Cara E. Stepp

Vibrotactile Sensory Substitution for Electromyographic Control of Object Manipulation

It has been shown that incorporating augmentative vibrotactile feedback can improve performance of a virtual object manipulation task using finger movement. Vibrotactile sensory substitution for prosthetic applications, however, will necessarily not involve actual finger movement for control. Here we study the utility of such feedback when using myoelectric (EMG) signals for control, and demonstrate task improvement and learning for a force-motion task in a virtual environment. Using vibrotactile feedback, a group of unimpaired participants (N = 10) were able to increase performance in a single session. We go on to study the feasibility of this method for two prosthetic hand users, one of whom had targeted muscle reinnervation allowing the augmentative feedback to be perceived as if it were on the absent hand.

Acoustics of the human middle-ear air space.

The impedance of the middle-ear air space was measured on three human cadaver ears with complete mastoid air-cell systems. Below 500 Hz, the impedance is approximately compliance-like, and at higher frequencies (500-6000 Hz) the impedance magnitude has several (five to nine) extrema. Mechanisms for these extrema are identified and described through circuit models of the middle-ear air space. The measurements demonstrate that the middle-ear air space impedance can affect the middle-ear impedance at the tympanic membrane by as much as 10 dB at frequencies greater than 1000 Hz. Thus, variations in the middle-ear air space impedance that result from variations in anatomy of the middle-ear air space can contribute to inter-ear variations in both impedance measurements and otoacoustic emissions, when measured at the tympanic membrane.

Relative to direct haptic feedback, remote vibrotactile feedback improves but slows object manipulation

Most prosthetic hand users are limited to visual feedback of movement performance. To characterize the benefit of vibrotactile feedback for a task that lacks haptic feedback, a virtual environment was used to experimentally manipulate visual, task-relevant haptic, and remote vibrotactile feedback on simple object manipulation for unimpaired subjects. The combination of visual and remote vibrotactile feedback was compared to visual feedback alone, and to simultaneous visual and direct haptic feedback to represent ideal performance. Visual and vibrotactile feedback resulted in improvement of most performance variables including difficulty ratings relative to visual feedback alone. However addition of sensory cues to visual feedback increased trial times and the increase was steeper for vibrotactile than for haptic feedback. Specifically, during vibrotactile feedback the velocity did not change, but the duration of execution increased due to improved performance, resulting in increased trial times. This result suggests future exploration of performance improvement and execution speed for augmented sensory feedback.

Repeated Training with Augmentative Vibrotactile Feedback Increases Object Manipulation Performance

Most users of prosthetic hands must rely on visual feedback alone, which requires visual attention and cognitive resources. Providing haptic feedback of variables relevant to manipulation, such as contact force, may thus improve the usability of prosthetic hands for tasks of daily living. Vibrotactile stimulation was explored as a feedback modality in ten unimpaired participants across eight sessions in a two-week period. Participants used their right index finger to perform a virtual object manipulation task with both visual and augmentative vibrotactile feedback related to force. Through repeated training, participants were able to learn to use the vibrotactile feedback to significantly improve object manipulation. Removal of vibrotactile feedback in session 8 significantly reduced task performance. These results suggest that vibrotactile feedback paired with training may enhance the manipulation ability of prosthetic hand users without the need for more invasive strategies.

Characteristics of phonatory function in singers and nonsingers with vocal fold nodules.

PURPOSE The goals of this study were to determine if there were significant differences between singers and nonsingers in the morphology of vocal nodules and the associated impact on vocal function. METHOD Participants were 10 professionally trained singers with nodules, eight nonsingers with nodules, and 10 individuals with healthy normal voice (controls). Surface electromyography (sEMG) from three anterior neck locations and acoustic rise times for vowels /a/ and /i/ were measured in all the participants. In individuals with nodules, dB SPL/cm H(2)O, glottal airflow, and nodule location and size were also measured. RESULTS There were no significant differences between singers and nonsingers with nodules in terms of airflow, dB SPL/cm H(2)O, nodule size, or nodule location. In nonsingers with nodules, airflow and nodule size were significantly correlated, but were not significantly correlated in singers. Vowel rise times and sEMG during vocal tasks did not differentiate among nodule and control groups. Sternocleidomastoid sEMG during initiation of the vowel /a/ was statistically significantly stronger in nonsingers with nodules relative to singers with nodules and controls. CONCLUSIONS Nodule morphology did not differ between singers and nonsingers, although some behavioral aspects of phonation differed between the groups.

Neck and Face Surface Electromyography for Prosthetic Voice Control After Total Laryngectomy

The electrolarynx (EL) is a common rehabilitative speech aid for individuals who have undergone total laryngectomy, but they typically lack pitch control and require the exclusive use of one hand. The viability of using neck and face surface electromyography (sEMG) to control the onset, offset, and pitch of an EMG-controlled EL (EMG-EL) was studied. Eight individuals who had undergone total laryngectomy produced serial and running speech using a typical handheld EL and the EMG-EL while attending to real-time visual sEMG biofeedback. Running speech tokens produced with the EMG-EL were examined for naturalness by 10 listeners relative to those produced with a typical EL using a visual analog scale. Serial speech performance was assessed as the percentage of words that were fully voiced and pauses that were successfully produced. Results of the visual analog scale assessment indicated that individuals were able to use the EMG-EL without training to produce running speech perceived as natural as that produced with a typical handheld EL. All participants were able to produce running and serial speech with the EMG-EL controlled by sEMG from multiple recording locations, with the superior ventral neck or submental surface locations providing at least one of the two best control locations.

Vibrotactile Sensory Substitution for Object Manipulation: Amplitude Versus Pulse Train Frequency Modulation

Incorporating sensory feedback with prosthetic devices is now possible, but the optimal methods of providing such feedback are still unknown. The relative utility of amplitude and pulse train frequency modulated stimulation paradigms for providing vibrotactile feedback for object manipulation was assessed in 10 participants. The two approaches were studied during virtual object manipulation using a robotic interface as a function of presentation order and a simultaneous cognitive load. Despite the potential pragmatic benefits associated with pulse train frequency modulated vibrotactile stimulation, comparison of the approach with amplitude modulation indicates that amplitude modulation vibrotactile stimulation provides superior feedback for object manipulation.

Comparison of Neck Tension Palpation Rating Systems With Surface Electromyographic and Acoustic Measures in Vocal Hyperfunction

The purpose of this study was to evaluate current neck tension palpation rating systems to determine interrater reliability and possible correlation with necksurface electromyography (sEMG, collected from three electrode recording locations) and to measure the third formant for /a/ during various vocal behaviors. This prospective study examined the neck muscle tension of 16 participants before and after a single session of voice therapy. Interrater reliability and relationships between palpation ratings and objective measures of sEMG (anterior neck) and the third formant for /a/ were assessed using Pearsons correlations (r). Interrater reliability was relatively low as measured by Pearsons correlations, although Wilcoxon signed-rank test results were similar as those in a previous study. Correlations between palpation ratings and sEMG and between ratings of laryngeal height and the third formant for /a/ were generally low. Correlations increased between anterior neck sEMG and ratings of suprahyoid muscle tension when examined in a reduced set of individuals with higher interrater reliability. Palpation rating scales do not reliably capture changes that may occur in neck muscle tension of typical voice therapy patients over one session. Consequently, little can be concluded from correlations between sEMG and palpation ratings.

A virtual trajectory model predicts differences in vocal fold kinematics in individuals with vocal hyperfunction.

A simple, one degree of freedom virtual trajectory model of vocal fold kinematics was developed to investigate whether kinematic features of vocal fold movement confirm increased muscle stiffness. Model simulations verified that increases in stiffness were associated with changes in kinematic parameters, suggesting that increases in gesture rate would affect kinematic features to a lesser degree in vocal hyperfunction patients given the increased levels of muscle tension they typically employ to phonate. This hypothesis was tested experimentally in individuals with muscle tension dysphonia (MTD; N = 10) and vocal nodules (N = 10) relative to controls with healthy normal voice (N = 10) who were examined with trans-nasal endoscopy during a simple vocal fold abductory-adductory task. Kinematic measures in MTD patients were less affected by increased gesture rate, consistent with the hypothesis that these individuals have elevated typical laryngeal muscle tension. Group comparisons of the difference between medium and fast gesture rates (Mann-Whitney, one-tailed) showed statistically significant differences between the control and MTD individuals on the two kinematic features examined (p<0.05). Results in nodules participants were mixed and are discussed independently. The findings support the potential use of vocal fold kinematics as an objective clinical assay of vocal hyperfunction.

Object Manipulation Improvements Due to Single Session Training Outweigh the Differences Among Stimulation Sites During Vibrotactile Feedback

Most hand prostheses do not provide intentional haptic feedback about movement performance; thus users must rely almost completely on visual feedback. This paper focuses on understanding the effects of learning and different stimulation sites when vibrotactile stimulation is used as the intentional haptic feedback. Eighteen unimpaired individuals participated in this study with a robotic interface to manipulate a virtual object with visual and vibrotactile feedback at four body sites (finger, arm, neck, and foot) presented in a random order. All participants showed improvements in object manipulation performance with the addition of vibrotactile feedback. Specifically, performance showed a strong learning effect across time, with learning transferring across different sites of vibrotactile stimulation. The effects of learning over the experiment overshadowed the effects of different stimulation sites. The addition of a cognitive task slowed participants and increased the subjective difficulty. User preference ratings showed no difference in their preference among vibrotactile stimulation sites. These findings indicate that the stimulation site may not be as critical as ensuring adequate training with vibrotactile feedback during object manipulation. Future research to identify improvements in vibrotactile-based feedback parameters with amputees is warranted.