Wyniki wyszukiwania - BazTech

1

Loudness Functions and Binaural Loudness Summation in Bilateral Cochlear Implant Users

Kordus M., Zera J.

Archives of Acoustics

|

2017

|

Vol. 42, No. 3

351--364

EN

Loudness functions and binaural loudness summation was investigated in acoustically stimulated bilaterally implanted cochlear implant users. The study was aimed at evaluating growth of loudness functions and binaural loudness summation in cochlear implant subjects as a function of stimulus presentation level at different frequencies. Loudness was assessed using a rating procedure on a scale of 0 to 100. Three experimental conditions were tested: monaural right, monaural left and binaural, each with bands of noise with center frequencies of 0.25, 1, and 4 kHz. Fifteen implanted and five normal-hearing subjects (control group) participated in the experiments. Results demonstrated large variability in the slopes of the loudness functions and the presence of loudness summation in bilateral cochlear implant users, with large individual differences among subjects.

2

Effects of Low- and High-Frequency Side Bands of Notched Noise on Masking and Auditory Filter Shape at Very High Frequencies

Kordus M., Kowalewski B.

Archives of Acoustics

|

2015

|

Vol. 40, No. 3

329--336

EN

This paper is concerned with the determination of the auditory filter shape using the notched noise method with noise bands symmetrically located above and below a probe frequency of 10 kHz. Unlike in the classical experiments conducted with the use of Patterson method the levels as well as power spectrum densities of the lower and upper component bands of the notched noise masker were not the same and were set such as to produce the same amount of masking at the 10-kHz frequency. The experiment consisted of three conditions in which the following values were determined: (I) the detection threshold for a 10-kHz probe tone in the presence of a noise masker presented below the tone’s frequency; (II) the level of a noise masker presented above the 10-kHz probe tone frequency, at which the masker just masked the probe tone, (III) the detection threshold for a probe tone in the presence of a notched-noise masker. The data show a considerable amount of variability across the subjects, however, the resulting frequency characteristics of the auditory filters are consistent with those presented in the literature so that the Equivalent Rectangular Bandwidth is less than 11% of their centre frequency.

3

An Influence of Directional Microphones on the Speech Intelligibility and Spatial Perception by Cochlear Implant Users

Kordus M., Tyler R. S., Żera J., Oleson J. J.

Archives of Acoustics

|

2015

|

Vol. 40, No. 1

81--92

EN

The objective of the study is to assess the hearing performance of cochlear implant users in three device microphone configurations: omni-directional, directional, and beamformer (BEAMformer two-adaptive noise reduction system), in localization and speech perception tasks in dynamically changing listening environments. Seven cochlear implant users aided with Cochlear CM-24 devices with Freedom speech processor participated in the study. For the localization test in quiet and in background noise, subjects demonstrated significant differences between different microphone settings. Confusion matrices showed that in about 70% cases cochlear implant subjects correctly localized sounds within a horizontal angle of 30–40◦ (±1◦ loudspeaker apart from signal source). However localization in noise was less accurate as shown by a large number of considerable errors in localization in the confusion matrices. Average results indicated no significant difference between three microphone configurations. For speech presented from the front 3 dB SNR improvements in speech intelligibility in three subjects can be observed for beamforming system compared to directional and omni-directional microphone settings. The benefits of using different microphone settings in cochlear implant devices in dynamically changing listening conditions depend on the particular sound environment.

4

Effect of cochlea damage on the detection of difference tone in signal envelope

Kordus M.

Archives of Acoustics

|

2006

|

Vol. 31, No. 4

551-554

EN

Recent studies have demonstrated that the detection of complex temporal envelopes relies on the perception of a distortion component generated by cochlear and postcochlear (central) nonlinearity. In the present study, 4-kHz carrier was modulated by tones f1 and f2 to produce the difference tone f3=f2-f1 in the amplitude modulation domain. Detection thresholds for canceling tone f3 were obtained for subjects with normal-hearing and hearing-impaired subjects. In three experimental conditions, monaural and binaural presentation of tones was used to test possible central origin of the nonlinearity in modulation domain. Modulation depth at threshold was measured as a function of the phase of the canceling component f3 varied from 0° to 270° in 45° steps. Results showed that level of canceling tone f3 was phase dependent at all signal frequencies. Thresholds for normal-hearing and hearing-impaired subjects were lower for the in-phase condition than for the antiphase condition. Results demonstrated that cochlear damage had no large effect on the nonlinearity in the AM envelope indicating that the distortion component must be generated by a more central non linear effects.

5

Binaural masking of amplitude modulation

Kordus M., Sęk A., Kociński J.

Archives of Acoustics

|

2005

|

Vol. 30, No. 1

5-17

EN

A new concept concerned with the transformation of acoustic stimuli in the auditory system postulates the existence of a form of spectral analysis applied to the amplitude changes of the stimuli. It is assumed that this analysis takes place in the so-called modulation filters, i.e. bandpass linear filters tuned to different rates of the amplitude changes. The most striking argument supporting this idea is an effect of masking in the amplitude modulation domain whose nature can be easily explained basing on this concept. As the modulation filters are situated on the higher levels of the auditory system, it is also assumed that this form of masking is entirely a central process. However, most of the studies concerned with masking in the modulation domain used monaural listening only. Therefore, the main purpose of the presented here experiments was to investigate whether this type of masking is entirely a central process. Using a Three-Alternative Forced-Choice (3AFC) procedure the binaural and monaural masked thresholds of amplitude modulation were determined. A sinusoidal carrier at a frequency of 4 kHz was amplitude modulated by a specially designed band of noise characterized by a very low value of the crest factor, which was used as a masking signals. Different bandwidths of the modulating masking signals were used as well as different center frequencies to investigate whether the masking patterns in the modulation domain depend on the masker bandwidth and its center frequency. The modulating target (masked) signal was a pure tone at a frequency range from 2 to 256 Hz. Both modulating signals were applied to the same sinusoidal carrier signal. The most effective masking was noticed when the rate of the sinusoidal modulation was close to the center frequency of the masking signal or when it was in its spectral range and decreased outside of this range. The character of this dependence confirms the existence of some form of a frequency selectivity in the modulation rate domain similarly to the audible frequency domain. The thresholds for monaural and binaural listening were very close to each other. This implies that masking in the modulation domain is a central process.

6

Monaural and binaural detection thresholds of amplitude modulation

Kordus M., Sęk A.

Archives of Acoustics

|

2004

|

Vol. 29, no. 4

537-553

EN

This study is concerned with the amplitude modulation (AM) detection thresholds for monaural and binaural listening. In the first experiment, using a Two-Alternative Forced-Choice (2AFC) method with an adaptive procedure 2-up 1-down, the monaural and binaural AM detection thresholds were measured. Sinusoidal carrier at a frequency of 160, 500, 1000 or 4000 Hz was amplitude-modulated by a single sinusoidal modulator at a frequency of 4, 32, 64 or 128 Hz. Due to a significant intersubject scatter of the results it was impossible to estimate the difference between the thresholds determined for monaural and binaural presentation of the stimuli. Therefore, in the next experiment, psychometric functions for AM detection for both monaural and binaural listening were determined. This experiment was carried out for sinusoidal carriers at frequencies of 5000, 2000 and 6000 Hz and for sinusoidal modulator at frequencies of 4, 64 and 128 Hz. The results of this experiment showed a statistically significant difference between slopes of the psychometric function (after the percent of correct responses was converted to the detectability, d', domain) for monaural and binaural stimuli presentation. Assuming that the AM threshold coincided with d' = 1 it can be stated that monaural and binaural AM thresholds are significantly different.