Effects of hemisphere-specific stimulation on academic performance and event-related potentials in dyslexic children
Date
2018-06-21
Authors
Grace, Gloria Mary
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Abstract
There exists a paucity of research addressing the
treatment of dyslexia despite its high prevalence and its
potential debilitating effects on an individual's cognitive and
emotional status. One of the few research programs addressing
this issue is headed by Dirk Bakker. Bakker proposes a balance
model of dyslexia, specifying L- and P-type dyslexics and an
associated treatment technique called hemisphere-specific
stimulation (HSS). In general, Bakker's findings suggest that
HSS may improve the accuracy and efficiency of reading
performance, particularly in L-type dyslexics. In addition,
HSS appears to modify the electrophysiological activity of the
brain, reflected by a relative change in the left- and right sided
amplitude of the event-related potential (ERP), elicited
by flashed words. Although Bakker's findings suggest that HSS
may be a potentially successful treatment approach to dyslexia,
no studies attempting replication of his results by independent
investigators have been published. The present study was
designed to replicate the major findings reported by Bakker
(Bakker & Vinke, 1985).
In the present study, 26 reading-disabled children were
classified into 17 L-type and 9 P-type readers (mean age = 11.0
years) and then randomly assigned to experimental and control
groups. Disabled readers in the experimental groups
(L1, N=8; P1, N=5) received 18 sessions (45 minutes twice
weekly) of HSS according to Bakker's specifications. HSS
involved the stimulation of the right or left cerebral
hemisphere through the computerized presentation of words and
letters flashed in the left and right visual fields for L- and
P-types respectively. Control subjects (L2, N=9; P2, N=4)
received no treatment, and remained in their classrooms during
training sessions. All subjects were tested with reading and
spelling measures prior to training (pre-test), halfway through
training (mid-test), and after training (post-test). In
addition, ERPs, in response to centrally flashed words, from
left and right parietal and temporal locations were collected
from all subjects before and after training.
In general, neither the academic nor the electrophysiological results of this study replicated those of
Bakker and Vinke (1985). Although all groups tended to show
improvements over time on most academic variables, experimental
groups did not improve significantly more than controls on most
measures of reading and spelling.
In terms of ERP changes, the P300 component of the
waveform corresponded most closely to the portion of the ERP on
which Bakker and Vinke based their findings. In contrast to
Bakker's results, L1 in the present study showed a "leftening"
effect (a relative increase in left hemisphere activity)
relative to L2. However, consistent with Bakker's findings, P1
showed a leftening effect relative to P2.
Although replication of Bakker's results did not occur,
the study was of considerable heuristic value in the critical
appraisal of Bakker's model of dyslexia and associated
treatment. Critical analysis of the L/P classification system
revealed that the most serious difficulty is poor internal
validity. It was argued that Bakker's classification system is
in need of revision and further testing before external
validity, i.e., the efficacy of HSS, can be accurately
assessed.
Description
Keywords
Dyslexia, Dyslexic children, Treatment