Pflugshaupt, T., Suchan, J., Mandler, M. A., Sokolov, A. N.,
Trauzettel-Klosinski, S., & Karnath, H. O. (2011). Do patients with pure
alexia suffer from a specific word form processing deficit? Evidence from 'wrods
with trasnpsoed letetrs'. Neuropsychologia, 49, 1294-1301.
Notes: It is widely accepted that letter-by-letter reading and a pronounced
increase in reading time as a function of word length are the hallmark
features of pure alexia. Why patients show these two phenomena with respect
to underlying cognitive mechanisms is, however, much less clear. Two main
hypotheses have been proposed, i.e. impaired discrimination of letters and
deficient processing of word forms. While the former deficit can easily be
investigated in isolation, previous findings favouring the latter seem
confounded. Applying a word reading paradigm with systematically manipulated
letter orders in two patients with pure alexia, we demonstrate a word form
processing deficit that is not attributable to sublexical letter
discrimination difficulties. Moreover, pure alexia-like fixation patterns
could be induced in healthy adults by having them read sentences including
words with transposed letters, so-called 'jumbled words'. This further
corroborates a key role of deficient word form processing in pure alexia.
With regard to basic reading research, the present study extends recent
evidence for relative, rather than precise, encoding of letter position in
the brain
Pflugshaupt, T., Gutbrod, K., Wurtz, P., von Wartburg, R., Nyffeler, T., De
Haan, B. et al. (2009). About the role of visual field defects in pure
alexia. Brain, 132, 1907-1917.
Notes: Pure alexia is an acquired reading disorder characterized by a
disproportionate prolongation of reading time as a function of word length.
Although the vast majority of cases reported in the literature show a
right-sided visual defect, little is known about the contribution of this
low-level visual impairment to their reading difficulties. The present study
was aimed at investigating this issue by comparing eye movement patterns
during text reading in six patients with pure alexia with those of six
patients with hemianopic dyslexia showing similar right-sided visual field
defects. We found that the role of the field defect in the reading
difficulties of pure alexics was highly deficit-specific. While the
amplitude of rightward saccades during text reading seems largely determined
by the restricted visual field, other visuo-motor impairments-particularly
the pronounced increases in fixation frequency and viewing time as a
function of word length-may have little to do with their visual field defect.
In addition, subtracting the lesions of the hemianopic dyslexics from those
found in pure alexics revealed the largest group differences in posterior
parts of the left fusiform gyrus, occipito-temporal sulcus and inferior
temporal gyrus. These regions included the coordinate assigned to the centre
of the visual word form area in healthy adults, which provides further
evidence for a relation between pure alexia and a damaged visual word form
area. Finally, we propose a list of three criteria that may improve the
differential diagnosis of pure alexia and allow appropriate therapy
recommendations
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