The planum temporale is clearly involved in language processing,
for it serves as the auditory association cortex. Research has
consistently demonstrated that 60 to 70% of the population has
leftward asymmetry of the planum temporale. Research has also
suggested that dyslexic individuals tend to have either rightward
asymmetry or symmetrical plana. Moreover, many studies have
found a relationship between the presence of dyslexia and/or
language impairment and deficits in the normal right ear advantage
found in dichotic listening paradigms. In this context, this
study examined the relationship between planum temporale asymmetry
and ear preference in dichotic listening performance in children
with Developmental Dyslexia and Attention-Deficit/Hyperactivity
Disorder (ADHD). Subjects included 19 children with dyslexia
(10 of whom had a comorbid diagnosis of ADHD), 23 children with
ADHD, and 12 diagnosed normal control children. Dichotic listening
data were not collected for 8 of the 12 normal control children
and for 3 of the 23 ADHD children. Results revealed no significant
difference between ADHD and dyslexic subjects in regard to ear
advantage on the free recall dichotic listening task. In addition,
although the directed dichotic listening tasks were not related
to degree of planum asymmetry, as predicted, results indicated
that subjects who consistently displayed an atypical left ear
advantage tended to have larger right bank lengths than those
who consistently displayed a typical right ear advantage. These
findings support the notion that some individuals with dyslexia
or language deficits tend to have a larger right planum temporale
and that performance on dichotic listening tasks may reflect
this relatively unusual pattern. (JINS, 2002, 8,
22–36.)
DICHOTIC RIGHT EAR ADVANTAGE FOR SPEECH PERCEPTION IN HEARING IMPAIRED CHILDREN : RELATION OF LATERALIZATION-SCORE AND AIDED EAR IN DICHOTIC LISTENING
