International Hearing Aid Research Conference: IHCON 2016 location:Tahoe City, California, US date:10-14 August 2016
Introduction. Spatial separation of speech and noise improves speech intelligibility, due to
interaural time and level differences (ITDs and ILDs respectively). This improvement is less for hearing-
impaired listeners; therefore, it is important to know how and which cues should be enhanced to alleviate
Spatial separation yields one ear with a better signal-to-noise ratio (SNR) than the other: the âbetter
earâ. In addition, listening with two ears (instead of the better ear only) yields an extra binaural benefit in
speech intelligibility: squelch. Mostly, squelch is attributed to binaural decorrelation. This is possible due
to ITDs yielding different correlation peaks (separated in time) for target and masker. Moreover, central
processing may be involved as well: the ability to better segregate target and masker based on the
perception of their spatial location. For the latter, both ITDs and ILDs provide the ability to localize
sounds. However, when only ILDs are present, squelch is not observed when using speech-weighted
noise (SWN) as a masker . We investigated whether squelch may be present with only ILDs when
using a fluctuating masker.
Hypotheses. Firstly, we hypothesize that ILD-only squelch may be observed if the masker is
modulated noise. During temporal gaps in the masker, the better and worse ear are equivalent in SNR;
therefore the listener may benefit from binaural redundancy. Secondly, we hypothesize that ILD-only
squelch may also be observed if the masker is a competing talker. We hypothesize that the spatial location
itself (as opposed to the physical cues induced by spatial location) may contribute to spatial release from
masking if the masker is not merely energetic.
Methods. A Dutch sentence test was used to measure speech intelligibility. We investigated three
different maskers, spectrally matched to target speech: SWN, a competing talker and modulated SWN
with the same temporal envelope as the competing talker. Spatial hearing was simulated with head-related
transfer functions; ITDs were set to zero for the ILD-only conditions (and vice versa).
Results. In preliminary results we did not observe ILD-only squelch with the modulated SWN. We
did however observe ILD-only squelch with a competing talker.
Conclusion. Squelch may be observed with only ILDs if the masker is a competing talker. Therefore,
it may be advisable to preserve ILDs in binaural hearing aids for better speech intelligibility.