Biomedical subjects

A Leijon

Publications and source records attributed to A Leijon.

6 recordsLinked to original sources

PubMed1992

Quantization error in clinical pure-tone audiometry.

The current clinical procedure for pure-tone audiometry was analysed for statistical measurement errors. Theoretically, the root-mean-square (RMS) error in a single threshold measurement is always greater than the standard deviation (SD) of measured intra-individual test-retest differences, divided by the square root of two. The RMS error includes an additional quantization component, caused by the finite step size between presented signal levels. In Monte-Carlo simulations with 2-dB and 5-dB steps the quantization error was negligible compared with other errors. Therefore, the single-test RMS error can be estimated with sufficient accuracy from the test-retest SD. The simulated single-test RMS error decreased from about 2.7 dB about 2.3 dB when the audiometric step size was reduced from 5 dB to 2 dB. Hearing thresholds appeared to be about 1.7 dB better with 2-dB steps than with 5-dB steps.

Acoustic Stimulation↗

PubMed1991

Hearing aid gain for loudness-density normalization in cochlear hearing losses with impaired frequency resolution.

A theoretical criterion for preliminary prescription of hearing aid gain and frequency response was formulated on the basis of Zwicker's loudness model, modified for impaired auditory frequency resolution in cochlear hearing losses. The procedure was designed to restore normal relative loudness contributions from each frequency band of input speech. Prescribed frequency responses had less steep bass cut than recommended by either the Prescription of Gain/Output or the National Acoustic Laboratories' procedures, regardless of various model assumptions. Prescribed overall gain depended on the loudness growth assumed in the model. In cases where auditory filters are wider than normal and loudness recruitment is complete, the procedure yielded a nonlinear relation between hearing aid gain and hearing loss: Required insertion gain (in dB) was 25 to 30% of hearing threshold loss (in dB HL) for mild to moderate losses, but this percentage increased for more severe impairments. For cases with incomplete loudness recruitment, the model prescribed that insertion gain should be 40 to 50% of hearing threshold loss for a wide range of impairments.

Amplifiers, Electronic↗

PubMed1991

Sound quality and speech reception for prescribed hearing aid frequency responses.

Four different prescriptions of hearing aid insertion gain versus frequency were validated with a group of 26 moderately hearing-impaired, elderly hearing aid users. Three prescriptions were based on calculating the loudness and articulation index (AI) for aided speech, and ranged from a frequency response with moderate high-frequency emphasis, restoring normal loudness for speech peaks, to a response with the greatest high-frequency emphasis, maximizing the AI. The fourth prescription was a well-established formula of the half-gain type. The frequency responses were evaluated by paired comparison ratings of the pleasantness and intelligibility of speech in noise, and by speech identification tests in noise. The subjects rated the flattest response as significantly more pleasant than the other responses, and significantly more intelligible than the prescription with maximal high-frequency emphasis. There were no detectable differences in signal/noise ratios required for 50% speech identification. These results indicate that a prescription that restores normal loudness for speech peaks in each critical band is probably more easily accepted than either a procedure which is intended to make all speech bands equally loud, or a prescription which maximizes the AI.

Aged↗

PubMed1990

Preferred hearing aid gain in everyday use after prescriptive fitting.

The insertion gain preferred by a group of 26 moderately hearing-impaired, elderly hearing-aid users was investigated in everyday listening situations. The subjects used monaural behind-the-ear aids, carefully fitted according to a prescription formula of the half-gain type, validated and used at National Acoustic Laboratories, Australia. The fitting was checked with real-ear measurements of insertion gain and reviewed at one or more follow-up sessions. The subjects were strictly instructed to try the recommended volume control setting before reporting which setting they preferred. The prescription significantly over-estimated preferred gain by about 7 dB. No correlation could be detected between prescribed versus preferred gain differences and the amount of previous hearing-aid use or the degree of subjective hearing problems.

Aged↗

PubMed1990

Multi-programmable hearing aid.

A basic problem in hearing-aid fitting is the difficulty in finding one setting optimal to all listening situations that might occur. The objective was to develop a behind-the-ear hearing-aid with a very flexible analog signal processor which is digitally controlled, and a memory with logic, so that the hearing-impaired person can select from eight completely different fittings. To program and adjust this multi-programmable hearing-aid (called MemoryMate) a hearing evaluation and recommendation system (called Master-Fit) has been developed, based on an IBM PS/2 computer. This system offers the dispenser prescriptive fitting methods and performance of real ear measurements. It can be used to manage a client database. Preliminary results from a clinical study conducted in 1988 are presented. The paper also describes the uniqueness of this multi-programmable hearing aid as a powerful new research tool.

Aged↗

PubMed1979

Programmable hearing aid with multichannel compression.

A portable programmable hearing aid with multichannel compression was constructed with three channels with two independently variable crossover frequencies. The compression knee-point and attenuation in each channel and the two crossover frequencies can be programmed from a separate programming unit. Speech discrimination for seven subjects with sensorineural hearing loss was evaluated, comparing each subject individually in three different cases--equalization, multichannel compression and the subject's own conventional hearing aid. Each subject wore each aid for about a week in his/her own environment and was then tested. The following speech discrimination tests were used: monosyllabic phonetically balanced words with and without background noise, nonsense syllables in quiet, and a constant test in quiet and in noise. The study showed that some patients with sensorineural hearing loss accompanied by recruitment can double their speech discrimination by using a hearing aid with multichannel compression.

Hearing Aids↗