Anna O'Brien

National Acoustic Laboratories, Chatswood, New South Wales, Australia

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Publications (9)9.17 Total impact

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    ABSTRACT: NAL-NL1, the first procedure from the National Acoustic Laboratories (NAL) for prescribing nonlinear gain, was a purely theoretically derived formula aimed at maximizing speech intelligibility for any input level of speech while keeping the overall loudness of speech at or below normal loudness. The formula was obtained through an optimization process in which speech intelligibility and loudness were predicted from selected models. Using updated models and applying some revisions to the derivation process, a theoretically derived NAL-NL2 formula was obtained in a similar way. Further adjustments, directed by empirical data collected in studies using NAL-NL1 as the baseline response, have been made to the theoretically derived formula. Specifically, empirical data have demonstrated that (a) female hearing aid users prefer lower overall gain than male users; (b) new hearing aid users with more than a mild hearing loss prefer increasingly less gain with increasing degree of hearing loss than experienced hearing aid users, and require up to 2 years to adapt to gain levels selected by experienced hearing aid users; (c) unilaterally and bilaterally fitted hearing aid users prefer overall gain levels that vary less than estimated by the bilateral correction factor; (d) adults prefer lower overall gain than children; and (e) people with severe/profound hearing loss prefer lower compression ratios than predicted when fitted with fast-acting compression. The literature and data leading to these conclusions are summarized and discussed in this article, and the procedure for implementing the adjustments to the theoretically derived NAL-NL2 formula is described.
    Trends in Amplification 11/2012; · 1.13 Impact Factor
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    ABSTRACT: Audiometric measurements through a hearing aid ('in-situ') may facilitate provision of hearing services where these are limited. This study investigated the validity and reliability of in-situ air conduction hearing thresholds measured with closed and open domes relative to thresholds measured with insert earphones, and explored sources of variability in the measures. Twenty-four adults with sensorineural hearing impairment attended two sessions in which thresholds and real-ear-to-dial-difference (REDD) values were measured. Without correction, significantly higher low-frequency thresholds in dB HL were measured in-situ than with insert earphones. Differences were due predominantly to differences in ear canal SPL, as measured with the REDD, which were attributed to leaking low-frequency energy. Test-retest data yielded higher variability with the closed dome coupling due to inconsistent seals achieved with this tip. For all three conditions, inter-participant variability in the REDD values was greater than intra-participant variability. Overall, in-situ audiometry is as valid and reliable as conventional audiometry provided appropriate REDD corrections are made and ambient sound in the test environment is controlled.
    International journal of audiology 12/2010; 49(12):868-76. · 1.34 Impact Factor
  • The Hearing Journal. 07/2010; 63(8):32,34-37.
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    ABSTRACT: To determine the effect of spectral differences between stimuli used for verification of hearing aid gain in nonlinear devices. The spectra of nine stimuli from five analyzing systems were obtained. Most stimuli closely duplicated one of two well-specified spectra. The difference between these two input spectra resulted in measured gain differences of up to 8 dB. Careful consideration of selected test stimulus for measuring hearing aid gain is recommended.
    Ear and hearing 06/2010; 31(3):437-40. · 2.06 Impact Factor
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    ABSTRACT: Frequency-dependent microphone directionality alters the spectral shape of sound as a function of arrival azimuth. The influence of this on horizontal-plane localization performance was investigated. Using a 360 degrees loudspeaker array and five stimuli with different spectral characteristics, localization performance was measured on 21 hearing-impaired listeners when wearing no hearing aids and aided with no directionality, partial (from 1 and 2 kHz) directionality, and full directionality. The test schemes were also evaluated in everyday life. Without hearing aids, localization accuracy was significantly poorer than normative data. Due to inaudibility of high-frequency energy, front/back reversals were prominent. Front/back reversals remained prominent when aided with omnidirectional microphones. For stimuli with low-frequency emphasis, directionality had no further effect on localization. For stimuli with sufficient mid- and high-frequency information, full directionality had a small positive effect on front/back localization but a negative effect on left/right localization. Partial directionality further improved front/back localization and had no significant effect on left/right localization. The field test revealed no significant effects. The alternative spectral cues provided by frequency-dependent directionality improve front/back localization in hearing-aid users.
    International journal of audiology 11/2009; 48(11):789-803. · 1.34 Impact Factor
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    ABSTRACT: This study examined the head orientation of young children in naturalistic settings and the acoustics of their everyday environments for quantifying the potential effects of directionality. Twenty-seven children (11 with normal hearing, 16 with impaired hearing) between 11 and 78 months of age were video recorded in naturalistic settings for analyses of head orientation. Reports on daily activities were obtained from caregivers. The effect of directionality in different environments was quantified by measuring the Speech Transmission Index (STI; H. J. M. Steeneken & T. Houtgast, 1980). Averaged across 4 scenarios, children looked in the direction of a talker for 40% of the time when speech was present. Head orientation was not affected by age or hearing status. The STI measurements revealed a directional advantage of 3 dB when a child looked at a talker but a deficit of 2.8 dB when the talker was sideways or behind the child. The overall directional effect in real life was between -0.4 and 0.2 dB. The findings suggest that directional microphones in personal hearing devices for young children are not detrimental and have much potential for benefits in real life. The benefits may be enhanced by fitting directionality early and by counseling caregivers on ways to maximize benefits in everyday situations.
    Journal of Speech Language and Hearing Research 07/2009; 52(5):1241-54. · 1.97 Impact Factor
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    ABSTRACT: This study aimed to determine whether gain adaptation occurs, and at which frequency bands, among new hearing aid (HA) users. Fifty new and 26 experienced HA users were fitted with three listening programs (NAL-NL1 and NAL-NL1 with low- and high-frequency cuts) in the same hearing instrument family. Real-life gain preferences and comfortable loudness levels were measured one, four, and 13 months post-fitting for the new HA users, and one month post-fitting for the experienced HA users. Relative to experienced HA users, new HA users preferred progressively less overall gain than prescribed as the hearing loss became more severe. Gain adaptation occurred in new HA users with greater hearing loss, but was not complete 13 months post-fitting, and was not explained by changes in loudness perception. Preferences for a high-frequency gain cut by half of all study participants could not be predicted from audiological data. Gain adaptation management is recommended for new HA users with more than a mild hearing loss.
    International journal of audiology 11/2008; 47(10):621-35. · 1.34 Impact Factor
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    ABSTRACT: An abstract is unavailable. This article is available as HTML full text and PDF.
    The Hearing Journal. 01/2007; 60(2):29,32,34,38-39.
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    ABSTRACT: An abstract is unavailable. This article is available as HTML full text and PDF.
    The Hearing Journal. 03/2003; 56(4):30,32,34,36,38,40.