W. Wiktor Jedrzejczak

Time–frequency analysis of transiently evoked otoacoustic emissions of subjects exposed to noise

Transiently evoked otoacoustic emissions (TEOAE) were measured from 124 ears from two subject groups: healthy subjects (62 ears), and workers (62 ears) exposed to noise of jet engines. The recordings were analyzed using the method of adaptive approximations based on a matching pursuit (MP) algorithm. The method allows for description of the signal components in terms of their amplitude, frequency, latency, and time-span (or duration). The purpose of this work was to determine the repeatability and usefulness of these parameters in studies of hearing impairment of populations exposed to potentially harmful noise. Good distinction between the two datasets was achieved in all investigated frequency bands when amplitude was used as a discrimination parameter. Also latency was affected in frequency bands starting at 2000 Hz, while the time-span parameter associated with the duration of the waveform was less influenced by noise.

Identification of otoacoustic emissions components by means of adaptive approximations.

Clicks and a set of tone bursts covering the same frequency band were applied as a stimuli evoking otoacoustic emissions (OAE). Recorded otoacoustic emissions were decomposed into the basic waveforms by means of high-resolution adaptive time-frequency approximation method based on the matching pursuit algorithm. The method allows for description of the signal components in terms of frequencies, time occurrences, time spans, and energy. The analysis of OAEs energy density distributions in time-frequency space revealed that click responses can be considered as linear superpositions of responses to tone bursts, The frequency-latency relationship was studied and compared with earlier works. The method made possible the exhaustive description of the resonant modes specific for given subject/ear. They were characterized not only by the close frequencies appearing for different tones, but they usually had similar latencies and time spans. Short-time and long-time resonant modes were identified. The second ones might be connected with spontaneous emissions. The method opens new perspectives in studying the fine structure of the OAE and testing of the theoretical models.

Otoacoustic emissions latency difference between full-term and preterm neonates

Transiently evoked otoacoustic emissions (TEOAEs) were recorded from full-term and preterm neonates. The responses were decomposed, by means of an adaptive approximation method, into waveforms of defined frequencies, amplitudes, latencies and time spans. Statistically significant differences in the latency values were found between the tested groups. Differences were also found in the time spans of the TEOAEs components. For the preterm neonates the contribution of long-duration components (i.e. long-time span) was higher. Those components were characterized by narrow frequency band and contrary to the short-time span components their latencies did not depend on frequency. The removal of the long-duration components, from the pool of analyzed data, decreased the latency differences between the tested groups. The results indicate that the origin of the longer latency values for preterm neonates (with a post conceptional age up to 33 weeks) in respect to full-term neonates can be attributed to the presence of long-lasting components. The correspondence, which was found between frequencies of long-duration components and the spectral peaks of spontaneous otoacoustic emissions (SOAEs), suggests that those components may be connected with SOAEs.

Synchronized spontaneous otoacoustic emissions analyzed in a time-frequency domain.

A synchronized spontaneous otoacoustic emission paradigm was used to measure the response in time intervals of 80 ms following a click stimulus. The responses obtained were decomposed into basic waveforms by means of adaptive approximations using a matching pursuit algorithm. High-resolution time-frequency distributions of signal energy were calculated and showed three types of component: (1) purely evoked of duration less than 5 ms, (2) longer lasting and decaying, with exponentially decreasing amplitude, and (3) long lasting and stable. The distributions of the frequencies of components of different durations were similar, with most components falling within the 1-2 kHz interval. It is shown that the presence of long-lasting components may influence the estimation of the latency of evoked emissions, especially at higher frequencies where the evoked part has a very short duration.

Otoacoustic emissions evoked by 0.5 kHz tone bursts

The aim of this research is to extend previous studies of the time-frequency features of otoacoustic emissions (OAEs) using information about the properties of the signals at low frequencies. Responses to 0.5 kHz tone bursts were compared to OAEs that were evoked by click stimuli and by 1, 2, and 4 kHz tone burst stimuli. The OAEs were measured using 20 and 30 ms intervals between stimuli. The analysis revealed no differences in the time-frequency properties of 1, 2, and 4 kHz bursts measured using these two different acquisition windows. However, at 0.5 kHz the latency of the response was affected significantly if a shorter time window was used. This was caused by the fact that the response reached a maximum after an average time of 15.4 ms, and lasted a few milliseconds longer. Therefore, for this particular stimulus, the use of a 30 ms time window seems more appropriate. In addition, as an example of the possible application of low-frequency OAEs, signals were measured in patients suffering from partial deafness, characterized by steep audiograms with normal thresholds up to 0.5 kHz and almost total deafness above this frequency. Although no response to clicks was observed in these subjects, the use of 0.5 kHz tone bursts did produce OAEs.

Resonant modes in transiently evoked otoacoustic emissions and asymmetries between left and right ear.

A number of single-frequency resonant modes in click evoked otoacoustic emissions (OAEs) was investigated. The OAE modes were identified by means of an adaptive approximation method based on the matching pursuit (MP) algorithm. The signals were decomposed into basic waveforms coming from a very large and redundant dictionary of Gabor functions. The study was performed on transiently evoked otoacoustic emissions (TEOAEs) from left and right ears of 108 subjects. The correspondence between waveforms found by the procedure and resonant modes was shown (both for simulated noisy data and for single-person TEOAEs). The decomposition of TEOAEs made distinction between short and long-lasting components possible. The number of main resonant modes was studied by means of different criteria and they all led to similar results, indicating that the main features of the signal are explained on average by 10 waveforms. The same number of resonant modes for the right ear accounted for more energy than for the left ear.

Time–frequency analysis of linear and nonlinear otoacoustic emissions and removal of a short-latency stimulus artifact

Click-evoked otoacoustic emissions (CEOAEs) are commonly recorded as average responses to a repetitive click stimulus. If the click train has constant polarity, a linear average results; if it contains a sequence of clicks of differing polarity and amplitude, a nonlinear average can be calculated. The purpose of this study was to record both protocols from the same set of ears and characterize the differences between them. The major features of CEOAEs were similar under both protocols with the exception of a region spanning 0-5 ms in time and 0-2.2 kHz in frequency. It was assumed that the signal derived from the linear protocol was contaminated by stimulus artifact, and so a simple procedure was used--involving high-pass filtering and time-windowing--to remove components of this artifact. This procedure preserved the short-latency, high-frequency responses; it also produced a marked similarity in the time-frequency plots of recordings made under the two protocols. This result means it is possible to take advantage of the better signal-to-noise ratio of the linear data compared to its nonlinear counterpart. Additionally, it was shown that CEOAEs recorded under the linear protocol appear to be less dependent on the presence of spontaneous otoacoustic emissions (SOAEs).

Tone-burst and click-evoked otoacoustic emissions in subjects with hearing loss above 0.25, 0.5, and 1 kHz.

Objective: The aim of this study was to assess the diagnostic value of click-evoked otoacoustic emissions (CEOAEs) and tone-burst evoked otoacoustic emissions (TBOAEs) in identifying the residual hearing of subjects with partial deafness (PD)—a condition in which subjects have normal thresholds at low frequencies and severe-to-profound sensorineural hearing loss at high frequencies. Design: Otoacoustic emissions (OAEs) were measured in 23 subjects with severe-to-profound sensorineural hearing loss, 46 with PD, and 15 with normal hearing (NH). The PD subjects were divided into three subgroups according to the frequency at which hearing loss started: PD250 (NH up to 250 Hz)—20 ears; PD500 (NH to 500 Hz)—18 ears; and PD1000 (NH up to 1000 Hz)—20 ears. Standard-click stimuli, and 0.5- and 1-kHz tone bursts (average amplitude 80 ± 3 peak dB SPL, nonlinear averaging protocol), were used. The tone bursts were four cycles long with equal rise/fall times and no plateau. Recordings were performed in two acquisition windows: a standard one 20-msec wide for clicks and 1-kHz tone bursts, and one 30-msec wide for 0.5-kHz tone bursts. OAE response levels, signal-to-noise ratios, and reproducibility were examined in terms of wide-band responses and in terms of half-octave bands centered at 0.5 and 1 kHz. Receiver operator characteristic analysis was used to determine which type of stimuli best differentiates partially deaf subjects from subjects with severe-to-profound sensorineural hearing loss through the range 125 to 8000 Hz. Results: Nearly all recordings from groups PD500 and PD1000 showed 0.5-kHz TBOAEs. By contrast, 1-kHz TBOAEs and CEOAEs were generally found only in the PD1000 group. It was also possible to detect 0.5-kHz TBOAE responses in approximately 50% of ears from the PD250 group. Receiver operator characteristic analysis demonstrated that click and 1-kHz tone bursts provide a good diagnostic measure of residual hearing even when hearing loss starts as low as 1 kHz; moreover, the 0.5-kHz TBOAE could identify residual hearing when hearing loss started just > 0.5 kHz, a situation in which clicks failed to elicit a response. In the case of partially deaf subjects, diagnosis was more accurate when OAEs were analyzed by 1/2 octave bands. Furthermore, the use of a 0.5-kHz tone burst gave responses in the highest number of subjects, even when there were hearing losses in neighboring bands. Conclusions: The results of this study indicate that a 0.5-kHz TBOAE is a more powerful test than the standard CEOAE when cochlear function at low frequencies is of interest. The 0.5-kHz TBOAE may be used to identify partial deafness in patients who generally fail to show a response to the commonly used clicks. In addition, use of 1/2 octave-band filtering can increase the reproducibility and power of the test.

Otoacoustic emissions in neonates measured with different acquisition protocols

OBJECTIVE The purpose of the study was to investigate the properties of neonatal transiently evoked otoacoustic emissions (TEOAEs) recorded with three most popular stimulation protocols. Differences between the recorded TEOAEs with and without spontaneous otoacoustic emissions (SOAEs), were also assessed. In addition two more issues were addressed: (i) the effect of windowing on the TEOAE responses; and (ii) the contribution of the TEOAE segment from 12.5 to 20 ms to the overall TEOAE response. METHODS TEOAEs and SOAEs were recorded from 50 normal hearing neonates using linear, non-linear, QuickScreen and standard synchronized SOAE stimulation protocols. Global and half-octave-band values of TEOAE reproducibility and response level were used to assess statistical differences in the recorded responses. Furthermore protocol differences were evaluated in different recording windows from 2.5 to 12.5 and 12 to 20 ms. RESULTS Data from the linear protocol presented TEOAE parameters with the highest values. The differences between recordings with longer and shorter acquisition windows were especially apparent in 1-1.4 kHz frequency range. Furthermore the data have shown that the low frequency TEOAE components are a significant part of the TEOAE response, especially in ears without SOAEs. CONCLUSIONS The results suggest that TEOAE protocols using short recording windows (i.e. QuickScreen) can be used only for a fast detection of a valid TEOAE. For more sophisticated clinical analyses the standard 20 ms TEOAE recording window is more appropriate. The presence of SOAEs significantly influences TEOAEs. Ears with SOAEs presented higher values of TEOAE parameters especially in the 2-4 kHz range. On the other hand, in the ears without SOAEs low frequency components contribute more to the signal.

Satisfaction With Cochlear Implants in Postlingually Deaf Adults and Its Nonaudiological Predictors: Psychological Distress, Coping Strategies, and Self-Esteem.

Objective: A postlingually deaf patient who receives a cochlear implant (CI) acquires multiple benefits, not just audiological but also nonaudiological: improvement in quality of life, psychological well-being, and social interaction. The aim of the study was to ascertain the relationship between the CI satisfaction experienced by adult, postlingually deaf individuals and their level of psychological distress, stress coping strategies, and global self-esteem. We also considered sociodemographic variables (such as sex, age, education, marital/partner status, and employment/study status), variables related to their deafness, and their length of experience with a CI. Design: The study had a cross-sectional design in which participants were asked to fill in a mailed personal inquiry form seeking sociodemographic data and one question related to CI satisfaction, and the following questionnaires: General Health Questionnaire-28, the Brief Coping Orientation to Problems Experienced, and the Rosenberg Self-Esteem Scale. This study included 98 patients with postlingual deafness between 19 and 85 years old who had unilateral CIs. For some analyses, the patients were also divided into two groups: younger (⩽60 years) and older (>60 years). Two other subgroups were those with shorter CI experience (1 to 2 years) and those with longer CI experience (5 to 6 years). As an objective reference, speech perception scores in quiet and in noise were also used. Results: The majority of postlingually deaf subjects rated their CI satisfaction as high or very high, and this was at similar levels in younger and older subjects, as well as in those who had used CIs for either a short or a long time. CI satisfaction was not related to speech perception scores, duration of deafness, length of CI use, or other sociodemographic factors. Positive self-esteem, having less severe symptoms of depression, and the use of humor or self-distraction were conducive to CI satisfaction. Using a coping strategy of denial had a negative association with CI satisfaction. Coping strategies and symptoms of mental distress varied between younger and older subjects. For younger subjects, higher CI satisfaction was associated with lower severity of depressive symptoms, whereas for the elderly, higher CI satisfaction was associated with less severe social dysfunction symptoms. Over the years of using a CI, the same strategy may have a different psychological function in providing satisfaction: for example, venting, which in the group with a short CI experience is negatively correlated to satisfaction, is positively correlated to satisfaction for those with longer CI experience. Conclusions: The results show that psychological factors—self-esteem, distress, and coping strategies—are important for CI satisfaction in postlingually deaf CI users. The results point to advantages in widening the availability of various tailored forms of psychological intervention for patients with postlingual deafness after receiving a CI.