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Visual processing and specific reading disability


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Martin, Frances 1986 , 'Visual processing and specific reading disability', PhD thesis, University of Tasmania.

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Specific reading disability is a pervasive disorder which affects
the academic, social and emotional lives of a large proportion of
people living in a world where literacy is taken for granted. While
many hypotheses have been raised as to the cause of this disorder,
the possibility that the disorder is related to visual processing
anomalies has not as yet been fully investigated.
Based on the proposal that the visual system contains two separate
mechanisms for the processing of spatial (sustained mechanism) and
flickering (transient mechanism) stimuli, the operation of these two
systems in groups of normal and specifically disabled readers was
investigated. Initially, parameters of the contrast sensitivity
function were investigated in specifically disabled and normal
readers. It was found that at luminance levels less than 30 cd/m2
specifically disabled readers were generally less sensitive than
normal readers at lower spatial frequencies and equally or more
sensitive at the higher spatial frequencies. This suggested a
deficit in some part of the transient system functioning in
specifically disabled readers. The operation of the transient and sustained systems was then
directly investigated through the use of flickering stimuli. In two
experiments - one manipulating spatial frequency and the other
temporal frequency - it was found that as spatial frequency and
temporal frequency increase so did the differences between
specifically disabled and normal readers with specifically disabled
readers being less sensitive than controls to all the stimuli. Four
experiments were then carried out investigating the effect of
masking by uniform field flicker. In the first of these experiments
using a 6 Hz uniform field flicker and a stationary test grating,
the presence of uniform field flicker decreased sensitivity in
normal readers at low spatial frequencies but had little effect on
sensitivity across that range in specifically disabled readers. At
higher spatial frequencies while no effect was seen in the results
of normal readers uniform field flicker decreased sensitivity in specifically disabled readers. Overall the effect of the uniform
field flicker was to make the contrast sensitivity function of
specifically disabled readers more like that of normal readers. In
the final three experiments it was generally found that low rates of
uniform field flicker had a depressing effect on the contrast
sensitivity to a moving or flickering grating of both specifically
disabled and normal readers. However, when higher rates of uniform
field flicker were used it was found that the contrast sensitivity
of specifically disabled readers was not further affected while that
of normal readers showed a further decrease in sensitivity.
These findings suggest that disabled readers have a deficiency in
some part of their transient system which would lead to disordered
interactions between the transient and sustained systems. This
deficiency would lead to information reaching the cognitive areas of
their brains in a degraded form thus making reading for these
children extremely difficult.

Item Type: Thesis - PhD
Authors/Creators:Martin, Frances
Keywords: Reading disability, Visual perception in children, Human information processing in children, Flicker fusion
Copyright Holders: The Author
Copyright Information:

Copyright 1986 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 1987. Bibliography: leaves 179-218

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