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As printed in Hearing Health, volume 20:1,
Spring 2004
By Mary Florentine, Ph.D.
You have hearing loss, this you know. You may be knowledgeable
about many aspects of your condition based on discussions
with your hearing healthcare provider. Chances are,
though, that you are unacquainted with a newly-coined
term for what may be a familiar hearing experience for
you.
Take my friend Karen, for example, who has had hearing
loss since she was a child. She recalls, “When
I was little, it seemed to me that the other children
never called my name in the usual way when they wanted
my attention on the playground. They just screamed it
and grabbed and pushed me in the direction they wanted
me to go.”
In retrospect, Karen realizes that her playmates had
probably attempted to call her several times before
resorting to loud voices and physical direction. But
why did she not hear them, at least softly, before they
yelled at her?
Evidence is building that many people with sensorineural
hearing loss have similar experiences. We call this
phenomenon softness imperception (SI), referring to
an
inability to hear soft sounds. This surprising finding
challenges over 60 years of thinking in hearing science
and adds greatly to the understanding of loudness perception.
It also agrees with modern findings in auditory physiology,
clinical observations and many aspects of current clinical
practice.
Tests specifically for SI are not yet available although
some experiments have been performed that give insight
into the condition. Recognizing the need for methods
of more definitive diagnosis, my colleagues and I at
the Communication Research Laboratory at Northeastern
University in Boston are currently involved in a large-scale
study of the subject. After hearing about our study,
a number of people with self-diagnosed SI have come
to our laboratory and find that our tests often confirm
their own observations.
Loudness is Subjective
To understand SI, it is helpful to understand a bit
about loudness perception. Not everyone experiences
loudness in the same way. One sound wave (that is, the
physical vibration) can elicit different perceived loudnesses
depending on the characteristics of each listener’s
hearing. As in the illustration above, an ambulance
siren may sound loud to someone in a nearby vehicle
and soft to a person in the next one. Loudness is in
fact quite subjective.
To further complicate matters, people do not use the
terms describing loudness in the same way. Two people
using the word “soft” may be reporting two
very different perceptions. For example, a person with
hearing loss who has never heard loudness in the usual
way might use the term “very, very soft”
to indicate the softest sound that he can hear. His
actual perception may be closer to what others perceive
and describe as “moderately soft.” Without
special testing, it is impossible to know how a person
is using a term.
There is one given in perceiving loudness: when the
physical intensity of a sound increases, so does its
loudness. However, two aspects of loudness perception
vary among people: the softest sound they can hear (their
hearing threshold) and the rate at which sound gets
louder as it gets more intense. Different combinations
of these dynamics result in four common types of loudness
perception.
- Typical – As the name suggests, this type
is how most people without hearing loss perceive loudness.
When a sound is at a very low intensity and no one
can hear it, we say it is below hearing threshold.
When intensity increases, the sound is first heard
as very, very, very soft. With each rise in intensity,
perception of loudness increases at a corresponding
rate. Eventually, sound gets so loud that it can be
uncomfortable or even painful. Fortunately, most people
have the good sense not to listen at this damaging
level!
- Attenuation – The attenuation type of loudness
perception is how most people assume everyone with
a hearing loss hears: obstructed normal hearing, similar
to plugging your ears with your fingers. The intensity
at which sound is first heard is higher than in the
typical type. Once sound reaches hearing threshold,
it will be heard as very, very, very soft and then
will increase in loudness at the same rate as in the
typical type. Although attenuation occurs in some
people, as in cases of impacted earwax, it is definitely
not how most people with hearing loss perceive
loudness.
- Rapid growth – People with rapid growth have
a higher threshold at which sound is first heard,
where it is perceived as very, very, very soft. As
the intensity of sound increases, the perception of
loudness grows at a very rapid rate that eventually
catches up with near normal loudness at high physical
intensities. Until recently, most audiologists and
scientists assumed that people with sensorineural
hearing loss experience this type of loudness perception,
also known as recruitment, but now we are learning
that some actually have SI.
- Softness imperception – In both rapid growth
and SI, high intensity sound is usually heard as loud
but there are two important differences. One is that
a person with SI perceives a sound at the lowest audible
intensity as louder than do people with any of the
other three types of loudness perception. The first
sound a person with SI can hear does not sound soft.
The first few times Karen’s friends called her,
the sound was not intense enough for her to hear but
once she was able to hear them (just above threshold),
their voices sounded quite loud.
The other difference between rapid growth and SI is
the rate of loudness growth above threshold. People
with rapid growth perceive a rapid increase in loudness
as sound intensity increases. People with SI experience
a more typical rate of loudness growth above threshold.
Only when sound is considerably more intense does loudness
increase at a somewhat faster rate until it catches
up to typical, or near typical, loudness.
SI and the other types of loudness perception may
be experienced to varying degrees and in varying combinations.
For example, a person may experience attenuation due
to one type of hearing loss and have SI due to another
type.
Hearing Aids & SI
For people with SI, realistic expectations are essential
for preventing dissatisfaction with hearing aids. Expecting
that hearing aids will provide typical loudness perception
can only lead to disappointment because they cannot
restore the lost ability to hear very, very soft sounds.
Hearing aids can, however, make sound with low physical
intensity audible to them.
Although its loudness may seem strange, most hearing
aid users can easily learn to identify the nature of
an amplified sound. Whispered speech, for example, can
be distinguished from normal speech even if both are
perceived to be equally loud. Whispered speech has a
different quality, sounding breathier to most people.
A frequent complaint of new hearing aid users with SI
is that low-level sound, like from an exhaust fan, is
irritatingly loud. By working with his/her hearing healthcare
provider in post-fitting counseling and adjustments,
a user may find the right compromise between making
sounds s/he wants to hear audible and making sounds
s/he does not want to hear too loud.
Although hearing aids cannot entirely compensate for
SI at this time, simply having a better understanding
of this aspect of hearing can lead to a better quality
of life for both the people who experience it and those
who interact with them. Misunderstandings can be avoided
by anticipating the kinds of difficulties that are likely
to occur.
One of the most common scenarios is a child being
reprimanded for startling an adult who has SI. Children
do not understand this type of loudness perception and
are unsure what they did wrong. Such ongoing misunderstandings
may have a negative effect on relationships.
Learning more about SI has been a big help to my friend
Karen as she now understands that when she hears people
call her name loudly and sometimes with a strident voice,
it is because they have already called her in a lower
voice several times. By the time she hears them, they
may be frustrated and annoyed at her for not responding.
They probably do not understand that she has a hearing
loss and incorrectly assume that they are being ignored.
In addition to developing increased awareness of SI’s
potential impact on her interactions, Karen has become
quite adept at educating others about this aspect of
her hearing. She tells me that most people are glad
to know that they are not being
ignored and are happy to try to accommodate her.
My colleagues and I as well as other researchers and
clinicians are eager to learn more about characteristics
of SI and methods of diagnosis. The ultimate goal is,
of course, to find the most beneficial ways to help
individuals understand and successfully manage this
aspect of their hearing loss.
Mary Florentine, Ph.D., is a Matthews
Distinguished University Professor in the Department
of Speech-language Pathology and Audiology and director
of the Institute for Hearing, Speech & Language
at Northeastern University in Boston. The internationally
renowned researcher has prepared over 100 original publications
and made several appearances in the media, working to
make the latest knowledge in hearing science accessible
to all.
She lives in Dover, Mass., with her husband Søren,
daughter Julia and Oliver, her cat who thinks he is
a dog and likes to play fetch. She wishes to thank Professor
Bertram Scharf and Julia B. Florentine for helpful comments
on this article and Julia for the illustration concept.
Related Articles:
From Pianissimo to Mezzopiano
Signs of SI
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