Words as Visual Objects: Neural and Behavioral Evidence for High-Level Visual Impairments in Dyslexia

Abstract

Developmental dyslexia is defined by reading impairments that are disproportionate to intelligence, motivation, and the educational opportunities considered necessary for reading. Its cause has traditionally been considered to be a phonological deficit, where people have difficulties with differentiating the sounds of spoken language. However, reading is a multidimensional skill and relies on various cognitive abilities. These may include high-level vision—the processes that support visual recognition despite innumerable image variations, such as in viewpoint, position, or size. According to our high-level visual dysfunction hypothesis, reading problems of some people with dyslexia can be a salient manifestation of a more general deficit of high-level vision. This paper provides a perspective on how such non-phonological impairments could, in some cases, cause dyslexia. To argue in favor of this hypothesis, we will discuss work on functional neuroimaging, structural imaging, electrophysiology, and behavior that provides evidence for a link between high-level visual impairment and dyslexia.

Shallow or deep? The impact of orthographic depth on visual processing impairments in developmental dyslexia

“…Such evidence of a specifically visual processing deficit in DD has been documented by studies investigating non-reading visual impairments that may be attributed to a dysfunctional left occipito-temporal cortex. This dysfunction not only reduces rapid and automatised recognition of letters and words (similar to the proposal of Wimmer, 1993) but is also implicated in speed of processing for other demanding visual stimuli (Behrmann & Plaut, 2013, 2020Behrmann et al, 1998;Kronbichler et al, 2008;Price & Devlin, 2011b;Sigurdardottir et al, 2021). For instance, this region is responsive when processing non-orthographic visual stimuli, such as faces and visually complex objects (Behrmann & Plaut, 2013, 2020Gabay et al, 2017a;Roberts et al, 2013Roberts et al, , 2015-stimuli which DD individuals are slow to process.…”