Methods and Applications of the Audibility Index in Hearing Aid Selection and Fitting

Abstract

During the first half of the 20th century, communications engineers at Bell Telephone Laboratories developed the articulation model for predicting speech intelligibility transmitted through different telecommunication devices under varying electroacoustic conditions. The profession of audiology adopted this model and its quantitative aspects, known as the Articulation Index and Speech Intelligibility Index, and applied these indices to the prediction of unaided and aided speech intelligibility in hearing-impaired listeners. Over time, the calculation methods of these indices-referred to collectively in this paper as the Audibility Index-have been continually refined and simplified for clinical use. This article provides (1) an overview of the basic principles and the calculation methods of the Audibility Index, the Speech Transmission Index and related indices, as well as the Speech Recognition Sensitivity Model, (2) a review of the literature on using the Audibility Index to predict speech intelligibility of hearing-impaired listeners, (3) a review of the literature on the applicability of the Audibility Index to the selection and fitting of hearing aids, and (4) a discussion of future scientific needs and clinical applications of the Audibility Index."Articulation measurement is a tedious and expensive business, and considerable attention has been devoted to the development of a computational device to replace, or at least to supplement,

Extending the articulation index to account for non-linear distortions introduced by noise-suppression algorithms

“…Figure 4 shows the scatter plot of fAI values and intelligibility scores. A logistic-type function of the form (Fletcher and Galt, 1950;Amlani et al, 2002): was used for the fitting of the fAI values, where I is the subject's intelligibility score (in proportion correct), x ¼ fAI, P ¼ 27.5, and Q ¼ 8.4. Based on the above fitting (transfer) function, high intelligibility (> 90% correct) is predicted for fAI values greater than 0.5.…”

“…Among these measures, the articulation index (AI) (French and Steinberg, 1947;Fletcher and Galt, 1950;Kryter, 1962a;ANSI, 1997;Amlani et al, 2002) and speechtransmission index (STI) (Steeneken and Houtgast, 1980;Houtgast and Steeneken, 1985) are by far the most commonly used today for predicting speech intelligibility. The AI measure was further refined to produce the speech intelligibility index (SII) (ANSI 1997).…”

“…The AI measure was further refined to produce the speech intelligibility index (SII) (ANSI 1997). The AI measure is based on the principle that the intelligibility of speech depends on the proportion of spectral information that is audible to the listener and is computed by dividing the spectrum into 20 bands (contributing equally to intelligibility) and estimating the weighted average of the signal-to-noise ratios (SNRs) in each band (Kryter, 1962a(Kryter, , 1962bPavlovic, 1987;ANSI, 1997;Amlani et al, 2002). The SNRs in each band are weighted by bandimportance functions which differ across speech materials (ANSI, 1997).…”

“…The STI measure (Steeneken and Houtgast, 1980) is based on the principle that the reduction in intelligibility caused by additive noise or reverberation distortions can be modeled in terms of the reduction in temporal envelope modulations. In contrast, the AI measure does not consider or account for any envelope modulation reduction/increase in its computation, but rather computes directly the SNR in each band (see review by Amlani et al, 2002).…”

The Effect of Hearing Impairment on Word Processing of Infant- and Adult-Directed Speech

“…The inclusion criteria for the HI group were: 1) bilateral, congenital, sensorineural hearing loss diagnosed with an auditory brainstem response test, 2) use of hearing aids and/or cochlear implants for at least 5 months, 3) no indication of auditory neuropathy spectrum disorder (defined as otoacoustic emissions present in combination with hearing loss greater than 40 dB and/or cochlear microphonic component recorded in combination with no obvious auditory brainstem response), and 4) if aided, an aided Speech Intelligibility Index (SII) score of > 20. This number is based on previous research indicating that an SII of 20 correlates with approximately 20% speech audibility (Amlani, Punch, & Ching, 2002;Stiles, Bentler, & McGregor, 2012). Since this study provided only an auditory presentation of the speech stimuli, an SII of 20 was included as a way to quantify sufficient access to the auditory signal.…”