Thread Subject: Re: Amplification and Research
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From: Brenda Battat
Date: Mon, Mar 26 2007 10:50 AM
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All your comments regarding the intelligibility problems are borne out
day in and day out by what we hear from consumers with sensorineural
hearing loss - the most common type
From: = EMAIL ADDRESS REMOVED =
[mailto: = EMAIL ADDRESS REMOVED = ] On Behalf Of Diane
Sent: Monday, March 26, 2007 12:05 PM
To: 'TEITAC Telecommunications Subcommittee'
Subject: Re: [teitac-telecom] Amplification and Research
> I have absolutely no idea whether our measures of perceived quality
correlate highly with intelligibility among
> listeners who are hard-of-hearing.
Yes, there needs to be research into mapping these metrics onto the
domain of hearing loss, either objectively or subjectively. But I can't
believe we'd be the first people asking for such a linkage.
>From Diane: Let my try a crack at this again -- first by saying that I
an audiologist by training (still licensed and practice a bit on the
side periodically . . . ) If audiologists had some way to "solve"
speech intelligibility problems for folks with sensorineural hearing
loss -- we'd have a lot more people lined up to buy hearing aids.
Audiologists pull out every "trick in the book" from digital
manipulation of the speech signal, venting and open fittings, etc. etc.
trying to improve speech discrimination through hearing aid fitting.
But for many individuals you still can't improve discrimination to a
decent level regardless of what signal
manipulation techniques are used. So there is no "metric" to be
a speech signal delivered by a phone that will ensure intelligibility
for individuals with sensorineural hearing loss -- and in fact the
technology doesn't exist to deliver intelligibility to everyone with
With telephones, for people with really poor discrimination, we're
forced to shift to text (regular VCO or captioned VCO) to allow them to
use the phone.
Many of these individuals can manage in face-to-face communication by
using speech reading cues; but since those are gone on the phone their
speech only discrimination is just too poor to deliver any reasonable
level of intelligibility. Just as a side note, we've found a good
number of people with poor discrimination, yet fairly good speeech
reception thresholds (maybe in the 50 dB HL range), are unable to use
captioned VCO (with combined text and speech) because the presence of
the speech (audible but
unintelligible) interferes with their ability to use the captioning.
These individuals are able to use captioned VCO with the speech off or
turned down below their threshold, but not when both are received as
incoming information. Yet other individuals with a similar hearing loss
configuration and similar speech discrimination are able to use combined
speech/text. This is just another example of the individual differences
between people with hearing loss in how they process speech signals.
So in a nutshell it is critical to get the speech signal to the speech
threshold of a person with a hearing loss to have any chance of
intelligibility. Past that, to improve speech discrimination for
individuals with significant cochlear and/or retro-cochlear damage means
buildling telephones with all kinds of adjustable features (similar to
what high end hearing aids have available) and even at that there is no
assurance that discrimination can be delivered. (And I'm thinking is
probably beyond the scope of 508 and/or 255 standards.) Generally
accepted practices like reducing ambient noise would work across the
board especially if user controlled. Other user adjustable features
like one to shift the frequency response might be helpful but trying to
require an adjustable frequency response could be a challenge in a
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