Effect of amplification on the intelligibility of speech produced with an electrolarynx.

The purpose of this study was to look at the effect of orolabial amplification on the intelligibility of speech spoken with a neck model electrolarynx for two distance conditions, three noise conditions, and in relative quiet. A speaker using a neck model electrolarynx read single-answer questions to six listeners. The questions were read with and without amplification at 1.5 and 2.5 m distance, in relative quiet as well as in 66 dB, 72 dB, and 76 dBSPL (A-weighted) prerecorded cafeteria noise. The results of the study showed that speech-to-noise ratios were improved for amplified speech, with improvement in intelligibility for speech spoken in moderate background noise (66 and 72 dBSPL). The effect of the "buzz" of the artificial larynx is reduced, and speakers are better understood in moderate background noise with this amplification system.

Effects of dehydration on phonation in excised canine larynges.

The effects of exposure to dry air on phonation were measured in an ex vivo model of vocal fold vibration. Excised canine larynges were mounted on an apparatus and made to phonate at a constant subglottal pressure by means of unhumidified airflow. The phonation threshold pressure (PTP), glottal airflow, sound intensity of the acoustic output, and effects on vocal efficiency were also assessed. Student's t-test was performed on the results. In 17 larynges, the average PTP increased from 10.0 cm H2O to 15.0 cm H2O after exposure to dry airflow (p < .001). In addition, the average flow increased from 585 mL/s to 801 mL/s at a constant suprathreshold subglottal pressure (p < .001), and from 323 mL/s to 610 mL/s at the PTP (p < .001). The average acoustic output levels, measured during stable phonation segments, markedly decreased with exposure to the dry airflow, from 91.5 dB to 88.5 dB (p < .001). The average vocal efficiency decreased from 3.63 x 10(-4) to 7.00 x 10(-5) (p < .001). No such changes were seen in control larynges phonated with 100% humidified air used for driving the airflow. The results support previously reported modeling and experimental findings that dehydration of the vocal fold generally degrades laryngeal performance.

Treatment efficacy: voice disorders.

This article reviews the literature on the efficacy of treatment for voice disorders primarily using studies published in peer-reviewed journals. Voice disorders are defined, their frequency of occurrence across the life span is reported, and their impact on the lives of individuals with voice disorders is documented. The goal of voice treatment is to maximize vocal effectiveness given the existing disorder and to reduce the handicapping effect of the voice problem. Voice treatment may be (a) the preferred treatment to resolve the voice disorder when medical (surgical or pharmacological) treatments are not indicated; (b) the initial treatment in cases where medical treatment appears indicated; it may obviate the need for medical treatment; (c) completed before and after surgical treatment to maximize long-term post-surgical voice; and (d) a preventative treatment to preserve vocal health. Experimental and clinical data are reviewed that support these roles applied to various disorder types: (a) vocal misuse, hyperfunction and muscular imbalance (frequently resulting in edema, vocal nodules, polyps or contact ulcers); (b) medical or physical conditions (e.g., laryngeal nerve trauma, Parkinson disease); and (c) psychogenic disorders (e.g., conversion reactions, personality disorders). Directions for future research are suggested which maximize clinical outcomes and scientific rigor to enhance knowledge on the efficacy of voice treatment.

A quantitative output-cost ratio in voice production.

A quantitative output-cost ratio (OCR) is proposed for objective use in voice production and is defined as the ratio of the acoustic output intensity to the collision intensity of the vocal folds. Measurement of the OCR is demonstrated in a laboratory experiment using 5 excised larynges and a transducer designed for use on human subjects. Data were gathered at constant fundamental frequency (150 Hz). Subglottal pressure was varied from 1.0 to 1.6 kPa, and glottal width at the vocal processes was varied from a pressed condition to a 2-mm gap. The OCR was plotted as a function of glottal width. With no vocal tract, the excised larynx experiments yielded a broad maxima in the OCR curves, across all subglottal pressure conditions, at about 0.6 mm. Computer simulations indicate that sharper maxima may occur when the influence of the vocal tract is taken into account. The potential clinical utility of the OCR is discussed for treatment of a wide range of voice disorders, including those involving both hyper- and hypoadduction.

Interrelation of mandibular laryngeal functions.

The purpose of the experiment was to explore relations between jaw and laryngeal functions. The general question was whether laryngeal adduction was affected by jaw opening or by jaw biting. Twelve untrained, vocally healthy male and female adults participated as subjects. Subjects produced repeated tokens of /uh/ in each of 12 experimental conditions involving combinations of 3 jaw openings (10 mm, 25 mm, 40 mm), 2 jaw biting pressures (10 kPa, 200 kPa), and 2 fundamental frequencies (conversational and high). For each token, laryngeal adduction was estimated from the electroglottographic closed quotient. The most straightforward results were that (1) laryngeal adduction increased as jaw opening increased at the conversational pitch, for all subjects, independent of biting pressure, and (2) laryngeal adduction increased as biting pressure increased, at the conversational pitch, for males, independent of jaw opening. Other relations between estimated laryngeal adduction and jaw manipulations were more complex, varying with fundamental frequency and gender. Speculations are made about possible biomechanical and neurological explanations for the findings.

Frequency and risk factors for voice problems in teachers of singing and control subjects.

Using a questionnaire format, 125 teachers of singing and 49 control subjects indicated whether they had a current or past voice problem, and provided information about their demographic characteristics, voice use patterns, and medication use. The results revealed similar rates of current voice problems reported by the two subject groups. However, teachers of singing were considerably more likely to report ever having had a voice problem than controls (64 vs. 33%). Risk factors were similar for the two groups. Dehydrating medications and a report of a past voice problem both increased the likelihood of perceiving a current problem, by a factor of three and five, respectively. Females were twice as likely to report a past voice problem as males, and younger subjects were slightly more likely to report a past problem as compared with older subjects. The implications of the findings are discussed from a theoretical as well as pragmatic perspective.

Nonspecific laryngeal granuloma: a case study of a professional singer.

A professional singer with laryngeal granuloma underwent surgery following failed response to conservative treatments. Two primary findings emerged. First, although a sizable lesion was present initially, presurgical voice measures were largely normal or superior. The exception was elevated phonatory effort during singing. Second, postsurgical voice functions were entirely normal or superior (including phonatory effort), despite demanding singing performances a few weeks following surgery. The results add to the limited corpus of quantitative, normative-referenced data on voice in patients with granulomas and are inconsistent with previous reports of voice abnormalities in such patients and poor functional response to surgery.

Laryngeal adduction in resonant voice.

The primary question in this study was whether subjects with nodules and subjects with healthy larynges would produce "resonant voice" with a similar laryngeal configuration. A second question regarded whether the electroglottographic closed quotient (EGG CQ) could be used to noninvasively distinguish resonant from other voice types. Twelve adult singers and actors served as subjects, including 6 persons with healthy larynges and 6 persons with nodules. Performers were used as an attempt to maximize token validity and stability. Subjects produced repeated tokens of resonant, pressed, normal, and breathy voice during sustained vowels. Laryngeal adduction was directly estimated using blinded, ordinal, visual-perceptual ratings based on videoscopic views of the larynx. EGG CQs were further calculated based on separate trials. The perceptual ratings indicated that subjects in both groups produced resonant voice with a barely adducted or barely abducted laryngeal configuration that was distinct from configurations for pressed and breathy (but not normal) voice. Previous literature suggests that this configuration may be relevant in many cases of voice therapy (1). Average CQs distinguished resonant from pressed voice, but inconsistently distinguished resonant from breathy voice. Further CQs were reliably different across healthy subjects and subjects with nodules. Thus, the utility of this measure to noninvasively estimate resonant voice may be limited, particularly without ongoing subject-specific calibration procedures.

Correspondence of electroglottographic closed quotient to vocal fold impact stress in excised canine larynges.

The purpose of this study was to explore the possible use of the electroglottographic closed quotient (EGG CQ) as a noninvasive estimate of vocal fold impact stress (SI). Two excised canine larynges were used. Each larynx was mounted and vocal fold oscillation was induced using a humidified air source. Twenty-seven experimental trials were conducted for each larynx. Trials involved variations in vocal process gap, vocal fold elongation, and subglottic pressure. Simultaneous measures were made of vocal fold SI at the midpoint of the membranous vocal folds, and EGG CQ (dimensionless ratio). The results indicated that when threshold and saturation effects were excluded, the SI and the CQ were strongly related (linear correlation r = .83 and .96 for the two individual larynges, and .81 for the combined data). Within the region of linear relation, an increase of.15 in the CQ corresponded to about 1 kPa increase in SI for the combined data. Discussion focuses on possible clinical implications and the likely reasons for threshold and saturation phenomena.

Endolaryngeal contact pressures.

In this work, we present a new method for in vivo endolaryngeal contact pressure measurement with a miniature pressure transducer. Using this methodology, contact pressures can be measured during videoendoscopy at different locations between the artyenoids and also at various locations along the membranous vocal folds. Twenty adults with organic and functional voice disorders and two vocally healthy adults participated as subjects. Endolaryngeal contact pressure measures were made during a series of phonatory tasks varying pitch, loudness, and phonatory onset and offset. Measures were also made during nonphonatory tasks, including throat clearing, coughing, Valsalva maneuvres, and gagging. The most remarkable findings were: (1) interarytenoid contact pressures were considerably greater than intraglottal contact pressures; (2) interarytenoid contact pressures were greater for lower than higher pitches; (3) both interarytenoid and intraglottal contact pressures were remarkably large during hard glottal attack; and (4) overall, the largest endolaryngeal pressures were recorded between the arytenoids, during a thoracic fixation maneuver and during gag reflex.

Time-of-day effects on voice range profile performance in young, vocally untrained adult females.

Time-of-day effects on voice range profile performance were investigated in 20 vocally healthy untrained women between the ages of 18 and 35 years. Each subject produced two complete voice range profiles: one in the morning and one in the evening, about 36 hours apart. The order of morning and evening trials was counterbalanced across subjects. Dependent variables were (1) average minimum and average maximum intensity, (2) Voice range profile area and (3) center of gravity (median semitone pitch and median intensity). In this study, the results failed to reveal any clear evidence of time-of-day effects on voice range profile performance, for any of the dependent variables. However, a reliable interaction of time-of-day and trial order was obtained for average minimum intensity. Investigation of other subject populations, in particular trained vocalists or those with laryngeal lesions, is required for any generalization of the results.

Investigation of vocal fold impact stress in human subjects.

The primary purpose of the study was to explore a methodology for measuring vocal fold impact stress (SI) in awake humans, and to provide information about the general magnitude of SIs that may occur at the midpoint of the membranous vocal folds during phonation. A secondary purpose was to examine the potential use of the electroglottographic closed quotient (EGG CQ) to indirectly reflect SI. Seven male and 13 female adults were enrolled as subjects, of whom 18 had normal larynges and normal voices, 1 had nodules, and 1 had vocal fold paresis and bowing. Subjects attempted to produce 3 different voice types (pressed, normal, breathy), at 3 different pitches (low, medium, high) and 3 different loudness levels (quiet, medium, loud). For a first set of trials, only EGG data were collected. For a second set, a sensor was also introduced to the midmembranous glottis for the collection of SI data. The primary findings were that (1) endolaryngeal sensor placement was achieved during phonation trials for 17 of 20 subjects; however, grossly consistent anteroposterior positioning was accomplished, and analyzable data were obtained, for only 7 subjects; (2) SIs ranged from less than 1 kPa to about 3 kPa for those 7 subjects; and (3) no relation was detected between simultaneous CQs and SIs for individual data, although a relation was reported in a prior canine study. One possible reason for the failure to show such a relation in the present study was subtle variations in vertical as well as anteroposterior positioning of the sensor during the trials. Future studies should focus on developing a methodology for ensuring invariant 3-dimensional sensor positioning between the membranous folds, so that the stability of both SI and simultaneous CQ data can be improved.

Vocal fold impact stress analysis.

Vocal fold impact stress (force/area) has been implicated as a factor possibly contributing to the formation of nodules and polyps. The force of impact of a moving body is related to its acceleration. Since the mass of the folds is relatively constant, one expects impact force to be directly proportional to acceleration. A measure that reflects the relative displacement of the vocal folds is photoglottography (PGG). The velocity and acceleration of the folds are easily obtained by calculating the first and second derivatives of the PGG displacement waveform. This study, therefore, compared the second derivative of the PGG signal with simultaneously measured impact stress in an excised canine larynx model. Glottal transillumination (PGG) was measured with a subglottic transducer. A miniature force transducer placed in the midline between the vocal folds measured impact stress at the midglottal position. For nine different larynges, there was a positive and linear relationship between the second derivative of PGG and impact stress. The statistically significant results support the hypothesis that the second derivative of PGG m ay provide a use fulnoninvasive way to estimate relative vocal fold impact stress.

Review: occupational risks for voice problems.

The purpose of this paper is to provide a cohesive review of the literature regarding the functional consequences of voice problems and occupational risk factors for them. The salient points are as follows. According to conservative estimates, approximately 28,000,000 workers in the US experience daily voice problems. Many people who experience voice problems perceive them to have a negative impact on their work and their quality of life. Estimates based on empirical data suggest that, considering only lost work days and treatment expenses, the societal cost of voice problems in teachers alone may be of the order of about $2.5 billion annually in the US. In fact, across several countries, "teacher" consistently emerges as the common occupation most likely to seek otorhinolaryngological (ORL) evaluation for a voice problem. Other occupational categories likely to seek ORL examination for a voice problem are singer, counselor/social worker, lawyer, and clergy. Finally, US Census data indicate that keyboard operators may be at special risk for voice problems because of a near-epidemic growth of repetitive strain injury (RSI), which can adversely affect the voice especially when speech recognition software is implemented. This paper discusses frequency data, quality of life data, and treatment considerations for these voice-related occupational issues.

Working conditions on stage: climatic considerations.

Singers and actors frequently complain about dusty and dry theater environments, which they believe induce respiratory tract indispositions and decrements in vocal performance. In the literature to date, extremely few quantitative data exist about actual climatic conditions on stage. A previous study by our group in an unhumidified theater found that it had too high temperatures, too dry and too dusty air, based on German occupational guidelines for the generic workplace. In the present study, humidification units were installed in the same theater, and the environmental measures were repeated. The primary findings indicated that, following the activation of the humidification units, temperatures, humidities and fine dust concentrations were improved and generally within acceptable ranges for the generic workplace, although not always optimal. Where unacceptable performance environments exist, special care should be taken to counsel performers with regard to possible prophylactic measures such as individual steam inhalation and fluid intake.

Dependence of phonatory effort on hydration level.

In this study, a double-blind placebo-controlled approach was used to assess the relation between hydration level and phonatory effort. Twelve adult, untrained voice users with normal voices participated as subjects. Each subject received a 4-hour hydration treatment, a 4-hour dehydration treatment, and a 4-hour placebo (control) treatment. Following each treatment, phonatory effort was measured with a physiological measure, phonation threshold pressure (PTP), and with a psychological measure, direct magnitude estimation of perceived phonatory effort (DMEPPE). Summarizing the results across these measures, the findings indicated an inverse relation between phonatory effort and hydration level, but primarily for high-pitched phonation tasks. The findings for PTPs replicated those from an earlier study conducted without double-blind experimental manipulations (Verdolini-Marston, Titze, & Druker, 1990). Theoretical discussion focuses on the possible role of vocal fold tissue viscosity for hydration and dehydration effects, although direct measures of tissue viscosity are lacking.