Fundamental frequency range and other acoustic factors that might contribute to the clear-speech benefit.

The main goal of the present study was to assess the role of the fundamental frequency (F0) range on the clear-speech benefit. Conversational- and clear-speech sentences were recorded for four male speakers: the speakers' clear-speech productions had slower speaking rates, wider F0 range, more high-frequency energy, expanded vowel space, and higher vocal intensity level relative to their conversational-speech productions. To examine if F0 range contributes to the clear-speech benefit, the F0 range of clear-speech sentences was compressed to match that of the speakers' conversational-speech sentences. Fifteen listeners were presented with conversational, clear, and F0-compressed sentences in sustained speech-shaped noise. All talkers elicited substantial intelligibility benefits (keyword percent correct) from clear and F0-compressed speech when compared with conversational speech. There was no significant difference in performance between clear and F0-compressed speech. These results leave open the possibility that a clear-speech benefit could be a result of its F0 contours rather than its wide F0 range. Intelligibility predictions based on acoustic characteristics of clear speech, specifically high-frequency emphasis and pauses, accounted for either small or negligible amounts of the clear-speech benefit.

Diagnostic Precision of Open-Set Versus Closed-Set Word Recognition Testing.

Purpose The aim of the study was to examine the precision of forced-choice (closed-set) and open-ended (open-set) word recognition (WR) tasks for identifying a change in hearing. Method WR performance for closed-set (4 and 6 choices) and open-set tasks was obtained from 70 listeners with normal hearing. Speech recognition was degraded by presenting monosyllabic words in noise (-8, -4, 0, and 4 signal-to-noise ratios) or processed by a sine wave vocoder (2, 4, 6, and 8 channels). Results The 2 degraded speech understanding conditions yielded similarly shaped, monotonically increasing psychometric functions with the closed-set tasks having shallower slopes and higher scores than the open-set task for the same listening condition. Fitted psychometric functions to the average data were the input to a computer simulation conducted to assess the ability of each task to identify a change in hearing. Individual data were also analyzed using 95% confidence intervals for significant changes in scores for words and phonemes. These analyses found the following for the most to least efficient condition: open-set (phoneme), open-set (word), closed-set (6 choices), and closed-set (4 choices). Conclusions Closed-set WR testing has distinct advantages for implementation, but its poorer precision for identifying a change than open-set WR testing must be considered.

Backward masking of tones and speech in people who do and do not stutter.

PURPOSE: There is evidence of an auditory-perceptual component of stuttering, and backward masking (BM) is a task to explore that role. Prior research reported poorer thresholds for BM tones in a group of children who persisted in stuttering compared to those for a group that did not persist. This study examined BM for adults who stutter for tones and for speech, which tests a phonetic aspect of hearing. METHOD: Eight persons who stutter (PWS) were closely matched with eight controls (PNS) in terms of phonological abilities, verbal span tasks, age, sex and non-verbal intelligence. These participants were examined for their ability to recognize vowel-consonant (VC) speech syllables and tones in BM paradigm with 0 ms and 300 ms masker to signal onset conditions. RESULTS: PWS showed significantly poorer performance for speech syllable recognition in quiet and in conditions with masking noise. The pattern of speech errors was similar in both groups, but the PWS produced more errors. A significant condition by group interaction in backward masking for tones was attributed to higher masked thresholds in PWS than in PNS in the 0 ms delay condition for BM for tones. CONCLUSION: This was the first study to examine BM for speech in PWS. Results provide support for a small auditory-perceptual deficit for speech understanding in adults who stutter that was revealed in the absence of a lexical context. The speech results are explained in terms of possible indistinct phoneme boundaries in PWS and the effects of vowel context in speech recognition.

Clinical Strategies for Sampling Word Recognition Performance.

Purpose: Computer simulation was used to estimate the statistical properties of searches for maximum word recognition ability (PB max). These involve presenting multiple lists and discarding all scores but that of the 1 list that produced the highest score. The simulations, which model limitations inherent in the precision of word recognition scores, were done to inform clinical protocols. A secondary consideration was a derivation of 95% confidence intervals for significant changes in score from phonemic scoring of a 50-word list. Method: The PB max simulations were conducted on a "client" with flat performance intensity functions. The client's performance was assumed to be 60% initially and 40% for a second assessment. Thousands of estimates were obtained to examine the precision of (a) single lists and (b) multiple lists using a PB max procedure. This method permitted summarizing the precision for assessing a 20% drop in performance. Results: A single 25-word list could identify only 58.4% of the cases in which performance fell from 60% to 40%. A single 125-word list identified 99.8% of the declines correctly. Presenting 3 or 5 lists to find PB max produced an undesirable finding: an increase in the word recognition score. Conclusions: A 25-word list produces unacceptably low precision for making clinical decisions. This finding holds in both single and multiple 25-word lists, as in a search for PB max. A table is provided, giving estimates of 95% critical ranges for successive presentations of a 50-word list analyzed by the number of phonemes correctly identified.

Pure-Tone-Spondee Threshold Relationships in Functional Hearing Loss: A Test of Loudness Contribution.

Purpose: The purpose of this article is to examine explanations for pure-tone average-spondee threshold differences in functional hearing loss. Method: Loudness magnitude estimation functions were obtained from 24 participants for pure tones (0.5 and 1.0 kHz), vowels, spondees, and speech-shaped noise as a function of level (20-90 dB SPL). Participants listened monaurally through earphones. Loudness predictions were obtained for the same stimuli by using a computational, dynamic loudness model. Results: When evaluated at the same SPL, speech-shaped noise was judged louder than vowels/spondees, which were judged louder than tones. Equal-loudness levels were inferred from fitted loudness functions for the group. For the clinical application, the 2.1-dB difference between spondees and tones at equal loudness became a 12.1-dB difference when the stimuli were converted from SPL to HL. Conclusions: Nearly all of the pure-tone average-spondee threshold differences in functional hearing loss are attributable to references for calibration for 0 dB HL for tones and speech, which are based on detection and recognition, respectively. The recognition threshold for spondees is roughly 9 dB higher than the speech detection threshold; persons feigning a loss, who base loss magnitude on loudness, do not consider this difference. Furthermore, the dynamic loudness model was more accurate than the static model.

Perceptual Temporal Asymmetry Associated with Distinct ON and OFF Responses to Time-Varying Sounds with Rising versus Falling Intensity: A Magnetoencephalography Study.

This magnetoencephalography (MEG) study investigated evoked ON and OFF responses to ramped and damped sounds in normal-hearing human adults. Two pairs of stimuli that differed in spectral complexity were used in a passive listening task; each pair contained identical acoustical properties except for the intensity envelope. Behavioral duration judgment was conducted in separate sessions, which replicated the perceptual bias in favour of the ramped sounds and the effect of spectral complexity on perceived duration asymmetry. MEG results showed similar cortical sites for the ON and OFF responses. There was a dominant ON response with stronger phase-locking factor (PLF) in the alpha (8-14 Hz) and theta (4-8 Hz) bands for the damped sounds. In contrast, the OFF response for sounds with rising intensity was associated with stronger PLF in the gamma band (30-70 Hz). Exploratory correlation analysis showed that the OFF response in the left auditory cortex was a good predictor of the perceived temporal asymmetry for the spectrally simpler pair. The results indicate distinct asymmetry in ON and OFF responses and neural oscillation patterns associated with the dynamic intensity changes, which provides important preliminary data for future studies to examine how the auditory system develops such an asymmetry as a function of age and learning experience and whether the absence of asymmetry or abnormal ON and OFF responses can be taken as a biomarker for certain neurological conditions associated with auditory processing deficits.

Effective identification of functional hearing loss using behavioral threshold measures.

PURPOSE: Four functional hearing loss protocols were evaluated. METHOD: For each protocol, 30 participants feigned a hearing loss first on an audiogram and then for a screening test that began a threshold search from extreme levels (-10 or 90 dB HL). Two-tone and 3-tone protocols compared thresholds for ascending and descending tones for 2 (0.5 and 1.0 kHz) and 3 (0.5, 1.0, and 2.0 kHz) frequencies, respectively. A noise-band protocol compared an ascending noise-band threshold with that for 2 descending tones (0.5 and 1.0 kHz). A spondee protocol compared an ascending spondee threshold with that for 2 descending tones (0.5 and 1.0 kHz). These measures were repeated without the participants feigning losses. RESULTS: With nonfeigning participants, ascending and descending threshold differences were minimal for all protocols. When the participants feigned a loss, the spondee protocol produced the largest average threshold difference (30.8 dB), whereas the other protocols produced smaller differences (19.6-22.2 dB). CONCLUSIONS: Using both the screening test and a comparison of the initial audiogram with the screening test, the spondee and 3-tone protocols resulted in 100% true positives and 0% false positives for functional hearing loss. Either of these protocols could be used clinically or in occupational hearing conservation programs.

The effect of visual cues on scoring of clinical word-recognition tests.

PURPOSE: During routine clinical speech assessment, if the person being tested were to write down what he or she heard, it would not always match what the audiologist heard while scoring the listener's vocal responses (Nelson & Chaiklin, 1970). This study demonstrated a method to assess examiner accuracy and whether speechreading cues reduce writedown-talkback errors. METHOD: Examiners were divided into 3 categories: normal hearing native speakers of English, normal hearing nonnative speakers of English, and native speakers with hearing loss. Each examiner assessed 4 normal-hearing listeners. Two NU-6 lists were presented to each listener; one was scored without visual cues and one with visual cues. Lists were presented at 50 dB HL in the presence of speech noise at 0 dB signal-to-noise ratio (SNR). RESULTS: Results analyzed by percentage of correct phonemes and words revealed fewer writedown-talkback discrepancies for all 3 examiner groups when visual cues were added, with a substantial improvement for examiners with hearing loss. CONCLUSION: The finding of errors between talkback versus writedown scoring of lists for all of the examiners, even with visual cues, suggests a need for modification of the clinical word-recognition procedure for applications that potentially affect diagnosis, rehabilitation choices, or financial compensation.

A demonstration of improved precision of word recognition scores.

PURPOSE The purpose of this study was to demonstrate improved precision of word recognition scores (WRSs) by increasing list length and analyzing phonemic errors. METHOD Pure-tone thresholds (frequencies between 0.25 and 8.0 kHz) and WRSs were measured in 3 levels of speech-shaped noise (50, 52, and 54 dB HL) for 24 listeners with normal hearing. WRSs were obtained for half-lists and full lists of Northwestern University Test No. 6 (Tillman & Carhart, 1966) words presented at 48 dB HL. A resampling procedure was used to derive dimensionless effect sizes for identifying a change in hearing using the data. This allowed the direct comparison of the magnitude of shifts in WRS (%) and in the average pure-tone threshold (dB), which provided a context for interpreting the WRS. RESULTS WRSs based on a 50-word list analyzed by the percentage of correct phonemes were significantly more sensitive for identifying a change in hearing than the WRSs based on 25-word lists analyzed by percentage of correct words. CONCLUSION Increasing the number of items that contribute to a WRS significantly increased the test's ability to identify a change in hearing. Clinical and research applications could potentially benefit from a more precise word recognition test, the only basic audiologic measure that estimates directly the distortion component of hearing loss and its effect on communication.

Hearing conservation program for marching band members: a risk for noise-induced hearing loss?

PURPOSE: To examine the risk for noise-induced hearing loss (NIHL) in university marching band members and to provide an overview of a hearing conservation program for a marching band. METHOD: Sound levels during band rehearsals were recorded and audiometric hearing thresholds and transient otoacoustic emission were measured over a 3-year period. Musician's earplugs and information about hearing loss were provided to the students. The hearing thresholds of other college students were tested as a partial control. RESULTS: There were no significant differences in hearing thresholds between the two groups. During initial testing, more marching band members showed apparent high-frequency notches than control students. Follow-up hearing tests in a subsequent year for the marching band members showed that almost all notches disappeared. Persistent standard threshold shift (STS) across tests was not observed in the band members. CONCLUSION: Band members showed no evidence of STS or persistent notched audiograms. Because accepted procedures for measuring hearing showed a lack of precision in reliably detecting early NIHL in marching band members, it is recommended that signs of NIHL be sought in repeated measurements compared to baseline audiograms rather than in a single measure (a single notch). A hearing conservation program for this population is still recommended because of lengthy rehearsal times with high sound-level exposure during rehearsals.

The challenge of detecting minimal hearing loss in audiometric surveys.

PURPOSE: This tutorial provides framework and context for understanding the complex interaction of hearing measurement methodology and cohort social factors, as well as their relation to approaches to data interpretation and identification of minimal hearing loss (HL) in audiometric surveys. METHOD: Pertinent archival studies were reviewed, and an original analysis on U.S. Centers for Disease Control and Prevention (CDC) audiometric survey data from children (ages 6-19) was performed. CONCLUSION: The definition of an otologically normal individual, the pass-fail criterion representing the upper limit of the range of normal hearing, and the quality of the audiometry affect the percentage of persons who are falsely identified as having a minimal HL. An upper limit of normal hearing of 15 dB HL yields an unacceptably high false-positive rate, particularly when the more variable higher audiometric frequencies are examined. When air-conduction thresholds are assessed in isolation to estimate potential noise damage, the failure to exclude persons who have possible middle and external ear problems, including earwax, results in high false-positive rates. When these factors and other limitations are considered, audiograms from teens from a recent CDC survey do not show evidence consistent with widespread noise-induced HL. Suggestions are made to improve the effectiveness of pure-tone audiometry and the identification of minimal HL.

Are false-positive rates leading to an overestimation of noise-induced hearing loss?

PURPOSE: To estimate false-positive rates for rules proposed to identify early noise-induced hearing loss (NIHL) using the presence of notches in audiograms. METHOD: Audiograms collected from school-age children in a national survey of health and nutrition (the Third National Health and Nutrition Examination Survey [NHANES III]; National Center for Health Statistics, 1994) were examined using published rules for identifying noise notches at various pass-fail criteria. These results were compared with computer-simulated "flat" audiograms. The proportion of these identified as having a noise notch is an estimate of the false-positive rate for a particular rule. RESULTS: Audiograms from the NHANES III for children 6-11 years of age yielded notched audiograms at rates consistent with simulations, suggesting that this group does not have significant NIHL. Further, pass-fail criteria for rules suggested by expert clinicians, applied to NHANES III audiometric data, yielded unacceptably high false-positive rates. CONCLUSIONS: Computer simulations provide an effective method for estimating false-positive rates for protocols used to identify notched audiograms. Audiometric precision could possibly be improved by (a) eliminating systematic calibration errors, including a possible problem with reference levels for TDH-style earphones; (b) repeating and averaging threshold measurements; and (c) using earphones that yield lower variability for 6.0 and 8.0 kHz--2 frequencies critical for identifying noise notches.

The effects of fundamental frequency contour manipulations on speech intelligibility in background noise.

Previous studies have documented that speech with flattened or inverted fundamental frequency (F0) contours is less intelligible than speech with natural variations in F0. The purpose of this present study was to further investigate how F0 manipulations affect speech intelligibility in background noise. Speech recognition in noise was measured for sentences having the following F0 contours: unmodified, flattened at the median, natural but exaggerated, inverted, and sinusoidally frequency modulated at rates of 2.5 and 5.0 Hz, rates shown to make vowels more perceptually salient in background noise. Five talkers produced 180 stimulus sentences, with 30 unique sentences per F0 contour condition. Flattening or exaggerating the F0 contour reduced key word recognition performance by 13% relative to the naturally produced speech. Inverting or sinusoidally frequency modulating the F0 contour reduced performance by 23% relative to typically produced speech. These results support the notion that linguistically incorrect or misleading cues have a greater deleterious effect on speech understanding than linguistically neutral cues.

Fundamental frequency variation with an electrolarynx improves speech understanding: a case study.

PURPOSE: This study examined the effect of fundamental frequency (F0) variation on the intelligibility of speech in an alaryngeal talker who used an electrolarynx (EL). METHOD: One experienced alaryngeal talker produced variable F0 and a constant F0 with his EL as he read sentences aloud. As a control, a group of sentences with variable F0 was flattened at a constant F0. Twenty listeners heard these sentences in background noise and wrote down what they heard. RESULTS: Speech understanding was on average 14% better with variable F0 controlled by the talker than the sentences produced with a constant F0 and the control sentences resynthesized with flattened F0. CONCLUSIONS: Variable F0 contributes to speech understanding in noise. Because speech produced by an EL is considered to have poorer intelligibility in relation to other alaryngeal methods, training alaryngeal talkers to use variable F0 may prove to be of significant benefit for communication for those who use electrolarynges.

The effect of fundamental frequency on the intelligibility of speech with flattened intonation contours.

PURPOSE: To examine the effect of fundamental frequency (F0) on the intelligibility of speech with flattened F0 contours in noise. METHOD: Participants listened to sentences produced by 2 female talkers in white noise. The listening conditions included the unmodified original sentences and sentences with resynthesized F0 that reflected the average low F0, the median F0, and the average high F0 of each talker's productions. RESULTS: The sentences with flattened F0 contours yielded poorer intelligibility than the unmodified ones, but the sentences with flattened F0 did not produce equivalent performance. The sentences with F0 contours flattened at the average low F0 yielded better performance than sentences at the median F0. The sentences with F0 flattened at the average high F0 yielded poorer performance than the sentences flattened at the median F0. CONCLUSIONS: F0 height accounted for only a small amount of the drop in speech understanding in speech with a flattened F0 in healthy talkers. Although this study used healthy talkers, the findings suggest that clinicians should focus on having clients produce speech with naturally varying F0; F0 height is a secondary factor in the drop in intelligibility seen in monotone speech for female talkers.

The role of temporal-masking patterns in the determination of subjective duration and loudness for ramped and damped sounds.

The association between temporal-masking patterns, duration, and loudness for broadband noises with ramped and damped envelopes was examined. Duration and loudness matches between the ramped and damped sounds differed significantly. Listeners perceived the ramped stimuli to be longer and louder than the damped stimuli, but the outcome was biased by the stimulus context. Next, temporal-masking patterns were measured for ramped- and damped-broadband noises using three (0.5, 1.5, and 4.0 kHz) 10 ms probe tones presented individually at various temporal delays. Predictions of subjective duration derived from masking results underpredicted the matching results. Loudness estimates derived from models that assume persistence of neural activity after stimulus offset [Glasberg B. R., and Moore, B. C. J. (2002). "A model of loudness applicable to time-varying sounds," J. Audio. Eng. Soc. 50, 331-341; Chalupper, J., and Fastl, H. (2002) "Dynamic loudness model (DLM) for normal and hearing-impaired listeners," Acust. Acta Acust. 88, 378-386] were greater for ramped sounds than for damped sounds and were close to the average results obtained via the matching task. Differences in simultaneous-masked thresholds for these stimuli could not account for the loudness-matching results. Decay suppression of the later occurring portion of the damped stimulus may account for the differences in perception due to the stimulus context; however, a parsimonious implementation of this process that accounts for both subjective duration and loudness judgments remains unclear.

A multinomial model for identifying significant pure-tone threshold shifts.

PURPOSE: Significant threshold differences on retest for pure-tone audiometry are often evaluated by application of ad hoc rules, such as a shift in a pure-tone average or in 2 adjacent frequencies that exceeds a predefined amount. Rules that are so derived do not consider the probability of observing a particular audiogram. METHODS: A general solution for evaluating threshold differences on retest was developed on the basis of multinomial probabilities. The model uses the standard deviation of inter-test differences for 1 frequency as a parameter of the underlying Gaussian distribution of test results. The number of test frequencies, the categories of threshold change, and the probability of each category's occurrence are used to calculate the probability that a given pattern of threshold differences on retest (or 1 rarer) could occur by chance. RESULTS: The multinomial model was compared with 2 other methods for identifying threshold shifts in persons exposed to high sound pressure levels during concerts. The multinomial model identified the same audiograms as the ad hoc methods. CONCLUSION: Tables developed using a multinomial model can provide a clinical tool for evaluating audiograms by identifying statistically significant patterns of test-retest differences in hearing thresholds.

Critical difference table for word recognition testing derived using computer simulation.

PURPOSE: To construct a table for upper and lower limits of the 95% critical range for changes in word recognition scores obtained with monosyllabic word lists (of lengths 10, 25, 50, and 100 words) using newly available methods. Although such a table has been available for nearly 30 years (A. R. Thornton & M. J. M. Raffin, 1978), the earlier table was constructed by calculation and used an approximation to the variance of the difference score between 2 administrations of word lists of identical size. It has been used clinically, reproduced, and recommended for use by clinicians in handbooks and textbooks. METHOD: The new table was created using computer simulation of the relevant distributions and a direct estimate of the variance of the difference score between 2 tests, calculated using the simulated results. RESULTS: The new table differed from the previous table in 23% of entries. Critical ranges were both narrowed (82%) and expanded (18%). No range changed by more than 1 word correct in any direction. The original table was most accurate for list sizes of 25 words each. CONCLUSION: Using the new table will provide more accurate estimates of the 95% critical range for successive administrations of word recognition tests.

A psychophysical evaluation of spectral enhancement.

Listeners with sensorineural hearing loss have well-documented elevated hearing thresholds; reduced auditory dynamic ranges; and reduced spectral (or frequency) resolution that may reduce speech intelligibility, especially in the presence of competing sounds. Amplification and amplitude compression partially compensate for elevated thresholds and reduced dynamic ranges but do not remediate the loss in spectral resolution. Spectral-enhancement processing algorithms have been developed that putatively compensate for decreased spectral resolution by increasing the spectral contrast, or the peak-to-trough ratio, of the speech spectrum. Several implementations have been proposed, with mixed success. It is unclear whether the lack of strong success was due to specific implementation parameters or whether the concept of spectral enhancement is fundamentally flawed. The goal of this study was to resolve this ambiguity by testing the effects of spectral enhancement on detection and discrimination of simple, well-defined signals. To that end, groups of normal-hearing (NH) and hearing-impaired (HI) participants listened in 2 psychophysical experiments, including detection and frequency discrimination of narrowband noise signals in the presence of broadband noise. The NH and HI listeners showed an improved ability to detect and discriminate narrowband increments when there were spectral decrements (notches) surrounding the narrowband signals. Spectral enhancements restored increment detection thresholds to within the normal range when both energy and spectral-profile cues were available to listeners. When only spectral-profile cues were available for frequency discrimination tasks, performance improved for HI listeners, but not all HI listeners reached normal levels of discrimination. These results suggest that listeners are able to take advantage of the local improvement in signal-to-noise ratio provided by the spectral decrements.