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Recent evidence on the perceptual performance of bilingual listeners suggests that a nonaudibility-based cost exists in processing a second language. That is, when compared to monolingual English speakers and early bilinguals, listeners who acquired English as a second language after puberty show reduced performance when listening to the second language in background noise, despite normal auditory thresholds. However, past studies have not controlled for the homogeneity of the bilingual participants used in auditory research; therefore, it is unknown whether the deficit observed in bilingual function is due to a lack of control for language-related variables. The ability of a homogeneous group of Spanish-English bilinguals and English monolingual listeners to perceive sentences in quiet and in noise at threshold levels was evaluated using the Hearing in Noise Test (HINT). Both groups performed similarly in quiet conditions. In the noise conditions, the bilingual group's performance was significantly poorer than the monolingual group's performance. However, both groups showed a binaural advantage of 7-8 dB when the signal and noise were separated by 90 degrees. [ABSTRACT FROM AUTHOR]

The developers of a computer-assisted language intervention program called Fast ForWord (FFW) have claimed that their software changes temporal processing abilities as a result of specialized modifications to the acoustic and temporal properties of the speech signal within the program. This pilot study compared changes in auditory temporal processing in children who received FFW training and in children who received training with computer-assisted language intervention programs that were not designed to improve auditory perceptual skills. Four boys with Language-Learning Impairments (LLI) and 3 boys with typical language participated. Two of the boys with LLI received the FFW program, and the other 2 received a bundle of computer-assisted instruction (CAI) programs published by Laureate Language Systems (LLS). The FFW and LLS programs were presented on the same schedule. To assess temporal processing, signal thresholds in backward and simultaneous masking conditions were evaluated just before, during, and immediately after language training. The boys with typically developing language received no training. Children with typical language produced signal thresholds in the backward masking condition that were markedly lower than those in the simultaneous masking condition. This disparity is indicative of normal temporal processing. Conversely, 3 of 4 children with LLI failed to demonstrate a simultaneous-backward difference during baseline. The lack of a difference implies that temporal processing was not normal in these children. The fourth child with LLI had signal thresholds that paralleled those of the children with normal language development. This child also had the mildest form of LLI. Of the 3 children whose temporal processing was abnormal, 2 boys showed decreased signal thresholds in the backward masking condition. However, the improvement was sudden, occurring relatively early in the training sequence, and observed with both treatment programs. The third child with abnormal temporal processing failed to show a change in backward masking at any time during treatment Over the course of the experiment, signal thresholds for all listeners decreased by similar amounts in both backward and simultaneous masking. Taken together, these results do not support the presence of a program-specific improvement in temporal processing. In addition to the temporal processing deficits revealed by backward masking, group differences in response patterns implicate auditory memory involvement or differences in maintaining attention. [ABSTRACT FROM AUTHOR]

A stethoscope or listening tube with a custom earmold is routinely used to evaluate the acoustic output of a hearing aid. The diameter and length of the tubes of these listening devices cause changes in the acoustic output relative to the in situ condition. To compare these effects across commonly used listening devices, three stethoscopes and three listening tubes were evaluated with two different hearing aids when six different complex stimuli were used as input signals. In general, the listening devices resulted in a decrease (up to 20 dB) below 1 kHz, an increase (up to 20 dB) between 1 kHz and 2 kHz, and a decrease (up to 30 dB) above 2 kHz relative to the in situ output. These changes should be considered when making decisions regarding hearing aid status on the basis of listening checks via stethoscopes or listening tubes. [ABSTRACT FROM AUTHOR]

We examined the relative contribution of auditory processing abilities (tone perception and speech perception in noise) after controlling for short-term memory capacity and vocabulary, to narrative language comprehension in children with developmental language disorder. Two hundred and sixteen children with developmental language disorder, ages 6 to 9 years ( Mean = 7; 6), were administered multiple measures. The dependent variable was children's score on the narrative comprehension scale of the Test of Narrative Language . Predictors were auditory processing abilities, phonological short-term memory capacity, and language (vocabulary) factors, with age, speech perception in quiet, and non-verbal IQ as covariates. Results showed that narrative comprehension was positively correlated with the majority of the predictors. Regression analysis suggested that speech perception in noise contributed uniquely to narrative comprehension in children with developmental language disorder, over and above all other predictors; however, tone perception tasks failed to explain unique variance. The relative importance of speech perception in noise over tone-perception measures for language comprehension reinforces the need for the assessment and management of listening in noise deficits and makes a compelling case for the functional implications of complex listening situations for children with developmental language disorder., Competing Interests: RG receives royalties from the sale of the Test of Narrative Language, which was administered to participants. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Magimairaj, Nagaraj, Champlin, Thibodeau, Loeb and Gillam.)

Auditory brainstem responses (ABRs) and auditory middle-latency responses (AMLRs) to a click stimulus were measured in about 100 subjects. Of interest were the sex differences in those auditory evoked potentials (AEPs), the correlations between the various AEP measures, and the correlations between the AEP measures and measures of otoacoustic emissions (OAEs) and behavioral performance also measured on the same subjects. Also of interest was how the menstrual cycle affected the various AEP measures. Most ABR measures and several AMLR measures exhibited sex differences, and many of the former were substantial. The sex differences tended to be larger for latency than for amplitude of the waves, and they tended to be larger for a weak click stimulus than for a strong click. The largest sex difference was for Wave-V latency (effect size ~1.2). When subjects were dichotomized into Non-Whites and Whites, the race differences in AEPs were small within sex. However, sex and race interacted so that the sex differences often were larger for the White subjects than for the Non-White subjects, particularly for the latency measures. Contrary to the literature, no AEP measures differed markedly across the menstrual cycle. Correlations between various AEP measures, and between AEP and OAE measures, were small and showed no consistent patterns across sex or race categories. Performance on seven common psychoacoustical tasks was only weakly correlated with individual AEP measures (just as was true for the OAEs also measured on these subjects). AMLR Wave Pa unexpectedly did not show the decrease in latency and increase in amplitude typically observed for AEPs when click level was varied from 40 to 70 dB nHL (normal Hearing Level). For the majority of the measures, the variability of the distribution of scores was greater for the males than for the females., Competing Interests: The authors have declared that no competing interests exist.

Temporal acuity is the ability to differentiate between sounds based on fluctuations in the waveform envelope. The proximity of successive sounds and background noise diminishes the ability to track rapid changes between consecutive sounds. We determined whether a physiological correlate of temporal acuity is also affected by these factors. We recorded the auditory brainstem response (ABR) from human listeners using a harmonic complex (S1) followed by a brief tone burst (S2) with the latter serving as the evoking signal. The duration and depth of the silent gap between S1 and S2 were manipulated, and the peak latency and amplitude of wave V were measured. The latency of the responses decreased significantly as the duration or depth of the gap increased. The amplitude of the responses was not affected by the duration or depth of the gap. These findings suggest that changing the physical parameters of the gap affects the auditory system's ability to encode successive sounds.

Purpose: Sections of the community face barriers to accessing audiology services. The aim of this study was to assess the barriers faced by people in typically underserved community settings and to provide audiology services in their natural environment. Information gathered by questionnaire was used to determine each site's candidacy as a potential tele-audiology site., Method: Sixty-three participants were recruited across 3 community sites that were identified as gathering places for individuals who experience barriers to accessing traditional clinical audiology services. Information about demographics and participant experience with barriers to access was gathered by a locally generated, self-administered questionnaire. Pure-tone air-conduction audiometric exams were performed on participants with an automated portable diagnostic audiometer. Afterward, the investigator provided counseling regarding hearing loss rehabilitation or hearing protection. Referrals were made when appropriate., Results: Pure-tone averages were similar within sites but varied across sites. At least 30% of individuals at each site reported they wanted to visit the audiologist more often. Each site reported different principal barriers to access, among them transportation, motivation, and money. Eleven individuals were referred to the next level of care. Questionnaire results revealed special accommodations should be considered at each potential tele-audiology site., Conclusion: The present study provided audiology services to individuals in their natural environment, identified many of the obstacles preventing individuals from pursuing traditional audiology services and provided information for the foundation of a tele-audiology practice.

Both otoacoustic emissions (OAEs) and auditory evoked potentials (AEPs) are sexually dimorphic, and both are believed to be influenced by prenatal androgen exposure. OAEs and AEPs were collected from people affected by 1 of 3 categories of disorders of sex development (DSD) - (1) women with complete androgen insensitivity syndrome (CAIS); (2) women with congenital adrenal hyperplasia (CAH); and (3) individuals with 46,XY DSD including prenatal androgen exposure who developed a male gender despite initial rearing as females (men with DSD). Gender identity (GI) and role (GR) were measured both retrospectively and at the time of study participation, using standardized questionnaires. The main objective of this study was to determine if patterns of OAEs and AEPs correlate with gender in people affected by DSD and in controls. A second objective was to assess if OAE and AEP patterns differed according to degrees of prenatal androgen exposure across groups. Control males, men with DSD, and women with CAH produced fewer spontaneous OAEs (SOAEs) - the male-typical pattern - than control females and women with CAIS. Additionally, the number of SOAEs produced correlated with gender development across all groups tested. Although some sex differences in AEPs were observed between control males and females, AEP measures did not correlate with gender development, nor did they vary according to degrees of prenatal androgen exposure, among people with DSD. Thus, OAEs, but not AEPs, may prove useful as bioassays for assessing early brain exposure to androgens and predicting gender development in people with DSD., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Brief tones of 1.0 and 8.0 kHz were used to evoke auditory brainstem responses (ABRs), and the differences between the wave-V latencies for those two frequencies were used as a proxy for cochlear length. The tone bursts (8 ms in duration including 2-ms rise/fall times, and 82 dB in level) were, or were not, accompanied by a continuous, moderately intense noise band, highpass filtered immediately above the tone. The proxy values for length were compared with various measures of otoacoustic emissions (OAEs) obtained from the same ears. All the correlations were low, suggesting that cochlear length, as measured by this proxy at least, is not strongly related to the various group and individual differences that exist in OAEs. Female latencies did not differ across the menstrual cycle, and the proxy length measure exhibited no sex difference (either for menses females vs. males or midluteal females vs. males) when the highpass noises were used. However, when the subjects were partitioned into Whites and Non-Whites, a substantial sex difference in cochlear length did emerge for the White group, although the correlations with OAEs remained low. Head size was not highly correlated with any of the ABR measures., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Event Related Potentials (ERPs) were recorded from Spanish-English bilinguals (N=10) to test pre-attentive speech discrimination in two language contexts. ERPs were recorded while participants silently read magazines in English or Spanish. Two speech contrast conditions were recorded in each language context. In the phonemic in English condition, the speech sounds represented two different phonemic categories in English, but represented the same phonemic category in Spanish. In the phonemic in Spanish condition, the speech sounds represented two different phonemic categories in Spanish, but represented the same phonemic categories in English. Results showed pre-attentive discrimination when the acoustics/phonetics of the speech sounds match the language context (e.g., phonemic in English condition during the English language context). The results suggest that language contexts can affect pre-attentive auditory change detection. Specifically, bilinguals' mental processing of stop consonants relies on contextual linguistic information., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Auditory evoked potential (AEP) data from two studies originally designed for other purposes were reanalyzed. The auditory brainstem response (ABR), middle-latency response (MLR), and long-latency response (LLR) were measured. The latencies to each of several peaks were measured for each subject for each ear of click presentation, and the time intervals between successive peaks were calculated. Of interest were differences in interpeak intervals between the sexes, between people of differing sexual orientations, and between the two ears of stimulation. Most of the differences obtained were small. The largest sex differences were for interval I → V in the ABR and interval N1 → N2 of the LLR (effect sizes > 0.6). The largest differences between heterosexuals and nonheterosexuals were for the latency to Wave I in both sexes, for the interval Na → Nb in females, and for intervals V → Na and Nb → N1 in males (effect sizes > 0.3). The largest difference for ear stimulated was for interval N1 → N2 in heterosexual females (effect size ∼0.5). No substantial differences were found in the AEP intervals between women using, and not using, oral contraceptives. Left/right correlations for the interpeak intervals were mostly between about 0.4 and 0.6. Correlations between the ipsilateral intervals were small; i.e., interval length early in the AEP series was not highly predictive of interval length later in the series. Interpeak intervals appear generally less informative than raw latencies about differences by sex and by sexual orientation., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Purpose: A randomized controlled trial was conducted to compare the language and auditory processing outcomes of children assigned to receive the Fast ForWord Language intervention (FFW-L) with the outcomes of children assigned to nonspecific or specific language intervention comparison treatments that did not contain modified speech., Method: Two hundred sixteen children between the ages of 6 and 9 years with language impairments were randomly assigned to 1 of 4 conditions: (a) Fast ForWord Language (FFW-L), (b) academic enrichment (AE), (c) computer-assisted language intervention (CALI), or (d) individualized language intervention (ILI) provided by a speech-language pathologist. All children received 1 hr and 40 min of treatment, 5 days per week, for 6 weeks. Language and auditory processing measures were administered to the children by blinded examiners before treatment, immediately after treatment, 3 months after treatment, and 6 months after treatment., Results: The children in all 4 conditions improved significantly on a global language test and a test of backward masking. Children with poor backward masking scores who were randomized to the FFW-L condition did not present greater improvement on the language measures than children with poor backward masking scores who were randomized to the other 3 conditions. Effect sizes, analyses of standard error of measurement, and normalization percentages supported the clinical significance of the improvements on the Comprehensive Assessment of Spoken Language (E. Carrow-Woolfolk, 1999). There was a treatment effect for the Blending Words subtest of the Comprehensive Test of Phonological Processing (R. K. Wagner, J. K. Torgesen, & C. A. Rashotte, 1999). Participants in the FFW-L and CALI conditions earned higher phonological awareness scores than children in the ILI and AE conditions at the 6-month follow-up testing., Conclusion: Fast ForWord Language, the intervention that provided modified speech to address a hypothesized underlying auditory processing deficit, was not more effective at improving general language skills or temporal processing skills than a nonspecific comparison treatment (AE) or specific language intervention comparison treatments (CALI and ILI) that did not contain modified speech stimuli. These findings call into question the temporal processing hypothesis of language impairment and the hypothesized benefits of using acoustically modified speech to improve language skills. The finding that children in the 3 treatment conditions and the active comparison condition made clinically relevant gains on measures of language and temporal auditory processing informs our understanding of the variety of intervention activities that can facilitate development.

The purpose of this study was to examine the possible contribution of sensory mechanisms to an auditory processing deficit shown by some children with language-learning impairment (LLI). Auditory brainstem responses (ABRs) were measured from 2 groups of school-aged (8-10 years) children. One group consisted of 10 children with LLI, and the other group (control) consisted of 10 children with normally developing language. The ABR was elicited with a brief tone burst presented either alone (no-masking condition) or immediately followed by a longer duration noise burst (backward-masking condition). The primary dependent variable was the latency of wave V of the ABR. The mean latencies were not significantly different for the 2 groups in the no-masking condition. However, in the backward-masking condition, the mean latency for the LLI group was significantly increased relative to the mean latency for the control group. Thus, the presence of successive sounds delay the neural response in children with LLI. The explanation for this delay at the level of the brainstem is not known, but it may be due to disruption of synchrony, activation of alternate (less direct) pathways, increased inhibition, or some combination of these (or other) factors.

During the simultaneous monaural presentation of two primary tones, distortion products can be measured acoustically in the ear canal (DPOAEs) and electrically as auditory evoked potentials (DPAEPs). The purpose of this investigation was to elucidate the sources of nonlinearity within the human auditory system responsible for generating quadratic (QDT) and cubic (CDT) difference tones. Measurements of DPOAEs and DPAEPs were obtained from 24 normal-hearing adults (12 male) in conditions with and without presentation of a 60 dB SPL contralateral noise. The effects of primary-tone signal duration and mode of presentation on measurements of DPAEPs were also examined. Results indicated that overall, both acoustic and electric distortion products were suppressed during presentation of a contralateral noise. Increases in the duration of the primary tones caused increases in DPAEP amplitudes. A greater proportion of individuals exhibited DPAEPs with monotic compared to dichotic presentation of the primary tones. The findings of the investigation supported the conjecture that a cochlear nonlinearity produced CDT acoustic and electric distortion products. Evidence concerning the origin of the QDT DPAEP was inconclusive, and contributions from both cochlear and neural nonlinear sources could not be ruled out.

This study was designed to investigate early auditory memory and its possible contribution to an auditory processing deficit shown by some children with language impairment. Ten children with language impairment and 10 age-matched controls participated in a series of simultaneous and backward masking tasks. The same backward masking stimulus was then used to elicit a mismatch negativity response. In the behavioral conditions, children in the language impairment group had significantly higher (poorer) signal thresholds than their nonimpaired controls in backward masking, but their thresholds in simultaneous masking were not significantly different. In the mismatch-negativity conditions, latency was prolonged and the amplitude was diminished in the children with language impairment. Taken together, these psychoacoustic and electrophysiological data suggest that in a group of children with language impairment, underlying the nonsensory language disorder, there is a neurophysiological impairment in auditory memory for complex, nonlinguistic sounds.

This paper is the first in a series of three investigating the role of cholinergic mechanisms in the auditory system by assessing the acute effects of nicotine, an acetylcholinomimetic drug, on aggregate responses within the auditory pathway. In a single-blind procedure, auditory responses were obtained from 20 normal-hearing, non-smokers (10 male) under two conditions (nicotine, placebo). After the drug session, plasma tests revealed a subject's nicotine concentration. The effects of nicotine on early, exogenous responses of the auditory system (otoacoustic emissions and auditory brainstem potentials) are described in this first paper. Results indicated that transdermal administration of nicotine to non-smokers does not significantly affect cochlear activity but does acutely affect the neural transmission of acoustic information. Overall, otoacoustic emissions were unaffected by transdermal nicotine while wave I of the auditory brainstem response was significantly increased in latency and decreased in amplitude.

This paper is the second in a series of three investigating the role of cholinergic mechanisms in the auditory system by assessing the acute effects of nicotine, an acetylcholinomimetic drug, on aggregate responses within the auditory pathway. In a single-blind procedure, auditory responses were obtained from 20 normal-hearing, non-smokers (10 male) under two conditions (nicotine, placebo). The effects of nicotine on central, mesogenous responses of the auditory system (middle latency and 40-Hz responses) are described in this second paper. Results indicated that transdermal administration of nicotine to non-smokers does significantly affect the central, neural transmission of acoustic information. Na-Pa amplitude and Nb latency of the middle latency response and latency measures of the 40-Hz response were acutely altered by the presence of nicotine.

This paper is the last in a series of three investigating the role of cholinergic mechanisms in the auditory system by assessing the acute effects of nicotine, an acetylcholinomimetic drug, on aggregate responses within the auditory pathway. In a single-blind procedure, auditory responses were obtained from 20 normal-hearing, non-smokers (10 male) under two conditions (nicotine, placebo). The effects of nicotine on long-latency responses of the auditory system and on electroencephalograms are described in this paper. Results indicated that transdermal administration of nicotine to non-smokers significantly affects the afferent and efferent transmission of acoustic information, as well as enhancing cortical activation. Long-latency response amplitudes and electroencephalogram activity (dominant power and frequencies) were altered by acute doses of transdermal nicotine.

Twenty subjects with normal hearing and 15 subjects with mild-to-moderate sensorineural hearing losses were tested with eight lists of words using monosyllabic pronunciation to determine word recognition scores. Four of the lists were taken from Northwestern University Test No. 6 and four were simply made up by randomly selecting words from a dictionary. All of the word lists were used to determine performance-intensity functions. No clinically meaningful differences were observed among the lists.

The auditory evoked potentials (AEPs) elicited by click stimuli were measured in heterosexual, homosexual, and bisexual males and females having normal hearing sensitivity. Estimates of latency and/or amplitude were extracted for nine peaks having latencies of about 2-240 ms, which are presumed to correspond to populations of neurons located from the auditory nerve through auditory cortex. For five of the 19 measures obtained, the mean latency or amplitude for the 57 homosexual and bisexual females was different from that of the 49 heterosexual females in a manner that implies a masculinization of the auditory systems of the homosexual and bisexual females. A similar masculinization effect was previously observed for the otoacoustic emissions generated by the cochlea. For five other measures, the mean latency or amplitude for the 53 homosexual and bisexual males was different from that of the 50 heterosexual males in a manner that implies a hypermasculinization of the auditory systems of the homosexual and bisexual males. Hypermasculinization has been reported recently for other physical characteristics of homosexual males. One parsimonious interpretation of these findings is that homosexual males and females both were exposed to higher than normal levels of androgens at some point(s) in development. Data are reported only for the female subjects not using oral contraceptives because those drugs can masculinize certain AEP measures.

A proposal is made that 15 dB HL, rather than 25 dB HL, be considered the upper limit of normal hearing sensitivity. This recommendation is based on an explanation of the change from an earlier philosophy and the fact that so many people with hearing levels that average less than 25 dB HL consider themselves to have hearing difficulty. Such reclassification of people with slight to mild hearing losses would dignify their clinical complaints and aid in counseling that would assist them with their hearing difficulties.

The efficacy of a screening procedure for detecting nonorganic hearing loss using standard audiometric instrumentation was examined. Thirty normal-hearing subjects' responses to continuous and standard and lengthened off-time pulsed tones, using an ascending-descending method, were compared. Subjects were asked to respond to test stimuli in normal-hearing and simulated hearing loss conditions. Data show that there are clinical and statistical differences between subjects' response patterns in the normal-hearing condition as compared to the feigned hearing loss condition. The procedure is offered as a simple method of screening for nonorganic hearing loss.

A 5-page questionnaire was sent to 500 audiologists who were randomly selected from the directory of members of the American Academy of Audiology to assess the clinical practices most commonly used by certified audiologists in the United States. Survey content was limited to only those practices and procedures routinely used by audiologists across the nation. The current results were then compared to those obtained in similar studies conducted in 1971, 1972, 1978, 1985, 1989, and 1994 to determine which clinical procedures are being retained, modified, or replaced.

Auditory filters were derived in 20 normal-hearing human listeners at center frequencies (CFs) of 913, 1095, 3651, and 4382 Hz using the roex (p,r) method. Comparisons were made between slopes of the filters' skirts at the neighboring CFs with filter output levels of 45 and 70 dB. The same comparisons were made with regard to filter equivalent rectangular bandwidth (ERB). In the 1000-Hz region, the low-frequency slopes (Pl) of filters centered at 913 and 1095 Hz were significantly correlated at both stimulus levels, while the high-frequency slopes (Pu) were similar only at the high test level. In the 4000-Hz region, for sinusoids of 3651 and 4382 Hz, the level effect was clearer as both Pu and Pl values diverged at the low level but were related at high levels. The ERBs centered at the same CFs displayed a similar level dependence. At the stimulus level most likely to be affected by an active feedback mechanism, auditory filters centered at nearly the same frequency displayed quite distinct frequency selectivity, and this trend was stronger in the 4000-Hz region than the 1000-Hz region. The findings suggest that a saturating, active cochlear mechanism may not be distributed evenly, or contribute to peripheral tuning with equal effectiveness throughout the length of the partition.

This study was primarily designed to explore the job satisfaction of audiologists in the United States. A total of 285 audiologists completed background questions, rated statements, and answered questions about their job satisfaction. Through the use of multiple regression analyses, six statements were identified as being statistically significant in predicting job satisfaction. The most important factor was in the category of challenge.

Recently there has been renewed interest in the auditory processing capabilities of children with specific language impairment. In this study, eight children with specific language impairment and eight nonimpaired, age-matched peers completed a task to assess temporal resolution abilities. Children were asked to detect a tone in three masking conditions wherein the masker contained silent gaps of 0 msec., 40 msec., or 64 msec. in duration. Thresholds were measured in each masking condition at 500 Hz and 2000 Hz. Across the groups, thresholds decreased (improved) significantly as a function of increases in the duration of the gaps. Children in the two groups exhibited remarkably similar thresholds for the three masking conditions. However, children with specific language impairment required a significantly greater number of ascending trials to achieve the threshold criterion than did age-matched children. Results suggest that language-impaired children perceive temporal aspects of acoustic stimuli as well as their normally developing peers. Attentional mechanisms may play an important role in the difficulties they exhibit in auditory processing.

The effects of absolute and relative masker duration were investigated using one- and two-tone forward maskers. In the absolute-duration conditions, the duration (D) of a one-component on-frequency (M1; Dm1-alone) or off-frequency (M2; Dm2-alone) masker or the common duration of a two-component masker (Dm1 = Dm2) was varied. Masked threshold increased as duration increased in all three conditions. In the relative-duration conditions, the duration of one masker component was fixed at a relatively long value and the duration of the other component was varied (Dm1 > Dm2 or Dm2 > Dm1). In the Dm1 > Dm2 condition, masked threshold decreased as the duration of Dm2 was increased. In the Dm2 > Dm1 conditions, masked threshold increased and then decreased slightly as the duration of Dm1 was increased. Masked threshold was frequently lower in the M1+M2 than in the M1-alone conditions, indicating psychophysical suppression. Further, masked threshold in the Dm2 > Dm1 condition was always higher than in the corresponding absolute-duration condition (Dm1 = Dm2) having the same M1 duration, indicating masker enhancement. A two-stage neural model was proposed to account for these forward-masking data.

Delaying the onset of a signal relative to the onset of a simultaneous notched masker often improves the ability of subjects to "hear out" the signal at both threshold and suprathreshold levels. Viemeister and Bacon [J. Acoust. Soc. Am. 71, 1502-1507 (1982)] suggested that such signal-enhancement effects might be attributable to adaptation of the suppression directed from the masker to the signal, thereby releasing the signal from suppression. In support of their hypothesis, Viemeister and Bacon reported that a masker, preceded by an enhancer having no component at the signal frequency, produced more forward masking than did the masker by itself. Here the masker enhancement described by Viemeister and Bacon, signal enhancement, and two-tone suppression were measured in the same six subjects. Parametric manipulations of the masker-enhancement stimulus produced results similar to those previously reported for parallel investigations of signal enhancement, indicating that the two types of enhancement are closely related effects. Although the present data reveal an inverse relationship between the amounts of suppression and enhancement, suggesting that the two processes may be interrelated, no support was obtained for the hypothesis that adaptation of suppression can account for enhancement.

Absolute thresholds were measured psychophysically (behaviorally) and physiologically in the same subjects. Psychophysical thresholds were obtained using a modified method of limits. Physiological thresholds were based on auditory steady-state potentials recorded from the scalp. The stimuli for both types of test were click trains, periodic tone bursts and amplitude-modulated tones. The center frequency of the bursts and amplitude-modulated tones was 480 or 2000 Hz. It was found that psychophysical thresholds improved, and physiological thresholds worsened as the stimulus became more frequency-specific. Because of this interaction, the differences between psychophysical and physiological thresholds increased monotonically as a function of frequency specificity. Physiological thresholds obtained with the low-frequency stimuli were lower than those acquired with the high-frequency stimuli, while psychophysical thresholds obtained with the two frequencies were essentially the same.

Auditory steady-state potentials were recorded from the scalp of adult humans. The stimuli were 100-microseconds clicks presented at a rate of 39.1/s. Four stimulus levels were used (-20, 0, 10, and 20 dB SL). The presence or absence of a response was determined by three frequency-domain methods and examiners. The frequency-domain methods were: magnitude-squared coherence (MSC), phase coherence (PC), and magnitude only (MO). The MSC method generally had the highest d' values, indicating that it was the most sensitive method for detecting responses. The hearing threshold predicted by the MSC method was the lowest, and it was within 4 dB of the behaviorally measured threshold for the click stimuli. Further, the amplitude of the response was significantly more variable than its phase, and no relation was found between the variability of the amplitude of the response and the amplitude of the noise. In summary, response detection methods that incorporate phase information (such as MSC and PC) should be chosen over methods which incorporate only amplitude information.

Ear canal sound pressure levels were measured from a 38-year-old woman who had experienced objective tinnitus in her right ear for approximately 2 years. The tinnitus sounded like a series of "sighs" that were synchronous with her pulse rate. Because the level of the tinnitus fluctuated in a pulsing manner, it appeared to be of vascular origin. Psychoacoustically, the tinnitus behaved like a low-pass masker (cutoff frequency = 1.5 kHz) of about 40 dB SPL. This masking effect was manifested as a low-frequency hearing loss in the subject's right ear. A miniature microphone system was used to monitor the tinnitus before, during, and after a jugular-vein ligation. Because the cause of the tinnitus was only generally known, acoustically monitoring the sound as the jugular vein and/or its tributaries were systematically clamped and then released enabled the site of generation to be known exactly. By monitoring the tinnitus during surgery, the effectiveness of the corrective procedure could be immediately evaluated. Hearing sensitivity in the affected ear returned to normal limits following the elimination of the tinnitus. One year after the surgery, the tinnitus was barely audible to the woman, but only when she positioned her head a specific way. The level of the tinnitus measured in this head-turned condition was markedly lower than the level obtained preoperatively.

The overshoot effect was measured before, during, and after the administration of a moderate dose of aspirin. Prior to the drug, detectability of the 6-ms, 3550-Hz signal was 5-11 dB worse when presented 2 ms after the onset of the 200-ms wideband masking noise than when presented 190 ms after masker onset. Following 4 days of aspirin use, detectability in the long-delay condition was unchanged from the predrug value, but (for four of the five subjects) detectability in the short-delay condition was improved by about 4-8 dB. Thus the overshoot effect was markedly reduced by aspirin because the drug partially counteracted the normally poor detectability for signals presented soon after masker onset. This paradoxical improvement in detectability was accompanied by an aspirin-induced loss in detectability of 5-16 dB for a 200-ms sample of that same signal presented in the quiet. Similar paradoxical effects have previously been obtained by inducing a temporary hearing loss with exposure to intense sound. It is presumed that the same basic mechanisms underlie the parallel outcomes. The so-called cochlear amplifier is discussed in this regard, and also the possibility that the known differences in those primary auditory fibers having high and low spontaneous rates may be involved. A supplementary experiment demonstrated that shifting audibility with either a wideband or a narrow-band background noise does not affect the overshoot effect in the same way as does aspirin or exposure to intense sound, further suggesting that the cochlear amplifier must be altered in order for overshoot to be diminished.

Overshoot refers to the poorer detectability of brief signals presented soon after the onset of a masking noise compared to those presented after longer delays. In the present experiment, brief tonal signals were presented 2 or 190 ms following the onset of a broadband masker that was 200 ms in duration. These two conditions of signal delay were tested before and after a series of exposures to a tone intense enough to induce temporary threshold shift (TTS). The magnitude of the overshoot was reduced after the exposure when a TTS of at least 10 dB was induced, but not when smaller amounts of TTS were induced. The reduction in overshoot was due to a decrease in the masked thresholds with the 2-ms delay; masked thresholds with the 190-ms delay were not different pre- and post-exposure. The implication is that the mechanisms responsible for the normal overshoot effect are temporarily inactivated by the same stimulus manipulations that produce a mild exposure-induced hearing loss. Thus the result is the paradox that exposure to intense sounds can produce a loss of signal detectability in certain stimulus conditions and a simultaneous improvement in detectability in other stimulus conditions.

Following presentation of brief, intense pure tones spontaneous otoacoustic emissions (SOAEs) were reduced in frequency and/or amplitude. The effects were highly tuned with exposures between 1/8 and 5/8 of an octave below the SOAE producing the maximum changes. Exposure frequencies above the SOAE had no effect. The degree of tuning observed depended upon the post-exposure time sampled, with sharpness maximal between 3 and 120 s post-exposure. The effects increased nonlinearly as exposure level and duration were increased. The recovery functions were biphasic, the first phase being rapid and non-monotonic over about 2 min, while the second phase was monotonic and slow, sometimes taking several hours. These data are consistent with changes in outer hair cell (OHC) function and support the hypothesis that OHC changes underlie behavioral temporary threshold shift (TTS).

Gap detection thresholds (GDTs) were obtained from human listeners before and after exposure to a brief 0.4- or 1.7-kHz tone. The temporary threshold shift (TTS) produced 2 min after an exposure was approximately 10 dB. GDT stimuli were octave-band noises centered at one of three frequencies: the exposure frequency, one-half octave above the exposure frequency or one octave above the exposure frequency. GDTs were obtained at 35, 55, and 75 dB SPL at each center frequency. GDT and TTS recovery were monitored at logarithmically-spaced time intervals after the exposures. Following the 1.7-kHz exposure, shifts in post-exposure GDT were only obtained with the low-level stimulus conditions--the magnitude of GDT shift was correlated with the size of the TTS, and the shifts in GDT and absolute threshold required similar amounts of time to recover. Significant post-exposure shifts in GDT were also observed following the 0.4-kHz exposure. However, shifts were found at frequencies where there was no measurable TTS, and they required longer periods of time to recover than did absolute threshold.