Visual processing of multiple elements in the dyslexic brain: evidence for a superior parietal dysfunction

Abstract

The visual attention (VA) span deficit hypothesis of developmental dyslexia posits that impaired multiple element processing can be responsible for poor reading outcomes. In VA span impaired dyslexic children, poor performance on letter report tasks is associated with reduced parietal activations for multiple letter processing. While this hints towards a non-specific, attention-based dysfunction, it is still unclear whether reduced parietal activity generalizes to other types of stimuli. Furthermore, putative links between reduced parietal activity and reduced ventral occipito-temporal (vOT) in dyslexia have yet to be explored. Using functional magnetic resonance imaging, we measured brain activity in 12 VA span impaired dyslexic adults and 12 adult skilled readers while they carried out a categorization task on single or multiple alphanumeric or non-alphanumeric characters. While healthy readers activated parietal areas more strongly for multiple than single element processing (right-sided for alphanumeric and bilateral for non-alphanumeric), similar stronger multiple element right parietal activations were absent for dyslexic participants. Contrasts between skilled and dyslexic readers revealed significantly reduced right superior parietal lobule (SPL) activity for dyslexic readers regardless of stimuli type. Using a priori anatomically defined regions of interest, we showed that neural activity was reduced for dyslexic participants in both SPL and vOT bilaterally. Finally, we used multiple regressions to test whether SPL activity was related to vOT activity in each group. In the left hemisphere, SPL activity covaried with vOT activity for both normal and dyslexic readers. In contrast, in the right hemisphere, SPL activity covaried with vOT activity only for dyslexic readers. These results bring critical support to the VA interpretation of the VA Span deficit. In addition, they offer a new insight on how deficits in automatic vOT based word recognition could arise in developmental dyslexia.

Do dyslexic individuals present a reduced visual attention span? Evidence from visual recognition tasks of non-verbal multi-character arrays

“…Similar results were obtained with dyslexic adults using the exact same task and visual characters (Jones, Branigan & Kelly, 2008). Lobier et al (2012Lobier et al ( , 2014 also demonstrated similar results using non-verbal characters and responses. However, they used a visual categorization task (rather than visual recognition task) which involves additional cognitive sub-processes that may be deficient in dyslexic individuals (see BGeneral Discussion^for a review of these and other related studies).…”

“…However, the use of verbal characters and verbal responses in these tasks has raised doubts regarding the interpretation of these findings (Collis, Kohnen & Kinoshita, 2013;Hawelka & Wimmer, 2008;Lobier, Zoubrinetzky & Valdois, 2012;Lobier, Peyrin, Pichat, Le Bas & Valdois, 2014;Ziegler, Pech-Georgel, Dufau & Grainger, 2010). In contrast to the visuoattention interpretation, these findings may reflect a verbal-phonological deficit that is widely accepted as a cause of development dyslexia.…”

“…In fact, this notion is consistent to some extent with the VAS deficit view which holds that dyslexic individuals experience more difficulties with diffused attention compare to focused attention. Lobier et al (2014), using a visual categorization task (i.e., classifying characters to predefined groups), found that dyslexic participants exhibited poor performance in categorizing a number of non-verbal characters, whereas performance was normal in categorizing single non-verbal characters.…”

“Shall We Play a Game?”: Improving Reading Through Action Video Games in Developmental Dyslexia

“…An improvement in the distribution and allocation of visuo-spatial attention was obtained in the Visual Attention Span task (e.g. [20,[101][102][103][104][105]), where participants have to discriminate one of six visual stimuli. The training with AVG, compared to a NAVG training, allowed children with DD to improve their abilities in stimulus discrimination both in a condition of distributed and focused attention [100•].…”

Visual attention span deficits and assessing causality in developmental dyslexia

“…http://dx.doi. org/10.1038/nrn3836-c1 (2015)) 2 , Lobier and Valdois bring together 12 of their studies to argue that a visual attention (VA) span deficit meets the criteria that are required to demonstrate causality in developmental dyslexia [3][4][5][6][7][8][9][10][11][12][13][14] . Unfortunately, all of the studies that were discussed used letters to assess VA span; thus, the demonstrated deficit only affects letters and is causally ambiguous , as the individuals with dyslexia and control individuals that were studied differed dramatically in their experience of recoding letters to sound.…”