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Urgency
Lecture 3
Northern and Downs (1991) and Ross and Seewald (1988) provide reviews of studies of
sensory deprivation in animals.
Although there are few human studies corroborating these findings, recent investigations
of the effect of temporary auditory deprivation, such as can occur with prolonged otitis
media in infants and young children.
In addition to sensory deprivation and its physiologic consequences, the effect on
language acquisition during this critical period is of great concern.
Northern and Downs define the critical period as
“Certain periods in development when the organism is programmed to receive and
utilize particular types of stimuli and that subsequently the stimuli will have diminishing
potency in effecting the organism’s development in the function represented”
Candidacy
Any child with a significant hearing loss is a candidate for amplification.
One cannot discuss candidacy issues without considering the plight of the unilaterally
hearing-impaired.
Auditorally, the following problems are obvious (Mueller and Hawkins, 1990):
1. Binaural summation. With two equally sensitive ears, threshold is 3 dB better than
with either ear alone; relative to loudness judgments, a stimulus presented
simultaneously to both ears at a 40 dB sensation level (SL) will require a 46 dB SL
presentation level for equal loudness when presented to either ear alone.
As pointed out by Bess and Tharpe (1986), this “advantage becomes rather
substantial when one considers the effect on speech recognition.”
Eighteen to 30% improvement in speech recognition can be expected from binaural
listening over monaural listening, depending on the stimulus used.
2. Head shadow effects. Head shadow refers to the reduction in signal intensity that
occurs as the signal moves from one side of the head to the other; this effect is more
substantial in the high frequencies.
For the unilaterally hearing impaired child, any signal presented on the side of the
impaired ear may be attenuated 10 to 16 dB above 1000 Hz by the time it reaches the
functional ear.
Obviously, this magnitude of attenuation can have significant effects on speech
intelligibility, because that area of the speech spectrum may account for 60% of
speech intelligibility.
3. Localization. The importance of localization, or directionality, is generally
considered a binaural phenomenon, the result of interaural time and intensity
differences.
For low-frequency stimuli, the primary cue for localization is the interaural time
difference, whereas for high frequencies (above 1500 Hz), the primary cue is the
interaural intensity difference.
What does amplification mean?
It means to make louder.
Through the years, it has become a euphemism for hearing aids but in a strict sense,
hearing aids are but one type of amplification device. There are others.
Let’s turn first to HA candidacy. Audiologists are very often called upon to make
determinations about an individual’s candidacy for a hearing aid.
Do I need one or does grandma need one. There is no simple litmus test that I know of
two make this determination. However, the process is different for children than
for adults.
As we have seen, with adults you have to factor in handicap, lifestyle, motivation, and
locus of control.
It is not so with children.
Any child with a significant hearing loss is a candidate for amplification.
What does significant mean?
Significant is not a real good word.
Perhaps it would be just the same to say any hearing impairment because they all are
significant. Lecture on the word significant....
I like what Ruth (Ruth Bender) says.
"Any hearing loss that places a child at a disadvantage in an academic, social, or,
in the case of older children, occupational setting warrants amplification
consideration.
Therefore, candidacy is not simply a matter of looking at the audiogram.
To me this would include:
1.
The child with a mild fluctuating conductive impairment from SOM
2.
The child with a unilateral hearing impairment
3.
The child with CAP
CROS.
Contralateral Routing of Sound
The history of hearing aids has been one of miniaturization.
The first wearable models began to be mass-produced in the 1930s.
Prior to that, there was a number of small mom and pop companies that sprung off new
technology in electronics.
Zenith, Siemens etc.