Do you hear the noise? Influence of background noise level on speech reception
Objective — The aim of this study was to determine the relationship between hearing loss and speech reception threshold (SRT) at different fixed background noise level conditions using the German Oldenburg Sentence Test (OLSA). In a previous study (Wardenga et al., 2015), 177 subjects with various hearing abilities were tested at a fixed noise level of 65 dB SPL. With this standard setting, SRT in noise could be determined for listeners with pure-tone averages (PTA, 0.5, 1, 2, 4 kHz) below about 45 dB HL. Above this PTA, the SRT was affected to an increasing degree by problems with listening in quiet. The present two-center study investigated the effect of changing the level of the background noise to lower or higher levels.
Design — All subjects were trained with two lists of the OLSA in easy listening conditions. The SRTs were determined monaurally with headphones using the standard noise of the OLSA (Olnoise) at different levels and a standard adaptive procedure converging to 50% speech intelligibility. The order of the noise levels was randomized. At the first center (Hörzentrum Oldenburg), listeners with normal to moderate hearing loss were tested in quiet and with fixed noise levels of 55, 65, 75, and 85 dB SPL (in total N=41 ears). At the second center (Medical University Hannover), listeners with normal to severe hearing loss were tested in quiet and with fixed noise levels of 65, 85, and 95 dB SPL (N=52 ears). In total, data for 93 ears with hearing losses ranging from 0 to 90 dB HL PTA were obtained.
Results — For all noise levels, two domains could be identified with a linear dependence of SRT on PTA. For PTAs < noise level – 20 dB HL, the SRT increased with slopes of approximately 0.09 dB SNR/dB HL. For higher PTAs, the identified domain includes very heterogeneous data, thus the corresponding regression differ in slope for the different background noise level.
Conclusion — The OLSA can be applied to listeners with a wide range of hearing losses. Preliminary results indicate that for real speech in noise testing, the selected background noise level should be 20 dB higher than the PTA - otherwise, the SRT is influenced predominantly by a reduced hearing ability in quiet.