Self-Reported Stuttering Severity Is Accurate: Informing Methods for Large-Scale Data Collection in Stuttering

PURPOSE

To our knowledge, there are no data examining the agreement between self-reported and clinician-rated stuttering severity. In the era of big data, self-reported ratings have great potential utility for large-scale data collection, where cost and time preclude in-depth assessment by a clinician. Equally, there is increasing emphasis on the need to recognize an individual's experience of their own condition. Here, we examined the agreement between self-reported stuttering severity compared to clinician ratings during a speech assessment. As a secondary objective, we determined whether self-reported stuttering severity correlated with an individual's subjective impact of stuttering.

METHOD

Speech-language pathologists conducted face-to-face speech assessments with 195 participants (137 males) aged 5-84 years, recruited from a cohort of people with self-reported stuttering. Stuttering severity was rated on a 10-point scale by the participant and by two speech-language pathologists. Participants also completed the Overall Assessment of the Subjective Experience of Stuttering (OASES). Clinician and participant ratings were compared. The association between stuttering severity and the OASES scores was examined.

RESULTS

There was a strong positive correlation between speech-language pathologist and participant-reported ratings of stuttering severity. Participant-reported stuttering severity correlated weakly with the four OASES domains and with the OASES overall impact score.

CONCLUSIONS

Participants were able to accurately rate their stuttering severity during a speech assessment using a simple one-item question. This finding indicates that self-report stuttering severity is a suitable method for large-scale data collection. Findings also support the collection of self-report subjective experience data using questionnaires, such as the OASES, which add vital information about the participants' experience of stuttering that is not captured by overt speech severity ratings alone.

A Cross-sectional Study of Perceptual and Acoustic Voice Characteristics in Healthy Aging

PURPOSE

The human voice qualitatively changes across the lifespan. Although some of these vocal changes may be pathologic, other changes likely reflect natural physiological aging. Normative data for voice characteristics in healthy aging is limited and disparate studies have used a range of different acoustic features, some of which are implicated in pathologic voice changes. We examined the perceptual and acoustic features that predict healthy aging.

METHOD

Participants (N = 150) aged between 50 and 92 years performed a sustained vowel task. Acoustic features were measured using the Multi-Dimensional Voice Program and the Analysis of Dysphonia in Speech and Voice. We used forward and backward variable elimination techniques based on the Bayesian information criterion and linear regression to assess which of these acoustic features predict age and perceptual features. Hearing thresholds were determined using pure-tone audiometry tests at frequencies 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz. We further explored potential relationships between these acoustic features and clinical assessments of voice quality using the Consensus Auditory-Perceptual Evaluation of Voice.

RESULTS

Chronological age was significantly predicted by greater voice turbulence, variability of cepstral fundamental frequency, low relative to high spectral energy, and cepstral intensity. When controlling for hearing loss, age was significantly predicted by amplitude perturbations and cepstral intensity. Clinical assessments of voice indicated perceptual characteristics of speech were predicted by different acoustic features. For example, breathiness was predicted by the soft phonation index, mean cepstral peak prominence, mean low-high spectral ratio, and mean cepstral intensity.

CONCLUSIONS

Findings suggest that acoustic features that predict healthy aging are different than those previously reported for the pathologic voice. We propose a model of healthy and pathologic voice development in which voice characteristics are mediated by the inability to monitor vocal productions associated with age-related hearing loss. This normative data of healthy vocal aging may assist in separating voice pathologies from healthy aging.

To speak may draw on epigenetic writing and reading: Unravelling the complexity of speech and language outcomes across chromatin-related neurodevelopmental disorders

Speech and language development are complex neurodevelopmental processes that are incompletely understood, yet current evidence suggests that speech and language disorders are prominent in those with disorders of chromatin regulation. This review aimed to unravel what is known about speech and language outcomes for individuals with chromatin-related neurodevelopmental disorders. A systematic literature search following PRISMA guidelines was conducted on 70 chromatin genes, to identify reports of speech/language outcomes across studies, including clinical reports, formal subjective measures, and standardised/objective measures. 3932 studies were identified and screened and 112 were systematically reviewed. Communication impairment was core across chromatin disorders, and specifically, chromatin writers and readers appear to play an important role in motor speech development. Identification of these relationships is important because chromatin disorders show promise as therapeutic targets due to the capacity for epigenetic modification. Further research is required using standardised and formal assessments to understand the nuanced speech/language profiles associated with variants in each gene, and the influence of chromatin dysregulation on the neurobiology of speech and language development.

Expanding the speech and language phenotype in Koolen-de Vries syndrome: late onset and periodic stuttering a novel feature

Speech and language impairment is core in Koolen-de Vries syndrome (KdVS), yet only one study has examined this empirically. Here we define speech, language, and functional/adaptive behaviour in KdVS; while deeply characterising the medical/neurodevelopmental phenotype in the largest cohort to date. Speech, language, literacy, and social skills were assessed using standardised measures, alongside an in-depth health and medical questionnaire. 81 individuals with KdVS were recruited (35 female, mean age 9y 10mo), 56 of whom harboured the typical 500-650 kb 17q21.31 deletion. The core medical phenotype was intellectual disability (largely moderate), eye anomalies/vision disturbances, structural brain anomalies, dental problems, sleep disturbance, musculoskeletal abnormalities, and cardiac defects. Most were verbal (62/81, 76.5%), while minimally-verbal communicators used alternative and augmentative communication (AAC) successfully in spite of speech production delays. Speech was characterised by apraxia (39/61, 63.9%) and dysarthria (28/61, 45.9%) in verbal participants. Stuttering was described in 36/47 (76.6%) verbal participants and followed a unique trajectory of late onset and fluctuating presence. Receptive and expressive language abilities were commensurate with one another, but literacy skills remained a relative weakness. Social competence, successful behavioural/emotional control, and coping skills were areas of relative strength, while communication difficulties impacted daily living skills as an area of comparative difficulty. Notably, KdVS individuals make communication gains beyond childhood and should continue to access targeted therapies throughout development, including early AAC implementation, motor speech therapy, language/literacy intervention, as well as strategies implemented to successfully navigate activities of daily living that rely on effective communication.

Speech and language development and genotype-phenotype correlation in 49 individuals with KAT6A syndrome

Pathogenic KAT6A variants cause syndromic neurodevelopmental disability. "Speech delay" is reported, yet none have examined specific speech and language features of KAT6A syndrome. Here we phenotype the communication profile of individuals with pathogenic KAT6A variants. Medical and communication data were acquired via standardized surveys and telehealth-assessment. Forty-nine individuals (25 females; aged 1;5-31;10) were recruited, most with truncating variants (44/49). Intellectual disability/developmental delay (42/45) was common, mostly moderate/severe, alongside concerns about vision (37/48), gastrointestinal function (33/48), and sleep (31/48). One-third (10/31) had a diagnosis of autism. Seventy-three percent (36/49) were minimally-verbal, relying on nonverbal behaviors to communicate. Verbal participants (13/49) displayed complex and co-occurring speech diagnoses regarding the perception/production of speech sounds, including phonological impairment (i.e., linguistic deficits) and speech apraxia (i.e., motor planning/programming deficits), which significantly impacted intelligibility. Receptive/expressive language and adaptive functioning were also severely impaired. Truncating variants in the last two exons of KAT6A were associated with poorer communication, daily-living skills, and socialization outcomes. In conclusion, severe communication difficulties are present in KAT6A syndrome, typically on a background of significant intellectual disability, vision, feeding and motor deficits, and autism in some. Most are minimally-verbal, with apparent contributions from underlying motor deficits and cognitive-linguistic impairment. Alternative/augmentative communication (AAC) approaches are required for many into adult life. Tailored AAC options should be fostered early, to accommodate the best communication outcomes.

Functional correlation of genome-wide DNA methylation profiles in genetic neurodevelopmental disorders

An expanding range of genetic syndromes are characterized by genome-wide disruptions in DNA methylation profiles referred to as episignatures. Episignatures are distinct, highly sensitive and specific biomarkers that have recently been applied in clinical diagnosis of genetic syndromes. Episignatures are contained within the broader disorder-specific genome-wide DNA methylation changes which can share significant overlap amongst different conditions. In this study we performed functional genomic assessment and comparison of disorder-specific and overlapping genome-wide DNA methylation changes related to 65 genetic syndromes with previously described episignatures. We demonstrate evidence of disorder-specific and recurring genome-wide differentially methylated probes (DMPs) and regions (DMRs). The overall distribution of DMPs and DMRs across the majority of the neurodevelopmental genetic syndromes analyzed showed substantial enrichment in gene promoters and CpG islands, and under-representation of the more variable intergenic regions. Analysis showed significant enrichment of the DMPs and DMRs in gene pathways and processes related to neurodevelopment, including neurogenesis, synaptic signaling and synaptic transmission. This study expands beyond the diagnostic utility of DNA methylation episignatures by demonstrating correlation between the function of the mutated genes and the consequent genomic DNA methylation profiles as a key functional element in the molecular etiology of genetic neurodevelopmental disorders. This article is protected by copyright. All rights reserved.

Novel diagnostic DNA methylation episignatures expand and refine the epigenetic landscapes of Mendelian disorders

Overlapping clinical phenotypes and an expanding breadth and complexity of genomic associations are a growing challenge in the diagnosis and clinical management of Mendelian disorders. The functional consequences and clinical impacts of genomic variation may involve unique, disorder-specific, genomic DNA methylation episignatures. In this study, we describe 19 novel episignature disorders and compare the findings alongside 38 previously established episignatures for a total of 57 episignatures associated with 65 genetic syndromes. We demonstrate increasing resolution and specificity ranging from protein complex, gene, sub-gene, protein domain, and even single nucleotide-level Mendelian episignatures. We show the power of multiclass modeling to develop highly accurate and disease-specific diagnostic classifiers. This study significantly expands the number and spectrum of disorders with detectable DNA methylation episignatures, improves the clinical diagnostic capabilities through the resolution of unsolved cases and the reclassification of variants of unknown clinical significance, and provides further insight into the molecular etiology of Mendelian conditions.

Predicting speech-sound disorder outcomes in school-age children with hearing loss: The VicCHILD experience

BACKGROUND

Congenital hearing loss is the most common birth anomaly, typically influencing speech and language development, with potential for later academic, social and employment impacts. Yet, surprisingly, the nuances of how speech is affected have not been well examined with regards to the subtypes of speech-sound disorder (SSD). Nor have the predictors of speech outcome been investigated within a sizeable population cohort.

AIMS

(1) To describe the subtypes and prevalence of SSD in children with hearing loss. (2) To determine which characteristics of hearing loss predict the presence of SSD.

METHODS & PROCEDURES

A total of 90 children (5-12 years of age) with permanent hearing loss were recruited from an Australian population cohort. Children completed a standardized speech assessment to determine the presence and subtype of SSD. Logistic regression was used to determine the predictors of speech outcome. Demographic, developmental and hearing-related predictors were examined.

OUTCOMES & RESULTS

The prevalence of speech disorder overall was 58%, with the most common subtype being phonological delay in 49% of the sample. Factors most predictive of speech disorder were being male, younger and a bimodal user (i.e., using both a hearing aid and a cochlear implant).

CONCLUSIONS & IMPLICATIONS

This is the first study, in a sizeable cohort, to describe the prevalence and predictive factors for SSD associated with hearing loss. Clinically, it could be beneficial to implement earlier targeted phonological interventions for children with hearing loss. What this paper adds What is already known on this subject Speech issues are common in children with hearing loss; however, the breakdown of subtypes of SSD (e.g., articulation versus phonological disorder) have not been previously described in a population cohort. This distinction is relevant, as each subtype calls for specific targeted intervention. Studies examining factors predictive of speech outcomes, across a range of hearing levels, are also lacking in a population cohort. What this paper adds to existing knowledge Data suggest the most common type of SSD in children with hearing loss is phonological delay. Males, younger children, and bimodal users were at greater risk of having a subtype of SSD. What are the potential or actual clinical implications of this work? The results are clinically pertinent as the speech diagnosis determines the targeted treatment. Phonological delay is responsive to treatment, and early targeted intervention may improve prognosis for speech outcomes for children with hearing loss.

Communication in children born very preterm: a prospective cohort study

AIM

To compare language, speech, and voice of children born preterm and at term, and determine relevant predictors of outcome.

METHOD

Three hundred infants (150 males, 150 females; 149 born at <30wks' gestation, 151 term-born) were prospectively recruited at birth from the Royal Women's Hospital. We administered the Preschool Language Scales, Fifth Edition, Diagnostic Evaluation of Articulation and Phonology, Grade Roughness Breathiness Asthenia Strain Scale, and Pediatric Voice Handicap Index at 3 years, and compared groups. We examined hypothesized predictors in children born preterm: gestational age at birth, birthweight, sex, chronic lung disease, high social risk, multilingualism, neurodevelopmental diagnosis, and oromotor feeding.

RESULTS

Children born preterm had poorer language than children born at term (coefficient -5.43). Speech and voice were similar between groups (coefficients -0.70 to 1.63). Chronic lung disease predicted voice (coefficient 6.05); male sex (coefficients 4.54-6.18), high social risk (coefficient -6.02 to -9.30), and neurodevelopmental diagnosis (coefficients -16.42 to -20.61) predicted language.

INTERPRETATION

Children born before 30 weeks' gestation had poorer language than children born at term. Children born preterm with neurodevelopmental disabilities or high social risk experience poorer language outcomes, and would benefit from enrichment of their language environment.

WHAT THIS PAPER ADDS

Speech and voice outcomes were similar between children born preterm and at term. Male sex, high social risk, and neurodevelopmental diagnosis predicted language outcomes.

Conversational Language in 3-Year-Old Children Born Very Preterm and at Term

Purpose Language difficulties are prevalent among children born preterm. Existing studies have largely used standardized language tests, providing limited scope for detailed descriptive examination of preterm language. This study aimed to examine differences in conversational language between children born < 30 weeks and at term as well as correlations between language sample analysis (LSA) and a standardized language tool. Method Two hundred four 3-year-olds (103 born < 30 weeks, 101 born at term) recruited at birth provided a 10-min language sample and completed the Preschool Language Scales-Fifth Edition (I. Zimmerman, Steiner, & Pond, 2011). LSA was conducted using the Systematic Analysis of Language Transcripts and Index of Productive Syntax. Group differences were analyzed using linear regression, and Pearson correlation coefficient (coef) was used to determine correlations between measures. Results Children born < 30 weeks scored lower than term-born peers on multiple metrics when controlled for confounding factors (sex, high social risk, multilingualism, and diagnosed neurodevelopmental disorders), including mean length of utterance in morphemes (coef = -0.28, 95% confidence interval [CI] [-0.56, 0.01]) and words (coef = -0.29, 95% CI [-0.53, -0.05]), number of different word roots (coef = -10.04, 95% CI [-17.93, -2.14]), and Index of Productive Syntax sentence structures (coef = -1.81, 95% CI [-3.10, -0.52]). Other variables (e.g., number of utterances, number of nouns and adjectives) were not significantly different between groups. LSA and the Preschool Language Scales-Fifth Edition were at most moderately correlated (≤ .45). Conclusions Three-year-old children born preterm demonstrated poorer conversational language than children born at term, with some specific areas of deficit emerging. Furthermore, formal assessment and LSA appear to provide relatively distinct and yet complementary data to guide diagnostic and intervention decisions. Supplemental Material https://doi.org/10.23641/asha.11368073.

Speech and language in children with Klinefelter syndrome

BACKGROUND

Speech and language deficits are frequent in males with Klinefelter syndrome (KS), yet the research base is slim and specific strengths and deficits in communication have not been well characterised. Nor have studies examined communication abilities across a wide age-range from infancy to adolescence.

OBJECTIVE

To characterise communication in children and adolescents with KS.

METHOD

Twenty-six males, aged 1;1-17;4 years, took part in the study. Oromotor, speech, language, literacy and pragmatic abilities were assessed.

RESULTS

Communication impairment was seen in 92% of cases (24/26), with salient findings being impairments in social-pragmatic language (15/18; 83%), language-memory (12/15; 80%) and literacy (13/17; 76%). Mild to severe receptive and expressive language deficits were common (16/23; 70%), although performance was varied across linguistic domains of semantics, syntax, and morphology. Oromotor impairment (21/21; 100%) and speech impairments were evident from preschool through to adolescence. Whilst speech was highly intelligible (22/26; 85%), articulation errors (12/26; 46%), phonological delay (12/26; 46%), phonological disorder (5/26; 19%) and dysarthria (2/23 8.7%) were observed. Other atypical, yet mild, speech features were noted such as hyponasality (16/23; 70%).

CONCLUSIONS

Language, literacy and social-pragmatic deficits are common in KS. Data suggested a trend for more notable deficits with age and increasing academic and social demands. We added novel data on the nature of speech production deficits, including persistent phonological errors in a number of cases. Earlier detection and intervention of phonological errors may reduce the risk for later language and literacy challenges and optimise academic, and ultimately social and behavioural difficulties later in life.

Characterization of speech and language phenotype in children with NRXN1 deletions

Neurexin 1 gene (NRXN1) deletions are associated with several neurodevelopmental disorders. Communication difficulties have been reported, yet no study has examined specific speech and language features of individuals with NRXN1 deletions. Here, we characterized speech and language phenotypes in 21 children (14 families), aged 1.8-17 years, with NRXN1 deletions. Deletions ranged from 74 to 702 kb and consisted mostly of either exons 1-3 or 1-5. Speech sound disorders were frequent (69%), although few were severe. The majority (57%) of children had difficulty with receptive and/or expressive language, although no homogeneous profiles of deficit were seen across semantic, morphological, or grammatical systems. Social language difficulties were seen in over half the sample (53%). All but two individuals with language difficulties also had intellectual disability/developmental delay. Overall, while speech and language difficulties were common, there was substantial heterogeneity in the severity and type of difficulties observed and no striking communication phenotype was seen. Rather, the speech and language deficits are likely part of broader concomitant neurodevelopmental profiles (e.g., intellectual disability, social skill deficits). Nevertheless, given the high rate of affectedness, it is important speech/language development is assessed so interventions can be applied during childhood in a targeted and timely manner.

A fiber optic biosensor (FOBS) to monitor mutans streptococci in human saliva

A fiber optic biosensor (FOBS) to monitor mutans streptococci activity in human saliva is developed. The biosensor utilizes e fiber optic evanescent wave spectroscopy to monitor a bacterial mediated biochemical reaction. To achieve this, a short length of the cladding is removed; the fiber core surface is treated and coated with a thin film of porous glass medium using sol-gel technique. The mutans streptococci mediated reaction with sucrose is monitored using a photosensitive indicator, which is immobilized within the porous glass coating. Spectroscopic analysis shows that the transmitted intensity at 597 nm increases conspicuously when monitored for 120 min. Two distinct phases are observed, one from 0 to 60 min and the other from 60 to 120 min. A negative correlation coefficient between the rate of increase in absorption peak intensity recorded by the FOBS and the decrease in pH measured using the pH meter, was calculated to be rho=-0.994. This investigation highlights the potential benefits of this sensor to monitor mutans streptococci activity in saliva.

Efficient Stimuli for Evoking Auditory Steady-State Responses

OBJECTIVE

To compare the magnitudes of the steady-state responses evoked by several types of stimuli, and the times required to recognize these responses as significant.

DESIGN

In the first two experiments, we examined auditory steady-state responses to pure tones, broadband noise and band-limited noise. The stimuli were amplitude modulated in the 75 to 100 Hz range with sinusoidal or exponential envelopes. A third experiment investigated the effects of exponential envelopes on the responses to broadband noise. The final experiment examined auditory steady-state responses evoked by rapidly presented transient stimuli, such as clicks, brief tones and brief noise-bursts. All stimuli were presented dichotically at intensities 30 to 50 dB above behavioral thresholds. The subjects were adults, who drowsed or slept during the recording sessions.

RESULTS

The responses to the noise were larger than the responses to the tones. At an intensity of 32 dB nHL, the average amount of time needed to obtain significant responses for the amplitude-modulated noise was 43 sec and the maximum time was 2 minutes. The average time for pure tone stimuli was approximately 2 minutes but 25% of the responses remained undetected after 5 minutes. Combining the responses to all the frequency-specific stimuli showed results similar to using noise stimuli. Using exponential envelopes did not increase response amplitudes for noise stimuli. At 45 dB nHL, the steady-state responses to clicks and other transient stimuli were larger than responses to the broadband noise. The average time to detect steady-state responses to transient stimuli was approximately 20 sec, which was a little faster than for amplitude modulated noise.

CONCLUSIONS

Auditory steady-state potentials evoked by amplitude modulated noise or transient stimuli might be useful in providing rapid and objective tests of hearing during screening procedures. Another approach might be to record responses to multiple frequency-specific stimuli and to evaluate the combined responses for a rapid indication that some hearing is present.

Total protein measurement using a fiber-optic evanescent wave-based biosensor

A novel method and instrumental system to determine the total protein concentration in a liquid sample is described. It uses a fiber optic total protein sensor (FOPS) based on the principles of fiber optic evanescent wave spectroscopy. The FOPS applies a dye-immobilized porous glass coating on a multi-mode optical fiber. The evanescent waves at the fiber optic core-cladding interface are used to monitor the protein-induced changes in the sensor element. The FOPS offers a single-step method for quantifying protein concentrations without destroying the sample. The response time and reusability of the FOPS are evaluated. This unique sensing method presents a sensitive and accurate platform for the quantification of protein.

The use of phase in the detection of auditory steady-state responses

OBJECTIVE

To investigate how phase measurements might facilitate the detection of auditory steady-state responses.

METHODS

Multiple steady-state responses were evoked by auditory stimuli modulated at rates between 78 and 95 Hz and with intensities between 50 and 0 dB SPL. The responses were evaluated in 20 subjects after 1, 2, 4, and 6 min. The responses were analyzed in the frequency domain using 4 different detection protocols: (1) phase-coherence, (2) phase-weighted coherence, (3) F test for hidden periodicity, and (4) phase-weighted t test. The phase-weighted measurements were either based on the mean phase of a group of normal subjects or derived for each subject from the phase of the response at higher intensities.

RESULTS

Detection protocols based on both phase and amplitude (F test and phase-weighted t test) were more effective than those based on phase alone (phase coherence and phase-weighted coherence) although the difference was small. Protocols using phase-weighting were more effective than those without phase-weighting. The lowest thresholds for the steady-state responses were obtained using the phase-weighted t test.

CONCLUSION

Threshold detection can be improved by weighting the detection protocols toward an expected phase, provided that the expected phase can be reliably predicted.

Human auditory steady-state responses to tones independently modulated in both frequency and amplitude

OBJECTIVE

Independent amplitude and frequency modulation (IAFM) of a carrier tone uses two different modulating frequencies, one for amplitude modulation (AM) and one for frequency modulation (FM). This study measured the human steady-state responses to multiple IAFM tones. The first question was whether the IAFM responses could be recorded without attenuation of the AM and FM components. The second question was whether IAFM stimuli would provide a more effective demonstration of responses at intensities near threshold than the responses to AM tones. The third question was whether the responses to multiple IAFM stimuli would relate to the discrimination of words at different intensities.

DESIGN

Multiple AM, FM, or IAFM stimuli were presented simultaneously. Responses were recorded between the vertex and the neck and analysed in the frequency domain. The first experiment compared IAFM responses with AM and FM responses. The second experiment compared IAFM responses with AM responses between intensities 20 to 50 dB SPL. The third experiment related the IAFM responses to the discrimination of monosyllabic words at intensities between 20 and 70 dB SPL.

RESULTS

Steady-state responses to the individual component of the IAFM stimuli were clearly recognizable although attenuated a little (14%) from the responses to AM or FM alone. Using IAFM stimuli was not different than simply using AM stimuli when trying to recognize responses at low intensities. The number of responses detected during multiple IAFM stimulation and the amplitudes of these responses correlated significantly with word discrimination.

CONCLUSIONS

IAFM of a carrier using two different modulating frequencies (one for AM and one for FM) elicits separate AM and FM responses that are relatively independent of each other. These separate responses can be used to detect whether a particular carrier has been processed in the cochlea, but they are not as effective as measuring responses to carriers that have been modulated in both amplitude and frequency at the same modulation frequency (mixed modulation). The detectability of eight different responses (four AM and four FM) to an IAFM stimuli relates well to the ability of subjects to discriminate words. IAFM stimuli therefore show promise as an objective test for assessing suprathreshold hearing.

Weighted averaging of steady-state responses

OBJECTIVE

To compare weighted averaging and artifact-rejection to normal averaging in the detection of steady-state responses.

METHODS

Multiple steady-state responses were evoked by auditory stimuli modulated at rates between 78 and 95 Hz. The responses were evaluated after recording periods of 3, 6 and 10 min, using 5 averaging protocols: (1) normal averaging; (2) sample-weighted averaging; (3) noise-weighted averaging; (4) amplitude-based artifact-rejection; and (5) percentage-based artifact rejection. The responses were analyzed in the frequency domain and the signal-to-noise ratio was estimated by comparing the signals at the modulation-frequencies to the noise at adjacent frequencies.

RESULTS

Weighted averaging gave the best signal-to-noise ratios. Artifact-rejection was better than normal averaging but not as good as weighted averaging. Responses that were not significant with normal averaging became significant with weighted averaging much more frequently than vice versa. False alarm rates did not significantly differ among the protocols. The advantage of weighted averaging was especially evident when stimuli were presented at lower intensities or when smaller amounts (e.g. only 3 or 6 min) of data were evaluated. Weighted averaging was most effective when the background noise levels were variable. Weighted averaging underestimated the amplitude of the responses by about 2%.

CONCLUSION

Weighted averaging should be used instead of normal averaging for detecting steady-state responses.

Multiple auditory steady-state responses to AM and FM stimuli

Multiple auditory steady-state responses were recorded using tonal stimuli that were amplitude-modulated (AM), frequency-modulated (FM) or modulated simultaneously in both amplitude and frequency (mixed modulation or MM). When MM stimuli combined 100% AM and 25% FM (12.5% above and below the carrier frequency) and the maximum frequency occurred simultaneously with maximum amplitude, the MM response was one third larger than the simple AM response. This enhancement occurred at intensities between 50 and 30 dB SPL and at carrier frequencies between 500 and 4000 Hz. The AM and FM components of a MM stimulus generate independent responses that add together to give the MM response. Since AM responses generally occur with a slightly later phase delay than FM responses, the largest MM response is recorded when the maximum frequency of the MM stimulus occurs just after the maximum amplitude.

Human auditory steady-state responses to amplitude-modulated tones: phase and latency measurements

Human auditory steady-state responses were recorded to four stimuli, with carrier frequencies (f(c)) of 750, 1500, 3000 and 6000 Hz, presented simultaneously at 60 dB SPL. Each carrier frequency was modulated by a specific modulation frequency (f(m)) of 80.6, 85.5, 90.3 or 95.2 Hz. By using four different recording conditions we obtained responses for all permutations of f(m) and f(c). The phase delays (P) of the responses were unwrapped and converted to latency (L) using the equation: L=P/(360xf(m)). The number of cycles of the stimulus that occurred prior to the recorded response was estimated by analyzing the effect of modulation frequency on the responses. These calculations provided latencies of 20.7, 17.7, 16.1 and 16.1 ms for carrier frequencies 750, 1500, 3000 and 6000 Hz. This latency difference of about 4.5 ms between low and high carrier frequencies remained constant over many different manipulations of the stimuli: faster modulation rates (150-190 Hz), binaural rather than monaural presentation, different intensities, stimuli presented alone or in conjunction with other stimuli, and modulation frequencies that were separated by as little as 0.24 Hz. This frequency-related delay is greater than that measured using transient evoked potentials, most likely because of differences in how transient and steady-state responses are generated and how their latencies are determined.

MASTER: a Windows program for recording multiple auditory steady-state responses

MASTER is a Windows-based data acquisition system designed to assess human hearing by recording auditory steady-state responses. The system simultaneously generates multiple amplitude-modulated and/or frequency-modulated auditory stimuli, acquires electrophysiological responses to these stimuli, displays these responses in the frequency-domain, and determines whether or not the responses are significantly larger than background electroencephalographic activity. The operator can print out the results, store the data on disk for more extensive analysis by other programs, review stored data, and combine results. The system design follows clear principles concerning the generation of acoustic signals, the acquisition of artifact-free data, the analysis of electrophysiological responses in the frequency-domain, and the objective detection of signals in noise. The instrument uses a popular programming language (LabVIEW) and a commercial data acquisition board (AT-MIO-16E-10), both of which are available from National Instruments.

Intracerebral sources of human auditory-evoked potentials

Evoked potentials to brief 1,000-Hz tones presented to either the left or the right ear were recorded from 30 electrodes arrayed over the head. These recordings were submitted to two different forms of source analysis: brain electric source analysis (BESA) and variable-resolution electromagnetic tomography (VARETA). Both analyses showed that the dominant intracerebral sources for the late auditory-evoked potentials (50-300 ms) were in the supratemporal plane and lateral temporal lobe contralateral to the ear of stimulation. The analyses also suggested the possibility of additional sources in the frontal lobes.

Multiple auditory steady-state responses (MASTER): stimulus and recording parameters

Steady-state responses evoked by simultaneously presented amplitude-modulated tones were measured by examining the spectral components in the recording that corresponded to the different modulation frequencies. When using modulation frequencies between 70 and 110 Hz and an intensity of 60 dB SPL, there were significant interactions between two stimuli when the carrier frequencies were closer than one half of an octave apart, with attenuation of the response to the lower carrier frequency. However, there were no significant decreases in response amplitude with four simultaneous stimuli provided the carrier frequencies differed by one octave or more. Higher intensities (70 dB SPL) resulted in greater interactions between the stimuli than when low intensities (35 dB SPL) were used. Modulation frequencies could be as closely spaced as 1.3 Hz without affecting the responses. Using broad-band noise as a carrier instead of a pure tone resulted in a significantly larger response when the stimuli were presented at the same sound pressure level. At modulation frequencies between 30 and 50 Hz, there were greater interactions between stimuli than at faster modulation frequencies. These results support the following recommendations for using multiple stimuli in evoked potential audiometry: (1) The multiple stimulus technique works well for steady state responses at frequencies between 70 and 110 Hz. (2) Up to four stimuli can be simultaneously presented to an ear without significant loss in amplitude of the response, provided the carrier frequencies are separated by an octave and the intensities are 60 dB SPL or less. (3) Bandpass noise might serve as a better carrier signal than pure tones.

Temperature and pressure dependence of viscosity of quantum liquid He according to significant structure theory

Both solid-like and gas-like flow structures are considered in the calculation of viscosity of liquid (4)He using the significant structure theory of liquids. The predominance of quantum mechanical zero-point motion over that arising from thermal excitation is taken into account for the solid-like motion of molecules. The viscosity of liquid (4)He under its own vapor pressure calculated over its whole temperature range is in reasonably good agreement with experimental data. The pressure dependence of viscosity also was obtained. The calculation does not yield good results at high densities where the free jumping of molecules into the nearest neighboring vacancies through the kinetic zero-point motion is no longer plausible.