing visual demands of closed-loop control. To advance the goal of developing a compact, multivariate vibrotactile display for BMIs, we performed two 2-alternative, forced choice experiments to determine the extent to which vibrotactile perception might vary across multiple stimulation sites. The first experiment assessed vibrotactile discrimination of sequentially presented stimuli within each of four dermatomes of the arm (C5, C7, C8, T1) and on the ulnar head. The second compared discrimination when pairs of vibrotactile stimuli were presented simultaneously vs. sequentially both within and across dermatomes. Although the first experiment found small but statistically significant differences across dermatomes C7 and T1, discrimination thresholds at the other three locations did not differ one from another or from those at either C7 or T1. These results suggest that stimuli applied to each of the sites may be able to convey approximately the same amount of information. The second experiment found that sequential delivery of vibrotactile stimuli resulted in better discrimination than simultaneous delivery, independent of whether the pairs were located within the same dermatome or across dermatomes. Taken together, our results suggest that the arm may be a viable site to transfer multivariate information via vibrotactile feedback for body-machine interfaces. However, user training may be needed to overcome the perceptual disadvantage of simultaneous vs. sequentially-presented stimuli.