Lecture Four Origin and effects of hearing loss

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Lecture Four Origin and effects of hearing
loss
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A closer look at the anatomy of the middle and
inner ear systems.
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Details of the haircells.
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Conductive
Main problem is during development otitis media
(glue ear) Ways in which specific hearing
disorders affect speech and what can be done
about the ensuing problems Relatively mild
otitis media More severe (operations to treat
destroyed parts of the hearing system) cochlear
implants
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Otitis media (OM)
Definition OM is an infectious disease that is a
result of the interplay between microbial load
(viral and bacterial) and immune response.
Microbial infection arises when pathogens in
the nasopharyngeal region enter into the middle
ear system through the Eustachian tube. Entry
of these pathogens into the middle ear is common
in childhood because childrens Eustachian tubes
are short, floppy, horizontal and function poorly
(Bluestone, 1996 Bluestone, 1999). OM varies
in acuity from simple OM, through OM with
effusion from the middle ear (OME) to acute OM
(AOM). AOM, like OME, has middle ear effusions
but also has signs or symptoms of inflammation in
the middle ear (e.g. fever or irritability)
(Rovers, Schilderm, Zielhuis Rosenfield, 2004).
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Otitis media (OM)
Host and environment risk factors Risk factors
can be broadly distinguished that derive from the
host and the environment. Host The immune
systems response is one host factor (Rovers et
al., 2004). Others (also associated with
stuttering), are age (Zielhuis, Rach, van den
Bosch van den Broek, 1990) and genetic
predisposition (Kvaerner, Harris, Tambs Magnus,
1997 Rovers, Haggard, Gannon, Koeppen-Schnomerus
Plomin, 2002). DS as a host factor (return to
later) Environment The environment the child
experiences affects contagion and progress of the
disease by increasing microbial load.
Environmental factors that have this effect
include whether the child has siblings (usually
older), whether the child attends a day-care
group and season of the year (Rovers et al.,
2004).
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Otitis media (OM)
Assessment, pure tone audiometry not designed to
detect OM. Tympanometry is the appropriate
procedure (Brooks, 1968). Treatment Treatments
usually involve antibiotics or tympanostomy tubes
(ventilation tubes inserted through the tympanic
membrane) though these only have moderate
efficacy (Rovers et al., 2004). A drawback to
treatment with antibiotics is that resistance can
build up (a particular problem with DS children).
Based on what has been said so far, there
appears to be little to recommend antibiotic or
surgical treatment. Offset against this, OM can
lead to hearing loss and concomitant problems in
language development (as well as associated
behavioral problems) (see Roberts, Hunter,
Gravel, Rosenfield, Berman, Haggard, Hall,
Lannon, Moore, Vernon-Feagans Wallace, 2004 for
a recent review of work on both these
topics). The high rate of spontaneous recovery
from OM during childhood suggests that OM is an
epiphenomenon associated with the normal course
of development of the immune system (Rovers et
al., 2004).
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Otitis media (OM)
Treatment of OME and effect on speech Typanostomy
tube reduces OME prevalence by 115 days per
child year which represents as 67 relative risk
reduction .
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Otitis media (OM)
Roberts et al. (2004). Conductive hearing loss
secondary to OME reduces sound intensity, delays
sound passing through the middle ear and often
results in asymmetrical hearing levels for the
right and left ears. How it affects hearing -
Stephenson et al. (1993) interaural fluctuations
occurring over a prolonged period could give
rise to development of abnormal ratios of ipsi-
and contra-lateral connections required for
binaural hearing. Sensorineural OME induces
(simulated in animals by plugging the ear) leads
to neural changes. Poor performance on central
hearing tests with animals and children with OME.
Prolongation and asymmetry of ABR waveforms
suggesting lateral asymmetries and poor binaural
interaction in children with OME. Children with
retrospectively documented prolonged OME history
had poorer MLDs before and after tympanostomy
tubes (consistent with long-term central
auditory changes). Resolve slowly after surgery.
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Cochlear implants and speech development
(sensori-neural)
Overview If the view is taken that the
development of speech is extremely limited
without adequate auditory input and feedback,
then auditory input ought to be encouraged
whenever possible. One way this can be done is
by giving a child a cochlear implant. This does
not restore hearing but does give a child the
sense of sound input and this can be tailored to
be effective for communication.
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Cochlear implants and speech development
(sensori-neural)
How is speech development affected in hearing
impaired children Fluent children Babbling begins
around 5-6 months of age. Verbal expression
starts around 12 months of age. Speech
production skills continue to be refined through
the school-age years and beyond. E.g. vowel
space, voice-onset times, and vocal control
adjust throughout early childhood (Assmann
Katz, 2000 Koenig, 2001 Lee, Pontamianos,
Narayanan, 1999). Evidence for development of
coarticulation, literature is not
definitive. Children appear to be less able than
adults to coarticulate their speech gestures in a
consistent manner, and as a consequence, their
speech is less intelligible than that of adults
(Katz, Kripke, Tallal, 1991 Nittrouer,
1993). Auditory processing of speech also
appears to be more susceptible to acoustic and
linguistic perturbations than is observed with
adults. Children are more adversely affected
than adults by background noise, reverberation,
talker variability, reductions in signal
bandwidth, and the number of signal channels
(Eisenberg et al., 2000 Ryalls Pisoni, 1997
Kortekaas Stelmachowicz, 2000).
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Cochlear implants and speech development
(sensori-neural)
Hearing Loss and Speech Production Hearing loss
is most pronounced with individuals whose hearing
loss is congenital or acquired in early
childhood. Most adults who acquire their
hearing losses later in life suffer little or no
deterioration in intelligibility, likely because
their residual hearing provides sufficient
feedback since their mature speech production
systems rely more on orosensory than auditory
information to maintain proper control (Guenther,
1995 Goehl Kaufman, 1984 Perkell et al.,
1997). Some adventitiously deafened adults
exhibit reduced speaking rate, and compromised
articulatory and phonatory precision
(Kishon-Rabin et al., 1999 Lane Webster, 1991
Lane et al., 1995 Leder et al., 1987 Perkell et
al., 1992 Waldstein, 1990). These speech
differences are similar in nature, but not in
severity, to those observed with prelingually
deafened speakers.
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Cochlear implants and speech development
(sensori-neural)
Hearing Loss and Speech Production (cont.) Most
infants and young children with hearing loss
demonstrate disordered phonation and
articulation, as well as delays in the
acquisition of sound categories. The entire
speech production system can be affected, from
respiratory support to the coarticulation of
ongoing speech (Pratt Tye-Murray, 1997). More
marked if the hearing loss is identified late or
after a period of protracted hearing loss.
Babbling generally does not appear before 12
months of age (Oller et al., 1985). Infants
include a more limited range of consonants in
their babble (Stoel-Gammon, 1988 Stoel-Gammon
Otomo, 1986 Wallace, et al., 2000). The
phonetic repertoires of infants with
severe-to-profound hearing loss often are
restricted
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Cochlear implants and speech development
(sensori-neural)
Hearing Loss and Speech Production (cont.) The
early speech inventories of infants with
severe-to-profound hearing loss predominately
consist of motorically easy sounds such as vowels
and bilabial consonants. The sounds of their
inventories also contain more low frequency
information, which is more audible. For example,
the babbling of infants with hearing loss often
has a high concentration of nasals and glides,
which include low-frequency continuant cues
(Stoel-Gammon Otomo, 1986). Sensory aids have
a substantial impact on speech outcomes, butthe
age at which infants and young children are
fitted with cochlear implants has not surfaced in
studies of speech production as a significant
predictor of later speech intelligibility (Geers
et al., 2002 Tobey et al., 2003). Early
implantation (less than 2 years) is, however,
related to more normal oral communication
development as a whole (both speech and oral
language).
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Cochlear implants and speech development
(sensori-neural)
Sensory Aids in Treatment Cochlear implants have
a positive impact on speech development (Geers et
al., 2002 Tobey et al., 2003). Augmenting the
communication channel Cochlear implants and
hearing aids are one way of doing this
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Speaker effects
Speakers who are hard of hearing report being
able to understand males better than females. Why
might this be so? Females have higher voice
pitch and this leads to poorer registration of
the formants Speaking clearly for the hearing
impaired leads to roughly 10 improved word
recognition scores (Picheny Durlach and Braida,
1986).