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Biomedical subjects

M P Haggard

Publications and source records attributed to M P Haggard.

At least 19 recordsLinked to original sources
PubMed1992

The clinical assessment of "Obscure Auditory Dysfunction" (OAD) 2. Case control analysis of determining factors.

Obscure Auditory Dysfunction (OAD) is defined as a clinical referral for self-reported auditory disability with no audiometric abnormality by stringent criteria. In stage 2 of a case control study of OAD, we have confirmed the general finding of stage 1 that OAD is multifactorial; compared with controls, patients as a group have a genuine performance deficit for understanding speech in noise, accompanied by personality-related factors. Paired logistic regression analysis optimally differentiated the 50 patients from their 50 matched controls on the basis of variables from three different domains: masked thresholds (psychoacoustic domain), dichotic listening ability (central/cognitive domain), and underestimation of own hearing ability (personality domain). A further and influential contributing variable was understanding of speech in noise supplementing the variables in both the psychoacoustic and the cognitive domains. With this model, 82.7% of the total group deviance was explained (i.e., the binary variable of case/control). A corresponding discriminant function analysis correctly classified 80% of patients and 90% of controls. When factors underlying the performance and personality-related variables were investigated with multiple linear regression within the two groups separately, relatively little of the within-group variance among OADs was explained. This is consistent with the multifactorial nature of OAD, in that the combinations of factors leading to OAD status differ between individuals. The research findings have been used to design a clinical test package to provide diagnostic information on the basis of OAD in individuals.

Adult↗
PubMed1992

The paediatric otological caseload resulting from improved screening in the first year of life.

Improved test technique by health visitors has been shown to lead to higher accuracy in the screen of hearing aimed traditionally at prelingual sensorineural deafness. However, it gives greatly increased referrals of children having otitis media with effusion (OME) around the end of the first year of life. Two samples of children (n = 29 and 61) were tested in a children's hearing assessment clinic with properly documented testing techniques and trained personnel. The samples were each formed on a fixed population base, one before and one after screen improvements. This enabled characterization of two outcome groups within each sample (severe/persistent enough to refer to ENT vs discharged, despite slight hearing impairment). The average audiometric criterion for onward referral to ENT rose only very little, despite the increased assessment caseload resulting from more detections by the screen. This usefully permitted the conclusion that the number of true cases found due to the screen and assessed as lying beyond a specifiable degree of severity (average cut-off approximately 47 dB(A) or 35 dBHTL) had increased not through lower criteria for referral to ENT, but through the improvements to the screen. The increase was from approximately 0.4% to 1.3% of the base population screened. Thus a change materially enhancing the sensitivity and positive predictive value of a screen considerably enlarges the eventual otological caseload of children with middle-ear disease thought to justify concern at around the end of their first year. If done properly, screening is hence in practical terms about OME, not about prelingual sensorineural hearing impairment. This conclusion presses the urgency of evaluation and consensus on the otological management of the young child with OME.

Analysis of Variance↗
PubMed1992

A clinical test battery for obscure auditory dysfunction (OAD): development, selection and use of tests.

Obscure auditory dysfunction (OAD) is defined as convincing self-report of auditory disability accompanied by normal pure-tone thresholds. This has been increasingly recognized as a clinical problem, but until now there has not been a standard clinical procedure for dealing with such patients. This paper summarizes a demographic and clinical characterization of a sample of 50 OAD patients, reports new norms on the tests in the version issued, and describes a test package developed from a case-control research study that can be routinely used with OAD patients. The package enables clinicians: (i) to confirm, or otherwise, OAD as the appropriate classification for individuals presenting with OAD-like symptoms; (ii) to elucidate the underlying basis of OAD in such individuals and hence in most cases to provide explanations that are justified by test findings; and (iii) to counsel cases in a fashion appropriate for each individual. The package consists of four performance tests, a specialized clinical interview and a brief questionnaire to determine the severity of OAD. The assessment takes approximately 37 min and can be run using a two-channel audiometer and a cassette recorder.

Adolescent↗
PubMed1990

Effects of flanking band proximity, number, and modulation pattern on comodulation masking release.

Comodulation masking release for a 700-Hz pure-tone signal was investigated as a function of the number and spectral positions of 20-Hz-wide comodulated flanking bands. In the first experiment, all stimuli were presented diotically. CMR was examined as a function of the number of flanking bands present, in conditions where the bands were arranged symmetrically around the signal frequency, were below the signal frequency, or were above the signal frequency. The number of flanking bands ranged from one to eight, and the magnitude of the diotic CMR ranged from approximately 5-16 dB. The results indicated: (1) bands closer to the signal resulted in larger masking release, and (2) more bands gave rise to larger CMR (but with diminishing returns above two flanking bands). Two additional sets of diotic conditions were examined and compared to the condition where all eight comodulated flanking bands were present: In one set of conditions, two of the eight flanking bands were removed; in the other set of conditions, two of the eight flanking bands were replaced with bands (termed "deviant" bands) that were not comodulated with respect to the other bands. There was very little effect of reducing eight bands to six, even when the removed bands were relatively near the signal frequency; however, CMR was substantially reduced when deviant bands were introduced, particularly when the deviant bands were placed relatively near the signal frequency. These reductions in CMR were slightly greater when each of the deviant bands had a unique modulation pattern (bideviant bands) than when the two deviant bands themselves shared the same modulation pattern (codeviant bands). In the second experiment, dichotic conditions were examined where the number and spectral positions of the flanking bands in the nonsignal ear were varied (the signal ear received only a 20-Hz-wide noise band centered on the signal frequency). The magnitude of the dichotic CMR ranged from approximately 2-10 dB, depending on condition. Effects of proximity and the number of flanking bands were similar to the effects obtained in diotic conditions. For both the diotic and the dichotic data, the effects of proximity were more consistent with an interpretation based upon across-channel processing than upon a within-channel interaction. The results obtained using deviant bands indicate that it is difficult for the auditory system to disregard the modulation pattern of flanking bands that differ from the modulation pattern of the on-signal band, particularly if such bands are proximal to the signal frequency.

Acoustic Stimulation↗
PubMed1990

Comodulation masking release as a function of bandwidth and test frequency.

Comodulation masking release (CMR) was investigated as a function of signal frequency (0.5-4.0 kHz) and the total bandwidth of noise centered on the signal frequency. Taking noncomodulated noise of the same bandwidth as the reference condition, CMR for modulated noise increased with increasing bandwidth of the flanking noise outside the critical band centered on the signal tone; however, this growth asymptoted for broad total bandwidths. These bandwidth effects were expressed by scaling the width of the flanking bands beyond the critical band centered on the signal frequency, approximately according to a critical bandwidth scale. After this scaling, signal frequency had negligible effect on CMR magnitude. For the low modulation frequencies involved, a beneficial effect on CMR at high carrier frequencies would not be expected, and none was observed. Some further trends in the masked thresholds in comodulated and noncomodulated conditions, and the choice of appropriate reference condition are discussed.

Adolescent↗
PubMed1989

The clinical assessment of obscure auditory dysfunction--1. Auditory and psychological factors.

We define obscure auditory dysfunction (OAD) as the clinical presentation of reported difficulty understanding speech in the presence of noise accompanied by clinically "normal" hearing thresholds, and no other obvious cause. The term deliberately avoids particular pathophysiological connotations. A detailed characterization of such patients was undertaken as the basis for future diagnosis and management of OAD by clinicians. Twenty patients were compared with 20 pairs of controls (matched for age, sex, educational level, and noise exposure) on tests of auditory, linguistic, and psychological function. Patients showed a genuine performance deficit on a speech-in-noise task, due in part to minor auditory dysfunction and poor linguistic ability. Their high level of self-rated disability and handicap cannot, however, be entirely explained by this genuine deficit. An anxious personality and a history of otological symptoms typified the patient group; either or both have presumably contributed to patients' seeking of medical or audiological advice. OAD is thus a multifactorial syndrome with contributions from auditory, psychological, and linguistic factors. The variance in (and correlation between) performance levels on two sentence-in-noise tests, present only within the patient group, indicates that these patients are not a homogenous group.

Adolescent↗
PubMed1989

Staffing and structure for paediatric audiology services in hospital and community units.

The component functions of a paediatric audiology service are outlined on the basis of the main broad categories of patient and their requirements, as seen from a 'good practice' standpoint; a service structure is offered in terms of patient flow. This leads to a distinction between the small, specifically medical requirement, and the large, specifically audiological testing requirement. Indications are given of the scale of audiology requiring to be done by community staff not specializing in audiology. Notional incidence figures (and acceptable screen failure rates) allow the number of audiological posts or sessions required for screening and related community paediatric audiology work to be estimated per million population served. This totals about 9.75 FTE professional posts of varying grades per million population plus 1.5 FTE support, but in nearly all circumstances there will be many more incumbents than this, each with diverse other duties. The recommended staffing of audiologists doing hospital-based assessment and rehabilitation work and requiring specialized audiology training totals about 7.0 full-time equivalent (FTE) audiology posts and 2.5 support posts in a hospital paediatric audiology department, per million population; this is above the currently prevailing level of provision. The resource requirements would be raised by the widespread introduction of a non-standard screen (other than for the standard 6 to 9 month screen and the school-entry screen) by about 40% for community services and 15% for consequential increases in hospital services. In hospital units, the staffing will usually be interleaved with that of adult audiology, even where the served population may be large enough (e.g. 0.5 million, three to four paediatric audiology staff) to make a separate section worthwhile. In community units, there does not appear to be a particularly good rationale for community doctors specializing full-time in audiology, although some medical staff time is needed to undertake the specifically medical components. A partial degree of specialization among health visitors (or at least greater audiological training and experience) would probably achieve better performance of screens and simplify the attainment and maintenance of testing standards. Activities in hospital and community units have strong mutual implications: adding an intermediate-age screen to the established first-year and school-entry screens, and adding an at-risk neonatal screen would together increase consequent demands upon hospital paediatric audiology about 35%, although in neither case would the screening activity itself be undertaken in the hospital audiology unit.(ABSTRACT TRUNCATED AT 400 WORDS)

Audiology↗
PubMed1988

Comodulation masking release for multicomponent signals.

Detection of signals composed of one, two, or three pure-tone components was examined in comodulated and noncomodulated masking noises. The masking noise was either a single 30-Hz-wide narrow band of noise, two narrow bands of noise, or three narrow bands of noise. Comodulation masking release (CMR) was greatest when (1) the signal was a single pure tone; (2) the masker was composed of three noise bands (as opposed to two); and (3) at least one flanking band was lower in frequency than the signal. Substantial CMRs did occur, however, for two- and three-component signals presented in two- and three-component maskers, respectively. The results of the present experiments did not support a "dip listening" hypothesis, nor models based strictly on across-frequency differences in stimulus envelope pattern or correlation. The results were more consistent with a model of CMR in which across-frequency envelope difference is coded by subtracting the envelope at the signal frequency from the envelope at a flanking frequency.

Acoustic Stimulation↗
PubMed1988

Spectro-temporal analysis in normal-hearing and cochlear-impaired listeners.

Detection thresholds for a 1.0-kHz pure tone were determined in unmodulated noise and in noise modulated by a 15-Hz square wave. Comodulation masking release (CMR) was calculated as the difference in threshold between the modulated and unmodulated conditions. The noise bandwidth varied between 100 and 1000 Hz. Frequency selectivity was also examined using an abbreviated notched-noise masking method. The subjects in the main experiment consisted of 12 normal-hearing and 12 hearing-impaired subjects with hearing loss of cochlear origin. The most discriminating conditions were repeated on 16 additional hearing-impaired subjects. The CMR of the hearing-impaired group was reduced for the 1000-Hz noise bandwidth. The reduced CMR at this bandwidth correlated significantly with reduced frequency selectivity, consistent with the hypothesis that the across-frequency difference cue used in CMR is diminished by poor frequency selectivity. The results indicated that good frequency selectivity is a prerequisite, but not a guarantee, of large CMR.

Adult↗
PubMed1987

The effects of air-bone gap and presentation level on word identification.

A sensorineural hearing loss is usually considered more disabling than a conductive loss of equivalent air conduction hearing level, due to the associated impairments in resolution which amplification does not overcome. In noise this generalization holds; however, in quiet, the generalization holds only for high intensity levels of presentation. Determination of isoperformance curves for word identification shows that at low stimulus levels the patient with conductive hearing loss suffers the greater disability for a given hearing loss. The crossover point between these regions, (i.e., where a single predictor from hearing level correctly predicts equal disability for conductives and sensorineurals) is in the region of 85 dB SPL--a level which approximates typical raised voice levels used when communicating under difficult circumstances. Given the long-standing distinction between conductive and sensorineural pathology, prediction of disability from dB HL as a general clinical substitute for actual disability measurement has rested upon a fortunate coincidence.

Acoustic Stimulation↗
PubMed1987

The four alternative auditory feature test (FAAF)--linguistic and psychometric properties of the material with normative data in noise.

The linguistic properties of the FAAF test material are expounded in relation to its objectives. It is shown from reference data that there are lexical effects inherent in the use of real-word minimal pairs rather than nonsense syllables. These are word-frequency effects upon phonemes in initial position and effects of imageability upon phonemes in final position. However, those effects are not large enough to undermine the use of the FAAF as an acoustical phonetically structured material reflecting the analysis of auditory information. Normative data on a range of signal-to-noise ratios are presented. These data have helped to delimit the subsets of items that best reflect variations in performance under easy and under difficult conditions. This offers a mapping of the percentage correct from scores at one or two fixed S/N ratios required for a given level of performance and hence permits comparison with SRT(N) measures.

Humans↗
PubMed1987

Two-state compression of spectral tilt: individual differences and psychoacoustical limitations to the benefit from compression.

A psychoacoustic rationale was developed for a hearing aid design in which compression of spectral tilt was incorporated without any instantaneous nonlinear distortion. This involved switching between a 'flat' and a 'rising' frequency response; the switching was done slowly to avoid audible transients and was controlled by feedback derived from comparison of output levels in low- and high-frequency channels, approximating voiced/unvoiced detection. The effect of this switching process was to narrow the distribution of spectral tilt values compared with the input. Asynchrony between the switching and the triggering speech structures was avoided by also delaying the signal path. Unfortunately, hearing-impaired listeners performed more poorly on the switching system than on either of the control 'flat' or 'rising' frequency-responses. An explanation is offered (on the basis of growing evidence from perceptual experiments) of the perceptual importance of temporal envelope contours within individual frequency bands. It was possible, in part, to predict individuals' results in the switching condition from age and audiometric or psychoacoustic characteristics. The results suggest a modification to the switching design, and they point to an intrinsic limit to the ability of all hearing aids of the compression type to enhance intelligibility.

Adult↗
PubMed1986

Psychoacoustical and audiometric prediction of auditory disability for different frequency responses at listener-adjusted presentation levels.

Audiometric prediction of word identification scores has typically used one fixed presentation level for all subjects in the sample, with presentation in quiet and a wide range of hearing impairment among the listeners; under such conditions it is hardly surprising that moderate to good predictions are found. To see if prediction is possible under clinically relevant conditions, that is, on a homogeneous clinical sample of new hearing-aid candidates and to listener-adjusted levels, as would obtain in use of a hearing aid. In addition to audiometric variables, we employed a clinical approximation to the psychoacoustic tuning curve. We tested speech identification (FAAF) performance both with a 'rising'(+9 dB/octave) and with a 'flat' frequency response. Prediction of performance in the 'flat' condition was only good when a full set of audiometric frequencies entered the multiple-regression formula, each with its own weighting. Audiometric prediction for the 'rising' frequency response was particularly poor. Thus, the fairly good predictability from thresholds found traditionally for word identification scores or other disability measures appears to be a special case, depending partly on the wide range of hearing levels employed. Within our clinical sample the predictive power of formulae based on the mean of all thresholds or of mid-frequency thresholds alone (as used in compensation schemes) or on a priori combinations of thresholds (such as slopes) was generally poor. However, a three-parameter model taking account separately of low (0.25 kHz) and high-frequency (greater than 2.0 kHz) thresholds was effective. This and other audiometric descriptions were valuably supplemented by a psychoacoustic measure of frequency resolution at 2 kHz. In particular, such supplementation here allowed a satisfactory level of prediction to be achieved for speech heard with a +9 dB/octave frequency response, which the audiogram alone did not. The limitations of the prediction paradigm are discussed and several conceptual and statistical problems not previously emphasised in the audiological literature are illustrated in relation to the data.

Adult↗