Biomedical subjects

G Keidser

Publications and source records attributed to G Keidser.

13 recordsLinked to original sources

PubMed1999

An efficient, adaptive method of measuring loudness growth functions.

This paper presents a new categorical loudness scaling procedure that differs from previously published loudness scaling procedures by (i) adaptively selecting a new set of levels for each new sequence, (ii) deriving levels that are equispaced on the loudness scale, and (iii) using a continuous scale with few labels. A major advantage of the adaptive procedure is that the individual dynamic range need not be measured prior to loudness testing. The adaptive procedure proved to be time efficient and to produce complete loudness functions from Not heard to Uncomfortably loud for normal hearing and hearing impaired subjects. The pattern of short-term and long-term reliability was similar to that reported for non-adaptive loudness scaling procedures. Three presentations produced a stable loudness function. Normative curves for one octave babble-noise at six test frequencies are presented and compared to normative data obtained with a selection of published categorical scaling procedures.

Adolescent↗

PubMed1996

Selecting different amplification for different listening conditions.

Ten subjects with diverse hearing impairment trialled a multiple-memory hearing aid in everyday life and in a paired-comparison laboratory test. Five subjects evaluated systematic variations of the compression characteristic in two bands, around an individually fitted response, using the Resound PHS-ED instrument. Another five subjects evaluated systematic variations of the frequency response characteristic, around an individually fitted NAL response, using the Widex Quattro B hearing device. In all, five subjects showed benefit from multiple amplification schemes. Both variations in compression and frequency response characteristics were used for different background noises and/or response criteria. There were some similarities across subjects in the choice of amplification schemes in the paired-comparison test. However, data were not sufficient to derive a relationship between preferred amplification schemes and listening conditions. For a number of audiometric and disability-related parameters, no differences were found between those who selected multiple amplification schemes and those who did not.

Adult↗

PubMed1996

Guidelines for fitting multiple memory hearing aids.

Fitting guidelines to determine candidacy for multiple memory hearing aids and the choice of amplification for each memory are devised by reviewing studies on the selection of amplification for different listening conditions. The guideline for determining candidacy comprises three factors: (1) difficulty hearing in acoustically diverse conditions, (2) an average high-frequency hearing loss greater than about 55 dB HL, and (3) ability to vary the low-frequency gain by at least 5 dB. People who meet all three criteria are highly likely to benefit from multiple memories. People who meet criteria 1 and 2 or 1 and 3 are possible candidates. The guideline for determining the amplification characteristics needed for each memory also enables the fitter to determine the number of memories needed. The following recommendations for amplification characteristic for various listening conditions are based on the literature review: linear amplification with the prescribed National Acoustic Laboratories' (NAL) frequency response is recommended for listening to speech in quiet; substantial high-frequency compression is recommended for ease of understanding two voices that differed by 10 dB in overall level; a linear response steeper than the NAL response is recommended for ease of understanding speech in a low-frequency background noise; low-frequency compression is recommended to reduce annoyance of low-frequency background noise; and a linear response flatter than the NAL response is recommended for listening in high-frequency background noise, and possibly for listening to music.

Equipment Design↗

PubMed1995

Candidates for multiple frequency response characteristics.

This study examined what types of subjects may benefit from the use of multiple memory hearing aids that offer variation in their frequency response characteristics. Thirty subjects with varied degrees and configurations of hearing loss compared an individually prescribed frequency response (NAL) and two variations in which the real-ear response slope was either increased (more high-frequency emphasis) or decreased by about 3 dB/octave over the range from 500 Hz to 4000 Hz. The evaluations consisted of paired comparison judgments of pleasantness and of ease of understanding speech, in quiet and in three background noises with substantially different acoustic spectra (traffic noise, speech babble, and high-frequency noise). Twelve of the 30 subjects selected different frequency responses for different background noises and/or for different response criteria. These subjects were characterized as having the more severe high-frequency hearing losses (averaged across 2000, 3000, and 4000 Hz). They also tended to be those for whom the three frequency responses provided the greatest variation in real-ear low-frequency gain. (Despite substantial electronic variations, some subjects received only small variations in real-ear gain at the low frequencies). When subjects chose a different response for different conditions, they tended to prefer responses for which the slope was negatively related to the spectrum of the stimulus. This was true for both response criteria. The conclusion is that hearing aid users with substantial high-frequency losses, and who can be fitted with sufficient variation in the low-frequency real-ear gain, have the potential to benefit from having a choice of frequency response characteristics.

Adolescent↗

PubMed1995

The relationship between listening conditions and alternative amplification schemes for multiple memory hearing aids.

OBJECTIVE: The aim of this study was to determine a relationship among selected listening conditions and amplification schemes that could be provided in a multiple memory hearing aid. DESIGN: The study consisted of three laboratory tests: 1) A screening test to select hearing impaired subjects who appeared to benefit from multiple amplification schemes. 2) A category scaling test to rank 16 amplification schemes in 15 listening conditions. The 16 schemes were simulated with a digital master hearing aid and comprised 5 linear systems and 11 compression characteristics. The 15 listening conditions comprised 6 listening environments combined with 2 or 3 response criteria. 3) A paired comparison test in which the two highest ranked amplification schemes were evaluated together with a reference linear frequency response (NAL) in a round-robin test. RESULTS: The screening test demonstrated that 21 hearing impaired people out of 25 with mild or moderate, flat or gently sloping hearing losses appeared to benefit from multiple amplification schemes. Age or audiometric factors did not serve to discriminate between those who selected different schemes and those who did not. In general, the NAL-response was preferred or was as good as any other for listening to speech in quiet, speech in reverberation, speech in babble-noise, and for naturalness of all listening environments. The subjects consistently selected an amplification scheme other than the NAL-response for four specific listening conditions. The findings suggest that substantial high-frequency compression is preferred for the ease of understanding multiple talkers, whose voices differ in overall level, in quiet environments. The annoyance of low-frequency background noise can be reduced by low-frequency compression, whereas a frequency response steeper than the NAL-response makes it easier to understand speech in low frequency background noise. Finally, a frequency response flatter than the NAL-response can be used to make a high-frequency background noise sound less annoying. CONCLUSION: Hearing aid users with mild or moderate, flat or gently sloping hearing losses, fitted with equal and sufficient variation in amplification, prefer different amplification schemes depending on the number of talkers, the background noise and the response criterion.

Adult↗

PubMed1994

Articulation index transfer functions for 'DANTALE' (200 monosyllabic words).

Articulation Index (AI) transfer functions are presented for a Danish speech test (DANTALE) which consists of 200 monosyllabic words. The transfer functions represent three different scoring methods. Using a word score, DANTALE is found to be more difficult on speech recognition than rhyme tests, unfamiliar sentences and 256 phonetically balanced (PB) monosyllabic words.

Acoustic Stimulation↗

PubMed1993

Normative data in quiet and in noise for "DANTALE"--a Danish speech material.

For a new Danish speech material, which consists of eight word lists, normative speech recognition curves are presented and the equivalence of the different lists is examined. The normative curves were obtained in quiet and in noise using three scoring methods, based on 25, 75 and 80 scoring units, respectively. Significant subject variations were found with respect to all three scoring methods due to different ways of processing the perceived sounds. Based on the test-retest SD, the two alternative scoring methods of 75 and 80 scoring units were found to be slightly more reliable than the usual word score of 25 scoring units. The equivalence of the eight word lists was accepted in quiet. Presented in noise, the difference between the lists was significant due to a different distribution of words with an initial "s" in the word lists and a significant difference in the spectra of the speech and the noise in the higher frequencies.

Acoustic Stimulation↗

PubMed1993

The design and testing of a noise reduction algorithm based on spectral subtraction.

Three noise reduction algorithms based on amplitude subtraction were designed and used to process speech mixed with babble noise in two signal-to-noise ratios. The estimation of the noise-magnitude spectrum was performed with a novel synchro method, which exploits specific characteristics of the speech signal. The unprocessed and processed signals were evaluated psychoacoustically by means of a four-alternative-forced choice test with monosyllabic words (minimal pairs) in carrier phrases. The testing was carried out on groups of normally hearing and hearing-impaired subjects and the long-term power spectra of the processed signals were shaped to be essentially identical with those from the corresponding unprocessed signals. For the hearing-impaired subjects all signals were spectrally shaped according to the POGO-fitting rule. None of the algorithms improved speech intelligibility for any group of listeners and no change in the overall pattern of confusion was observed.

Acoustic Stimulation↗

PubMed1993

Evaluation of a noise reduction method--comparison between observed scores and scores predicted from STI.

Speech was mixed with different noise signals and then processed according to the well-known noise reduction method of 'spectral subtraction'. Three different algorithms were examined. The speech signals were subjected to a four alternative forced choice (4AFC) test. Both the processed and unprocessed signals were evaluated psycho-acoustically and objectively. Speech intelligibility was measured with the 4AFC test by presenting the signals via headphones to a group of normal-hearing and to a group of hearing-impaired listeners. The intelligibility scores were compared with the intelligibility scores predicted from a modified version of the Speech Transmission Index (STI). It appeared that although the noise reduction algorithms reduced the noise level, they did not improve the measured speech intelligibility, either for normal-hearing or for hearing-impaired listeners. This, however, was inconsistent with the scores estimated from STI, which erroneously predicted a significant improvement in intelligibility due to the noise reduction processing.

Acoustic Stimulation↗

PubMed1991

Speech recognition in young and elderly normal-hearing listeners in a closed response test.

Speech recognition has been measured in a group of elderly (age range 55-70 years) subjects with normal hearing. The results from this group were compared with the results from a young, normal-hearing group (age 19-36 years). The two groups were matched as regards education, occupation and dialect. The test material used was a four-alternative closed-response speech test composed of monosyllabic words. Each word was presented in a carrier sentence and masked by a speech-spectrum shaped modulated background noise. No significant difference was found between the speech recognition in the two groups.

Aged↗

PubMed1991

Computerized measurement of speech intelligibility. I. Development of system and procedures.

An experimental system for the measurement of speech intelligibility has been developed. It uses a Personal Computer (PC), together with appropriate software to handle playback of test words in carrier phrases, presented in a 'closed response' test condition. Information about the intelligibility, based on the correct responses and the confusions, is immediately available due to simultaneous collecting and sorting of subjects' responses. The system works satisfactorily and reliably and has been well received by experimenters as well as by adult test subjects in the age range 18-70 years. From a new Danish standard speech material for audiological purposes, a Multiple Choice speech intelligibility test has been devised. The test is called 4AFC (Four Alternative Forced Choice) and is based on monosyllabic words with consonant confusions. Normative data for the 4AFC test, obtained with the computerized system, are presented in an accompanying paper.

Adolescent↗

PubMed1991

Computerized measurement of speech intelligibility. II. Normative data from a 'closed response' test.

A Danish Four Alternative Forced Choice (4AFC) test was presented to normal-hearing and cochlearly hearing-impaired listeners in two background noises: a modulated, speech-spectrum-shaped noise and an 8-persons babble noise. At the presentation to the hearing-impaired subjects the test signals were given a frequency-dependent amplification in accordance with the POGO-fitting method. Normative data are presented which indicate that 4AFC is a valid test in spite of lack of homogeneity between the alternatives allowed. On the other hand, a learning effect is demonstrated which affects the reliability. A computer-assisted analysis of the obtained consonant confusions reveals a predominance of confusions among initial consonants having the same voicing.

Adult↗

PubMed1990

Prediction of intelligibility of non-linearly processed speech.

Speech in various noise backgrounds was processed through four different non-linear devices and the intelligibility of the processed signals was predicted from the Speech Transmission Index (STI). A novel calculation method was applied in order to avoid artifacts. Running speech was used as input signal and STI was calculated from the envelopes of the squared, noise-free speech signal and of the processed, squared, noisy signal in 23 critical bands. In situations with linearly processed speech and a stationary background noise, this calculation method gives results identical with the procedure described by Steeneken & Houtgast (6). However, in a number of situations with non-linearly processed speech, or a time varying background noise level, the calculation method used here is preferable. The predictions were evaluated in a psycho-acoustic listening test and the predictions agreed well with the listening test results.

Hearing Aids↗