Comparative investigation of perceptual organization, postural stability and receptive vocabulary among dyslexics with and without ADHD

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1996). Given the dearth of the research in this area, this exploratory study 
examined executive functioning focusing on affects of co morbidity. 
Dyslexia is a disorder of children that appears as a difficulty in the 
acquisition of reading ability, despite mental abilities, adequate school training or 
positive social environment. It is a disorder of written and not of spoken language, 
although it is possible for a dyslexic child to have limitations in some aspects of 
spoken language as well. Such a child is very likely to learn how to read with 
adequate training, but will always remain dyslexic. American Psychological 
Association (APA, 1994) defines dyslexia as "a specific disability in learning to 
read and to spell adequately despite at least normal intelligence, adequate 
instruction and socio-cultural opportunities, and the absence of sensory defects in 
vision and hearing”.  
This definition rests, not upon etiologically grounded criteria, but upon a 
criterion of discrepancy between the reading performance as expected from 
measures of general intelligence, and the reading performance actually observed. 
In these terms, dyslexia is understood as a homogeneous developmental disorder. 
The abundance of partially contradicting experimental results, however, suggests 
that dyslexia is in fact a poly-etiological syndrome that is influenced by structural 
and functional characteristics of the central nervous system in interaction with 
exogenous factors (Livingstone, Rosen, Drislane & Galaburda, 1991). 
The consensus of most dyslexia researchers is that dyslexia is a 
phonological deficit characterized by difficulty distinguishing speech sounds 
(phonemes) aurally and as represented in written language (Shaywitz and 
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Shaywitz, 1999). In these two studies, evidence was observed that dyslexia is 
associated with a specific visual-spatial ability. 
Since the earliest descriptions of dyslexia (Hinshelwood, 1909; Morgan, 
1896; Orton, 1925), there has been speculation that this condition is associated 
with enhanced visual-spatial abilities (Geschwind, 1982; Gordon, 1983; Rourke 
and Finlayson, 1978; Vail, 1990; West, 1991; Winner and Casey, 1993). 
Neurological evidence is consistent with the possibility that the dyslexic brain 
might process visual-spatial information in an atypical manner (Riccio and Hynd, 
1996). Dyslexic brains are atypical in the structure, development, and 
organization of their cells (Galaburda & Kemper, 1979; Galaburda, 1985; 
Sherman, 1998). Dyslexic brains are also different in patterns of hemispheric 
activation during both linguistic and nonlinguistic tasks (Rumsey, 1996; Shaywitz 
and Shaywitz, 1999).  
Investigations into the possibility that individuals with dyslexia are 
superior in visual-spatial abilities have, however, yielded conflicting findings. 
Individuals with Dyslexia have been found to have visual-spatial abilities that are 
superior (Bannatyne, 1971; Rugel, 1974; Sinatra, 1988; Swanson, 1984), inferior 
(Bannatyne, 1971; Benton, 1984; Rourke, 1985), and comparable (Koenig, 1991; 
Rudel and Denckla, 1976; Rugel, 1974; Siegel and Ryan, 1989; Sinatra, 1988) to 
controls.  
Attention Deficit Hyperactivity Disorder (ADHD) was also included as a 
factor comorbid with Dyslexia. Although ADHD is a common behavioral 
disorder that exhibits substantial Comorbidity with Dyslexia, affecting 30–70% of 
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the Dyslexic population depending on the sample and how the disorder is defined 
(Shaywitz, 1994), many studies of perception in children with Dyslexia do not 
take the potential presence of ADHD into account in a systematic fashion. 
Behavioral deficits associated with ADHD include an inability to sustain focused 
attention (Barkley, Grodzinsky, & DuPaul, 1992), an impulsive response bias 
(Barkley, 1997a,b), and reduced working memory (Barkley, 1997b), all of which 
potentially affect performance on perceptual tasks. The present study specifically 
included a group with both RD and ADHD to account for the possibility of a 
synergistic interaction between the two disorders. 
Research into neurological functioning has provided insight into brain that 
may relate to the visual, auditory and motor functioning of Dyslexics with and 
without ADHD.    
The brain consists of modules specialized for processing specific data. 
These modules are independent to a degree in both function and neural 
representation (Fodor, 1983). The outermost layer of the brain represents the 
cerebral cortex. The cortical (frontal) section of the brain is related to learning and 
thinking. The layer underneath, the subcortex, comprises a relay system that is 
involved in sending messages to the processing and memory parts of the brain. 
This subcortical system consists of the brain stem's reticular activating system, 
thalamus, hypothalamus, and basal ganglia. Recent research suggests that ADHD 
children generally have impaired functioning in the cortical, and subcortical areas 
(Garber, Garber, Spizman, 1990). In particular, frontal lobe and prefrontal lobe 
dysfunction have been suggested (Hynd, Riccio, Cohen, & Gonzalez, 1991).  
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This is significant because the frontal and motor cortex play a role in 
attention, visual-spatial tasks, and motor activity. It has been proposed that within 
the prefrontal area, different sections specialize in certain representative 
functions. For instance, the dorsal convexity maintains spatial representations, 
while the orbital area maintains representations of rewards or motivators, 
including social rewards (Pennington, 1991). Positron emission tomography 
(PET) scan studies have shown reduced brain glucose utilization, particularly as 
related to the right frontal lobe, in ADHD children (Zametkin & Rapoport, 1987). 
Further, ADHD children may show decreased blood flow in the frontal lobes 
(Hynd, Kytja,Voeller, Hem,& Marshall, 1993).   
Research has shown that Attention Deficit Disorder (ADD), ADHD, 
reading disability (RD), and Slight Learning Impairment (SLI) frequently co-
occur with symptoms of Dyslexia (Dewey., 2002; Dewey, 2000; Gillberg, 1998; 
Gillberg and Kadesjö, 1998 and Gillberg and Kadesjö, 2000; Hill, 2001; Kadesjö 
and Gillberg, 1999 and Kadesjö and Gillberg, 2001; Kaplan, 1997; Martini, 1999; 
Wilson and McKenzie, 1998). Hill (2001), who conducted a review of the 
literature on SLI, reports a substantial comorbidity between SLI and poor motor 
skills and suggests that SLI is, in fact, not a specific disorder of language.  
Present research is based on three major executive functions i.e., 
perceptual organization (visual motor assembling ability and ability to give 
attention to details), receptive vocabulary (temporal lobe functional integrity) and 
postural stability (control of eye movements, motor skills, and balance). 
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Children with reading difficulties frequently exhibit deficits in multiple 
areas like perceptual organization, receptive vocabulary and postural stability. 
(Fletcher, Shaywitz, Shankweiler, Katz, Liberman, Stuebing, Blachman, 1994; 
Winner, Casey, DaSilva & Hayes 1991). Reading is a complex task requiring 
coordination of multiple brain areas. Although functional neuro-imaging studies 
highlight the cortical brain areas associated with specific cognitive task 
(Pennington, 2001). The researchers found lower regional white matter 
connectivity. There has been general assumption that Dyslexia may be associated 
with enhanced visual-spatial abilities (Geschwind, 1982; Gordon, 1983; Rourke & 
Finlayson, 1978; Silverman & Vail, 1990; West, 1991; Winner & Casey, 1993; 
Winner, 1991). 
Perceptual organization refers to visuospatial constructional ability which 
is complex, comprising multiple distinct, but interrelated subcomponents; the 
ability to combine elements into a meaningful wholes, the ability to discriminate 
between objects, distinguish between left and right, the ability to understand 
relationships among objects in space, the ability to adopt various perspectives and 
to represent and rotate objects mentally; the ability to comprehend and interpret 
symbolic representations of external space and the ability to work out the solution 
for non-verbal problems (Cronin-Galomb & Braun, 1997). According to 
Interhemispheric theory, these disturbances in visual spatial processing may be 
due to inappropriate communication between the two hemispheres (Gjurgjica, Jeff 
& Karen, 2004).  
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 Several studies have targeted perceptual abnormalities in Dyslexics 
children with assumption that deficits in appreciating the visuo-constructional 
stimuli are associated with abnormal neuropsychological activity in temporo-
parietal language areas in children with Dyslexia (Brier 2003). 
Children with ADHD are often found to be slow, inaccurate performers 
(Jennings, van der Molen, Pelham, Debski, & Hoza, 1997; Oosterlaan & 
Sergeant, 1996; Scheres, Oosterlaan, & Sergeant, 2001; van der Meere, 1996; van 
der Meere & Sergeant, 1988) where delayed motor processing is considered a 
core deficit.  
The cerebellum has been identified as playing a critical role in the learning 
of a new motor sequence in addition to the performance of an automated sequence 
(Jenkins, 1994). Indeed, relative to controls, adults with dyslexia have displayed 
deficient cerebellar activation during poorer performance of a new and a 
previously learned sequential motor task (Nicolson, 1999). Taking the 
Phonological Deficit hypothesis into account, learning, comprehending, and 
communicating with verbal language requires an ability to assemble and address a 
word's phonology automatically, an ability inextricably tied to the ordering of 
sequence specific information. As such, a competent grasp of language requires 
the ability to, at various levels, string together independent parts to form a whole 
(Brady, 1997).  
Studies examining a relationship between ADHD and relative visual 
inattention towards left space have produced inconsistent results.  In one of the 
research study based on previous studies with adult neurological patients who 
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show very severe inattention to the left, it was examined whether any spatial bias 
in ADHD may be modulated by changes in alertness levels. In this single case, 
Melanie and others found that inattention to the left (that was intermittently 
apparent) dramatically increased as a function of time-on-task. No significant 
changes were observed on the right. (Melanie , 2005). 
Dyslexics were found relatively poor in performing a spatial selective 
attention-shifting task in a study conducted by Albertus, Pieter and Koos (2004). 
They compared performance and event-related brain potentials between dyslexic 
subjects and control subjects on these tasks. Dyslexics and controls differed with 
respect to the frontal attention effect. Whereas the controls showed this effect 
almost exclusively over the right hemisphere, the dyslexics showed both left and 
right hemispheric effects. They propose that this might support the idea that in 
dyslexia the development of Interhemispheric asymmetry is deregulated.   
Tallal & Piercy (1973), Tallal (1980) and Tallal (1985) have argued not 
only that childhood language impairments, including specific language (SLI) and 
reading (SRI) impairment, are due to perceptual problems, but that they are due to 
a specific problem usually referred to as ‘auditory temporal processing. Other 
advocates of a perceptual involvement in language impairments have found a 
wider variety of auditory processing problems in many children and adults with 
SLI (McArthur and Hogben, 2001 and Wright, 1997), SRI (e.g., Amitay, 2002 
and Ramus, 2003), attention deficit disorder (Kraus, 1996), autistic spectrum 
disorders (Siegal & Blades, 2003), and behavior problems (Hill, 2000 and King & 
Stephens, 1992).