Articulation index predictions for hearing-impaired listeners with and without cochlear dead regions

Abstract

Vickers, Moore, and Baer [J. Acoust. Soc. Am. 110, 1164–1175 (2001)] reported that hearing-impaired subjects with cochlear “dead regions” benefited from amplification of frequencies up to an octave above the estimated edge frequency of the dead region, but not beyond, whereas hearing-impaired subjects without dead regions did show benefit beyond this boundary. Dead regions are thought to have no functioning inner hair cells. Vickers et al. indicated that a clinical test for detecting dead regions would provide supplementary information that is important for hearing aid fitting. Furthermore, they suggested that the articulation index (AI) may overestimate the potential benefit of amplification for listeners with dead regions because the AI does not account for the presence of dead regions. To evaluate their claims, we conducted an AI analysis [H. Fletcher, Speech and Hearing in Communication (Van Nostrand, New York, 1953); H. Fletcher and R. H. Galt, J. Acoust. Soc. Am. 22, 89–151 (1950)]. Results show that the AI is generally accurate in predicting the consonant recognition test scores of Vickers et al.’s subjects irrespective of the presence/absence of dead regions. This suggests that audiogram differences account for the observed performance differences; it was not necessary to invoke dead regions to explain the speech test results. The results of the AI analysis are sufficiently accurate to call in to question whether a clinical test for dead regions would offer additional predictive information.

Dead Regions in the Cochlea: Conceptual Foundations, Diagnosis, and Clinical Applications

“…It should be noted that not all researchers agree that the TEN test provides useful information over that provided by the audiogram; see Rankovic (2002) and the response by Moore (2002). However, as argued earlier, a dead region cannot be reliably diagnosed from the audiogram.…”

“…One important issue is the extent to which amplification according to the Cambridge formula was successful in providing audibility (Moore, 2002;Rankovic, 2002). The failure to find a benefit of amplification for frequencies well inside a dead region might have been caused by insufficient amplification of those frequencies; if the speech is not made audible, there can be no benefit from amplification.…”

Relationship Between Age of Hearing-Loss Onset, Hearing-Loss Duration, and Speech Recognition in Individuals with Severe-to-Profound High-Frequency Hearing Loss

“…The factors responsible for this interindividual variability are not entirely clear. While audibility plays an important role (Dubno et al 1989b;Rankovic 1991;Hogan and Turner 1998;Rankovic 1998Rankovic , 2002, listeners with severe hearing losses have often been found not to benefit from amplification, even when audibility calculations indicate that they should (Pavlovic 1984;Kamm et al 1985;Dubno et al 1989a;Ching et al 1998;Hogan and Turner 1998;Baer et al 2002).…”

Benefits of audibility for listeners with severe high-frequency hearing loss

“…This lack of audibility was likely to have contributed to the poor scores these subjects obtained. Rankovic (2002) calculated articulation index (AI) predictions using the Fletcher method of calculation (Fletcher, 1953;Fletcher and Galt, 1950) for the data published by Vickers et al (2001). The AI was generally accurate in predicting the consonant recognition test scores of the subjects irrespective of the presence or absence of dead regions.…”