Sound design for auditory biofeedback and motor performance in participants with stroke: a pilot study.

Background: Although auditory biofeedback (ABF) has proved to be effective in stroke rehabilitation, there are a variety of means by which to present information through sound. Objectives: To examine if ABF sound design influences the motor performance of patients with stroke. Methods: A total of four people with chronic stroke participated . They were asked to track target signals by their paretic ankle dorsiflexion. Half of the participants were assigned to one of the two groups. Those in the Error ABF group heard ABF that alerted them to the error between the target and the joint angle. Those in the Full ABF group heard ABF that presented both the target and the angle separately by modulating the frequencies of two sounds. Therefore, when there was no error, no sound or two sounds with the identical frequency were heard in the Error and Full ABF sessions, respectively. The same visual BF (VBF) was always present regardless of the group. The accuracy of the task was quantified via an accuracy index (AI, ranging from -100 to 100). All participants were trained by repeating tracking, and the pre- and post-training AIs were obtained. Results: The AIs of all participants increased after training, but the increase was greater for the Error ABF group (mean increase = 8.9 and 14.9 for the Full and Error groups, respectively). Conclusions: The Full ABF was less effective than the Error ABF, probably because the VBF was present, and the information provided by the Full ABF was therefore redundant.

Comparative Effects of Auditory Electromyographic Biofeedback for Participants Who Are Blind and Sighted.

This study examined differences in auditory electromyographic biofeedback (AEB) effects between participants who were sighted and blind. Past research makes clear that AEB is effective for people who are blind, particularly because of their reported superiority in auditory processing, but no study has directly compared AEB efficacy between participants who are sighted and blind. A total of 11 participants who were sighted and 10 who were blind performed a motor task requiring 20 nonfatiguing muscle contractions at 20% maximal voluntary contraction (MVC) with or without AEB. AEB reduced the error (calculated as the absolute difference of two consecutive contractions) among both participant groups, and the error for the group without biofeedback was greater for the participants who were blind than that for the sighted participants (5.20% ± 2.05% MVC and 3.30% ± 1.26% MVC, respectively; p < .05). This finding was consistent with subjective rating data, also indicating a trend toward greater difficulty for participants who were blind when performing without biofeedback. Moreover, the AEB/no biofeedback condition showed fewer errors for the participants who were blind than for the participants who were sighted during the last part of the task ( p = .036), indicating that participants who were blind were better at maintaining the AEB effect. These data suggest that the poor motor performance of participants who were blind was greatly improved with AEB, suggesting important applications of AEB for assistive technologies, adapted sports, and activities of daily living.

Repetitive eccentric muscle contractions increase torque unsteadiness in the human triceps brachii.

Torque steadiness and low-frequency fatigue (LFF) were examined in the human triceps brachii after concentric or eccentric fatigue protocols. Healthy young males (n=17) performed either concentric or eccentric elbow extensor contractions until the eccentric maximal voluntary torque decreased to 75% of pre-fatigue for both (concentric and eccentric) protocols. The number of concentric contractions was greater than the number of eccentric contractions needed to induce the same 25% decrease in eccentric MVC torque (52.2+/-2.9 vs. 41.5+/-2.1 for the concentric and eccentric protocols, respectively, p<.01). The extent of peripheral fatigue was approximately 12% greater after the concentric compared to the eccentric protocol (twitch amplitude), whereas LFF (increase in double pulse torque/single pulse torque), was similar across protocols. Steadiness, or the ability for a subject to hold a submaximal isometric contraction, was approximately 20 % more impaired during the Ecc protocol (p=.052). Similarly, the EMG activity required to hold the torque steady was nearly 20% greater after the eccentric compared to concentric protocol. These findings support that task dependent eccentric contractions preferentially alter CNS control during a precision based steadiness task.