gms | German Medical Science

Introduction: Patients with a high-grade interaural asymmetry in pure tone hearing threshold (PTA), although having normal hearing in one ear, often report to suffer from problems with speech comprehension in difficult listening situations, particularly in the presence of background noise. It was the aim of this study to characterize at which level the affected ear will contribute towards improved speech-in noise intelligibility in binaural listening situations.

Method: Up to now 22 patients with chronic unilateral cochlear hearing loss (4-PTA(0,5-3kHZ)≥50dB HL) after sudden idiopathic sensorineural hearing loss (6 to 98 months) and normal hearing on the contralateral ear were examined with the "Oldenburger Sentence Test" (OLSA). The speech signal was presented in front of the subject (0 degree, S0). The noise signal (65 dB SPL) was randomly presented from four different directions (N: 0, 90 (right), 180, 270 degree). Speech reception threshold (∆S/N) was determined for each of the four situations as the difference (in dB) of noise level and speech level at which 50% of the words were understood. Results were compared to those from normal hearing control subjects.

Results: In all four test situations the mean ∆S/N was worse in patients with unilateral sensorineural hearing loss (median in dB of patients/controls: S0N0: -3.6/-5.7, p=0.0002; S0N180: -5.1/-8.2, p=0.0089; S0Naffected: -6.7/-10.3, p<0.0001; S0Nunaffected: -2.3/-10.9, p<0.0001; Wilcoxon-test). This effect was most pronounced in the S0Nunaffected situation, i.e. if the noise was presented to the healthy ear. Intersubject variability was largest for the S0N180 situation. Hearing threshold (4-PTA) correlated with OLSA results in the S0N0 (rs=0.6), S0Nunaffected (rs =0.7), S0Naffected (rs =0.8) situations but less for noise from behind (S0N180, rs=0.36).

Conclusions: The present data demonstrate that severe to profound unilateral sensorineural hearing loss (4-PTA ≥50 dB HL) significantly decreases speech-in noise intelligibility. There was a relation between threshold and ∆S/N as measured with the "Oldenburger Sentence Test". In order to estimate at which level the affected ear significantly contributes towards speech-in noise intelligibility more data on unilateral mild to moderate hearing loss are necessary. Measurements showed a high interindividual variability which might be due to factors such as age of the subject or time after sudden hearing loss. These influences need to be investigated further.