Electrophysiological Evidence against the Magnocellular Deficit Theory in Developmental Dyslexia

Abstract

<p class="MsoNormal"> <span lang="EN-CA" style="font-size:10px;font-family:Verdana;">Over the last two decades, the hypothesis of a magnocellular deficit in dyslexia has raised considerable interest and controversy. Using an electrophysiological procedure (visual evoked potentials, VEP), we compared magnocellular and parvocellular contrast and spatial frequency-response functions between phonological dyslexics (n</span><span lang="EN-CA"> </span><span lang="EN-CA" style="font-size:10px;font-family:Verdana;">=</span><span lang="EN-CA"> </span><span lang="EN-CA" style="font-size:10px;font-family:Verdana;">16) and a typical reading group (n</span><span lang="EN-CA"> </span><span lang="EN-CA" style="font-size:10px;font-family:Verdana;">=</span><span lang="EN-CA"> </span><span lang="EN-CA" style="font-size:10px;font-family:Verdana;">12) matched for age and socioeconomic background. No significant differences were found between the two groups in the amplitude of the VEP components associated with either magnocellular or parvocellular responses. However, topographic analyses revealed a group difference in the distribution of amplitude in the right frontal and left temporal regions, which appeared to be underactivated in dyslexics. These results suggest a deficit in the higher-level cortical regions involved in phonological and/or linguistic processing, and calls into question the notion of a magnocel</span><span lang="EN-CA" style="font-size:10px;font-family:Verdana;">lular involvement in dyslexia.</span><span lang="EN-US"><o:p></o:p></span> </p

Electrophysiological signatures of visual temporal processing deficits in developmental dyslexia

“…Regarding dyslexia, evidence reporting P1 modulations is mixed (Kubová et al, 2015; Meng et al, 2022; Sayeur et al, 2013). As the current study does not test magnocellular function directly, the absence of a P1 reduction cannot be used as evidence against a magnocellular deficit in dyslexia.…”

Electrophysiological signatures of visual temporal processing deficits in developmental dyslexia

“…Regarding dyslexia, evidence reporting P1 modulations is mixed (Kubová et al, 2015; Meng et al, 2022; Sayeur et al, 2013). As the current study does not test magnocellular function directly, the absence of a P1 reduction cannot be used as evidence against a magnocellular deficit in dyslexia.…”

Comparison of visual information processing in school-age dyslexics and normal readers via motion-onset visual evoked potentials

“…Several VEP studies reported a magnocellular deficit in dyslexics when using pattern-reversal stimuli modified to target the magnocellular system and/or the dorsal stream of the visual pathway (M-D pathway) by means of a lower spatial frequency and lower contrast applications (Brannan et al, 1998;Livingstone et al, 1991;Romani et al, 2001;Vaegan & Hollows, 2006). On the contrary, some other studies failed to confirm a magnocellular deficit in this way (Brecelj, Strucl, & Raic, 1996;Sayeur et al, 2013;Victor et al, 1993). Nevertheless, the use of the pattern-reversal for the selective activation (testing) of the magnocellular system need not be fully appropriate (Kubova et al, 1995), and the analysis of motion-onset VEPs (M-VEPs) to test the M-D pathway in dyslexics may be more specific and precise (Kubova, 2006 Robust M-VEPs with low variability can be acquired in adults when motion stimuli are optimized for M-D pathway activation (Heinrich, 2007;Kuba & Kubova, 1992;Kuba et al, 2007), however, the interpretation of the variable M-VEP recordings in children is often difficult.…”

Electrophysiological signatures of visual temporal processing deficits in developmental dyslexia

“…Regarding dyslexia, evidence reporting P1 modulations is mixed (Kubová et al, 2015; Meng et al, 2022; Sayeur et al, 2013). As the current study does not test magnocellular function directly, the absence of a P1 reduction cannot be used as evidence against a magnocellular deficit in dyslexia.…”

Comparison of visual information processing in school-age dyslexics and normal readers via motion-onset visual evoked potentials

“…Several VEP studies reported a magnocellular deficit in dyslexics when using pattern-reversal stimuli modified to target the magnocellular system and/or the dorsal stream of the visual pathway (M-D pathway) by means of a lower spatial frequency and lower contrast applications (Brannan et al, 1998;Livingstone et al, 1991;Romani et al, 2001;Vaegan & Hollows, 2006). On the contrary, some other studies failed to confirm a magnocellular deficit in this way (Brecelj, Strucl, & Raic, 1996;Sayeur et al, 2013;Victor et al, 1993). Nevertheless, the use of the pattern-reversal for the selective activation (testing) of the magnocellular system need not be fully appropriate (Kubova et al, 1995), and the analysis of motion-onset VEPs (M-VEPs) to test the M-D pathway in dyslexics may be more specific and precise (Kubova, 2006 Robust M-VEPs with low variability can be acquired in adults when motion stimuli are optimized for M-D pathway activation (Heinrich, 2007;Kuba & Kubova, 1992;Kuba et al, 2007), however, the interpretation of the variable M-VEP recordings in children is often difficult.…”

Electrophysiological signatures of visual temporal processing deficits in developmental dyslexia

“…Regarding dyslexia, evidence reporting P1 modulations is mixed (Kubová et al, 2015; Meng et al, 2022; Sayeur et al, 2013). As the current study does not test magnocellular function directly, the absence of a P1 reduction cannot be used as evidence against a magnocellular deficit in dyslexia.…”

Comparison of visual information processing in school-age dyslexics and normal readers via motion-onset visual evoked potentials

“…Several VEP studies reported a magnocellular deficit in dyslexics when using pattern-reversal stimuli modified to target the magnocellular system and/or the dorsal stream of the visual pathway (M-D pathway) by means of a lower spatial frequency and lower contrast applications (Brannan et al, 1998;Livingstone et al, 1991;Romani et al, 2001;Vaegan & Hollows, 2006). On the contrary, some other studies failed to confirm a magnocellular deficit in this way (Brecelj, Strucl, & Raic, 1996;Sayeur et al, 2013;Victor et al, 1993). Nevertheless, the use of the pattern-reversal for the selective activation (testing) of the magnocellular system need not be fully appropriate (Kubova et al, 1995), and the analysis of motion-onset VEPs (M-VEPs) to test the M-D pathway in dyslexics may be more specific and precise (Kubova, 2006 Robust M-VEPs with low variability can be acquired in adults when motion stimuli are optimized for M-D pathway activation (Heinrich, 2007;Kuba & Kubova, 1992;Kuba et al, 2007), however, the interpretation of the variable M-VEP recordings in children is often difficult.…”