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Biomedical subjects

H Dillon

Publications and source records attributed to H Dillon.

At least 19 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↗
PubMed1999

Control of hearing-aid saturated sound pressure level by frequency-shaped output compression limiting.

To fit a hearing aid successfully, it is important to set the Saturated Sound Pressure Level (SSPL) or Maximum Power Output (MPO) appropriately. The SSPL should be low enough to prevent sounds from being amplified to uncomfortable loudness, and yet high enough to maximize speech intelligibility and signal quality. To help attain an optimum SSPL setting, a novel output compression limiting scheme, with shapable MPO (ShaMPO), has been devised. In ShaMPO, the SSPL is shaped across frequencies in accordance with the individual user's loudness discomfort levels (LDLs). The contributions of different frequency regions to loudness are controlled by summing the amplified signal power relative to the LDLs across frequencies, and using this signal to control a wideband compressor. This scheme and a conventional output compression limiting (AGCo) scheme have been implemented in a digital hearing aid. Ten subjects, with moderately-severe to profound sensorineural hearing losses, participated in a study comparing speech intelligibility and listening comfort for the two schemes. Results showed that there were no significant differences in the speech perception scores between AGCo and ShaMPO, even when the speech was presented at 80 dBA, at which level both schemes were in compression much of the time. However, an examination of how subjects selected the SSPL for the two schemes revealed that, in many instances, AGCo would permit some sounds with compact spectra to be amplified above LDL, whereas ShaMPO would not. Thus the ShaMPO scheme can improve listening comfort for some intense sounds without a loss of speech intelligibility. In contrast, half the subjects found speech at 80 dBA to be uncomfortably loud when listening through their own aids.

Aged↗
PubMed1999

Client preferences for compression threshold in single-channel wide dynamic range compression hearing aids.

OBJECTIVE: Compression in hearing aids can be applied with low compression ratios over a wide range of input levels, but reverts to linear amplification below the compression threshold (CT). In this study, we aimed to determine which of two CTs was preferred by subjects as they used their hearing aids in their own environments, and whether they would prefer to have no low ratio compression at all. DESIGN: Subjects were fitted with a multimemory hearing aid incorporating input controlled compression with a 2:1 compression ratio and output controlled compression limiting. The two memories contained identical programs except that they differed in CT. Sixteen mild to moderately sensorineurally hearing-impaired subjects compared low (approximately 40 dB SPL) and moderate (approximately 65 dB SPL) CTs over 2 mo of field trials using hand held remote controls to switch between the alternatives. In a third month's trial, the preferred option (which also included output controlled compression limiting) was compared with compression limiting alone. RESULTS: The higher CT was preferred by 14 of the subjects. The combination of input compression and output compression limiting was preferred to compression limiting alone by 14 of the subjects. CONCLUSIONS: Several real world advantages of frequency independent 2:1 compression with a CT of about 65 dB SPL were demonstrated over linear amplification. Extending the compression to much lower input levels appears to carry more disadvantages than advantages, at least for clients with mild and moderate hearing losses, when fitted with single-channel compression aids with a 2:1 compression ratio.

Aged↗
PubMed1998

The National Acoustic Laboratories' procedure for selecting the saturation sound pressure level of hearing aids: theoretical derivation.

This paper presents the derivation of a procedure for prescribing the saturation sound pressure level (SSPL) of hearing aids. The procedure is designed to be used with either measured values of loudness discomfort level (LDL) or with hearing threshold values alone. SSPL needs to be low enough to prevent the hearing aid from causing loudness discomfort to the aid wearer but high enough to prevent the hearing aid from being excessively saturated by speech. The maximum SSPL likely to be acceptable can be predicted by measuring LDL or by estimating LDL from hearing thresholds. The minimum SSPL likely to be acceptable can be predicted by calculating, for any particular hearing loss, the amount of gain likely to be needed and hence the SSPL needed if the speech input signal is continuous discourse at an overall level of 75 dB SPL. The midpoint between the minimum and maximum acceptable SSPL values is defined as the optimal or prescribed SSPL, and the three frequency average (3FA; 500, 1000, and 2000 Hz) value of this can be predicted from the 3FA hearing thresholds. Alternatively, the SSPL prescription at each frequency can be prescribed on the basis of the hearing aid gain at each frequency. For either method, the SSPL prescription needs to be increased for people with a conductive component to their hearing losses. The SSPL prescription, when referred to a 2-cc coupler, needs to be decreased for infants, for deeply inserted hearing aids, for multichannel hearing aids that limit SSPL separately in each band, and possibly for nonlinear hearing aids. The 3FA SSPL prescribed for persons with a sensorineural hearing loss increases linearly from 89 dB SPL for normal hearing to 107 dB SPL for a person with a 60 dB HL 3FA loss, and then linearly again to 139 dB SPL for a person with a 120 dB HL 3FA loss. The procedure predicts that the acceptable range of SSPLs is very wide for people with mild losses but is vanishingly small for people with profound losses.

Adult↗
PubMed1998

The National Acoustic Laboratories' procedure for selecting the saturation sound pressure level of hearing aids: experimental validation.

OBJECTIVE: The primary aim of this study is to evaluate the accuracy of a new procedure for selecting the saturation sound pressure level (SSPL) of hearing aids. Secondary aims are to investigate what limits the minimum SSPL that is acceptable to clients and whether the type of limiting (peak clipping or compression limiting) affects the SSPL required. DESIGN: The study comprised two experiments. In the first, subjects increased the SSPL of a laboratory master hearing aid until they experienced loudness discomfort and decreased it until the sound became less acceptable in some way. In the second study, subjects wore multi-memory programmable hearing aids in their own environments and reported which of the two programs, differing only in SSPL setting, provided the more acceptable sound quality and comfort. RESULTS: The theoretical procedure being investigated prescribed SSPLs that were within the acceptable range for 86% of the subjects in the laboratory study and for 63% of the subjects in the field experiment. On average, the theoretical predictions were neither too high nor too low. Incorporating individual measurements of loudness discomfort level into the prescription formula increased accuracy by such a small amount that it was not considered worthwhile. For a compression limiting hearing aid, the first thing that subjects noticed as SSPL was reduced was inadequate loudness. For the peak clipping hearing aid, however, both inadequate loudness and perception of distortion limited the acceptable SSPL range. CONCLUSION: The theoretical procedure provides a good initial prescription of three frequency average SSPL, but it is still essential to evaluate the fitting and, if necessary, fine tune the individual's hearing aid. Compression limiting hearing aids can have slightly lower SSPL settings than peak clipping hearing aids for the same acceptability.

Acoustic Stimulation↗
PubMed1998

Speech recognition of hearing-impaired listeners: predictions from audibility and the limited role of high-frequency amplification.

Two experiments were conducted to examine the relationship between audibility and speech recognition for individuals with sensorineural hearing losses ranging from mild to profound degrees. Speech scores measured using filtered sentences were compared to predictions based on the Speech Intelligibility Index (SII). The SII greatly overpredicted performance at high sensation levels, and for many listeners, it underpredicted performance at low sensation levels. To improve predictive accuracy, the SII needed to be modified. Scaling the index by a multiplicative proficiency factor was found to be inappropriate, and alternative modifications were explored. The data were best fitted using a method that combined the standard level distortion factor (which accounted for decrease in speech intelligibility at high presentation levels based on measurements of normal-hearing people) with individual frequency-dependent proficiency. This method was evaluated using broadband sentences and nonsense syllables tests. Results indicate that audibility cannot adequately explain speech recognition of many hearing-impaired listeners. Considerable variations from audibility-based predictions remained, especially for people with severe losses listening at high sensation levels. The data suggest that, contrary to the basis of the SII, information contained in each frequency band is not strictly additive. The data also suggest that for people with severe or profound losses at the high frequencies, amplification should only achieve a low or zero sensation level at this region, contrary to the implications of the unmodified SII.

Adult↗
PubMed1997

Converting insertion gain to and from headphone coupler responses.

OBJECTIVE: The paper aims to show how insertion gain responses can be translated into equivalent headphone responses, and vice versa. DESIGN: The relationship between the response types is theoretically derived by allowing for real ear to coupler differences and for real ear unaided responses. RESULTS: The necessary corrections for each of these factors are obtained from published data, and the combined correction factors are compared with independently obtained published data. CONCLUSIONS: The equations and data presented can be used to translate insertion gain responses into responses suitable for use with equipment using headphones and, by inference, insert phones.

Hearing Aids↗
PubMed1997

Client Oriented Scale of Improvement (COSI) and its relationship to several other measures of benefit and satisfaction provided by hearing aids.

Several methods for measuring the self-reported benefit and satisfaction provided by a hearing aid were compared by administering all methods to each of 98 subjects. Significant correlations between many of the measures and reasonably high test-retest correlations for two of the measures administered twice suggest that most of the measures provide valid estimates of benefit and/or satisfaction. One of the methods included is a new tool called the Client Oriented Scale of Improvement (COSI). In this method, the client effectively writes the self-report questionnaire by nominating up to five listening situations in which help with hearing is required. At the conclusion of rehabilitation, reduction in disability and the resulting ability to communicate in these specific situations is quantified. Based on correlation analysis, the COSI method is as statistically valid as the much longer, more traditional questionnaires. Other features, such as relevance, diagnostic utility, compatibility with normal interviewing techniques, and good test-retest reliability, make it particularly suitable for routine clinical use.

Aged↗
PubMed1996

Compression? Yes, but for low or high frequencies, for low or high intensities, and with what response times?

Several rationales for using compression in hearing aids are outlined. These rationales comprise discomfort avoidance, loudness normalization, noise reduction, short term signal dynamic range reduction, empirically determined compression, and long-term signal dynamic range reduction. The compression systems needed to implement each of these differ greatly, and these differences can be viewed as differences in the frequency range undergoing most compression, the intensity range undergoing most compression, and the speed at which the compressor(s) operate. A classification system along these lines is introduced and examples of currently available hearing aids falling into each category are given. The effects of each type of compression on speech intelligibility is investigated via a review of published research. The results of this indicate that, for speech in quiet at a comfortable level, no compression scheme yet tested offers better intelligibility than individually selected linear amplification. If input level is then decreased and the aid wearer is prevented from adjusting the volume control, many types of compression provide intelligibility superior to that available from linear amplification. In broadband noise, only one system, containing wideband compression followed by fast acting high-frequency compression, has so far been shown to provide significant intelligibility advantages.

Equipment Design↗
PubMed1996

An equivalent input noise level criterion for hearing aids.

The purpose of this project was to establish a maximum acceptable equivalent input noise level (EINL) for hearing aids. It was found that, if the version of the National Acoustic Laboratories (NAL) procedure for selecting the gain and frequency response of hearing aids, which includes modifications for severe and profound hearing loss is used, the EINL criterion can be relaxed for higher gain hearing aids, as a function of the gain of the aid. The relationship between relaxation of the criterion and 2-cc coupler gain is nonlinear, in different amounts, at the various frequencies, so no simple rule can be used to describe the manner in which the criterion can be relaxed.

Auditory Perception↗
PubMed1996

Gain, frequency response, and maximum output requirements for hearing aids.

This article applies the gain and frequency response and maximum output selection procedures currently recommended by the National Acoustic Laboratories (NAL) of Australia to the audiograms of a representative group of adult and child clients of Australian Hearing Services (AHS) to specify the performance that is required of various types of hearing aids in order to ensure that they can provide adequate gain, frequency response, and maximum output levels for at least 90% of the AHS client population. Cumulative frequency distributions of required 2-cc coupler gain slopes were calculated for each type of aid and used to design required frequency response variations. Coupler slope requirements in different octaves were found to be independent of one another. The required range of gain-maximum output combinations was determined for each type of aid.

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

The effect of a depleting anti-CD4 monoclonal antibody on T cells and fetal pig islet xenograft survival in various strains of mice.

The effect of a cell-depleting anti-CD4 monoclonal antibody (mAb), GK1.5, was studied in a number of strains of inbred mice. Young adult female NOD/Lt, CBA and BALB/c mice were transplanted with organ cultured fetal pig pancreas and given 0.3 mg of the mAb (as ascites) on days -1, 0 and +1. The grafts were mostly rejected within 13 days in CBA mice but BALB/c and NOD recipients still had essentially intact grafts with the NOD mice showing evidence of early rejection. By 28 days posttransplantation the BALB/c recipients still had well-preserved grafts with minimal infiltration, but NOD and CBA mice had generally rejected their grafts totally. Peritransplant mAb treatment reduced CD4+ T cells in the spleen and they showed only incomplete recovery by 28 days. To further analyse the effect of anti-CD4 treatment, these strains as well as C57BL/6 mice were given a single dose (0.3 mg) of GK1.5 either as ascites or as affinity purified mAb. There was no obvious difference in effect between the ascites and the purified mAb within a strain but the various strains showed consistent differences in their blood, spleen and lymph node lymphocytes and in their response to the mAb. C57BL/6 mice differed from the other strains in having fewer T cells but more B cells in the blood, spleen and lymph nodes and a low CD4/CD8 ratio. Recovery of CD4+ T cells was most rapid in NOD mice and this together with the relatively high number of these cells may account for the ability of these mice to reject grafts despite immunosuppression that can allow prolonged graft survival in other strains. This study emphasizes the need to examine various strains of mice when making general statements about the efficacy of immunosuppression in transplantation and stresses the need to be aware of the frequent use of 'permissive' strains in reports where excellent graft survival is reported.

Animals↗
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↗
PubMed1993

Hearing aid evaluation: predicting speech gain from insertion gain.

In this study, hearing aid gain for speech was defined as the difference in level between the aided and unaided performance-intensity functions measured at any specific value of percentage of items correct. The articulation index method was used to predict speech gain based on the subject's unaided sound field thresholds, ambient room noise, hearing aid internal noise, hearing aid insertion gain, and the subject's unaided performance-intensity function. Predicted speech gain agreed with measured speech gain with rms errors of only 3 dB for 11 subjects with mild or moderate hearing loss tested with monosyllabic words and continuous discourse. The speech gain provided by a hearing aid can thus be predicted from electroacoustic measures, which generally can be obtained in a shorter time. Importance functions believed to be applicable to nonsense syllables, words, and continuous discourse were used to make the predictions, but prediction accuracy was not affected by the importance function chosen. Speech gain measured with the monosyllabic word test was highly correlated with speech gain measured with the continuous discourse test, provided that similar presentation levels were used.

Aged↗
PubMed1992

Cephalexin and penicillin in the treatment of group A beta-hemolytic streptococcal throat infections.

OBJECTIVE: To determine whether cephalexin or penicillin is more effective in the treatment of group A beta-hemolytic streptococcal tonsillopharyngitis in children. DESIGN: Randomized, double-blind, crossover study conducted from 1981 to 1984. SETTING: Seven pediatric practices in the United States, including private offices and pediatric clinics. PARTICIPANTS: Of the 654 patients, 525 children and adolescents with clinical evidence of tonsillitis or pharyngitis and throat cultures positive for group A beta-hemolytic streptococcal infection were evaluable. Eighty percent of patients completed the study; none were withdrawn because of adverse reaction. SELECTION CRITERIA: Children and adolescents who had acute illness suggestive of group A beta-hemolytic streptococcal infection were enrolled in the study. Treatment was continued if the throat culture was positive for group A beta-hemolytic streptococcal infection. INTERVENTIONS: Four doses of cephalexin and penicillin (27 mg/kg per day) were prescribed to be taken on an empty stomach for 10 days. MEASUREMENTS/MAIN RESULTS: Symptomatic clinical failure occurred in 8% of penicillin-treated patients and in 3% of cephalexin-treated patients. Bacteriologic failure rates were 11% in the penicillin treatment group and 7% in the cephalexin treatment group. The combined treatment failure rate of clinical relapse plus asymptomatic bacteriologic failure was 19% in the penicillin treatment group and 10% in the cephalexin treatment group. Paired antistreptolysin-O titer increased significantly in 62.3% of penicillin-treated patients and in 64.2% of cephalexin-treated patients. Similarly, anti-DNase B titers rose 52.2% in penicillin-treated patients and 52.4% in cephalexin-treated patients. CONCLUSION: Cephalexin is a more effective drug than penicillin in the treatment of group A beta-hemolytic streptococcal throat infection in children.

Adolescent↗