Speech discrimination in the sensorineural hearing loss patient: how is it affected by background noise?

There are patients who have normal hearing below 3,000 Hz and normal speech discrimination who still complain of hearing difficulty, especially when background noise is present. The objective of this study is to document the fact that these individuals have a significant hearing impairment that is not detected with routine testing. We retrospectively reviewed 67 audiograms selected for 50-dB loss or greater at 3, 4, 6, and 8 kHz and speech discrimination scores better than 80%. Patients in this group had also previously undergone speech discrimination testing in the presence of 50-dB calibrated cafeteria noise at the time of the initial audiogram. Identical testing was carried out on 48 control subjects without hearing loss. The speech discrimination scores of the hearing-impaired group were lower than in the control group when tested in a quiet booth (88.2 and 98.2%, respectively). The significant finding was the change in the speech discrimination score when tested in noise. We found that the study group had a 33.1% loss in speech discrimination when tested in the presence of background noise. The control group had only a 5.2% loss in speech discrimination in the presence of the same noisy background; this was statistically different (p = 0.001). Our conclusion is that patients complaining of hearing loss who have normal low- to mid-frequency hearing and good speech discrimination should be tested in the presence of noise to adequately document their degree of impairment. Our findings also support the theories of signal attenuation and secondary auditory pathway distortions as causes of the loss of speech discrimination.