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In recent
years, several researchers have suggested that there is considerable overlap
between ADHD and Central Auditory Processing Disorder (CAPD). In fact, some have
questioned whether CAPD and ADHD are really distinct disorders, or have
suggested that children diagnosed with ADHD often have CAPD instead. A
recently published study takes a careful look at this issue (Gomez, R., &
Condon, M. (1999). Central auditory processing ability in children with ADHD
with and without learning disabilities. Journal of Learning Disabilities,
32, 150-158).
Since many people are unfamiliar with CAPD (at least I was until relatively recently),
I'll begin with a brief overview of what this condition actually is. CAPD is
defined as a deficiency in one or more of the following processes: sound
localization and lateralization (i.e. being able to determine where sounds
are coming from), auditory discrimination (i.e. being able to detect
differences between sounds), auditory pattern recognition (i.e. being able to
correctly identify/recognize patterns of sounds), temporal aspects of
audition (i.e. being able to identify the ordering of different sounds), and
auditory performance decrements in the presence of competing sounds (i.e.
being able to screen out extraneous auditory stimuli to correctly identify
important sounds).
Deficits in one or more of these areas are believed to adversely affect an
individual's speech and language functioning. Thus, someone with CAPD may
have unusual difficulty being able to accurately process spoken language,
particularly in the presence of background noise, and thus have a difficult
time comprehending what is being said.
One can certainly see how such a problem would make it difficult for a
child sitting in a crowded and noisy classroom, and how this child might
display symptoms of inattention and hyperactivity as a result. This is why
some professionals, professional speech and language specialists, suggests
that CAPD may often be misdiagnosed as ADHD. (Note that it is certainly been
shown than speech and language problems are more common in children with
ADHD.) Prior studies have shown that children with ADHD tend to perform
poorly on central auditory processing tasks and that as many as 50% of
children diagnosed with CAPD also have ADHD.
The authors of this study were interested in examining what might account for
the considerable overlap between ADHD and CAPD, and hypothesized that the
common link may be learning disabilities (LD). Children with ADHD and
children with CAPD both have significantly higher rates of LD than is found
in the general population. Although learning disabilities are defined in
several different ways, a commonly used procedure for identifying a child as
LD is to determine the discrepancy between the child's IQ score and
achievement test scores using standardized IQ and achievement tests. When a
child is achievement at a level that is significantly below what the child
should be capable of based on their intellectual level, the child is
considered to have a learning disability (i.e. the learning disability is
what is hypothesized to prevent the child from achieving at the level he/she
should be capable of). Learning disabilities can occur in a number of areas
including basic reading skills, reading comprehension, math, and written
language. A child may have a LD in one area but not others, or may have
multiple learning disabilities.
In the study, the authors began with 3 groups of 15 school-age children. One
group was comprised of children with ADHD alone; a second group included
children with ADHD with a learning disability in reading; the third group was
made up of children without either diagnosis. The ratio of boys to girls in
each group was about 3:1. (Note: It would have been nice if they included a
fourth group comprised of children diagnosed with CAPD but not ADHD, and a
final group of children with both CAPD and LD as this would have allowed for
a more complete set of comparisons).
Each child was given several different tests of central auditory processing
ability. These included being required to completed words that were presented
with portions missing; an auditory discrimination task in which participants
were asked to repeat words that are presented with background noise; a
dichotic listening tasks in which different words are presented in each ear,
and participants have to repeat both words in a specified order; and an
auditory conceptualization task in which children had to discriminate
different speech sounds (e.g. the sound of /p/ from the sound of /b/,) and to
perceive and compare the number and order of sounds within a pattern. All these tasks are elements of determining
whether an individual child has CAPD. All testing was done individually, and
care was taken to be sure that children with ADHD had not received any
medication for at least 48 hours prior to testing.
The results were really quite clear-cut. Based on a composite score derived
from the different auditory processing tests, children with ADHD alone did
not differ from the control group. Children with both ADHD and LD, however,
scored significantly lower than both control children, and children with
ADHD. This clearly suggests that problems in central auditory processing
ability are associated with LD and not ADHD. It is also provides strong
evidence that ADHD and CAPD are truly different disorders, rather than being
slightly different expressions of the same basic disorder.
Now, even though these results suggest that ADHD and CAPD are distinct
conditions, it is still quite possible that some children with CAPD are
misdiagnosed as having ADHD. If this were to occur, it seems less likely that
proper treatment would be unlikely to be instituted, although there is some
data to indicate that stimulant medication is helpful to children with CAPD.
These results also suggest that children with ADHD who are also learning
disabled in reading may be especially likely to have CAPD. For such children,
a careful evaluation of this possibility may prove to be quite helpful in
developing the most effective treatment plan. The most appropriate
professional to consult for such an evaluation would be a speech and language
specialist. Most physicians and clinical psychologists are not likely to have
much experience in this area.
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