Reprinted with permission from ENT & audiology news, NOVEMBER/DECEMBER 2013 98, VOL 22 NO 5

1. Auditory Processing Problems
and Specific Language
Impairment
Prof Dorothy VM
Bishop,
MA, MPhil,DPhil
Wellcome Principal
Research Fellow /
Professor of
Developmental
Neuropsychology,
Department of
Experimental
Psychology, University
of Oxford,
South Parks Road,
Oxford, OX1 3UD, UK.
Correspondence
E: dorothy.bishop@
psy.ox.ac.uk
Declaration of
Competing Interests
None declared.
pecific language impairment (SLI) is
identified when a child has problems understanding or producing
spoken language for no obvious reason [1].
Some children catch up after a slow start,
but others have more persistent problems.
By school age, the language difficulties may
be less obvious to outsiders, but formal
assessment can reveal that the child has a
limited vocabulary, uses only simple sentence structures, and may have difficulty
understanding complex instructions.
These language difficulties typically have a
knock-on effect on educational progress,
because children with SLI have difficulty
learning to decode print and understand
written texts.
Many of these children will be referred
to an audiologist with the aim of excluding
hearing loss as a cause of language learning
problems. High frequency hearing loss can
produce a clinical picture that resembles
SLI [2]. However, in children with SLI,
sensorineural hearing is normal. Fluctuating
conductive loss associated with middle ear
disease is a common problem in young
children, and was once thought to be a risk
factor for SLI. However, more recent
epidemiological studies suggest that
middle ear disease is unlikely to be a major
cause of persisting language problems in
children, unless other risk factors are
present [3].
S
There is, however, much more to auditory processing than peripheral hearing,
and for several decades now there has
been interest in the idea that SLI may be
caused by an impairment in the higher
auditory pathways going from the auditory
nerve to the brain. However, whereas there
are well-established methods for assessing
integrity of the peripheral auditory system,
there is much less consensus about how to
test for higher-level auditory dysfunction.
There are some test batteries for ‘auditory
processing disorder’ (APD), but they are
problematic for several reasons [4].
We can distinguish between three kinds
of processing that are involved in translating heard speech into meaning (Figure 1)
[5]. First, the sound must be detected:
problems with this stage will be picked up
on a conventional hearing test. Next, key
features of the sound must be discriminated. It has been suggested that, just as
some people are colour-blind, and so
cannot see the difference between red and
green, there may be children who are
unable to distinguish between aspects of
sound such as frequency, duration or
intensity. This might leave them unable to
tell the difference between sounds in their
language, such as ‘t’ and ‘k’. Another kind of
discrimination problem is difficulty in separating important aspects of sound, such as
a speech signal, from background noise. An
Detection:
Which interval
contains a stimulus?
Discrimination:
Are the two stimuli the
same or different?
Identification:
Which interval contains
an A?
Figure 1: Illustration of the distinction between detection, discrimination and identification using a
visual analogy. The identification stage involves matching what is perceived to stored knowledge
in the brain. Identification of speech sounds will be influenced by knowledge of language.
98
ENT & audiology news | NOVEMBER/DECEMBER 2013 | VOL 22 NO 5

2. feature
Many children who present with listening difficulties
meet criteria for a neurodevelopmental disorder such as
SLI, developmental dyslexia, autism spectrum disorder,
or attention deficit-hyperactivity disorder.
important aspect of language comprehension is the next step, that of identification.
This involves matching what has been
heard against existing stored templates in
the brain. This final step is completely
dependent on prior learning. If somebody
talks to me in Chinese, I won’t be able to
identify the individual speech sounds, let
alone make any sense of what was said,
even if my hearing and auditory discrimination are entirely normal.
The reason why tests of auditory
processing are often controversial is
because they typically assess identification
of sounds, often using real words. For
instance, the task may be to repeat words
that have been acoustically modified by
filtering, or to listen to words that are
presented dichotically. Failure on this kind
of task is difficult to interpret, because it
could reflect either a bottom-up problem
in discriminating certain sound features, or
a lack of the top-down knowledge that is
needed for speech identification. If a child
with language difficulties fails one of these
tests, there is a tendency to conclude that
they have an auditory processing problem
that has caused the language difficulty.
However, there’s another possibility, which
is that they may have a language difficulty
that was caused by something else, but
which impairs their ability to do tasks that
involve word identification. So the APD
test might just be picking up the consequences of having a language problem.
We therefore need to be very careful in
how we interpret the results from APD
tests with children. Just because the test
says it is measuring auditory processing
does not mean it is valid for that purpose.
A useful armchair exercise when evaluating
an APD test is to consider how you would
perform on such a test if it were administered in a language you didn’t know well. If
language knowledge has an impact on test
performance, then poor performance
could reflect language impairment rather
than auditory processing difficulties [6].
This is not the only issue affecting interpretation. Many tests of auditory discrimination and identification also place
demands on sustained attention and
memory skills – two areas where children
with language problems are often impaired.
Anyone who has tried establishing an auditory discrimination threshold by asking a
rambunctious six-year-old to judge if pairs
of sounds are same or different will know it
can be well-nigh impossible to get reliable
results. Typically the child will start to ask
how much more they have to do after
about six trials.
For reasons like this, a team at the MRC
Institute of Hearing Research in
Nottingham developed a new battery of
tests for APD that had two important
features. First, they did not involve
language: instead they used meaningless
sounds. Second, for each test, there were
two versions: one that taxed the auditory
system, and another that adopted exactly
the same format, but did not require the
child to discriminate auditory stimuli on a
key dimension. By subtracting the thresholds obtained for the two tests, one could
get an estimate of ability to discriminate
that dimension, after taking into account
‘task variables’ – e.g. ability to attend to the
task, to remember the stimuli, to make
appropriate responses and so on [7].
However, the resulting measures were
generally not very reliable and did not
relate closely to parents’ reports of listening
or communication problems.
It’s often thought that neurophysiological methods can solve the problems
inherent in behavioural APD tests, because
you can directly measure the brain’s
response to sounds, without requiring a
behavioural response from the child.
However, the more such methods are used,
the more it becomes clear that they too
are influenced by top-down knowledge. To
take one example, the mismatch negativity
– an event-related potential (ERP) component that is recorded when a rare sound
occurs in a sequence of standard sounds –
varies depending on whether the sounds
are used meaningfully in the person’s native
language [8].
So it’s complicated! It’s entirely possible
that there are children who have genuine
problems in the central auditory system
that affect discrimination and identifica-
tion of sounds. However, in practice it can
be very hard to distinguish such problems
from higher-level difficulties with language,
attention and motivation. In some children, poor performance on auditory
processing tests may be the consequence of
having a specific learning disability, rather
than the cause. Many children who present
with listening difficulties meet criteria for a
neurodevelopmental disorder such as SLI,
developmental dyslexia, autism spectrum
disorder, or attention deficit-hyperactivity
disorder [9, 10]. Presence of one of these
conditions does not preclude the possibility that auditory processing problems
are part of the clinical picture, but
attempting to unravel causation is
complex. It is important to work closely
with other professionals who can assess
language, cognitive ability and attentional
skills when assessing children who present
with possible APD.
References
1. Bishop D, Norbury CF. In Rutter M et al. (Editors),
Rutter's Child and Adolescent Psychiatry. Oxford,
Blackwell Publishing, 2008: 782-801.
2. Stelmachowicz P, Pittman AL, Hoover BM, Lewis
DE. The importance of high-frequency audibility in
the speech and language development of children
with hearing loss. Archives of Otolaryngology–Head
& Neck Surgery 2004;130:556.
3. Roberts JE, Rosenfeld RM, Zeisel SA. Otitis media
and speech and language: A meta-analysis of
prospective studies. Pediatrics 2004;113:E238.
4. Moore DR. Auditory processing disorder (APD):
Definition, diagnosis, neural basis, and intervention.
Audiological Medicine 2006;4:4.
5. Bishop DVM. Uncommon Understanding:
Development and Disorders of Language
Comprehension in Children. Hove, Psychology Press;
1997.
6. Crandell CC, Smaldino JJ. Speech perception in
noise by children for whom English is a second language. American Journal of Audiology 1996;5:47.
7. Moore DR, Ferguson MA, Edmondson-Jones AM,
Ratib S, Riley A. Nature of auditory processing disorder in children. Pediatrics 2010;126:e382.
8. Näätänen R, et al. Language-specific phoneme representations revealed by electric and magnetic
brain responses. Nature 1997;385:432.
9. Dawes P, Bishop D. Psychometric profile of children
with auditory processing disorder (APD) and children with dyslexia. Arch Dis Child 2010;95:432.
10. Ferguson MA, Hall RL, Riley A, Moore DR.
Communication, listening, cognitive and speech
perception skills in children with auditory processing disorder (APD) or specific language impairment
(SLI). J Speech Lang Hear Res 2011;54:211.
Further reading
Dawes P, Bishop D. Auditory processing disorder in
relation to developmental disorders of language, communication and attention: a review and critique.
International Journal of Language and Communication
Disorders 2009;44:440-65.
Website with short videos explaining aspects of
Specific Language Impairment
http://www.youtube.com/RALLIcampaign
ENT & audiology news | NOVEMBER/DECEMBER 2013 | VOL 22 NO 5
99