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Biomedical subjects

J Koehnke

Publications and source records attributed to J Koehnke.

13 recordsLinked to original sources
PubMed1998

Effects of sensorineural hearing loss on interaural discrimination and virtual localization.

Cross-frequency binaural processing was investigated in listeners with normal hearing (NH) and with bilateral high-frequency sensorineural hearing impairment (IH). In experiment 1 just-noticeable-differences for interaural time and interaural intensity were measured using 1/3-octave narrow-band noises (NBNs) centered at 0.5 and 4 kHz. These stimuli were presented in isolation and in different cross-frequency interaural combinations. IH listeners displayed the best interaural time discrimination when the 0.5-kHz NBN was dichotic and the best intensity discrimination when both bands were dichotic. Both NH listeners (time) and IH listeners (time and intensity) displayed the poorest interaural discrimination when the NBNs were presented simultaneously with interaural differences in only the 4-kHz NBN (0.5 kHz NBN dichotic). Localization accuracy was measured in experiment 2 using the 0.5- and 4-kHz NBNs in isolation and with 0.5-kHz target/4-kHz interferer and 4-kHz target/0.5-kHz interferer conditions. Best localization of NH and IH subjects was seen for the 0.5-kHz target, with or without an interferer. Poorest localization of IH subjects was observed for the 4-kHz target and 0.5-kHz interferer. Results suggest that for these IH subjects, localization is most difficult when they are forced to rely on interaural information in a higher-frequency region with conflicting interaural information at low frequencies.

Adult↗
PubMed1998

Spatial audiometry: detection of spondaic words in noise.

It is important to select appropriate stimuli and test conditions for developing standardized spatial audiometric tests. In three experiments, binaural detection thresholds (BDTs) for a target signal, located at either 0, 45, 90, 135, 180, 225, 270, or 315 degrees azimuth, were measured in the presence of a masker positioned at one of these eight locations. Target signals included spondaic words from the CID W-1 list. The masker was speech spectrum noise (SSN) or multitalker noise (MTN) presented at a constant level (65 dBA). Bekesy tracking was used to measure BDTs in listeners with normal hearing. Results indicate that BDTs are significantly influenced by the (a) angular separation between the target and noise source and (b) choice of spondaic words used as target stimuli. BDTs for various spondaic words differed as much as 13 dB for a given angular separation. BDTs measured in SSN and MTN for otherwise identical test conditions differed less than 3 dB. A single spondaic word appears to be appropriate for spatial audiometric tests of detection. Nonsignificant differences between masked BDTs obtained for SSN and MTN noises indicate that for spatial detection, the masking effects of these noises are comparable. These results indicate that the development of a clinical test of spatial detection should include the use of SSN and a single spondaic word, with detection being measured for a set of four or five signal and noise source configurations.

Adolescent↗
PubMed1996

A procedure for testing speech intelligibility in a virtual listening environment.

OBJECTIVE: The development of a test of virtual speech intelligibility in noise that enables assessment in typical, everyday listening situations. To eliminate extraneous confounding factors, digital signal processing was incorporated to simulate listening environments and source locations and allow presentation of stimuli via earphones. DESIGN: Source-to-eardrum transfer functions measured on KEMAR for various source locations in anechoic and reverberant environments were used to process monosyllabic words and speech-spectrum noise. Speech intelligibility was measured for three speech and noise configurations in two environments using an adaptive procedure to determine the signal-to-noise (S/N) ratio for 50% intelligibility. RESULTS: Normal-hearing listeners achieved 50% intelligibility of monosyllabic words at significantly lower S/N ratios in a virtual anechoic environment than in a virtual reverberant environment. Speech intelligibility improved significantly in both environments when the speech and noise sources were separated, but the intelligibility gain in the anechoic environment was four times larger than in the reverberant environment. CONCLUSIONS: This test is easy to administer and score, and it provides a means for measuring: 1) the effects of separating speech and noise sources and 2) the effects of reverberation on speech intelligibility in noise while eliminating confounding factors such as calibration.

Hearing↗
PubMed1995

A test of virtual auditory localization.

OBJECTIVE: The purpose of this study was to evaluate a test of virtual auditory localization including assessment of its ease of administration and its sensitivity to differences in binaural performance in children and adults. This test eliminates many potential problems inherent in any free-field localization test such as calibration problems, problems replicating source and listener locations, and issues associated with head movements. DESIGN: Binaural performance was measured using the virtual localization test and a simple binaural detection task, the masking-level difference (MLD), for three groups of subjects: adults, children with a negative history of otitis media, and children with a positive history of otitis media. There were five subjects in each group. The adults were all student volunteers; the children were recruited first and subsequently placed into groups based on their medical histories obtained from their physicians and parental reports. RESULTS: Results indicate that this test of virtual auditory localization is useful for measuring binaural performance in children and adults and is sensitive to differences in binaural processing. Performance of the adults and children with a negative history of otitis media was comparable on both of the binaural tests, and on the binaural detection task, was similar to that reported in the literature for normal-hearing listeners; but the children with a positive history of otitis media performed more poorly on both tests. CONCLUSIONS: The results of this study indicate that the virtual localization test described here is easy to administer to children and adults. The signal processing techniques used in this virtual auditory localization test lend themselves to straightforward comparisons across different laboratories and clinics and make this test a potentially useful clinical tool. The development of such a clinical test is currently under study.

Adult↗
PubMed1995

Effects of reference interaural time and intensity differences on binaural performance in listeners with normal and impaired hearing.

OBJECTIVE: The purpose of this research was to measure the effects of reference interaural time and intensity differences on binaural performance in listeners with normal hearing and impaired hearing for a number of different binaural tests. Experiment 1 measures the dependence of binaural detection and discrimination performance on reference interaural intensity differences (IID) in the range of +/- 12 dB for listeners with normal hearing. Experiment 2 extends these measures to include reference IIDs and interaural time differences (ITD) for two groups of listeners with normal hearing with offsets in the range of +/- 12 dB and +/- 300 microseconds (group 1) and +/-24 dB and +/- 600 microseconds (group 2). Experiment 3 includes the same tests and conditions as experiment 2 for listeners with various hearing impairments. DESIGN: A set of psychophysical measurements was completed on 11 listeners with sensorineural hearing losses and 9 listeners with clinically normal hearing. The primary measurements were a set of four binaural detection and interaural discrimination thresholds measured for two 1/3-octave bands of Gaussian noise, one centered at 500 Hz and the other at 4000 Hz. Specifically, we measured binaural (antiphasic) detection thresholds for tones centered in the masking noise as well as the just-noticeable differences (JNDs) in IID, ITD, and interaural cross-correlation (ICC) for each of the noise-band stimuli. All measurements were done for a number of combinations of reference IID and ITD. In addition to these primary measurements, several other measurements were made on each subject, including monaural absolute thresholds, monaural intensity discrimination, monaural masked thresholds, and intensity levels required for interaurally balanced loudness and for a centered image. All measurements were made using a relatively quick, adaptive procedure. RESULTS: For the subjects with normal hearing, measured dependencies of the IID and ITD JNDs using noise stimuli on reference ITD and IID are different from those previously reported for tonal stimuli. Binaural performance of the listeners with impaired hearing varies widely across subjects and tests and is generally poorer than that of listeners with normal hearing. CONCLUSIONS: On the basis of the results for subjects with hearing impairments, we have reached several conclusions. First, the results for the binaural measurements cannot be explained in terms of available monaural audiometric and psychophysical measurements on these subjects. Second, the subjects' binaural abilities show no significant improvement with any combinations in the reference values of ITD and IID, providing negative evidence for the hypothesis that degraded performance for some subjects may be due to internal interaural offsets in ITD or IID. Third, the hypothesis that binaural detection and ICC discrimination are related, suggested by Durlach et al (1986), is generally supported. Fourth, binaural detection performance is not simply explained in terms of sensitivities to ITD and IID.

Adolescent↗
PubMed1992

Frequency dependence of binaural performance in listeners with impaired binaural hearing.

Binaural performance was measured as a function of stimulus frequency for four impaired listeners, each with bilaterally symmetric audiograms. The subjects had various degrees and configurations of audiometric losses: two had high-frequency, sensorineural losses; one had a flat sensorineural loss; and one had multiple sclerosis with normal audiometric thresholds. Just noticeable differences (jnd's) in interaural time, interaural intensity, and interaural correlation as well as detection thresholds for NoSo and NoS pi conditions were obtained for narrow-band noise stimuli at octave frequencies from 250-4000 Hz. Performance of the impaired listeners was generally poorer than that of normal-hearing listeners, although it was comparable to normal in a few instances. The patterns of binaural performance showed no apparent relation to the audiometric patterns; even the two subjects with similar degree and configuration of hearing loss have very different binaural performance, both in the level and frequency dependence of their performance. The frequency dependence of performance on individual tests is irregular enough that one cannot confidently interpolate between octaves. In addition, it appears that no subset of the measurements is adequate to characterize the performance in the rest of the measurements with the exception that, within limits, interaural correlation discrimination and NoS pi detection performance are related.

Acoustic Stimulation↗
PubMed1992

Effects of roving level variation on monaural detection with a contralateral cue.

Monaural detection with a contralateral cue (MDCC) was measured with and without a 20-dB overall roving level to determine the contribution of loudness to performance on this task. Psychometric functions were obtained for three normal-hearing subjects as a function of the signal-to-noise ratio for pure-tone and 1/3-oct noiseband signals at 500 and 4000 Hz with a wideband noise masker. At 4000 Hz, the roving level degrades performance for the narrow-band noise signal by about 5.3 dB. In addition, the presence of the contralateral cue degrades performance for both the pure-tone and narrow-band noise signals at 4000 Hz by 3 to 6 dB. At 500 Hz, however, performance is not affected by the roving level, and is improved by 3 to 6 dB by the contralateral cue. These results indicate that loudness is being used as a cue only for detection of the 4000-Hz narrow-band noise.

Acoustics↗
PubMed1991

Fringed correlation discrimination and binaural detection.

Results are reported from a series of binaural detection and interaural correlation discrimination experiments at 500 Hz. The experiments include fringed correlation discrimination in which the correlation change is restricted to a narrow (38 Hz) target band of frequencies and the reference correlation is maintained in a fringe band of frequencies. This experiment is designed to be analogous to a detection experiment with a narrow-band target; in both cases the correlation changes only inside the target band. A simplified theoretical framework is used to compare the results of the detection and correlation discrimination experiments. Results are consistent with the notion that binaural detection and interaural correlation discrimination are effected by a common mechanism when the reference correlation is unity (as in the NoS pi case). When the reference correlation is zero (as in the NuSo case), detection performance is significantly better than predicted from the measured ability to discriminate interaural correlation.

Attention↗
PubMed1989

Range effects in the identification of lateral position.

Experiments on the identification of interaural time and interaural amplitude differences were conducted to evaluate the effects of stimulus range on identification performance. Three stimulus sets, large range (LR), small-range center (SRC), and small-range side (SRS), were used in experiments on interaural time and amplitude identification. As expected, data for both sets of measurements show worse resolution for LR than SRC or SRS, demonstrating that the ability to distinguish between two fixed interaural differences can be strongly influenced by the total range of such differences in the stimulus set.

Auditory Perception↗
PubMed1987

Masking effects in binaural detection and interaural time discrimination.

This study was designed to investigate the effects of masker level and frequency on binaural detection and interaural time discrimination. Detection and interaural time discrimination of a 700-Hz sinusoidal signal were measured as a function of the center frequency and level of a narrow-band masking noise. The masker was a continuous, diotic, 80-Hz-wide noise that varied in center frequency from 250 to 1370 Hz. In the detection experiment, the signal was presented either diotically (NoSo) or interaurally phase reversed (NoS pi). In the interaural time discrimination experiment, the signal level needed to discriminate a 30-microseconds interaural delay was measured. As would be expected, the presence of the masker has a greater effect on NoSo detection than NoS pi detection, and for masker frequencies at or near the signal frequency. In contrast, interaural time discrimination can be improved by the presence of a low-level masker. Also, performance improves more rapidly as the signal/masker frequency separation increases for NoSo detection than for interaural time discrimination and NoS pi detection. For all three tasks, significant upward spread of masking occurs only at the highest masker level; at low masker levels, there is a tendency toward downward spread of masking.

Adult↗
PubMed1986

Performance in several binaural-interaction experiments.

The relationship between interaural correlation discrimination and binaural detection was investigated using common experimental procedures and common subjects. Psychometric functions were obtained for four normal-hearing subjects at 500 and 4000 Hz using third-octave noise signals for the correlation discrimination experiment, and pure-tone signals and third-octave noise maskers for the detection experiment. Results from these two measurements, which were compared by expressing the signal-to-noise ratio as an equivalent change in interaural correlation, support the idea that interaural correlation discrimination and binaural detection are closely related. Since large intersubject differences in binaural performance were observed in these experiments, interaural-time, interaural-intensity, and monaural-intensity discrimination were measured in a second experiment. The results of the second experiment show large intersubject differences for the interaural tasks, but not for the monaural task.

Acoustic Stimulation↗
PubMed1985

The comparative effects of signal sensation level and sound-pressure level on interaural time discrimination.

A series of experiments was performed to examine the extent to which precision of interaural time discrimination depends on the sound-pressure level (SPL) and/or sensation level (SL) of the signal. All experiments used a tone burst signal and a continuous white noise masker, which was either diotic or interaurally phase reversed. Results of the first experiment indicate that (1) at equal signal SLs, interaural time and intensity discrimination is more precise when measured with the added diotic noise, and (2) addition of the phase reversed noise, previously shown to cause less precise interaural time discrimination, has a similar effect on interaural intensity discrimination. In the second experiment, interaural time JNDs for a signal of constant SPL were measured as a function of noise level. Results show that a low-level diotic noise can benefit interaural time discrimination, particularly at 500 Hz. The third and fourth experiments were performed to measure interaural time discrimination as a function of increasing signal SPL but constant signal-to-noise ratio. The data show the JND decreasing with increasing signal SPL at nearly the same rate with or without the added noise, indicating that an increase in signal-to-noise ratio is not necessary for improved discrimination.

Auditory Perception↗