Dear Nedra,
I have a slightly different
understanding in the regard of auditory illusions such as the Mc Gurk effect
not contributing to hearing aid design. I think these illusions may have more
to contribute to not only hearing aid design but also to psycho-acoustics. One of the key uses of the Mc
Gurk effect was in terms of studying the re-organisation/remapping process in
the auditory and visual cortex which has been recently reported due to auditory
deprivation (deafness) in hearing impaired children and the changes to the same
with cochlear implantation and I guess the same would apply to hearing aids as
well (especially the ones with severe hearing loss). One of the other
interesting illusions (although not purely an auditory illusion â or maybe with
the current discussion that I have noticed in the list may be not even an
illusion) I remember working with hearing aid and cochlear implanted users is
the Kiki-Bouba effect which helps us study the sound-shape correspondences in
the brain. One of the key missing link I think in the current wave of hearing
aid technology which is mainly driven via psycho-acoustical difficulties that a
hearing impaired user faces is the overall auditory processing (central auditory
processing as well as Auditory- visual processing) difficulties that a hearing
loss impinges along-with the lower level psycho-acoustic deficits like poor
frequency selectivity, temporal resolution etc. Maybe broadening the definition
of psycho-acoustics a bit these aspects may also be well under its domain. The
subtle but existing difference between two hearing aid users with the same type
of hearing loss characteristics may well be in terms of their central auditory
visual processing abilities which might have been differently affected by the
loss (although there may be alternative aspects such as difference in some
relatively less explored low level psycho-acoustic abilities adding to it). In a
nutshell what I want to express is that studying these illusions is to somehow
ensure that we reach limitations which are imposed by an impaired ear and not
those imposed by inadequate amplification systems and may be try to find out
and compensate for the additional auditory-visual processing/integration limitations that
the hearing loss has added using appropriate rehabilitative/training measures.
I donât know why there were those
strange characters visible in my previous post for this topic so I thought of
attaching that previous message at the end as a paragraph for better
readability. Apologies to all for any inconvenience caused.
Although I am not an expert in
this area, but I have done some preliminary (unpublished) work on the use of
the Mc Gurk effect for the evaluation of current day multichannel digital
hearing aids. Few of the basic assumptions for the rationale and implications
were as follows. One of the main benefits of audio visual integration is in
difficult listening situations when either the speech is degraded or there is
background noise. The visual cue in an auditory visual integration task is
relatively unaffected by noise. Hearing impaired listeners especially those
with relatively larger auditory deprivation periods rely more on visual cues
(the AV balance is slightly tilted towards visual dominance) in speech
perception than normal hearing listeners, thus making them better speech
readers and also relatively poor AV integrators. The psycho-acoustical aspects
of sensory-neural hearing loss suggest a reduction in the possibility of
perceiving certain classes of speech sounds especially in presence of noise. Moreover
some of the speech sounds may not be heard in noisy environments no matter how
intensely they are amplified by the hearing aids. The Digital multichannel
hearing aids may also have some amount of internal distortion and delay due to
digital processing and filtering. In such scenarios the hearing aid user may
benefit from the visual cues provided by a speakers facial and lip movements which
should relatively be unaffected by noise and thus boost speech perception for
energetic masking at poor signal to noise ratios as well as in informational
masking. We presented hearing aid users (relatively homogenous group in terms
of hearing aid used) the Mc Gurk stimuli in both congruent and in-congruent
conditions in quiet and in noise (three different SNRs) at comfortable level at
which the subjects scored > 70% on a screening test using PB words. A
criterion of 3/4th fusion responses was kept to determine the presence of Mc
Gurk effect. The results indicated that subjects with normal hearing performed
better than the subjects using HAâs in all conditions. The presence of auditory
and visual information simultaneously in the congruent condition was beneficial
for speech perception in quiet and in noise. Noise reduced the subjects ability
to perceive speech at poor SNR and had a more severe impact on the performance
of the HA users than in normal subjects. The Mc Gurk effect was absent in the
HA users at the poorer SNRs compared to normal listeners and in these
conditions the HA users responses to the Mc Gurk stimuli were mainly visually
dominated. Background noise and increased listening effort are significant
factors influencing hearing-aid satisfaction and one of the major reason for
rejection of HAâs. Testing Mc Gurk effect in a noisy environment may be a
useful way to understand auditory visual speech perception in HA users and
verify the benefits of aided AV speech perception in noise in HA users. Some of
the implications in terms of hearing aid rehabilitation for the same may be in
terms of enhancing optimal HA fitting to achieve not only good auditory
perception in noise but also optimum auditory visual perception in noise and
the emphasis on auditory training and the use of speech reading skills. The
study that I have mentioned above was in no way devoid of limitations like
lesser sample size and the hearing aids were used at the same programs that the
HA users were using in their everyday listening environments and thus all the
user had different program settings. May be the rationale and implications
might be of some interest to you though.
Regards,
Imran Dhamani