Aided and unaided speech perception by older hearing impaired listeners

Abstract

The most common complaint of older hearing impaired (OHI) listeners is difficulty understanding speech in the presence of noise. However, tests of consonant-identification and sentence reception threshold (SeRT) provide different perspectives on the magnitude of impairment. Here we quantified speech perception difficulties in 24 OHI listeners in unaided and aided conditions by analyzing (1) consonant-identification thresholds and consonant confusions for 20 onset and 20 coda consonants in consonant-vowel-consonant (CVC) syllables presented at consonant-specific signal-to-noise (SNR) levels, and (2) SeRTs obtained with the Quick Speech in Noise Test (QSIN) and the Hearing in Noise Test (HINT). Compared to older normal hearing (ONH) listeners, nearly all unaided OHI listeners showed abnormal consonant-identification thresholds, abnormal consonant confusions, and reduced psychometric function slopes. Average elevations in consonant-identification thresholds exceeded 35 dB, correlated strongly with impairments in mid-frequency hearing, and were greater for hard-to-identify consonants. Advanced digital hearing aids (HAs) improved average consonant-identification thresholds by more than 17 dB, with significant HA benefit seen in 83% of OHI listeners. HAs partially normalized consonant-identification thresholds, reduced abnormal consonant confusions, and increased the slope of psychometric functions. Unaided OHI listeners showed much smaller elevations in SeRTs (mean 6.9 dB) than in consonant-identification thresholds and SeRTs in unaided listening conditions correlated strongly (r = 0.91) with identification thresholds of easily identified consonants. HAs produced minimal SeRT benefit (2.0 dB), with only 38% of OHI listeners showing significant improvement. HA benefit on SeRTs was accurately predicted (r = 0.86) by HA benefit on easily identified consonants. Consonant-identification tests can accurately predict sentence processing deficits and HA benefit in OHI listeners.

Fig 1. Average audiograms for 24 OHI listeners (green) and 16 ONH listeners (blue).

Error bars show standard deviation. The dotted red line shows the estimated average aided audiogram based on prescriptive target for the average OHI audiogram.

Fig 2. Percent correct scores for the ONH listeners (gray) and for aided (red) and unaided OHI (green) listeners averaged over all consonants in onset and coda positions.

The horizontal positions of the curves were determined by the mean levels of SNRs for ONH and OHI listener groups. Error bars show standard errors.

Fig 3. (top). Identification thresholds of the 21 consonants, averaged over onset and coda position where possible.

Blue diamonds show ONH thresholds; green circles show unaided OHI thresholds; and red squares show aided OHI thresholds. The consonants on the abscissa are arranged according to increasing thresholds for normal-hearing listeners, which also determined membership in consonant Groups A, B, and C. (Bottom) HA benefit for the 21 consonants. Error bars show standard errors.

Fig 4. HA benefit plotted as a function of unaided threshold elevation.

The dotted line illustrates the case where the HA benefit equals the unaided threshold elevation, i.e., where aided-OHI and ONH consonant identification would be the same. The solid curve is the second-order polynomial fit for these data. The consonants are color-coded according to their unaided threshold elevations (brown for under 30 dB, yellow for 30–45 dB and dark blue for over 45 dB). See text for further discussion.

Fig 5. Incidence of different types of phonetic errors for ONH listeners, and for unaided (green) and aided (red) OHI listeners.

Error bars show standard errors.

Fig 6. Barycentric plots for unaided (green) and aided (red) OHI listeners, and for ONH listeners (blue) in SNR conditions producing similar overall consonant identification performance.

Fig 7. Scatter plots showing the relation between listeners’ SeRTs and unaided Group A consonant identification thresholds (Panel A) and the relation between HA benefit on Group A consonants and HA benefit on SeRTs (Panel B).