Decline of speech understanding and auditory thresholds in the elderly

Abstract

A group of 29 elderly subjects between 60.0 and 83.7 years of age at the beginning of the study, and whose hearing loss was not greater than moderate, was tested twice, an average of 5.27 years apart. The tests measured pure-tone thresholds, word recognition in quiet, and understanding of speech with various types of distortion (low-pass filtering, time compression) or interference (single speaker, babble noise, reverberation). Performance declined consistently and significantly between the two testing phases. In addition, the variability of speech understanding measures increased significantly between testing phases, though the variability of audiometric measurements did not. A right-ear superiority was observed but this lateral asymmetry did not increase between testing phases. Comparison of the elderly subjects with a group of young subjects with normal hearing shows that the decline of speech understanding measures accelerated significantly relative to the decline in audiometric measures in the seventh to ninth decades of life. On the assumption that speech understanding depends linearly on age and audiometric variables, there is evidence that this linear relationship changes with age, suggesting that not only the accuracy but also the nature of speech understanding evolves with age.

Figure 1

Average of right and left-ear audiograms of the 29 subjects measured in the first phase (round symbols/solid lines) and second phase (square symbols/broken lines). Error barsare one standard deviation.

Figure 2

Performance means and standard deviations of the 29 subjects in the first phase (solid bars) and second phase (open bars) for four audiometric tests (PTA4, PTSLP, PT8K, and SRT) and ten tests of speech understanding in interference, averaged across the right and left ears. Data for individual subjects in the second testing phase were interpolated to correspond to a 5.27-year lapse between phases. The P-values above the data bars indicate the significance level for a permutation test of the difference between phases for the raw data. The measure acronyms are PTA4: average of four pure-tone thresholds; PTSLP: slope of the audiogram (4 kHz – 0.5 kHz thresholds); PT8K: threshold at 8 KHz; SRT: speech recognition threshold; LP750: recognition of speech low-pass filtered at 750 Hz; TC60: recognition of speech compressed 60%; CSTI: sentence intelligibility in the presence of a monaurally mixed sentence by another speaker; BCST: sentence intelligibility in the presence of mixed with a contralaterally presented sentence by another speaker; SPMon: average monaural SPIN test score; SPMonCEf: monaural SPIN sentence context effect; SPSpat: average scores for spatially distributed speech target and four babble sources; SPSpatCEf: sentence context effect for spatially distributed SPIN test; RT75: reverberation time estimated to correspond to 75% word recognition. Statistical significance of the difference between results obtained in the two testing phases (see Table I) is indicated for each measure (***: P<0.001, **: P<0.005, +: P<0.05).

Figure 3

Average normalized decline of three audiometric measures (solid line) and eight measures of speech understanding in interference (broken line), as a function of the subjects' average age.

Figure 4

Estimated coefficients in the linear model of equation (3) for the five top principal components of speech understanding measures as a function of age and the two top principal components of audiometric measures, in testing Phase 1 (solid symbols) and 2 (open symbols).