Impact of complex noise maskers and reverberation on speech perception in EAS-users

Background:

Electric acoustic stimulation either in the same ear (EAS) or combined with the opposite ear (bimodal stimulation) can support perception compared to pure electrical stimulation. The additional detrimental effect of reverberation needs to be addressed. In addition, the influence of “informational masking” as central masking effect in speech perception is unclear.

Methods:

The present study compares the impact of different noise conditions and investigates the impact of reverberation and informational masking on speech perception in noise in a cohort of 8 unilateral EAS-users. Performance was assessed with the German matrix sentence test (Oldenburger Satztest, OLSA) in closed set condition. Speech level was adapted in order to determine speech reception thresholds. In total, six noise conditions (static, 2 Hz AM, 4 Hz AM, 8 Hz AM, ISTS, Japanese speech, noise level fixed 65 dB) and four reverberation conditions (0 s 0,35 s 0,51 s 1,03 s) either with or without additional noise were tested.

Results:

On average, listening into short temporal gaps ("glimpsing") aided speech perception in all tested conditions with modulated noise (SRT =-5 dB). Compared to the static OLnoise condition, SRT improved by 2 dB equivalent to approximately 20% perception score. However, with more prosodic disturbances as introduced with the ISTS signal, the glimpsing effect was absent. Even worse, with the Japanese speaker competing signal, the SRT increased to +5 dB. Compared to normal hearing listeners, a difference amounting 20 dB SRT was observed. In comparison to bilateral CI-Users, results obtained in the unilateral EAS user cohort were equivalent. Spacial release from masking was present only in free field conditions.