Lab-based electroencephalography (EEG) techniques have matured over decades of research and can produce high-quality scientific data. It is often assumed that the specific choice of EEG system has limited impact on the data and does not add variance to the results. However, many low cost and mobile EEG systems are now available, and there is some doubt as to the how EEG data vary across these newer systems. We sought to determine how variance across systems compares to variance across subjects or repeated sessions. We tested four EEG systems: two standard research-grade systems, one system designed for mobile use with dry electrodes, and an affordable mobile system with a lower channel count. We recorded four subjects three times with each of the four EEG systems. This setup allowed us to assess the influence of all three factors on the variance of data. Subjects performed a battery of six short standard EEG paradigms based on event-related potentials (ERPs) and steady-state visually evoked potential (SSVEP). Results demonstrated that subjects account for 32% of the variance, systems for 9% of the variance, and repeated sessions for each subject-system combination for 1% of the variance. In most lab-based EEG research, the number of subjects per study typically ranges from 10 to 20, and error of uncertainty in estimates of the mean (like ERP) will improve by the square root of the number of subjects. As a result, the variance due to EEG system (9%) is of the same order of magnitude as variance due to subjects (32%/sqrt(16) = 8%) with a pool of 16 subjects. The two standard research-grade EEG systems had no significantly different means from each other across all paradigms. However, the two other EEG systems demonstrated different mean values from one or both of the two standard research-grade EEG systems in at least half of the paradigms. In addition to providing specific estimates of the variability across EEG systems, subjects, and repeated sessions, we also propose a benchmark to evaluate new mobile EEG systems by means of ERP responses.

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Recurrent laryngeal nerve injury resulting in chronic unilateral vocal fold paralysis has been treated traditionally by implantation of various materials into the paralyzed vocal fold. Although the usage of these techniques, especially Teflon-glycerin paste injection, has been clinically established, they do not restore full functionality to the larynx (abduction, adduction, and vibratory synchronization of the vocal folds). Restoration of these functions, necessary for improved phonation, has been achieved at least on an experimental basis by reinnervation techniques previously described. This study demonstrates excellent human voice quality following reinnervation of the vocal folds in two cases using ansa hypoglossi-recurrent laryngeal nerve anastomosis. Although the reinnervated vocal fold neither abducted nor adducted, it presented itself in the midline for precise apposition with the nonparalyzed cord. Voice data were analyzed within a single subject experimental design at the following intervals; preoperatively, immediately postoperatively, midterm, and long-term (3 and 6 years). The data was analyzed by subjective and objective means, including acoustics and electroglottography. Patient selection, surgical techniques, results, and implications are reviewed.

Ventricular dysphonia is a poorly understood disorder involving ventricular fold participation during phonation. A population of ventricular dysphonia patients was evaluated using phonatory function studies such as laryngovideostroboscopy, advanced acoustic analysis, and electroglottography to identify shared epidemiologic characteristics and to discuss possible neuromuscular mechanisms and causes. Forty patients with ventricular dysphonia were studied and epidemiologic, acoustic, and histologic data were analyzed. In almost all cases, the authors found abnormalities affecting the glottis caused by a related medical condition. The abnormalities included true vocal cord (TVC) aperiodicity in 100% of the patients, TVC asymmetry in 65%, a laryngeal mass or foreign body (usually Teflon) in 35%, TVC erythema or edema in 32.5%, and TVC bowing in 22.5%. Ventricular dysphonia seems to be primarily a compensatory mechanism for glottic dysfunction. Therapy is based on identifying and correcting the underlying abnormalities. Laryngovideostroboscopy is a particularly important tool in examining chronic dysphonia.

Measurements were taken from lateral still photographs of the vertical larynx position of four professional singers and four nonsingers. Subjects sustained phonation at seven discrete intervals between 90 and 350 Hz. Nonsingers generally positioned their larynx upward with increased voice frequency and tended to maintain a level at or above the larynx physiologic rest position throughout their vocal range. Singers usually maintained a laryngeal position below the physiologic rest level throughout their vocal frequency range. Subject Classification: 70.20; 75.70.

Laryngectomized patients fitted with tracheoesophageal (TE) puncture voice prosthesis may experience frequent failures in adequate production of neophonation. In some cases, these phonatory problems result from obstruction of the voice prosthesis with various deposits. The nature of these deposits was studied with mycologic techniques and by light and scanning electron microscopy. Candida albicans and other fungal species were identified.

Teflon injection for unilateral vocal cord paralysis frequently produces an improved yet breathy voice. Ansa hypoglossi-recurrent laryngeal nerve anastomosis has been performed in five patients. In the four patients discussed in this paper, excellent phonatory quality has been achieved. Electroacoustic analysis indicates that this technique may produce normal phonatory function in paralyzed larynges. There have been no serious side effects or complications in our first five patients. Denervation of the sternothyroid muscle, which results from sectioning its nerve in preparation for suture to the RLN, appears to further improve the voice by medially positioning the vocal cord. Gelfoam paste is injected at the time of nerve transfer to rehabilitate the voice during the 2 months required for nerve regeneration. For younger patients, or those with professional use of their voices, this technique offers superior speech results when compared with Teflon injection.

To test for the existence of laryngeal “microtremors” two experiments were conducted on humans. The first analyzed the acoustic characteristics of observable tremors (macrotremors) in the voice of singers using vocal vibrato and in pathologic subjects producing vocal tremor. In both of these groups acoustic oscillations between 4 and 8 Hz were found. The second study, using a normal subject, sampled electromyographic (EMG) activity from laryngeal and arm muscles during isometric contraction to determine if a periodic component (microtremor) was present in either muscle's contraction pattern. A 9-Hz signal was detected in limb muscle contraction, whereas no periodicity was found in signals from laryngeal muscles. The application of these findings to the theory behind voice “stress” analyzers is discussed.