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Dan Bub has
contributed to the study of the alexias for a long time - Selected alexia
references:
Bub, D., Cancelliere, A., & Kertesz, A. (1985). Whole-word and analytic
translation of spelling to sound in a non-semantic reader. In K.E.Patterson,
J. C. Marshall, & M. Coltheart (Eds.), Surface dyslexia:
Neuropsychological and cognitive studies of phonological reading (pp.
15-34). London: Erlbaum.
Bub, D. N., Black, S., & Howell, J. (1989). Word recognition and
orthographic context effects in a letter-by- letter reader. Brain and
Language, 36, 357-376.
Notes: Montreal Neurological Institute, Quebec, Canada The performance of
letter-by-letter readers when attempting to decipher written material gives
the impression that words fail to directly evoke any higher-level
representation. As a consequence, spelling patterns appear to be treated
perceptually as if they were a collection of random letters. We tested the
hypothesis that words are no longer mapped onto orthographic descriptions by
examining the ability of a letter-by-letter reader to identify letters in
familiar words, pseudowords, and random strings. A clear effect of
orthographic context was obtained on the accuracy of letter recognition,
indicating that spelling patterns do gain access to more central components
of the reading mechanism. The implications of this result for our
understanding of the syndrome are discussed
Behrmann, M., Black, S. E., & Bub, D. (1990). The evolution of pure alexia:
a longitudinal study of recovery. Brain and Language, 39, 405-427.
Notes: Department of Psychology, University of Toronto, Ontario, Canada This
case report documents the partial recovery, over a 12-month period, of pure
alexia in an adult female following a left occipital infarction. Measures of
speed and accuracy were obtained on an oral reading and a lexical decision
task immediately postonset and then on 10 subsequent occasions. Explicit
letter-by-letter reading was observed only during the first week poststroke
but a significant effect of word length was seen in all testing sessions.
Reading accuracy was relatively good at all stages and reading latency
showed a remarkable decrease over time but did not reach normal reading
rates. The inability to use higher-order orthographic knowledge, as manifest
in the absence of a word superiority effect, was still noted at one year
postonset. We therefore concluded that the change in behavior was
attributable to increased proficiency in the use of the adaptive
letter-by-letter procedure rather than to the resolution of the underlying
deficit. It is suggested that longitudinal neurobehavioral studies add to
our understanding of the alexic deficit and provide insight into the
recovery process
Behrmann, M. & Bub, D. (1992). Surface dyslexia and dysgraphia: Dual routes,
single lexicon. Cognitive Neuropsychology, 9, 209-251.
Notes: The dual route interpretation of surface dyslexia as a deficit in
word-specific activation has been challenged recently by computational
models that incorporate a unitary print-to-sound mechanism. The most current
of these makes no allowance for word-specific nodes, but obtains the
pronounciation of regular and exception words by weighted connections
between graphemic and phonemic units. Damaging the model in a variety of
ways produces a pattern that appears consistent with the performance of many
surface dyslexic patients. Exception words are mispronounced more often than
regular words, though accuracy deteriorates on both categories. In addition,
frequency has no clear-cut effect on the probability of reading an exception
word correctly. We describe the existence of a variant of the syndrome that
is not fully captured by the above simulations. MP, a surface dyslexic,
demonstrates a dissociation between lexical and nonlexical pronounciation of
written words. We also show that performance on irregular words varies as a
function of their frequency. We provide evidence that the locus of the
subject's deficit arises at the level of the representations in a single
orthographic lexicon that subserves both reading and writing
Arguin, M. & Bub, D. N. (1993). Single-character processing in a case of
pure alexia. Neuropsychologia, 31, 435-458.
Notes: Montreal Neurological Institute, Quebec, Canada The processing of
single characters in a pure alexic patient was studied in an attempt to
identify the impairment responsible for his reading disorder. Observations
from Experiments 1 to 4 suggested a deficit of identification of
alphanumeric stimuli without any impairment affecting the elaboration of a
structural description of visual stimulation. Experiment 5 indicated that
the identification disorder results from a defect in the selective
processes--activation and/or inhibition--that must come into play for
achieving an appropriate match between a structural description of the
stimulation and representations of the identities of known stimuli. The
possible implications of this deficit in single-character identification for
word reading are discussed
Arguin, M. & Bub, D. N. (1994). Functional mechanisms in pure alexia:
Evidence from letter processing. In M.J.Farah & G. Ratcliff (Eds.), The
neuropsychology of high-level vision. Collected tutorial essays (pp.
149-171). Hillsdale,NJ: Erlbaum.
Arguin, M. & Bub, D. N. (1994). Pure alexia: attempted rehabilitation and
its implications for interpretation of the deficit. Brain and Language,
47, 233-268.
Notes: AD: Departement de psychologie, Universite de Montreal, Quebec,
Canada AB: On the basis of data indicating the failure to encode letters as
abstract orthographic identities in a pure alexic patient (D.M.) coupled
with hypotheses about the effect of such a failure on word reading, an
attempt at changing the nature of letter processing in D.M. was conducted.
The training procedures failed to produce any fundamental change in the
operations used by D.M. to encode isolated letters or words. However, rapid
and massive benefits occurred in the overall speed of reading as a result of
the training program. These appear to result from an increased rate of
letter identification and the faster integration of individual letters into
letter combinations. The observations gathered throughout this
rehabilitation attempt provided evidence which constrains the range of
possible explanations for the characteristic features of pure alexia. It is
proposed that the letter-by-letter reading procedure which is the hallmark
of the disorder may follow from an incapacity to directly encode visual
letters as abstract orthographic types
Bub, D. N. & Arguin, M. (1995). Visual word activation in pure alexia.
Brain and Language, 49, 77-103.
Notes: Montreal Neurological Institute, Canada A patient with pure alexia
(DM) is shown to perform rapid and accurate lexical decisions for common
words without the ability to recover their complete identity. We provide
evidence using a speeded decision task that DM is not forced to rely on a
laborious analysis of individual letter forms when judging the lexical
status of orthographic patterns varying in length, though he clearly must
use this approach to fully identify a word for explicit report. By contrast,
the ability to rapidly classify a word apparently does not extend to
judgements of its superordinate category. DM makes semantic decisions for
visual words by adopting the same inefficient procedure he uses for verbal
report of their identity. The results provide further constraints on the
functional deficit responsible for pure alexia. We argue that DM is able to
monitor the overall activation of word units without achieving full
identification and that such a process may be a characteristic of the normal
reading mechanism
Bowers, J. S., Arguin, M., & Bub, D. N. (1996). Fast and specific access to
orthographic knowledge in a case of letter-by-letter surface alexia.
Cognitive Neuropsychology, 13, 525-567.
Notes: A series of experiments assessed priming for single letters and words
in a letter-by-letter reader (IH) when primes were displayed briefly
(between 100-500 msec) and masked. Consistent with previous claims that
letter-by-letter readers have difficulties accessing orthographic letter
codes, IH failed to show normal cross-case priming for single letters in a
naming task (e.g., a/A ). Nevertheless, IH showed robust cross-case priming
for four-letter words that have few if any perceptual features in common
between upper and lower case (e.g. read/READ ; the letters r/R, e/E, a/A ,
and d/D are visually dissimilar in lower/upper case), even at prime
durations that failed to support priming for single letters. Furthermore,
priming extended to pseudowords (e.g. DEAT ), and was highly specific given
that no priming was obtained between orthographic neighbors (e.g. face did
not prime FACT). Based on this pattern of results, we argue that IH gains
relatively normal access to orthographic representations, and that his
letter-by-letter reading reflects a partial disconnection between
orthographic and phonological representations. Within the context of a
disconnection account, we provide an explanation of the paradoxical finding
of robust word priming in the absence of single letter priming
Bowers, J. S., Bub, D. N., & Arguin, M. (1996). A characterisation of the
word superiority effect in a case of letter-by-letter surface alexia.
Cognitive Neuropsychology, 13, 415-441.
Bub, D. N. (1996). Dyslexia. In J.G.Beaumont, P. M. Kenealy, & M. J. C.
Rogers (Eds.), The Blackwell dictionary of neuropsychology (pp.
291-300). Oxford: Blackwell.
Notes: (Paperback 1999)
Arguin, M.,
Fiset, S., & Bub, D. (2002). Sequential and parallel letter processing in
letter-by-letter dyslexia. Cognitive Neuropsychology, 19, 535-555.
Notes: Dr. M. Arguin, Departement de Psychologie, Universite de Montreal,
Succ. Centre-ville, Montreal, Que. H3C 3J7, Canada
Four experiments are reported that focus on the issue of sequential vs.
parallel letter processing in letter-by-letter (LBL) dyslexia; these were
conducted on patient III. Expt. 1 showed a large linear reduction of word
naming times with an increase in the number of orthographic neighbours of
the target (i.e., words of the same length differing by just one letter; N
size). Given the large negative linear correlation existing between word
length and N size, this result raises the possibility that the large word
length effect diagnostic of LBL dyslexia may be, in fact, an artefact of
uncontrolled N size. Expt. 2 falsified this possibility by showing that the
word length effect is unaffected by whether N size is controlled for or not.
This result also suggested that the facilitatory effect of increased N size
in LBL dyslexia is based on the parallel processing of the constituent
letters of the target. Further supporting a contribution of parallel letter
processing to overt word recognition performance in the disorder, Expt. 3
showed significant but independent effects of word length and letter
confusability (i.e., similarity of the constituent letters of the target
word with other letters of the alphabet). The letter confusability effect
therefore appears to rest on the parallel analysis of the letters in the
target word. Finally, Expt. 4 showed that the facilitatory effect of N size
is prevented with high letter-confusability targets. These observations
suggest that LBL dyslexia rests on an impairment of letter encoding that
results in an excessive level of background noise in the activation of
lexical-orthographic representations when letters are processed in parallel.
This prevents overt identification of the target and forces sequential
letter processing in order to achieve this goal
Bub, D.
(2003). Alexia and related reading disorders. Neurologic Clinics, 21,
549-568.
Notes: Department of Psychology, Faculty of Social Sciences, University of
Victoria, Victoria, BC V8W 3P5, Canada. dbub@uvic.ca
Peripheral dyslexias are the result of impairment to processes that convert
letters on the page into an abstract orthographic representation. Many
aspects of these disorders are difficult to understand in depth. Invariably,
there is evidence that some type of word-level perception occurs rapidly in
many patients with LBL reading or neglect dyslexia, yet apparently
contradictory evidence indicates that part of the word has been misperceived
or that the letters must be analyzed laboriously for conscious
identification to occur. Current theories attempt to synthesize these
different aspects of the patients' performance, but their development is at
an early stage. Questions remain also about the domain specificity of the
perceptual impairment in LBL reading and about the nature of spatial
attention and spatial frames in neglect dyslexia and other forms of
attentional disorder. Current understanding of central dyslexias has perhaps
advanced further. Well-developed computational models exist of these
dyslexias, as do plausible experimental techniques for revealing the
activity of semantic and non-semantic routes in normal readers. Nevertheless,
the difficult issue of domain specificity arises again with respect to some
of the mechanisms invoked, and in this regard, central and peripheral
dyslexias continue to pose the same challenge
Arguin, M. &
Bub, D. (2005). Parallel processing blocked by letter similarity in
letter-by-letter dyslexia: A replication. Cognitive Neuropsychology, 22,
589-602.
Notes: Dr. M. Arguin, Departement de Psychologie, Universite de Montreal,
Succ. Centre-ville, Montreal, Que. H3C 3J7
An investigation of the joint effects of orthographic neighbourhood size (N
size) and of letter confusability in three letter-by-letter (LBL) dyslexics
is reported. All three patients showed a facilitatory effect of increased N
size with low letter-confusability words, but no N size effect with high
confusability words. This exactly replicates previous observations by Arguin,
Fiset, and Bub (2002) in another LBL dyslexic. A facilitatory N size effect
requires parallel letter processing and the word recognition performance of
normal readers is unaffected by letter confusability. The present findings
therefore signal that the residual capacity for parallel letter processing
in LBL dyslexic is blocked by letter similarity. This implies a deficit of
letter encoding or identification, which appears to be a general feature of
LBL dyslexia since it is exhibited by all of the four patients so tested.
Fiset, D.,
Arguin, M., Bub, D., Humphreys, G. W., & Riddoch, M. J. (2005). How to make
the word-length effect disappear in letter-by-letter dyslexia: implications
for an account of the disorder. Psychological Science, 16, 535-541.
Notes: Centre de Recherche en Neuropsychologie et Cognition, Departement de
Psychologie, Universite de Montreal, CP 6128, Succ. Centre-ville, Montreal,
Quebec H3C 3J7, Canada
The diagnosis of letter-by-letter (LBL) dyslexia is based on the observation
of a substantial and monotonic increase of word naming latencies as the
number of letters in the stimulus increases. This pattern of performance is
typically interpreted as indicating that word recognition in LBL dyslexia
depends on the sequential identification of individual letters. We show, in
7 LBL patients, that the word-length effect can be eliminated if words of
different lengths are matched on the sum of the confusability (visual
similarity between a letter and the remainder of the alphabet) of their
constituent letters. Additional experiments demonstrate that this result is
mediated by parallel letter processing and not by any compensatory serial
processing strategy. These findings indicate that parallel processing
contributes significantly to explicit word recognition in LBL dyslexia and
that a letter-processing impairment is fundamental in causing the disorder
Fiset, D.,
Blais, C., Arguin, M., Tadros, K., Ethier-Majcher, C., Bub, D. et al.
(2009). The spatio-temporal dynamics of visual letter recognition.
Cognitive Neuropsychology, 26, 23-35.
Notes: We applied the Bubbles technique to reveal directly the
spatio-temporal features of uppercase Arial letter identification. We asked
four normal readers to each identify 26,000 letters that were randomly
sampled in space and time; afterwards, we performed multiple linear
regressions on the participant's response accuracy and the space-time
samples. We contend that each cluster of connected significant regression
coefficients is a letter feature. To bridge the gap between the letter
identification literature and this experiment, we also determined the
relative importance of the features proposed in the letter identification
literature. Results show clear modulations of the relative importance of the
letter features of some letters across time, demonstrating that letter
features are not always extracted simultaneously at constant speeds.
Furthermore, of all the feature classes proposed in the literature, line
terminations and horizontals appear to be the two most important for letter
identification
University of Victoria, Victoria, British Columbia, Canada
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