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Tadros, K., Dupuis-Roy, N., Fiset, D., Arguin, M., & Gosselin, F. (2013).
Reading laterally: the cerebral hemispheric use of spatial frequencies in
visual word recognition. Journal of Vision, 13, 4.
Notes: It is generally accepted that the left hemisphere (LH) is more
capable for reading than the right hemisphere (RH). Left hemifield
presentations (initially processed by the RH) lead to a globally higher
error rate, slower word identification, and a significantly stronger word
length effect (i.e., slower reaction times for longer words). Because the
visuo-perceptual mechanisms of the brain for word recognition are primarily
localized in the LH (Cohen et al., 2003), it is possible that this part of
the brain possesses better spatial frequency (SF) tuning for processing the
visual properties of words than the RH. The main objective of this study is
to determine the SF tuning functions of the LH and RH for word recognition.
Each word image was randomly sampled in the SF domain using the SF bubbles
method (Willenbockel et al., 2010) and was presented laterally to the left
or right visual hemifield. As expected, the LH requires less visual
information than the RH to reach the same level of performance, illustrating
the well-known LH advantage for word recognition. Globally, the SF tuning of
both hemispheres is similar. However, these seemingly identical tuning
functions hide important differences. Most importantly, we argue that the RH
requires higher SFs to identify longer words because of crowding
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.
Fiset, D., Blais, C., Ethier-Majcher, C., Arguin, M., Bub, D., & Gosselin,
F. (2008). Features for identification of uppercase and lowercase letters.
Psychological Science, 19, 1161-1168.
Notes: The determination of the visual features mediating letter
identification has a long-standing history in cognitive science. Researchers
have proposed many sets of letter features as important for letter
identification, but no such sets have yet been derived directly from
empirical data. In the study reported here, we applied the Bubbles technique
to reveal directly which areas at five different spatial scales are
efficient for the identification of lowercase and uppercase Arial letters.
We provide the first empirical evidence that line terminations are the most
important features for letter identification. We propose that these small
features, represented at several spatial scales, help readers to
discriminate among visually similar letters
Fiset, D., Gosselin, F., Blais, C., & Arguin, M. (2006). Inducing
letter-by-letter dyslexia in normal readers. Journal of Cognitive
Neuroscience, 18, 1466-1476.
Notes: Departement de Psychologie, Universite de Montreal, Canada
Letter-by-letter (LBL) dyslexia is an acquired reading disorder
characterized by very slow reading and a large linear word length effect.
This suggests the use of a sequential LBL strategy, in sharp contrast with
the parallel letter processing used by normal subjects. Recently, we have
proposed that the reading difficulty of LBL dyslexics is due to a deficit in
discriminating visually similar letters based on parallel letter processing
[Arguin, M., Fiset, S., & Bub, D. Sequential and parallel letter processing
in letter-by-letter dyslexia. Cognitive Neuropsychology, 19, 535-555, 2002].
The visual mechanisms underlying this deficit and the LBL strategy, however,
are still unknown. In this article, we propose that LBL dyslexic patients
have lost the ability to use, for parallel letter processing, the optimal
spatial frequency band for letter and word recognition. We claim that,
instead, they rely on lower spatial frequencies for parallel processing,
that these lower spatial frequencies produce confusions between visually
similar letters, and that the LBL compensatory strategy allows them to
extract higher spatial frequencies. The LBL strategy would thus increase the
spatial resolution of the visual system, effectively resolving the issue
pertaining to between-letter similarity. In Experiments 1 and 2, we
succeeded in replicating the main features characterizing LBL dyslexia by
having normal individuals read low-contrast, high-pass-filtered words.
Experiment 3, conducted in LBL dyslexic L.H., shows that, indeed, the letter
confusability effect is based on low spatial frequencies, whereas this
effect was not supported by high spatial frequencies
Fiset, D., Arguin, M., & McCabe, E. (2006). The breakdown of parallel letter
processing in letter-by-letter dyslexia. Cognitive Neuropsychology, 23,
240-260.
Notes: Dr. M. Arguin, Departement de Psychologie, Universite de Montreal,
Succ. Centre-ville, Montreal, Que. H3C 3J7
Two critical issues were examined regarding letter-by-letter (LBL) dyslexia:
(1) What is the nature of the functional impairment responsible for the
incapacity of LBL patients to overtly recognise words on the sole basis of
parallel letter processing? (2) What is the purpose of sequential letter
processing? Four experiments focusing on these issues were conducted in LH,
an LBL dyslexic. Expt 1 showed facilitatory effects of increased
phonographic neighbourhood size, lexical frequency, and imageability on the
word naming performance of LH. These high-order effects reflect a modulation
of parallel letter processing in LH and demonstrate that he is able to
rapidly access phonological, lexical, and semantic knowledge during reading.
Congruently, Expt 2 demonstrated that all three high-order effects are
eliminated when words are presented one letter at a time, from left to
right. Expt 3 showed that these high-level effects are also abolished if
target words are made of letters that are highly confusable (i.e., visually
similar) to other letters of the alphabet. These observations suggest that
LBL dyslexia may rest on an impairment at the letter encoding level that
causes an excessive level of background noise in the activation of
higher-order representations (i.e., letter combinations) when letters are
processed in parallel. An additional experiment (Expt 4) shows that the
letter confusability effect is also eliminated when words are presented one
letter at a time, from left to right. This latter finding suggests that
compensatory sequential processing invoked by LBL dyslexics serves to avoid
the confusion between visually similar letters, which is present with
parallel letter processing, and to amplify the signal-to-noise ratio
required to achieve overt word identification.
Fiset,
S., Arguin, M., & Fiset, D. (2006).
An attempt to simulate letter-by-letter dyslexia in normal readers. Brain
and Language, 98, 251-263.
Notes: Groupe de Recherche en Neuropsychologie et Cognition, Departement de
psychologie, Universite de Montreal, C.P. 6128, succ. Centre-ville, Montreal
QC, Canada H3C 3J7
We attempted to simulate the main features of letter-by-letter (LBL)
dyslexia in normal readers through stimulus degradation (i.e. contrast
reduction and removal of high spatial frequencies). The results showed the
word length and the letter confusability effects characteristic of LBL
dyslexia. However, the interaction of letter confusability and N size (i.e.
a facilitatory effect only for low confusability targets) previously
observed in LBL dyslexics [Arguin, M., Fiset, S., & Bub, D. (2002).
Sequential and parallel letter processing in letter-by-letter reading.
Cognitive Neuropsychology, 19, 535-555; Arguin, M., & Bub, D. (2006).
Parallel processing blocked by letter similarity in letter dyslexia: a
replication. Cognitive Neuropsychology, 22, 589-602; Fiset, D., Arguin, M. &
McCabe, E. (2005a). The breakdown of parallel letter processing in
letter-by-letter dyslexia. Cognitive Neuropsychology, 22, 1-22] was not
found. Our results suggest that the type of visual degradation employed here
may only partially correspond to the visual deficit present in LBL dyslexia
and that this degradation may have prevented the normal readers from
accessing visual information available to LBL dyslexics when they use the
compensatory strategy of serial letter processing
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
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