Daniel Fiset


Université du Quebec


Selected references on reading and pure alexia

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



Anders Gade