Differential Diagnosis and Management of Central Auditory

J Am Acad Audiol 10 : 289-303 (1999)
Differential Diagnosis and Management
of Central Auditory Processing Disorder and
Attention Deficit Hyperactivity Disorder
Gail D. Chermak*
James W. Hall 111'
Frank E. Musiekl,
Abstract
Children diagnosed with attention deficit hyperactivity disorder (ADHD) frequently present
difficulties performing tasks that challenge the central auditory nervous system . The relationship between ADHD and central auditory processing disorder (CAPD) is examined from
the perspectives of cognitive neuroscience, audiology, and neuropsychology. The accumulating evidence provides a basis for the overlapping clinical profiles yet differentiates CAPD
and ADHD as clinically distinct entities . Common and distinctive management strategies are
outlined .
Key Words : Attention deficit hyperactivity disorder, central auditory processing disorder
Abbreviations: ADHD = attention deficit hyperactivity disorder, CAPD = central auditory processing disorder
hildren diagnosed with attention deficit
hyperactivity disorder (ADHD) frequently present difficulties performing
tasks that challenge the central auditory nervous
system. The association observed between attention deficits and performance on central auditory
tests (Campbell and McNeil, 1985 ; Gascon et al,
1986 ; Cook et al, 1993 ; Pillsbury et al, 1995) has
elicited suggestions of linkage between ADHD
and central auditory processing disorder (CAPD) .
Some have questioned whether CAPD is a manifestation of impaired attention (Burd and Fisher,
1986 ; DeMarco et al, 1989 ; Robin et al, 1989) and
whether CAPD and ADHD reflect a single developmental disorder (Gascon et al, 1986 ; Cook et
al, 1993). Others have interpreted central auditory performance deficits among children with
ADHD as a reflection of the co-occurrence or
C
*Department of Speech and Hearing Science, Washington State University, Pullman, Washington; tVanderbilt University School of Medicine, Nashville, Tennessee ; tSection
of Otolaryngology, Dartmouth-Hitchcock Medical Center,
Lebanon, New Hampshire
Reprint requests : Gail Chermak, Department of Speech
and Hearing Science. Washington State University, Pullman,
WA 99164-2420
comorbidity of CAPD and ADHD (Keith and
Engineer, 1991 ; Riccio et al, 1993, 1996). For
example, finding low correlations between performance on the Staggered Spondaic Word Test
and behaviors characteristic of ADHD (i .e ., inattention, hyperactivity, and impulsivity), Riccio
et al (1996) concluded that ADHD and CAPD are
distinct entities that may nonetheless both
involve deficits in auditory processing . It is also
possible that the observed comorbidity of CAPD
and ADHD reflects a shortcoming in the accuracy of differential diagnosis using current procedures and criteria (Riccio et al, 1994).
That central auditory performance deficits
among children with ADHD may reflect the
presence of CA-PD rather than the ADHD per
se is supported further by the frequently
reported history of chronic otitis media in children with ADHD (Silva et al, 1982 ; Feagans et
al, 1987 ; Roberts et al, 1989 ; Adesman et al,
1990 ; Pillsbury et al, 1995). The association
between chronic otitis media and CAPD, with
persistence of central auditory processing
deficits even after resolution of the otitis media
and return to normal hearing levels (Jerger et
al, 1983 ; Silva et al, 1986 ; Adesman et al, 1990 ;
Moore et al, 1991 ; Pillsbury et al, 1991 ; Gravel
and Wallace, 1992 ; Hutchings et al, 1992 ; Hall
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Journal of the American Academy of Audiology/Volume 10, Number 6, June 1999
and Grose, 1993, 1994 ; Brown, 1994 ; Hall et al,
1994, 1995), suggests that children with ADHD
may experience central auditory performance
deficits subsequent to chronic otitis media .
Indeed, the frequently observed co-occurrence
of CAPD and learning disability (Ferre and
Wilber, 1986 ; Jerger et al, 1987 ; Elliott and
Hammer, 1988 ; Breedin et al, 1989 ; Chermak
et al, 1989) and CAPD and language impairment
(Tallal and Piercy, 1973a; Sloan, 1980 ; Tallal,
1980a, b; Lubert, 1981 ; Tallal et al, 1985, 1996)
has led to speculation that these deficits also
may be causally related (Katz and Illmer, 1972 ;
Tallal and Piercy, 1973a; Knox and Roeser,
1980 ; Sloan, 1980 ; Keith, 1981 ; Lubert, 1981 ;
Tallal et al, 1985, 1996).
The literature is replete with reports of individuals with concurrent diagnoses of CAPD,
attention deficits, and learning disabilities
(Keith, 1986 ; Katz, 1992 ; Keller, 1992; Newhoff
et al, 1992 ; Riccio et al, 1993, 1996 ; Pillsbury et
al, 1995). However, the relationships among
CAPD, ADHD, and learning disabilities are complex and not completely understood, and the
primacy of any one of these disorders as causal
to another remains unclear (Chermak and
Musiek, 1997). Recent behavioral and neuroanatomical data, as well as a bottom-up model
of information processing and the reconceptualization of ADHD as a behavior regulation disorder, provide fresh insights regarding probable
linkages and distinctions . Drawing upon these
converging lines of evidence, we argue that
CAPD and ADHD reflect two distinct clinical disorders, notwithstanding some overlap in their
behavioral profiles (Chermak and Musiek, 1997).
CENTRAL AUDITORY
PROCESSING DISORDER
C
APD results from dysfunction of processes
dedicated to audition ; however, CAPD also
may coexist with more global dysfunction that
affects performance across modalities (e .g., attention deficit, neural timing deficit, language representation deficit) (ASHA, 1996). CAPD has
been observed in diverse clinical populations,
including those where central nervous system
pathology or neurodevelopmental disorder is
suspected (e .g ., developmental language disorder, dyslexia, learning disabilities, attention
deficit disorder) and those where evidence of
central nervous system pathology is clear (e .g .,
aphasia, multiple sclerosis, epilepsy, traumatic
brain injury, tumor, and Alzheimer's disease)
290
(ASHA, 1996). CAPD has also been observed in
older adults, presumably due to nonpathologic
neurologic changes associated with aging (Committee on Hearing, Bioacoustics, and Biomechanics [CHABAI Working Group on Speech
Understanding and Aging, 1988 ; Gulya, 1991 ;
Stach et al, 1990).
A CAPD involves a deficit in one or more of
the central auditory processes responsible for
generating the auditory evoked potentials and
the behaviors of sound localization and lateralization, auditory discrimination, auditory pattern recognition, temporal processing (e .g .,
temporal resolution, temporal masking, temporal integration, and temporal ordering), auditory
performance with competing acoustic signals,
and auditory performance with degraded
acoustic signals (Chermak and Musiek, 1997).
Characteristically, patients with CAPD have
difficulty comprehending spoken language in
competing speech or noise backgrounds and in
reverberation (Olsen et al, 1975 ; Musiek et al,
1982 ; Jerger et al, 1987, 1988). Children with
CAPD ask frequently for repetitions, say "what"
and "huh" a lot, show extreme auditory inattentiveness and have trouble paying attention,
are easily distracted, often misunderstand messages, and have trouble following complex auditory directions or commands and localizing sound
(Bornstein and Musiek, 1992).
CAPD is diagnosed on the basis of performance on a battery of auditory tests, which may
include electrophysiologic as well as behavioral
procedures, administered under acoustically
controlled conditions (Jirsa and Clontz, 1990 ;
Kraus et al, 1993 ; Musiek and Chermak, 1994 ;
Chermak and Musiek, 1997).
Prevalence data for CAPD are sparse, particularly for children . Cooper and Gates (1991)
estimated CAPD in 10 percent to 20 percent of
older adults . Stach et al (1990) reported CAPD
in 70 percent of clinical patients over age 60
years . Chermak and Musiek (1997) estimated
that CAPD occurs in 2 percent to 3 percent of
children, with a 2 :1 ratio between boys and girls .
Similarly, Musiek et al (1990) estimated prevalence of CAPD in children at 3 percent to 7
percent .
ATTENTION DEFICIT
HYPERACTIVITY DISORDER
DHD is characterized as the most common
Aneurobehavioral disorder of childhood
(Shaywitz et al, 1994) . ADHD consists of a per-
Differential Diagnosis of CAPD and ADHD/Chermak et al
sistent pattern of inattention and/or hyperactivity-impulsivity that is more frequent and
severe than is typically observed in individuals
at a comparable level of development; manifests in at least two settings ; interferes with
developmentally appropriate social, academic, or
occupational functions ; and is present since
before age 7 years (APA, 1994).
Patterns of inattention, hyperactivity, and
impulsivity are used to differentiate ADHD into
three subtypes . The predominantly inattentive
type presents primary symptoms of inattention
(APA, 1994) . The predominantly hyperactiveimpulsive type is considered a behavioral regulation disorder (Barkley,1990, 1994 ; APA,1994) .
The combined type is characterized by hyperactivity-impulsivity (i .e ., behavioral regulation
disorder) and inattention (APA, 1994) . Criteria
for diagnosis of ADHD subtypes are listed in
Table 1 .
According to the DSM-IV impulsivity is
characterized by blurting out answers, failing to
take turns, and interrupting or intruding on
others . Hyperactivity is characterized by fidgeting with hands or feet or squirming in seat,
difficulty remaining seated, running or climbing
excessively in inappropriate contexts, difficulty
engaging in quiet activity, constantly moving
or engaging in activity, and talking excessively.
Inattention in ADHD is marked by difficulty
attending to details, sustaining attention to
tasks, listening when spoken to, following
through on instructions or finishing tasks, organizing tasks and activities, initiating tasks that
require sustained mental effort, keeping track
of objects needed for a task, ignoring extraneous
stimuli, and remembering routine procedures or
familiar information .
There are no empirical markers that identify ADHD (Taylor, 1986 ; Gordon, 1991 ; Reid et
al, 1993) . Therefore, diagnosis of ADHD is based
on observational criteria defined as a cluster of
behaviors involving impaired attention and distractibility, impulsivity, and hyperactivity (APA,
1994) .
Some 3 percent to 4 percent of children,
aged 2 to 8 years, may present with ADHD
(APA, 1994). Szatmari (1992) estimated that
5 percent to 7 percent of the childhood population presents with ADHD . Among the schoolaged population, 10 percent to 20 percent may
present with ADHD (Shaywitz and Shaywitz,
1988 ; Szatmari et al, 1989). The prevalence of
ADHD is higher among boys, with estimates
ranging between 3:1 and 6 :1 (Szatmari et al,
1989) .
Table 1 DSM-IV Criteria for
Diagnosis of ADHD Subtypes
A. Inattention
1 . Poor attention to details or careless mistakes
2 . Difficulty sustaining attention in tasks
Does not seem to listen when spoken to
Does not follow through on instructions or tasks
Difficulty organizing tasks
Difficulty with sustained mental effort
Loses things necessary for tasks
Often distracted by extraneous stimuli
Often forgetful in daily activities
8. Hyperactivity- Impulsivity
Hyperactivity
1 . Fidgets or squirms
2. Leaves seat in classroom
3. Runs or climbs excessively
4. Difficulty in engaging in quiet activity
5 . "On the go" or acts as if "driven by a motor"
6 . Talks excessively
Impulsivity
1 . Blurts out answers
2. Difficulty waiting turn
3 . Interrupts or intrudes on others
DSM-IV criteria for diagnosis of ADHD subtypes requires
the presence of six or more symptoms of inattention and/or
hyperactivity-impulsivity persisting for 6 or more months . ADHD,
Combined Type (meets criteria A and B) ; ADHD, Predominantly
Inattentive Type (meets criterion A, but not B) ; ADHD,
Predominantly Hyperactive-Impulsive Type (meets criterion B,
but not A) .
DIFFERENTIATING ATTENTION
DEFICIT HYPERACTIVITY DISORDER
AND CENTRAL AUDITORY
PROCESSING DISORDER
Nature of Attention Deficits
Although attention deficits frequently characterize CAPD and ADHD (particularly the combined and predominantly inattentive types),
there are distinctions to be drawn regarding
the nature of the inattention observed in the two
disorders. The attention deficits of ADHD typically are pervasive and supramodal, impacting
more than one sensory modality (Keller, 1992 ;
APA, 1994). In contrast, individuals with CAPD
experience attention deficits that may be
restricted to the auditory modality (Chermak and
Musiek, 1997). As noted by Chermak and Musiek
(1997), the commonly observed left-ear deficit on
dichotic speech tests seen in individuals with
CAPD, as well as their depressed auditory performance under conditions of either contralateral or ipsilateral competition as a function of
the level of brain dysfunction, argues against a
pervasive attention deficit in CAPD and helps
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distinguish CAPD from ADHD (Musiek et al,
1984, 1994 ; Jerger et al, 1988). Nonetheless,
further research is needed to ascertain the degree
to which modality specificity of processing deficits
characterizes CAPD (McFarland and Cacace,
1995).
Different types of attention deficits may be
seen in ADHD and CAPD (Chermak and Musiek,
1997). Although the neural mechanisms underlying the different behaviors associated with
various attention tasks are unknown, research
suggests that attention deficits associated with
the combined and predominantly hyperactiveimpulsive ADHD subtypes may be restricted to
sustained attention, albeit in multiple modalities (Seidel and Joschko, 1990 ; Hooks et al,
1994 ; Barkley, 1997a, b) . Selective (multimodal)
attention and speed of information processing
deficits may characterize the predominantly
inattentive ADHD subtype (Barkley, 1997a) .
Selective (focused) and divided auditory attention deficits characterize CAPD (Katz and Illmer,
1972 ; Lasky and Tobin, 1973 ; Cherry, 1980 ;
Jerger and Jerger, 1984 ; Keith, 1986). Inclusion of a recently released test of sustained auditory attention (vigilance) in the central auditory
test battery (Keith, 1994) should prove helpful
in substantiating this distinction .
While additional research is needed to clarify differences in the nature and type of attention deficits observed in ADHD and CAPD, it is
clear that the clinical inattention profiles differ
significantly. The inattention profile of ADHD
involves difficulty initiating, tracking, and
remembering tasks (APA, 1994), in addition to
sustaining allocation of attentional resources.
The focused and divided attention deficits that
characterize CAPD impact monaural and binaural separation and binaural integration tasks
(Chermak and Musiek, 1997). Most importantly,
the inattentiveness seen in CAPD is a primary
deficit resulting from an input or information
processing deficit . In contrast, the hyperactiveimpulsive and combined ADHD subtypes are
characterized as output or response programming and execution disorders (Barkley, 1997a,
b) . Behavioral disinhibition ultimately results in
poor goal-directed persistence and defective
resistance to distraction subsequent to poor selfregulation and executive control of behavior
(Goodyear and Hynd, 1992 ; Barkley, 1997a, b) .
Consistent with this conceptualization, inattention is a secondary deficit in the combined and
predominantly hyperactive-impulsive ADHD
subtypes (Barkley, 1997a, b) . As elaborated
below, the ADHD inattention profile may impli292
cate a primary executive control deficit, rather
than an attention deficit per se . Differentiating
the predominantly inattentive ADHD subtype
from CAPD is more challenging since the inattention in both disorders is considered to be a primary and input or information processing deficit.
Differential diagnosis requires examination of
auditory test outcomes as discussed above.
Reconceptualization of ADHD
The recent shift in conceptualizing ADHD
as a behavioral regulation disorder rather than
a primary attention disorder further distinguishes CAPD and ADHD (Chermak and
Musiek, 1997). Symptoms of impulsivity and
behavioral disinhibition are considered the result
of neurologically based, "developmental deficiencies in the regulation and maintenance of
behavior by rules and consequences" (Barkley,
1990, p. 71). Deficits in rule-governed behavior,
perhaps resulting from elevated arousal thresholds (Zentall, 1985) or elevated reinforcement
thresholds (Haenlein and Caul, 1987), lead to
problems initiating, inhibiting, or sustaining
responses to tasks or stimuli (Barkley, 1990),
which heretofore had been considered characteristics of attention deficits . Deficits in rule-governed behavior lead to problems in executive
functioning and self-regulation (Barkley, 1990).
Consistent with this reconceptualization, ADHD
is seen, essentially, as a motivational deficit,
rather than an attention deficit (Barkley, 1990,
1994 ; Chermak and Musiek, 1997). This reconceptualization ofADHD as one of poor rule-governed behavior may also explain the self-control
problems, social skill deficits, and language disorders (e .g ., difficulty topic switching, turn taking, and sustaining dialogue) so frequently
observed in ADHD (Augustine and Damico,
1995).
Behavioral Differences
Despite some overlapping symptomatology,
clinicians seem able to distinguish behavioral
profiles for CAPD and ADHD. Chermak et al
(1998) found that pediatricians and audiologists
view the predominant symptoms of ADHD and
CAPD as being rather distinct, with only 2 (i .e.,
inattention and distractibility) of the 11 most frequently cited behaviors reported as common to
both conditions (Table 2) . Inattention and distractibility were ranked as the first and second
most typical behaviors characterizing ADHD .
Audiologists ranked these same behaviors as
Differential Diagnosis of CAPD andADHD/Chermak et al
Table 2 Rank Order of Behavioral Means Greater than
1 Standard Deviation above the Respective Grand Mean
CAPD
ADHD
1 . Inattentive
2 . Distracted
3 . Hyperactive
4. Fidgety/restless
5. Hasty/impulsive
6. Interrupts/Intrudes
Grand mean
Standard deviation
4.36
1 . Difficulty hearing in background noise
4.40
3 . Poor listening skills
4. Academic difficulties
4.10
4 .00
6. Distracted
7. Inattentive"
3.55
4 .27
4 .14
2. Difficulty following oral instructions
4.14
3.86
5 . Poor auditory association skills
4.14
3 .25
0 .55
4.20
3 .75
3 .70
2 .90
0 .66
'Note that inattentive was included based upon an "evens-down/odds-up" rounding rule, the standard deviation was 0.01 points
below the criterion of +1 SD above the grand mean .
From Chermak et al, 1998 . Reprinted by permission .
seventh and sixth, respectively, in cases of CAPD.
CAPD was characterized by a selective attention
deficit and associated language processing and
academic difficulties ; ADHD was characterized
by inappropriate motor activity, restlessness,
and socially inappropriate interaction patterns .
Other investigators have reported that behavior problems, such as difficulty waiting one's
turn, playing quietly, and excessive talking,
more often characterize children with ADHD
than CAPD (Newhoff et al, 1992) . Similarly,
severe socioemotional sequelae (i .e ., conduct
disorders, juvenile delinquency) are more common among children with ADHD (Newhoff et al,
1992) . Interestingly, the predominantly inattentive ADHD subtype shares little if any comorbidity with disruptive behavior disorders, in
contrast to the predominantly hyperactive-impulsive and combined ADHD subtypes (Barkley,
1997a) .
RECONCILING THE COMORBIDITY OF
ATTENTION DEFICITS AND CENTRAL
AUDITORY PROCESSING DISORDERS
Modeling Information Processing
Insofar as attention is essential to higher
level processing, poor attention can compromise
listening. Musiek and Chermak (1995) proposed
that viewing the relationship between attention and auditory processing within the topdown and bottom-up information processing
models provides a theoretical framework that
clarifies the nature of the relationship between
ADHD and CAPD . The inability to sustain sufficient attention to auditory stimuli might cause
auditory processing deficits (i .e ., top down) ; con-
versely, deficient auditory processing (i .e ., bottom up) might impair attention (Chermak and
Musiek, 1997). Understanding the relationship
between the attention deficits of ADHD and
CAPD hinges on the interaction between perception and higher level cognitive processing
(Chermak and Musiek, 1997). Most germane is
whether an auditory processing deficit causes
some attention deficit (as we argue occurs in
CAPD) or whether a more global attention deficit
impedes auditory processing (as we argue occurs
in ADHD).
Consistent with a bottom-up model, attention is driven by incoming sensory stimulation
and garnered by properly integrated and
processed sensory stimuli (Musiek and Chermak, 1995 ; Chermak and Musiek, 1997). If
acoustic stimuli are not properly processed, as
occurs in CAPD, then optimal attention cannot
be focused on these stimuli in a timely manner
(Phillips, 1990). Attention deficits are seen as secondary to auditory perceptual processing deficits
within the framework of a bottom-up model
(Chermak and Musiek, 1997). In contrast, CAPD
would be seen as a manifestation of a global
attention deficit within a top-down information
processing model (Chermak and Musiek, 1997).
While it is likely that bidirectional interactions between central auditory processing and
attention are necessary for optimal listening
comprehension, experimental evidence from
basic science supports a bottom-up view of attention deficits whereby deficiencies in auditory
perceptual processes trigger attention deficits
(Hassamannova et al, 1981 ; Robertson and
Irvine, 1989; Farah and Wallace, 1991 ; Harrison
et al, 1992 ; Irvine et al, 1992 ; Mogdans and
Knudsen, 1992, 1993, 1994 ; Recanzone et al,
1993 ; Phillips, 1995). Experimental evidence
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Journal of the American Academy of Audiology/Volume 10, Number 6, June 1999
regarding the plasticity of the central auditory
nervous system supports the authors' bottom-up
view of auditory perceptual deficits as causal to
CAPDs. This evidence suggests that central
changes are contingent on sensory function and
experience (Moore, 1993). For example, cortical
reorganization has been observed in young and
adult mammals following induced cochlear
lesions (Robertson and Irvine, 1989 ; Harrison et
al, 1992 ; Irvine et al, 1992 ; Rajan et al, 1993 ;
Schwaber et al, 1993 ; Willott et al, 1993).
Consistent with a bottom-up perspective,
listening difficulties seen in CAPD result from
specific auditory perceptual deficiencies rather
than global attention deficits (ADD subtype) or
behavioral regulation deficits (combined ADHD
and predominantly hyperactive-impulsive ADHD
subtypes) (Phillips, 1990, 1995 ; Tallal et al,
1996). As outlined in Table 3 and discussed earlier, CAPD is considered an input disorder that
impedes selective and divided auditory attention.
The combined and predominantly hyperactiveimpulsive ADHD subtypes are seen as output
disorders in response programming and execution that indirectly cause sustained attention
deficits across modalities . Dual diagnoses of
both CAPD and ADHD may result, therefore,
from comorbid attention deficits at different levels and primacy of sensory and global dysfunction (Chermak and Musiek, 1997).
Neuromorphologic Correlates
Brain imaging studies and postmortem
examinations of individuals with dyslexia,
learning disabilities, ADHD, and normal controls have revealed morphologic and structural
differences in auditory areas of the brain that
are activated when listening to simple tonal
complexes, language, and music (i .e ., superior
temporal gyrus, Heschl's gyrus, planum temporale, posterior portion of the insula, sulcus
of the corpus callosum) (Galaburda and Kemper, 1978 ; Hynd et al, 1990, 1991). The accumulating data suggest a neuroanatomical basis
for the often observed co-occurrence of CAPD,
auditory attention deficits, dyslexia, and learning disabilities .
Postmortem studies have documented brain
abnormalities (e .g ., nests of ectopic [misplaced]
and underdeveloped cells) involving auditory
regions of the brain in children with learning disabilities and dyslexia (Galaburda and Kemper,
1978; Galaburda and Eidelberg,1982 ; Galaburda
et al, 1985) . Developmental abnormalities of
the cerebral cortex were observed in all four
294
Table 3 Differentiating Attention
Deficits in ADHD Disorder and CAPD
ADHD Combined and Predominantly
Hyperactive-Impulsive Subtypes
Output disorder
Sustained attention deficit secondary to behavioral
disinhibition and poor self-regulation
Executive dysfunction
ADHD Predominantly Inattentive Subtype
Input disorder
Global attention deficit
Selective (focused) attention deficit
Reduced rate of information processing
CAPD
Input disorder
Specific auditory perceptual deficit
Selective (focused) and divided attention deficits
Executive dysfunction as secondary source of listening
problems
brains studied of men diagnosed as dyslexic
during life (Galaburda et al, 1985). Cerebrocortical abnormalities may be observed in normal
brains, albeit in far smaller numbers and in different locations relative to the brains of abnormal subjects (see Kaufmann and Galaburda,
1989). Brain imaging studies have revealed morphologic and structural differences in auditory
areas as well as motor regulation/behavioral
inhibition areas (prefrontal lobes and striatum)
of the brains of children with ADHD, as compared with the brains of normal children, implicating some deviation in normal brain
development (Hynd and Semrud-Clikeman,
1989 ; Lou et al, 1989; Hynd et al, 1990 ; Zametkin
et al, 1990 ; Weller, 1991 ; Mann et al, 1992).
The corpus callosum was reported smaller
in children with ADHD relative to normal controls (Hynd et al, 1991). Hynd (personal communication, 1992) indicated that the morphology
of Heschl's gyrus may also differ in children
with ADHD, as compared with normal controls .
The planum temporale was reported shorter in
the left hemisphere and of reversed asymmetry
(R > L) in subjects with dyslexia relative to normal controls (Hynd et al, 1990). Seventy percent
of the normal children and the children with
ADHD presented the expected left greater than
right pattern of plana asymmetry, while only 10
percent of the children with dyslexia demonstrated this normal pattern (Hynd et al, 1990).
Similarly, the insular region of the brains of
children with dyslexia are smaller bilaterally
than normal controls (Hynd et al, 1990).
Differential Diagnosis of CAPD and ADHD/Chermak et al
Morphologic differences and possible dysfunction in areas of the brain associated with
motor regulation and self-control (e .g ., frontal
region, caudate nucleus) suggest a neurobiological basis for co-occurring central auditory
deficits and behavioral regulation problems in
ADHD . Lou et al (1989) reported decreased
metabolism in the caudate nucleus associated
with ADHD . Mann et al (1992) found increased
slow wave activity in the frontal regions and
decreased beta activity in the temporal regions
in boys with ADHD, compared to normal control
subjects . Hynd et al (1990) reported bilaterally
smaller anterior cortexes in children with ADHD
and dyslexia relative to a control group of children, reflecting significantly decreased right
frontal lobe width . In addition, the children with
dyslexia showed hemispheric symmetry in this
region in contrast to the typical pattern of the
right frontal lobe being larger than the left
(Hynd et al, 1990) .
Executive Function
Executive functioning provides a construct
useful in understanding a wide range of symptoms observed across many disorders with overlapping clinical profiles (Pennington et al, 1996),
including ADHD and CAPD . Because executive
functions place significant demands on attention
(both sustained and selective attention to enable
sensory and perceptual processing of events)
and memory to register, store, and make knowledge and experience available to the individual
(Butterfield and Albertson, 1995 ; Barkley, 1996 ;
Pennington et al, 1996), executive dysfunction
may be related to deficits characterizing ADHD
and CAPD .
Executive function is a component of metacognition that refers to a set of general control
processes that ensure that an individual's behavior is adaptive, consistent with some goal, and
beneficial to the individual (Brown et al, 1983 ;
Sternberg, 1985 ; Borkowski et al, 1988 ; Denckla,
1996 ; Torgesen; 1996). Executive control processes coordinate knowledge (i .e ., cognition) and
metacognitive knowledge in support of task
analyses, planning, and reflective decision making, ultimately transforming this knowledge
into behavioral strategies (Butterfield and
Albertson, 1995 ; Barkley, 1996). They are crucial to the execution of novel behavioral
sequences; learning and problem solving; psychosocial function, including self-image, selfregulation of emotion, and motivation ; and
goal-directed behaviors, including listening
(Grattan and Eslinger, 1992 ; Grattan et al, 1994 ;
Borkowski and Burke, 1996). Executive function
may be assessed by a variety of procedures and
tests including auditory and visual continuous
performance tests, the Wisconsin Card Sorting
Test, the Stroop tasks, Matching Familiar Figures Test, and measures of verbal fluency
(Denckla, 1989).
Executive function deficits have been
described in a wide variety of clinical populations,
often in association with brain disease or injury,
and may underlie childhood neurologic disorders,
in particular, the academic problems experienced by children with learning disabilities or
ADHD (Stanovich, 1986 ; Pennington, 1991 ;
Torgesen, 1994 ; Fletcher et al, 1995 ; Denckla,
1996 ; Graham and Harris, 1996) . Executive
function deficits also have been identified in
children who do not meet eligibility criteria for
learning disabilities or ADHD but experience significant difficulties in school (Denckla,1989) . The
prevalence of CAPD in the latter group of children has not been determined (Chermak and
Musiek, 1997).
Linkages among executive function, rulegoverned behavior, and self-control (Hayes et al,
1996) have led to suggestions that executive
dysfunction is the source of the behavioral regulation and inattention problems manifested in
ADHD (Denckla and Reader, 1993 ; Barkley,
1994 ; Smith et al, 1995). Recognizing that pragmatic and metacognitive behaviors associated
with communication are both language based
and rule governed, Westby and Cutler (1994) reasoned that executive dysfunction also may
explain language deficits in ADHD, such as poor
topic maintenance, inappropriate topic switching, poor problem solving, and difficulty producing coherent extended discourse such as
stories and expository texts (Heyer, 1995), as well
as contribute to the pragmatic problems observed
in individuals with ADHD, which include excessive talking, interrupting others, blurting out
answers, difficulty waiting one's turn, and difficulty negotiating peer interactions .
Although executive dysfunction in CAPD
has not been examined, it is reasonable to expect
that auditory perceptual deficits impede operation of executive functions (Chermak and
Musiek, 1997). Difficulty organizing, monitoring,
and understanding acoustic signals may reflect
limited use of executive function . In contrast to
the proposed causal role of executive dysfunction
in ADHD (Denckla and Reader, 1993 ; Barkley,
1994 ; Smith et al, 1995), and consistent with a
bottom-up processing model, executive dys295
Journal of the American Academy of Audiology/ Volume 10, Number 6, June 1999
function in CAPD would be considered a secondary feature, not a primary cause, of listening difficulties (Chermak and Musiek, 1997).
These secondary deficits could compound auditory processing deficits, impede generalization
of strategic listening behaviors across settings,
and thereby jeopardize treatment efficacy
(Borkowski and Burke, 1996 ; Chermak and
Musiek, 1997). The distinctions we have posited
between ADHD and CAPD are summarized in
Table 3.
IMPLICATIONS FOR
ASSESSMENT AND INTERVENTION
inkages between ADHD and CAPD underL score the importance of thorough and multidisciplinary assessment with individuals
suspected of these disorders. Individuals with
diagnoses of CAPD, ADHD, and learning disabilities commonly experience some degree of
spoken language processing deficit (Wiig and
Semel, 1984 ; Gravel and Wallace, 1992 ; Westby
and Cutler, 1994). Given the well-known relationship between structure and function, the
emerging neuromorphologic data suggesting
some dysfunction in auditory areas of the brain
in cases of learning disability, dyslexia, ADHD,
and CAPD offer compelling rationale for thorough assessment of the auditory system and
auditory perceptual abilities. Clinicians must use
sensitive measures to evaluate the integrity of
underlying perceptual, linguistic, and cognitive
systems to determine the predominant and primary deficits, as well as secondary problems
that may underlie these deficits (McFarland
and Cacace, 1995). Such an approach requires
the interdisciplinary efforts of audiologists,
speech-language pathologists, teachers, psychologists, and physicians for assessment and for
intervention . Differentiating ADHD and CAPD
hinges on accurate diagnosis of these conditions .
Special Strategies for the
Assessment of Central Auditory
Processing in Children with Attention
Deficit Hyperactivity Disorder
Audiologic assessment of children with
ADHD is clinically challenging. Valid behavioral measurement of auditory status requires
that the child willingly cooperate in the assessment, understand the instructions, and attend
to the task. Each of these requirements may be
compromised in the ADHD population . The likelihood of successfully assessing central audi296
tory nervous system function in children with
ADHD or suspected ADHD is enhanced by several practical modifications in the test strategy.
However, when behavioral audiometric findings
remain incomplete, inconclusive, or invalid
despite the implementation of these modifications, one must rely more on electrophysiologic
techniques (Musiek et al, 1991 ; Hall, 1992 ;
Chermak and Musiek, 1997). Indeed, electrophysiologic procedures may inform differential
diagnosis of CAPD and ADHD . For example,
children with CAPD present significantly
delayed
P30 latencies and reduced
P30 amplitudes compared to children with ADHD whose
P30 latencies and amplitudes do not differ from
those of normal control subjects (Jirsa and
Clontz, 1990 ; Sangal et al, 1995).
Perhaps the single most important step in
successful audiologic assessment of the child
with diagnosed and medically managed ADHD
is to ensure that the child received an effective
dose of medication immediately before the test
session. Although this statement seems obvious, it is important to specifically instruct caregivers to follow the typical school day routine for
medication on the day of the audiologic assessment . Some might argue that audiologic assessment should be conducted with the child in his
or her natural state (e.g., without medication) .
Others might express concerns about the possible
confounding effects of the medication on test
performance. Our clinical experience suggests at
least three responses to these arguments. First,
if the child is regularly given medication on
school days, then following the prescribed medication schedule will result in a typical state. Second, there is no evidence that the medications
used in management of ADHD (e .g ., Ritalin,
Cylert, Adderall) have any influence on the
peripheral or central auditory nervous system
functioning . Finally, for children with diagnosed
ADHD who are treated medically, valid audiologic assessment would rarely be possible without medication . Therefore, it is advisable to
verify that the child received appropriate medication on the test day. Also, the assessment is
best scheduled to begin first thing in the morning (e .g ., 8:30 or 9:00 AM).
Peripheral auditory function should be evaluated thoroughly, but expediently, prior to central auditory assessment . Afeasible test sequence
is immittance measurement (tympanometry
and both uncrossed and crossed acoustic
reflexes), pure-tone audiometry (including interoctave frequencies of 3000 and 6000 Hz), speech
reception thresholds, word recognition perfor-
Differential Diagnosis of CAPD and ADHD/Chermak et al
mance, and otoacoustic emissions . Since the
overall objective is assessment of central auditory function, the evaluation of peripheral auditory function should be conducted as quickly as
possible, without sacrificing vital information .
To save test time, pure-tone audiometry is limited to air-conduction signal whenever immittance measurement yields findings consistent
with normal middle ear function . As an aside,
acoustic reflex thresholds should be measured
very cautiously, or not at all, when history suggests the possibility of hyperacusis, or intolerance to loud sounds . Speech reception threshold
measurement can be bypassed if pure-tone
audiometry is reliable and entirely normal . Most
patients have normal hearing sensitivity. If so,
word recognition performance can be efficiently
assessed with lists constructed with the most
difficult 10 words first. If the child correctly recognizes these first 10 words, testing is discontinued . Twenty-five word lists are appropriate
for children with peripheral hearing loss, or
when performance for the shortened lists is less
than 100 percent . Otoacoustic emissions recording with a cooperative child will generally require
less than 2 minutes per ear, even with a protocol that is sensitive to cochlear dysfunction (e .g .,
distortion product otoacoustic emissions with
Ll = 65 dB and L2 = 55 dB or transient evoked
otoacoustic emissions with an 80 dB SPL click
stimulus) . By employing these test-time-saving
strategies, the experienced audiologist can usually complete the peripheral assessment in less
than 30 minutes .
A description of the CAPD test battery is
beyond the scope of this paper . The overall
objective of the test battery is to determine
whether the child shows a deficit in one or more
of the central auditory processes noted earlier
in this paper (ASHA, 1996) . Comparison of
speech identification/recognition performance
in quiet versus competition, as well as comparisons in the presence of ipsilateral versus contralateral competition, may inform differential
diagnosis of attention deficits and CAPD .
Phoneme processing difficulties in quiet are
unlikely to be the result of a pervasive attention
deficit (Jerger et al, 1987) . Similarly, deficits in
word identification in noise for phonemically
similar words, but not for semantically similar
words, argue against a pervasive attention deficit
as the cause of the abnormal performance (Jerger
et al, 1987) . Likewise, speech recognition deficits
seen only in the presence of either ipsilateral or
contralateral competition or only under more
challenging, but not all, signal-to-competition
ratios would suggest a specific auditory perceptual deficit rather than a pervasive attention
deficit. The reader is referred to recent textbooks by the authors for detailed discussions of
CAPD assessment procedures and protocols and
the analyses and interpretation of CAPD findings (Chermak and Musiek, 1997 ; Hall and
Mueller, 1997). Throughout the audiologic test
battery, attention level and cooperation will be
enhanced by two or three breaks during which
the child is given the opportunity to move about
and, perhaps, have a light snack. In addition, test
performance is often optimized when the child
is given frequent praise for his/her efforts.
Implications for Intervention
The clinical utility of the CAPD and ADHD
diagnoses is perhaps of most consequence relative to management . Management programming will depend on the diagnostic category of
the primary disorder. Strategies for managing
CAPD generally include acoustic signal modifications, auditory training, and metalinguistic
and metacognitive approaches . Management of
ADHD generally involves medication and
metacognitive or executive control strategies .
Some combination of these approaches may be
required to effectively manage CAPD in individuals also diagnosed with ADHD .
Central Auditory Processing Disorders
A comprehensive approach to managing
CAPD is designed to improve listening skills
and spoken language comprehension (Chermak
and Musiek, 1997) . The complementary interventions listed in Table 4 target auditory skills,
linguistic and metalinguistic skills and strategies, executive control strategies, and signal
quality enhancement (Chermak and Musiek,
1997) . Fundamental central auditory processing
skills (e .g ., auditory discrimination, temporal
processing) are targeted through auditory training. Auditory training is directed toward improving the basic auditory skills listed in Table 5 .
Table 4
CAPD Management
Signal enhancement
Auditory training
Environmental modifications
Metacognitive (executive) strategies
Linguistic strategies
Metalinguistic strategies
Collaboration
Learning strategies
297
Journal of the American Academy of Audiology/ Volume 10, Number 6, June 1999
Table 5
Auditory Skills Training
Vigilance
Temporal gap detection
Intensity discrimination
Frequency discrimination
Tone glide discrimination
Phoneme/syllable discrimination
Temporal gap discrimination
Temporal, order discrimination
Syllable recognition in competition
Dichotic syllable recognition
Flutter fusion
Lateralization
Interhemispheric transfer
These skills encompass both spectral processing
(e .g ., frequency discrimination) and temporal
processing (e .g ., gap detection) and underlie
phonetic distinctions essential to spoken language processing (Chermak and Musiek, 1997).
Aconcurrent emphasis on metacognitive or executive control (e .g ., schema induction and selfinstruction), as well as linguistic (e .g ., vocabulary
building) and metalinguistic knowledge (e .g .,
segmentation and closure) and strategy development, strengthens self-regulation of spoken
language processing (Chermak and Musiek,
1997). To complement these remedial efforts,
compensatory techniques (e .g ., acoustic signal
enhancement and environmental modifications)
are recommended to address processing deficits
considered more resistant to treatment (Chermak and Musiek, 1997). Given the range of listening and associated learning problems, all
management efforts are conducted in collaboration with other professionals and the family.
Learning difficulties often associated with CAPD
and ADHD may require intervention by education specialists, learning specialists, and psychologists .
Attention Deficit Hyperactivity Disorder
Managing individuals with ADHD typically
involves medication that in almost all cases
requires additional intervention for success
(Anastopoulos and Barkley, 1990). Recent reports
suggest that stimulant medication may be the
most effective treatment for the majority of children and adults with predominantly hyperactiveimpulsive and combined ADHD (Barkley, 1997a) .
Indeed, reconceptualizing ADHD as a developmental disorder of self-regulation related to
defective motor inhibition supports the use of
pharmacologic management . Metacognitive or
executive control strategy training (e .g ., self298
regulation, cognitive behavior modification),
social-pragmatic skills training (e .g., role playing in use of appropriate language in social and
academic interactions, developing vocabulary,
social cognition, and pragmatics for reflection,
planning, and problem solving), and collaboration with teachers and families, especially in
regard to medication and contingency management systems (i .e ., structuring the environment,
reinforcement schedules, token systems), are
essential (Anastopoulos and Barkley, 1990 ;
Guevremont, 1990 ; Westby and Cutler, 1994 ;
Heyer, 1995 ; Maag and Reid, 1996). Barkley
(1997b) emphasized the use of behavioral performance programs in natural settings . Typical
goals include increasing on-task behavior, task
completion, compliance, and impulse control.
Metacognitive strategies involve the use of language as an internal and self-regulating control
to foster sustained attention and control impulsivity and hyperactivity. Approaches to managing ADHD are listed in Table 6.
CONCLUSIONS
A
ttention deficits, listening deficits, and poor
academic achievement associated with both
ADHD and CAPD (Willeford and Burleigh, 1985 ;
Chermak and Musiek, 1992, 1997 ; Keller, 1992 ;
APA, 1994 ; Chermak et al, 1998) render differential diagnosis especially challenging. The data
and perspectives reviewed in this paper, however,
support the clinical utility of CAPD and ADHD
as valid clinical diagnoses, notwithstanding
overlapping clinical profiles .
Differences in auditory areas of the brain,
relative to normal controls, suggest a neuroanatomical basis for the frequently observed
central auditory performance deficits among
children diagnosed with ADHD . Providing additional insight as to the observed comorbidity of
CAPD and ADHD is the reconceptualization of
ADHD as a behavioral regulation disorder associated with executive dysfunction (Denckla and
Reader, 1993 ; Barkley, 1994 ; Smith et al, 1995),
coupled with the suggestion that the auditory
perceptual deficits of CAPD may impede execTable 6
ADHD Management
Medication
Executive control strategy training
Social-pragmatic skills training
Contingency management systems
Collaboration
Learning strategies
Differential Diagnosis of CAPD and ADHD/Chermak et al
utive functions and thereby serve as a secondary
source of the difficulties seen in CAPD in organizing, monitoring, and understanding acoustic
signals (Chermak and Musiek, 1997).
The distributed nature of information processing may lead to auditory attention deficits
at sensory and/or cognitive levels . ADHD and
CAPD may differ in the extent of the attention
deficit (i.e ., cognitive and supramodal vs sensory
and restricted to the auditory modality), as well
as the type of attention deficit (i .e ., sustained vs
selective and divided attention) . Within an
information processing framework, the sustained attention problems observed in ADHD are
seen as the consequence of a supramodal cognitive deficit, whereas CAPD results from a specific auditory perceptual deficit. Inattention in
ADHD may reflect deficiencies in behavioral
regulation rather than attention per se . In contrast, the selective auditory attention deficits of
CAPD result from deficient auditory perceptual
processing .
Additional research is needed to determine
the neurologic mechanisms and associated behavioral criteria consistent with these clinical diagnoses . Such information will improve the
differential diagnosis ofADHD and CAPD, as well
as subtype ADHD, where a unidimensional perspective on diagnosis has been shown to be inadequate in explaining behavior (Schaughency and
Hynd, 1989 ; Goodyear and Hynd, 1992) . More
definitive diagnostic information should lead to
more effective intervention .
Acknowledgment. Portions of this paper were presented
at the 9th Annual Convention of the American Academy
of Audiology, Ft . Lauderdale, FL, April 18, 1997 .
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