Distortion Product Otoacoustic Emission (DPOAE) Growth in Aging Ears with Clinically Normal Behavioral Thresholds.

Age-related hearing loss (ARHL) is a devastating public health issue. To successfully address ARHL using existing and future treatments, it is imperative to detect the earliest signs of age-related auditory decline and understand the mechanisms driving it. Here, we explore early signs of age-related auditory decline by characterizing cochlear function in 199 ears aged 10-65 years, all of which had clinically defined normal hearing (i.e., behavioral thresholds ≤ 25 dB HL from .25 to 8 kHz bilaterally) and no history of noise exposure. We characterized cochlear function by measuring behavioral thresholds in two paradigms (traditional audiometric thresholds from .25 to 8 kHz and Békésy tracking thresholds from .125 to 20 kHz) and distortion product otoacoustic emission (DPOAE) growth functions at f2 = 2, 4, and 8 kHz. Behavioral thresholds through a standard clinical frequency range (up to 8 kHz) showed statistically, but not clinically, significant declines across increasing decades of life. In contrast, DPOAE growth measured in the same frequency range showed clear declines as early 30 years of age, particularly across moderate stimulus levels (L2 = 25-45 dB SPL). These substantial declines in DPOAE growth were not fully explained by differences in behavioral thresholds measured in the same frequency region. Additionally, high-frequency Békésy tracking thresholds above ~11.2 kHz showed frank declines with increasing age. Collectively, these results suggest that early age-related cochlear decline (1) begins as early as the third or fourth decade of life, (2) is greatest in the cochlear base but apparent through the length of the cochlear partition, (3) cannot be detected fully by traditional clinical measures, and (4) is likely due to a complex mix of etiologies.

Auditory hallucinations, top-down processing and language perception: a general population study.

BACKGROUND: Studies investigating the underlying mechanisms of hallucinations in patients with schizophrenia suggest that an imbalance in top-down expectations v. bottom-up processing underlies these errors in perception. This study evaluates this hypothesis by testing if individuals drawn from the general population who have had auditory hallucinations (AH) have more misperceptions in auditory language perception than those who have never hallucinated. METHODS: We used an online survey to determine the presence of hallucinations. Participants filled out the Questionnaire for Psychotic Experiences and participated in an auditory verbal recognition task to assess both correct perceptions (hits) and misperceptions (false alarms). A hearing test was performed to screen for hearing problems. RESULTS: A total of 5115 individuals from the general Dutch population participated in this study. Participants who reported AH in the week preceding the test had a higher false alarm rate in their auditory perception compared with those without such (recent) experiences. The more recent the AH were experienced, the more mistakes participants made. While the presence of verbal AH (AVH) was predictive for false alarm rate in auditory language perception, the presence of non-verbal or visual hallucinations were not. CONCLUSIONS: The presence of AVH predicted false alarm rate in auditory language perception, whereas the presence of non-verbal auditory or visual hallucinations was not, suggesting that enhanced top-down processing does not transfer across modalities. More false alarms were observed in participants who reported more recent AVHs. This is in line with models of enhanced influence of top-down expectations in persons who hallucinate.

Effects of noise overexposure on tone detection in noise in nonhuman primates.

This report explores the consequences of acoustic overexposures on hearing in noisy environments for two macaque monkeys trained to perform a reaction time detection task using a Go/No-Go lever release paradigm. Behavioral and non-invasive physiological assessments were obtained before and after narrowband noise exposure. Physiological measurements showed elevated auditory brainstem response (ABR) thresholds and absent distortion product otoacoustic emissions (DPOAEs) post-exposure relative to pre-exposure. Audiograms revealed frequency specific increases in tone detection thresholds, with the greatest increases at the exposure band frequency and higher. Masked detection was affected in a similar frequency specific manner: threshold shift rates (change of masked threshold per dB increase in noise level) were lower than pre-exposure values at frequencies higher than the exposure band. Detection thresholds in sinusoidally amplitude modulated (SAM) noise post-exposure showed no difference from those in unmodulated noise, whereas pre-exposure masked detection thresholds were lower in the presence of SAM noise compared to unmodulated noise. These frequency-dependent results were correlated with cochlear histopathological changes in monkeys that underwent similar noise exposure. These results reveal that behavioral and physiological effects of noise exposure in macaques are similar to those seen in humans and provide preliminary information on the relationship between noise exposure, cochlear pathology and perceptual changes in hearing within individual subjects.

Stability of the medial olivocochlear reflex as measured by distortion product otoacoustic emissions.

PURPOSE: The purpose of this study was to assess the repeatability of a fine-resolution, distortion product otoacoustic emission (DPOAE)-based assay of the medial olivocochlear (MOC) reflex in normal-hearing adults. METHOD: Data were collected during 36 test sessions from 4 normal-hearing adults to assess short-term stability and 5 normal-hearing adults to assess long-term stability. DPOAE level and phase measurements were recorded with and without contralateral acoustic stimulation. MOC reflex indices were computed by (a) noting contralateral acoustic stimulation-induced changes in DPOAE level (both absolute and normalized) at fine-structure peaks, (b) recording the effect as a vector difference, and (c) separating DPOAE components and considering a component-specific metric. RESULTS: Analyses indicated good repeatability of all indices of the MOC reflex in most frequency ranges. Short- and long-term repeatability were generally comparable. Indices normalized to a subject's own baseline fared best, showing strong short- and long-term stability across all frequency intervals. CONCLUSIONS: These results suggest that fine-resolution DPOAE-based measures of the MOC reflex measured at strategic frequencies are stable, and natural variance from day-to-day or week-to-week durations is small enough to detect between-group differences and possibly to monitor intervention-related success. However, this is an empirical question that must be directly tested to confirm its utility.

[Hypnotic communication and hypnosis in clinical practice]. / Hypnotische Kommunikation und Hypnose in der ärztlichen Praxis.

In addition to usual medical care it is often critical to consider the patient's inner world in order to sensitively differentiate between harmful and helpful suggestive elements. The respective abilities in terms of hypnotic communication can be easily learned. Confident, empathic attention and a calm, understanding and figurative language narrowing the focus on positive emotions and positive change, which have been shown to improve the patient's chances of healing, are of particular importance. Proper clinical hypnosis goes one step further: it makes explicit use of suggestions, trance, and trance phenomena. The major clinical indications for hypnosis include psychosomatic disorders, anxiety disorders, obsessive-compulsive disorders, depression, and pain syndromes. Hypnosis can also be employed as an adjunct for surgical therapy.

En plus d'appliquer les mesures médicales générales il est aussi important d'observer le monde interne des malades, ceci pour pouvoir différencier entre les éléments suggestifs ayant un effet néfaste ou bénéfique. Les capacités correspondantes en ce qui concerne la communication par hypnose peuvent être apprises. Particulièrement important sont à cet égard un suivi fiable et empathique et un parler calme, compréhensible et imagé, ce qui accroît le sentiment de bien être et de changements positifs et augmente les chances de guérison. L'hypnose médicale véritable va encore un pas plus loin. Elle inclut des suggestions et des états de transe. Les indications en sont les troubles psychosomatiques, les états d'angoisse ou de contrainte, la dépression et la douleur.

Vowel discrimination by hearing infants as a function of number of spectral channels.

Reduced spectral resolution negatively impacts speech perception, particularly perception of vowels and consonant place. This study assessed impact of number of spectral channels on vowel discrimination by 6-month-old infants with normal hearing by comparing three listening conditions: Unprocessed speech, 32 channels, and 16 channels. Auditory stimuli (/ti/ and /ta/) were spectrally reduced using a noiseband vocoder and presented to infants with normal hearing via visual habituation. Results supported a significant effect of number of channels on vowel discrimination by 6-month-old infants. No differences emerged between unprocessed and 32-channel conditions in which infants looked longer during novel stimulus trials (i.e., discrimination). The 16-channel condition yielded a significantly different pattern: Infants demonstrated no significant difference in looking time to familiar vs novel stimulus trials, suggesting infants cannot discriminate /ti/ and /ta/ with only 16 channels. Results support effects of spectral resolution on vowel discrimination. Relative to published reports, young infants need more spectral detail than older children and adults to perceive spectrally degraded speech. Results have implications for development of perception by infants with hearing loss who receive auditory prostheses.

Becoming a Lunari or Taiyo expert: learned attention to parts drives holistic processing of faces.

Faces are processed holistically, but the locus of holistic processing remains unclear. We created two novel races of faces (Lunaris and Taiyos) to study how experience with face parts influences holistic processing. In Experiment 1, subjects individuated Lunaris wherein the top, bottom, or both face halves contained diagnostic information. Subjects who learned to attend to face parts exhibited no holistic processing. This suggests that individuation only leads to holistic processing when the whole face is attended. In Experiment 2, subjects individuated both Lunaris and Taiyos, with diagnostic information in complementary face halves of the two races. Holistic processing was measured with composites made of either diagnostic or nondiagnostic face parts. Holistic processing was only observed for composites made from diagnostic face parts, demonstrating that holistic processing can occur for diagnostic face parts that were never seen together. These results suggest that holistic processing is an expression of learned attention to diagnostic face parts.

Effect of calibration method on distortion-product otoacoustic emission measurements at and around 4 kHz.

OBJECTIVES: Distortion-product otoacoustic emissions (DPOAEs) collected after sound pressure level (SPL) calibration are susceptible to standing waves that affect measurements at the plane of the probe microphone due to overlap of incident and reflected waves. These standing-wave effects can be as large as 20 dB, and may affect frequencies both above and below 4 kHz. It has been shown that forward pressure level (FPL) calibration minimizes standing-wave effects by isolating the forward-propagating component of the stimulus. Yet, previous work has failed to demonstrate more than a small difference in test performance and behavioral-threshold prediction with DPOAEs after SPL and FPL calibration. One potential limitation in prior studies is that measurements were restricted to octave and interoctave frequencies; as a consequence, data were not necessarily collected at the standing-wave null frequency. In the present study, DPOAE responses were measured with f2 set to each participant's standing-wave frequency in an effort to increase the possibility that differences in test performance and threshold prediction would be observed for SPL and FPL calibration methods. DESIGN: Data were collected from 42 normal-hearing participants and 93 participants with hearing loss. DPOAEs were measured with f2 set to 4 kHz and at each participant's notch frequency after SPL and FPL calibration. DPOAE input/output functions were obtained from -10 to 80 dB in 5 dB steps for each calibration/stimulus condition. Test performance was evaluated using clinical decision theory. Both area under receiver operating characteristic curves for all stimulus levels and cumulative distributions when L2 = 50 dB (a level at which the best performance was observed regardless of calibration method) were used to evaluate the accuracy with which auditory status was determined. A bootstrap procedure was used to evaluate the significance of the differences in test performance between SPL and FPL calibrations. DPOAE predictions of behavioral threshold were evaluated by correlating actual behavioral thresholds and predicted thresholds using a multiple linear regression model. RESULTS: First, larger DPOAE levels were measured after SPL calibration than after FPL calibration, which demonstrated the expected impact of standing waves. Second, for both FPL and SPL calibration, test performance was best for moderate stimulus levels. Third, differences in test performance between calibration methods were evident at low- and high-stimulus levels. Fourth, there were small but statistically significant improvements in test performance after FPL calibration for clinically relevant conditions. Fifth, calibration method had no effect on threshold prediction. CONCLUSIONS: Standing waves after SPL calibration have an impact on DPOAE levels. Although the effect of calibration method on test performance was small, test performance was better after FPL calibration than after SPL calibration. There was no effect of calibration method on predictions of behavioral threshold.

Understanding excessive SNR loss in hearing-impaired listeners.

BACKGROUND: Traditional audiometric measures, such as pure-tone thresholds or unaided word-recognition in quiet, appear to be of marginal use in predicting speech understanding by hearing-impaired (HI) individuals in background noise with or without amplification. Suprathreshold measures of auditory function (tolerance of noise, temporal and frequency resolution) appear to contribute more to success with amplification and may describe more effectively the distortion component of hearing. However, these measures are not typically measured clinically. When combined with measures of audibility, suprathreshold measures of auditory distortion may provide a much more complete understanding of speech deficits in noise by HI individuals. PURPOSE: The primary goal of this study was to investigate the relationship among measures of speech recognition in noise, frequency selectivity, temporal acuity, modulation masking release, and informational masking in adult and elderly patients with sensorineural hearing loss to determine whether peripheral distortion for suprathreshold sounds contributes to the varied outcomes experienced by patients with sensorineural hearing loss listening to speech in noise. RESEARCH DESIGN: A correlational study. STUDY SAMPLE: Twenty-seven patients with sensorineural hearing loss and four adults with normal hearing were enrolled in the study. DATA COLLECTION AND ANALYSIS: The data were collected in a sound attenuated test booth. For speech testing, subjects' verbal responses were scored by the experimenter and entered into a custom computer program. For frequency selectivity and temporal acuity measures, subject responses were recorded via a touch screen. Simple correlation, step-wise multiple linear regression analyses and a repeated analysis of variance were performed. RESULTS: Results showed that the signal-to-noise ratio (SNR) loss could only be partially predicted by a listener's thresholds or audibility measures such as the Speech Intelligibility Index (SII). Correlations between SII and SNR loss were higher using the Hearing-in-Noise Test (HINT) than the Quick Speech-in-Noise test (QSIN) with the SII accounting for 71% of the variance in SNR loss for the HINT but only 49% for the QSIN. However, listener age and the addition of suprathreshold measures improved the prediction of SNR loss using the QSIN, accounting for nearly 71% of the variance. CONCLUSIONS: Two standard clinical speech-in-noise tests, QSIN and HINT, were used in this study to obtain a measure of SNR loss. When administered clinically, the QSIN appears to be less redundant with hearing thresholds than the HINT and is a better indicator of a patient's suprathreshold deficit and its impact on understanding speech in noise. Additional factors related to aging, spectral resolution, and, to a lesser extent, temporal resolution improved the ability to predict SNR loss measured with the QSIN. For the HINT, a listener's audibility and age were the only two significant factors. For both QSIN and HINT, roughly 25-30% of the variance in individual differences in SNR loss (i.e., the dB difference in SNR between an individual HI listener and a control group of NH listeners at a specified performance level, usually 50% word or sentence recognition) remained unexplained, suggesting the need for additional measures of suprathreshold acuity (e.g., sensitivity to temporal fine structure) or cognitive function (e.g., memory and attention) to further improve the ability to understand individual variability in SNR loss.

Differences between psychoacoustic and frequency following response measures of distortion tone level and masking.

The scalp-recorded frequency following response (FFR) in humans was measured for a 244-Hz pure tone at a range of input levels and for complex tones containing harmonics 2-4 of a 300-Hz fundamental, but shifted by ±56 Hz. The effective magnitude of the cubic difference tone (CDT) and the quadratic difference tone (QDT, at F(2)-F(1)) in the FFR for the complex was estimated by comparing the magnitude spectrum of the FFR at the distortion product (DP) frequency with that for the pure tone. The effective DP levels in the FFR were higher than those commonly estimated in psychophysical experiments, indicating contributions to the DP in the FFR in addition to the audible propagated component. A low-frequency narrowband noise masker reduced the magnitude of FFR responses to the CDT but also to primary components over a wide range of frequencies. The results indicate that audible DPs may contribute very little to the DPs observed in the FFR and that using a narrowband noise for the purpose of masking audible DPs can have undesired effects on the FFR over a wide frequency range. The results are consistent with the notion that broadly tuned mechanisms central to the auditory nerve strongly influence the FFR.

Audibility of aliasing distortion in sawtooth signals and its implications for oscillator algorithm design.

This paper investigates the audibility threshold of aliasing in computer-generated sawtooth signals. Listening tests were conducted to find out how much the aliased frequency components below and above the fundamental must be attenuated for them to be inaudible. The tested tones comprised the fundamental frequencies 415, 932, 1480, 2093, 3136, and 3951 Hz, presented at 60-dB SPL and 44.1-kHz sampling rate. The results indicate that above the fundamental the aliased components must be attenuated 0, 19, 26, 27, 32, and 41 dB for the corresponding fundamental frequencies, and below the fundamental the attenuation of 0, 3, 6, 11, 12, and 11 dB, respectively, is sufficient. The results imply that the frequency-masking phenomenon affects the perception of aliasing and that the masking effect is more prominent above the fundamental than below it. The A-weighted noise-to-mask ratio is proposed as a suitable quality measure for sawtooth signals containing aliasing. It was shown that the bandlimited impulse train, the differentiated parabolic waveform, and the fourth-order polynomial bandlimited step function synthesis algorithms are perceptually alias-free up to 1, 2, and 4 kHz, respectively. General design rules for antialiasing sawtooth oscillators are derived based on the results and on knowledge of level-dependence of masking.

Comparing live to recorded speech in training the perception of spectrally shifted noise-vocoded speech.

Two experimental groups were trained for 2 h with live or recorded speech that was noise-vocoded and spectrally shifted and was from the same text and talker. These two groups showed equivalent improvements in performance for vocoded and shifted sentences, and the group trained with recorded speech showed consistently greater improvements than untrained controls. Another group trained with unshifted noise-vocoded speech improved no more than untrained controls. Computer-based training thus appears at least as effective as labor-intensive live-voice training for improving the perception of spectrally shifted noise-vocoded speech, and by implication, for training of users of cochlear implants.

The influence of semantic top-down processing in auditory verbal hallucinations.

BACKGROUND: Auditory verbal hallucinations (AVH) are one of the most prominent symptoms of schizophrenia but have also been reported in the general population. Several cognitive models have tried to elucidate the mechanism behind auditory verbal hallucinations, among which a top-down model. According to this model, perception is biased towards top-down information (e.g., expectations), reducing the influence of bottom-up information coming from the sense organs. This bias predisposes to false perceptions, i.e., hallucinations. METHODS: The current study investigated this hypothesis in non-psychotic individuals with frequent AVH, psychotic patients with AVH and healthy control subjects by applying a semantic top-down task. In this task, top-down processes are manipulated through the semantic context of a sentence. In addition, the association between hallucination proneness and semantic top-down errors was investigated. RESULTS: Non-psychotic individuals with AVH made significantly more top-down errors compared to healthy controls, while overall accuracy was similar. The number of top-down errors, corrected for overall accuracy, in the patient group was in between those of the other two groups and did not differ significantly from either the non-psychotic individuals with AVH or the healthy controls. The severity of hallucination proneness correlated with the number of top-down errors. DISCUSSION: These findings confirm that non-psychotic individuals with AVH are stronger influenced by top-down processing (i.e., perceptual expectations) than healthy controls. In contrast, our data suggest that in psychotic patients semantic expectations do not play a role in the etiology of AVH. This finding may point towards different cognitive mechanisms for pathological and nonpathological hallucinations.

Fast recognition of musical sounds based on timbre.

Human listeners seem to have an impressive ability to recognize a wide variety of natural sounds. However, there is surprisingly little quantitative evidence to characterize this fundamental ability. Here the speed and accuracy of musical-sound recognition were measured psychophysically with a rich but acoustically balanced stimulus set. The set comprised recordings of notes from musical instruments and sung vowels. In a first experiment, reaction times were collected for three target categories: voice, percussion, and strings. In a go/no-go task, listeners reacted as quickly as possible to members of a target category while withholding responses to distractors (a diverse set of musical instruments). Results showed near-perfect accuracy and fast reaction times, particularly for voices. In a second experiment, voices were recognized among strings and vice-versa. Again, reaction times to voices were faster. In a third experiment, auditory chimeras were created to retain only spectral or temporal features of the voice. Chimeras were recognized accurately, but not as quickly as natural voices. Altogether, the data suggest rapid and accurate neural mechanisms for musical-sound recognition based on selectivity to complex spectro-temporal signatures of sound sources.

Word recognition for temporally and spectrally distorted materials: the effects of age and hearing loss.

OBJECTIVES: The purpose of Experiment 1 was to measure word recognition in younger adults with normal hearing when speech or babble was temporally or spectrally distorted. In Experiment 2, older listeners with near-normal hearing and with hearing loss (for pure tones) were tested to evaluate their susceptibility to changes in speech level and distortion types. The results across groups and listening conditions were compared to assess the extent to which the effects of the distortions on word recognition resembled the effects of age-related differences in auditory processing or pure-tone hearing loss. DESIGN: In Experiment 1, word recognition was measured in 16 younger adults with normal hearing using Northwestern University Auditory Test No. 6 words in quiet and the Words-in-Noise test distorted by temporal jittering, spectral smearing, or combined jittering and smearing. Another 16 younger adults were evaluated in four conditions using the Words-in-Noise test in combinations of unaltered or jittered speech and unaltered or jittered babble. In Experiment 2, word recognition in quiet and in babble was measured in 72 older adults with near-normal hearing and 72 older adults with hearing loss in four conditions: unaltered, jittered, smeared, and combined jittering and smearing. RESULTS: For the listeners in Experiment 1, word recognition was poorer in the distorted conditions compared with the unaltered condition. The signal to noise ratio at 50% correct word recognition was 4.6 dB for the unaltered condition, 6.3 dB for the jittered, 6.8 dB for the smeared, 6.9 dB for the double-jitter, and 8.2 dB for the combined jitter-smear conditions. Jittering both the babble and speech signals did not significantly reduce performance compared with jittering only the speech. In Experiment 2, the older listeners with near-normal hearing and hearing loss performed best in the unaltered condition, followed by the jitter and smear conditions, with the poorest performance in the combined jitter-smear condition in both quiet and noise. Overall, listeners with near-normal hearing performed better than listeners with hearing loss by ~30% in quiet and ~6 dB in noise. In the quiet distorted conditions, when the level of the speech was increased, performance improved for the hearing loss group, but decreased for the older group with near-normal hearing. Recognition performance of younger listeners in the jitter-smear condition and the performance of older listeners with near-normal hearing in the unaltered conditions were similar. Likewise, the performance of older listeners with near-normal hearing in the jitter-smear condition and the performance of older listeners with hearing loss in the unaltered conditions were similar. CONCLUSIONS: The present experiments advance our understanding regarding how spectral or temporal distortions of the fine structure of speech affect word recognition in older listeners with and without clinically significant hearing loss. The Speech Intelligibility Index was able to predict group differences, but not the effects of distortion. Individual differences in performance were similar across all distortion conditions with both age and hearing loss being implicated. The speech materials needed to be both spectrally and temporally distorted to mimic the effects of age-related differences in auditory processing and hearing loss.

Reliability of distortion-product otoacoustic emissions and their relation to loudness.

The reliability of distortion-product otoacoustic emission (DPOAE) measurements and their relation to loudness measurements was examined in 16 normal-hearing subjects and 58 subjects with hearing loss. The level of the distortion product (L(d)) was compared across two sessions and resulted in correlations that exceeded 0.90. The reliability of DPOAEs was less when parameters from nonlinear fits to the input/output (I/O) functions were compared across visits. Next, the relationship between DPOAE I/O parameters and the slope of the low-level portion of the categorical loudness scaling (CLS) function (soft slope) was assessed. Correlations of 0.65, 0.74, and 0.81 at 1, 2, and 4 kHz were observed between CLS soft slope and combined DPOAE parameters. Behavioral threshold had correlations of 0.82, 0.83, and 0.88 at 1, 2, and 4 kHz with CLS soft slope. Combining DPOAEs and behavioral threshold provided little additional information. Lastly, a multivariate approach utilizing the entire DPOAE I/O function was used to predict the CLS rating for each input level (dB SPL). Standard error of the estimate when using this method ranged from 2.4 to 3.0 categorical units (CU), suggesting that DPOAE I/O functions can predict CLS measures within the CU step size used in this study (5).

Using a semi-structured interview to explore imagery experienced during social anxiety for clients with a diagnosis of psychosis: an exploratory study conducted within an early intervention for psychosis service.

BACKGROUND: Social phobia frequently occurs as a comorbid condition, with high rates reported among people with psychosis. Little is known about the nature of social anxiety in this population or whether current psychological theories apply. AIMS: This paper aims to develop and pilot a suitable measure to explore imagery experienced by participants with comorbid psychosis and social anxiety and to provide preliminary indications as to its nature. METHOD: A semi-structured interview exploring imagery was used with seven participants (adapted from Hackmann, Surawy and Clark, 1998) and the results were analysed using qualitative template analysis. RESULTS: Initial indications from this sample suggest that some participants experience typical social anxiety images, as identified by Hackmann et al. (1998). However, some experience images that appear more threatening, and may be related to residual psychotic paranoia. Image perspective was also explored: typical social anxiety images tended to be seen from an observer perspective, while those that may have been more related to psychosis tended to be seen from a field perspective. CONCLUSIONS: This exploratory study has facilitated the careful adaptation and development of an imagery interview for use in this population and has suggested areas for further research and raised questions around clinical implications.

The influence of common stimulus parameters on distortion product otoacoustic emission fine structure.

OBJECTIVES: To determine whether common approaches to setting stimulus parameters influence the depth of fine structure present in the distortion product otoacoustic emission (DPOAE) response. Because the presence of fine structure has been suggested as a possible source of errors, if one of the common parametric approaches results in reduced fine-structure depth, it may be preferred over other approaches. DESIGN: DPOAE responses were recorded in a group of 21 subjects with normal hearing for 1/3-octave intervals surrounding 3 f2s (1, 2, and 4 kHz) at three L2s (30, 45, and 55 dB SPL). For each f2 and L2 combination, L1 and f2/f1 were set according to three commonly used parametric approaches. These included a simple approach, the approach recommended by Kummer et al., and the approach described by Johnson et al. These three approaches primarily differ in the recommended relationship between L1 and L2. For each parametric approach, DPOAE fine structure was evaluated by varying f2 in small steps. Differences in DPOAE level and DPOAE fine-structure depth across f2, L2, and the various stimulus parameters were evaluated using repeated-measures analysis of variance. RESULTS: As expected, significant variations in DPOAE level were observed across the three parametric approaches. For stimulus levels #45 dB SPL, the simple stimuli resulted in lower DPOAE levels than were observed for other approaches. An unexpected finding was that stimulus parameters developed by Johnson et al., which were believed to produce higher DPOAE levels than other approaches, produced the lowest DPOAE levels of the three approaches when f2 = 4 kHz. Significant differences in fine-structure depth were also observed. Greater fine-structure depth was observed with the simple parameters, although this effect was restricted to L2 # 45 dB SPL. When L2 = 55 dB SPL, all three parametric approaches resulted in equivalent fine-structure depth. A significant difference in fine-structure depth across the 3 f2s was also observed. The interval surrounding 2 kHz was associated with greater fine-structure depth than the intervals surrounding 1 and 4 kHz. CONCLUSIONS: The simple stimulus parameters resulted in more fine structure than the other parametric approaches; however, this effect was restricted to L2 # 45 dB SPL. At the moderate stimulus levels used in most clinical applications of DPOAEs (L2 = 55 dB SPL), all three approaches resulted in similar fine-structure depths. These findings suggest that manipulating stimulus parameters, particularly the L1, L2 relationship, is not an effective technique for reducing fine structure, except at the lowest stimulus levels, and that all the common parameters result in equivalent fine structure for moderate stimulus levels. These results also suggest that the stimulus parameters used in future studies of the clinical implications of fine structure may be relatively unimportant, unless stimulus levels #45 dB SPL will be evaluated.

On the use of the distortion-sensitivity approach in examining the role of linguistic abilities in speech understanding in noise.

PURPOSE: Researchers have used the distortion-sensitivity approach in the psychoacoustical domain to investigate the role of auditory processing abilities in speech perception in noise (van Schijndel, Houtgast, & Festen, 2001; Goverts & Houtgast, 2010). In this study, the authors examined the potential applicability of the distortion-sensitivity approach for investigating the role of linguistic abilities in speech understanding in noise. METHOD: The authors applied the distortion-sensitivity approach by measuring the processing of visually presented masked text in a condition with manipulated syntactic, lexical, and semantic cues and while using the Text Reception Threshold (George et al., 2007; Kramer, Zekveld, & Houtgast, 2009; Zekveld, George, Kramer, Goverts, & Houtgast, 2007) method. Two groups that differed in linguistic abilities were studied: 13 native and 10 non-native speakers of Dutch, all typically hearing university students. RESULTS: As expected, the non-native subjects showed substantially reduced performance. The results of the distortion-sensitivity approach yielded differentiated results on the use of specific linguistic cues in the 2 groups. CONCLUSION: The results show the potential value of the distortion-sensitivity approach in studying the role of linguistic abilities in speech understanding in noise of individuals with hearing impairment.

Characterization of the perceived sound of trauma-induced tinnitus in gerbils.

Tinnitus often develops following inner ear pathologies, like acoustic trauma. Therefore, an acoustic trauma model of tinnitus in gerbils was established using a modulated acoustic startle response. Cochlear trauma evoked by exposure to narrow-band noise at 10 kHz was assessed by auditory brainstem responses (ABR) and distortion product otoacoustic emissions (DPOAE). Threshold shift amounted to about 25 dB at frequencies > 10 kHz. Induction of a phantom-noise perception was documented by an acoustic startle response paradigm. A reduction of the gap-prepulse inhibition of acoustic startle (GPIAS) was taken as evidence for tinnitus at the behavioral level. Three to five weeks after trauma the ABR and DPOAE thresholds were back to normal. At that time, a reduction of GPIAS in the frequency range 16-20 kHz indicated a phantom noise perception. Seven weeks post trauma the tinnitus-affected frequency range became narrow and shifted to the center-trauma frequency at 10 kHz. Taken together, by investigating frequency-dependent effects in detail, this study in gerbils found trauma-evoked tinnitus developing in the frequency range bordering the low frequency slope of the induced noise trauma. This supports the theory of lateral inhibition as the physiological basis of tinnitus.