Effects of unilateral eye closure on middle ear muscle contractions.

Middle ear muscle contractions (MEMCs) are most commonly considered a response to high-level acoustic stimuli. However, MEMCs have also been observed in the absence of sound, either as a response to somatosensory stimulation or in concert with other motor activity. The relationship between MEMCs and non-acoustic sources is unclear. This study examined associations between measures of voluntary unilateral eye closure and impedance-based measures indicative of middle ear muscle activity while controlling for demographic and clinical factors in a large group of participants (N=190) with present clinical acoustic reflexes and no evidence of auditory dysfunction. Participants were instructed to voluntarily close the eye ipsilateral to the ear canal containing a detection probe at three levels of effort. Orbicularis oculi muscle activity was measured using surface electromyography. Middle ear muscle activity was inferred from changes in total energy reflected in the ear canal using a filtered (0.2 to 8 kHz) click train. Results revealed that middle ear muscle activity was positively associated with eye muscle activity. MEMC occurrence rates for eye closure observed in this study were generally higher than previously published rates for high-level brief acoustic stimuli in the same participant pool suggesting that motor activity may be a more reliable elicitor of MEMCs than acoustic stimuli. These results suggest motor activity can serve as a confounding factor for auditory exposure studies as well as complicate the interpretation of any impulsive noise damage risk criteria that assume MEMCs serve as a consistent, uniform protective factor. The mechanism linking eye and middle ear muscle activity is not understood and is an avenue for future research.

Generalizability of clinically measured acoustic reflexes to brief sounds.

Middle ear muscle contractions (MEMC) can be elicited in response to high-level sounds, and have been used clinically as acoustic reflexes (ARs) during evaluations of auditory system integrity. The results of clinical AR evaluations do not necessarily generalize to different signal types or durations. The purpose of this study was to evaluate the likelihood of observing MEMC in response to brief sound stimuli (tones, recorded gunshots, noise) in adult participants (N = 190) exhibiting clinical ARs and excellent hearing sensitivity. Results revealed that the presence of clinical ARs was not a sufficient indication that listeners will also exhibit MEMC for brief sounds. Detection rates varied across stimulus types between approximately 20% and 80%. Probabilities of observing MEMC also differed by clinical AR magnitude and latency, and declined over the period of minutes during the course of the MEMC measurement series. These results provide no support for the inclusion of MEMC as a protective factor in damage-risk criteria for impulsive noises, and the limited predictability of whether a given individual will exhibit MEMC in response to a brief sound indicates a need to measure and control for MEMC in studies evaluating pharmaceutical interventions for hearing loss.

The reduction of gunshot noise and auditory risk through the use of firearm suppressors and low-velocity ammunition.

OBJECTIVE: This research assessed the reduction of peak levels, equivalent energy and sound power of firearm suppressors. DESIGN: The first study evaluated the effect of three suppressors at four microphone positions around four firearms. The second study assessed the suppressor-related reduction of sound power with a 3 m hemispherical microphone array for two firearms. RESULTS: The suppressors reduced exposures at the ear between 17 and 24 dB peak sound pressure level and reduced the 8 h equivalent A-weighted energy between 9 and 21 dB depending upon the firearm and ammunition. Noise reductions observed for the instructor's position about a metre behind the shooter were between 20 and 28 dB peak sound pressure level and between 11 and 26 dB LAeq,8h. Firearm suppressors reduced the measured sound power levels between 2 and 23 dB. Sound power reductions were greater for the low-velocity ammunition than for the same firearms fired with high-velocity ammunition due to the effect of N-waves produced by a supersonic bullet. CONCLUSIONS: Firearm suppressors may reduce noise exposure, and the cumulative exposures of suppressed firearms can still present a significant hearing risk. Therefore, firearm users should always wear hearing protection whenever target shooting or hunting.

Acoustic reflexes are common but not pervasive: evidence using a diagnostic middle ear analyser.

OBJECTIVE: The objective of this study is to determine whether acoustic reflexes are pervasive (i.e. known with 95% confidence to be observed in at least 95% of people) by examining the frequency of occurrence using a friction-fit diagnostic middle ear analyser. DESIGN: Adult participants with very good hearing sensitivity underwent audiometric and middle ear testing. Acoustic reflexes were tested ipsilaterally and contralaterally in both ears across a range of elicitor frequencies. Reflex elicitors were 700 ms tones presented at maximum level of 100 dB HL. Two automated methods were used to detect the presence of an acoustic reflex. STUDY SAMPLE: A group of 285 adult volunteers with normal hearing. RESULTS: There were no conditions in which the proportion of participants exhibiting acoustic reflexes was high enough to be deemed pervasive. Ipsilateral reflexes were more likely to be observed than contralateral reflexes and reflexes were more common at 0.5 and 1 kHz elicitor frequencies as compared with 2 and 4 kHz elicitor frequencies. CONCLUSIONS: Acoustic reflexes are common among individuals with good hearing. However, acoustic reflexes are not pervasive and should not be included in damage risk criteria and health hazard assessments for impulsive noise.

Prevention of Noise-Induced Hearing Loss from Recreational Firearms.

In the United States and other parts of the world, recreational firearm shooting is a popular sport that puts the hearing of the shooter at risk. Peak sound pressure levels (SPLs) from firearms range from ∼140 to 175 dB. The majority of recreational firearms (excluding small-caliber 0.17 and 0.22 rifles and air rifles) generate between 150 and 165 dB peak SPLs. High-intensity impulse sounds will permanently damage delicate cochlear structures, and thus individuals who shoot firearms are at a higher risk of bilateral, high-frequency, noise-induced hearing loss (NIHL) than peer groups who do not shoot. In this article, we describe several factors that influence the risk of NIHL including the use of a muzzle brake, the number of shots fired, the distance between shooters, the shooting environment, the choice of ammunition, the use of a suppressor, and hearing protection fit and use. Prevention strategies that address these factors and recommendations for specialized hearing protectors designed for shooting sports are offered. Partnerships are needed between the hearing health community, shooting sport groups, and wildlife conservation organizations to develop and disseminate accurate information and promote organizational resources that support hearing loss prevention efforts.

Acoustic reflexes are common but not pervasive: evidence from the National Health and Nutrition Examination Survey, 1999-2012.

OBJECTIVE: To determine whether acoustic reflexes are pervasive (i.e. sufficiently prevalent to provide 95% confidence of at least 95% prevalence) and might be invoked in damage-risk criteria (DRC) and health hazard assessments (HHA) for impulsive noise. DESIGN: Cross-sectional analyses of a nationally-representative study. STUDY SAMPLE: National Health and Nutrition Examination Survey (NHANES) data collected between 1999 and 2012 were used. Over 60 thousand reflex traces obtained from 15,106 NHANES participants were used in the study, along with demographic, audiometric, health and exposure variables obtained in that study. RESULTS: Acoustic reflexes were not sufficiently prevalent to be deemed pervasive by any detection method or in any subgroup defined by age or audiometric characteristics. The odds of observing acoustic reflexes were greater for women, young adults, and people with better hearing sensitivity. Abnormally high tympanometric admittance and "Other" race/ethnicity (i.e. people who do not self-identify as exclusively Non-Hispanic White, Non-Hispanic Black, Mexican-American, or Hispanic) were associated with lower odds. CONCLUSIONS: Acoustic reflexes are not sufficiently prevalent to be included in DRC and HHA for impulsive noise.

Auditory risk of air rifles.

OBJECTIVE: To characterize the impulse noise exposure and auditory risk for air rifle users for both youth and adults. DESIGN: Acoustic characteristics were examined and the auditory risk estimates were evaluated using contemporary damage-risk criteria for unprotected adult listeners and the 120-dB peak limit and LAeq75 exposure limit suggested by the World Health Organization (1999) for children. STUDY SAMPLE: Impulses were generated by nine pellet air rifles and one BB air rifle. RESULTS: None of the air rifles generated peak levels that exceeded the 140 dB peak limit for adults, and eight (80%) exceeded the 120 dB peak SPL limit for youth. In general, for both adults and youth, there is minimal auditory risk when shooting fewer than 100 unprotected shots with pellet air rifles. Air rifles with suppressors were less hazardous than those without suppressors, and the pellet air rifles with higher velocities were generally more hazardous than those with lower velocities. CONCLUSION: To minimize auditory risk, youth should utilize air rifles with an integrated suppressor and lower velocity ratings. Air rifle shooters are advised to wear hearing protection whenever engaging in shooting activities in order to gain self-efficacy and model appropriate hearing health behaviors necessary for recreational firearm use.

Overreliance on auditory feedback may lead to sound/syllable repetitions: simulations of stuttering and fluency-inducing conditions with a neural model of speech production.

UNLABELLED: This paper investigates the hypothesis that stuttering may result in part from impaired readout of feedforward control of speech, which forces persons who stutter (PWS) to produce speech with a motor strategy that is weighted too much toward auditory feedback control. Over-reliance on feedback control leads to production errors which if they grow large enough, can cause the motor system to "reset" and repeat the current syllable. This hypothesis is investigated using computer simulations of a "neurally impaired" version of the DIVA model, a neural network model of speech acquisition and production. The model's outputs are compared to published acoustic data from PWS' fluent speech, and to combined acoustic and articulatory movement data collected from the dysfluent speech of one PWS. The simulations mimic the errors observed in the PWS subject's speech, as well as the repairs of these errors. Additional simulations were able to account for enhancements of fluency gained by slowed/prolonged speech and masking noise. Together these results support the hypothesis that many dysfluencies in stuttering are due to a bias away from feedforward control and toward feedback control. EDUCATIONAL OBJECTIVES: The reader will be able to (a) describe the contribution of auditory feedback control and feedforward control to normal and stuttered speech production, (b) summarize the neural modeling approach to speech production and its application to stuttering, and (c) explain how the DIVA model accounts for enhancements of fluency gained by slowed/prolonged speech and masking noise.

Acoustic and articulatory features of diphthong production: a speech clarity study.

PURPOSE: The purpose of this study was to evaluate how speaking clearly influences selected acoustic and orofacial kinematic measures associated with diphthong production. METHOD: Forty-nine speakers, drawn from the University of Wisconsin X-Ray Microbeam Speech Production Database (J. R. Westbury, 1994), served as participants. Samples of clear and conversational productions of the word combine were extracted for analysis. Analyses included listener ratings of speech clarity and a number of acoustic and articulatory kinematic measures associated with production of the diphthong /aI/. RESULTS: Key results indicate that speaking clearly is associated with (a) increased duration of diphthong-related acoustic and kinematic events, (b) larger F1 and F2 excursions and associated tongue and mandible movements, and (c) minimal evidence of change in formant transition rate. CONCLUSIONS: Overall, the results suggest that clarity-related changes in diphthong production are accomplished through larger, longer, but not necessarily faster diphthong-related transitions. The clarity-related adjustments in diphthong production observed in this study conform to a simple model that assumes speech clarity arises out of reduced overlap of articulatory gestures.

Speech motor correlates of treatment-related changes in stuttering severity and speech naturalness.

Participants of stuttering treatment programs provide an opportunity to evaluate persons who stutter as they demonstrate varying levels of fluency. Identifying physiologic correlates of altered fluency levels may lead to insights about mechanisms of speech disfluency. This study examined respiratory, orofacial kinematic and acoustic measures in 35 persons who stutter prior to and as they were completing a 1-month intensive stuttering treatment program. Participants showed a marked reduction in stuttering severity as they completed the treatment program. Coincident with reduced stuttering severity, participants increased the amplitude and duration of speech breaths, reduced the rate of lung volume change during inspiration, reduced the amplitude and speed of lip movements early in the test utterance, increased lip and jaw movement durations, and reduced syllable rate. A multiple regression model that included two respiratory measures and one orofacial kinematic measure accounted for 62% of the variance in changes in stuttering severity. Finally, there was a weak but significant tendency for speech of participants with the largest reductions in stuttering severity to be rated as more unnatural as they completed the treatment program.

Correlation of orofacial speeds with voice acoustic measures in the fluent speech of persons who stutter.

Stuttering is often viewed as a problem in coordinating the movements of different muscle systems involved in speech production. From this perspective, it is logical that efforts be made to quantify and compare the strength of neural coupling between muscle systems in persons who stutter (PS) and those who do not stutter (NS). This problem was addressed by correlating the speeds of different orofacial structures with vowel fundamental frequency (F0) and intensity as subjects produced fluent repetitions of a simple nonsense phrase at habitual, high, and low intensity levels. It is assumed that resulting correlations indirectly reflect the strength of neural coupling between particular orofacial structures and the respiratory-laryngeal system. An electromagnetic system was employed to record movements of the upper lip, lower lip, tongue, and jaw in 43 NS and 39 PS. The acoustic speech signal was recorded and used to obtain measures of vowel F0 and intensity. For each subject, correlation measures were obtained relating peak orofacial speeds to F0 and intensity. Correlations were significantly reduced in PS compared to NS for the lower lip and tongue, although the magnitude of these group differences covaried with the correlation levels relating F0 and intensity. It is suggested that the group difference in correlation pattern reflects a reduced strength of neural coupling of the lower lip and tongue systems to the respiratory-laryngeal system in PS. Consideration is given to how this may contribute to temporal discoordination and stuttering.

Orofacial movements associated with fluent speech in persons who stutter.

This study was intended to replicate and extend previous findings that (a) during fluent speech persons who stutter (PS) and those who do not (NS) differ in their vocal tract closing movements (L. Max, A. J. Caruso, and V. L. Gracco, 2003) and (b) ratios relating lip and tongue speed to jaw speed increase with stuttering severity (M. D. McClean and C. R. Runyan, 2000). An electromagnetic system was used to record movements of the upper lip, lower lip, tongue, and jaw of 43 NS and 37 PS during productions of a nonsense phrase and a sentence. Measurement and analysis of movement speeds, durations, and ratios of lip and tongue speed to jaw speed were performed on fluent productions of a nonsense phrase and sentence. Statistical comparisons were made between PS with low and high stuttering severity levels (LPS and HPS) and NS. Significant variations across groups in movement speed and duration were observed, but the pattern of these effects was complex and did not replicate the results of the two earlier studies. In the nonsense phrase, significant reductions in lower lip closing duration, jaw closing duration, and jaw closing speed were seen in PS. In the sentence task, HPS showed elevated tongue opening and closing durations. For tongue opening in the sentence, LPS showed elevated speeds and HPS showed reduced speeds. The elevated speeds for LPS are interpreted as a contributing factor to speech disfluency, whereas the reduced speeds and increased durations in HPS are attributed to adaptive behavior intended to facilitate fluent speech. Significant group effects were not seen for the speed ratio measures. Results are discussed in relation to multivariate analyses intended to identify subgroups of PS.

Variations in articulatory movement with changes in speech task.

Studies of normal and disordered articulatory movement often rely on the use of short, simple speech tasks. However, the severity of speech disorders can be observed to vary markedly with task. Understanding task-related variations in articulatory kinematic behavior may allow for an improved understanding of normal and disordered speech motor behavior in varying communication contexts. This study evaluated how orofacial kinematic behavior varies as a function of speaking task in a group of 15 healthy male speakers. The speech tasks included a nonsense phrase with a high frequency of stop consonants, a sentence, an oral reading passage, and a spontaneous monologue. In addition, rate and intensity conditions were varied for the nonsense phrase and sentence. The articulatory positions of the upper lip, lower lip, tongue blade, and mandible were recorded, and measures reflecting (a). average features of individual movements or strokes (i.e., peak speed, distance, and duration) and (b). overall spatial variability of the articulators for each task were extracted, derived, and analyzed. Results showed a number of task- and condition-related differences in speech kinematic behavior. The most prominent result from the task comparison was that the nonsense speech task exhibited larger, faster, and longer movement strokes than the other speech tasks. For some articulators (lower lip and tongue), there were task-related differences in spatial variability. Changes in loudness and rate revealed variation in kinematic measures that were often complicated by articulator identity and task type. The results suggest that an expanded range of speech tasks and conditions may aid in the study of normal and disordered speech motor behavior.

Association of orofacial muscle activity and movement during changes in speech rate and intensity.

Understanding how orofacial muscle activity and movement covary across changes in speech rate and intensity has implications for the neural control of speech production and the use of clinical procedures that manipulate speech prosody. The present study involved a correlation analysis relating average lower-lip and jaw-muscle activity to lip and jaw movement distance, speed, and duration. Recordings were obtained on orofacial movement, muscle activity, and the acoustic signal in 3 normal speakers as they repeated a simple test utterance with targeted speech rates varying from 60% to 160% of their habitual rate and at targeted vocal intensities of -6 dB and +6 dB relative to their habitual intensity. Surface electromyographic (EMG) recordings were obtained with electrodes positioned to sample primarily the mentalis, depressor labii inferior, anterior belly of the digastric, and masseter muscles. Two-dimensional displacements of the lower lip and jaw in the midsagittal plane were recorded with an electromagnetic system. All participants produced linear changes in percent utterance duration relative to the auditory targets for speech rate variation. Intensity variations ranged from -10 dB to +8 dB. Average EMG levels for all 4 muscles were well correlated with specific parameters of movement. Across the intensity conditions, EMG level was positively correlated with movement speed and distance in all participants. Across the rate conditions, EMG level was negatively correlated with movement duration in all participants, while greater interparticipant variability was noted for correlations relating EMG to speed and distance. For intensity control, it is suggested that converging neural input to orofacial motoneurons varies monotonically with movement distance and speed. In contrast, rate control appears to be more strongly related to the temporal characteristics of neural input than activation level.

Association of orofacial with laryngeal and respiratory motor output during speech.

Speech motor coordination most likely involves synaptic coupling among neural systems that innervate orofacial, laryngeal, and respiratory muscles. The nature and strength of coupling of the orofacial with the respiratory and laryngeal systems was studied indirectly by correlating orofacial speeds with fundamental frequency, vocal intensity, and inspiratory volume during speech. Fourteen adult subjects repeated a simple test utterance at varying rates and vocal intensities while recordings were obtained of the acoustic signal and movements of the upper lip, lower lip, tongue, jaw, rib cage, and abdomen. Across subjects and orofacial speed measures (14 subjects x 4 structures), significant correlations were obtained for fundamental frequency in 42 of 56 cases, for intensity in 35 of 56 cases, and for inspiratory volume in 14 of 56 cases. These results suggest that during speech production there is significant neural coupling of orofacial muscle systems with the laryngeal and respiratory systems as they are involved in vocalization. Comparisons across the four orofacial structures revealed higher correlations for the jaw relative to other orofacial structures. This suggests stronger connectivity between neural systems linking the jaw with the laryngeal and respiratory systems. This finding may be relevant to the frame/content theory of speech production, which suggests that the neural circuitry involved in jaw motor control for speech has evolved to form relatively strong linkages with systems involved in vocalization.

Variability in tongue movement kinematics during normal liquid swallowing.

This study sought to develop a quantitative kinematic description of tongue movement for liquid swallowing in a group of 12 healthy subjects. X-ray microbeam technology was used to track the positions of six small pellets attached to the tongue and jaw while subjects swallowed water at 2- and 10-mL bolus volumes. A feature common to all subjects was a prominent rostral movement of the dorsal region of the tongue. In addition, all subjects consistently increased the displacement and maximum speed of this tongue movement with increased bolus volume. However, detailed movement analysis showed a variety of tongue movement patterns for the group. This variability across subjects was large enough that it was surprisingly difficult to provide a low-dimension quantitative description of the tongue kinematics during liquid swallowing.

Defining and measuring speech movement events.

A long-held view in speech research is that utterances are built up from a series of discrete units joined together. However, it is difficult to reconcile this view with the observation that speech movement waveforms are smooth and continuous. Developing methods for reliable identification of speech movement units is necessary for describing speech motor behavior and for addressing theoretically relevant questions about its organization. We describe a simple method of parsing movement signals into a series of individual movement "strokes," where a stroke is defined as the period between two successive local minima in the speed history of an articulator point, and use that method to segment speech-related movement of marker points placed on the tongue blade, tongue dorsum, lower lip, and jaw in a group of healthy young speakers. Articulator fleshpoints could be distinguished on the basis of kinematic features (i.e., peak and boundary speed, duration and distance) of the strokes they produce. Further, tongue blade and jaw fleshpoint strokes identified to temporally overlap with acoustic events identified as alveolar fricatives could be distinguished from speech strokes in general on the basis of a number of kinematic measures. Finally, the acoustic timing of alveolar fricatives did not appear to be related to the kinematic features of strokes presumed to be related to their production in any direct way. The advantages and disadvantages of this simple approach to defining movement units are discussed.