Timing the impact of literacy on visual processing

Abstract

Learning to read requires the acquisition of an efficient visual procedure for quickly recognizing fine print. Thus, reading practice could induce a perceptual learning effect in early vision. Using functional magnetic resonance imaging (fMRI) in literate and illiterate adults, we previously demonstrated an impact of reading acquisition on both high-and low-level occipitotemporal visual areas, but could not resolve the time course of these effects. To clarify whether literacy affects early vs. late stages of visual processing, we measured event-related potentials to various categories of visual stimuli in healthy adults with variable levels of literacy, including completely illiterate subjects, early-schooled literate subjects, and subjects who learned to read in adulthood (ex-illiterates). The stimuli included written letter strings forming pseudowords, on which literacy is expected to have a major impact, as well as faces, houses, tools, checkerboards, and false fonts. To evaluate the precision with which these stimuli were encoded, we studied repetition effects by presenting the stimuli in pairs composed of repeated, mirrored, or unrelated pictures from the same category. The results indicate that reading ability is correlated with a broad enhancement of early visual processing, including increased repetition suppression, suggesting better exemplar discrimination, and increased mirror discrimination, as early as ∼100-150 ms in the left occipitotemporal region. These effects were found with letter strings and false fonts, but also were partially generalized to other visual categories. Thus, learning to read affects the magnitude, precision, and invariance of early visual processing.reading | brain plasticity | education R eading is a cultural activity in which contemporary humans have considerable training. Fluently accessing the sounds and meanings of written words requires very fast and efficient visual recognition of letter strings, at rates exceeding 100 words/ min. Neuroimaging studies have begun to show how learning to read modulates the functioning of the visual system, from early retinotopic areas (1, 2) to extrastriate occipital and temporal cortex (1, 3, 4). In particular, a restricted region of the left occipitotemporal cortex, the visual word form area (VWFA), is robustly activated when orthographic stimuli are presented to literate subjects.This VWFA activation is reproducible across participants and writing systems (5, 6), even when orthographic stimuli are flashed unconsciously (7). Orthographic processing in the VWFA is thought to be very fast, peaking at ∼170-200 ms (8-10), and is colateralized to the dominant hemisphere for language (11,12). Reading practice enhances activation of the VWFA (1, 13, 14), even in dyslexic children (15). Reading also modulates nonvisual circuits, such as the spoken language network (1,14,16,17).In addition to these positive effects of learning to read, the theory of neuronal recycling (18) proposes that literacy acquisition also may have a negative "unlearning" e...

Origins of the specialization for letters and numbers in ventral occipitotemporal cortex

“…Comparison of literate and illiterate adults has established that learning to recognize letter strings produced a modest but significant competition with face and checkerboard stimuli at the canonical site of the VWFA, resulting in shrinking of face-selective responses to within 10 mm of the VWFA and a shift to right-hemisphere FFA ( [20], see also [34,35] for a similar observation reported in the comparison of the responses of dyslexic and normal readers at 9 years of age). In a follow-up study with the same adult subjects, the posterior arcuate fasciculuswhich connects the VWFA to posterior superior temporal and inferior parietal regions involved in phonological representations (among others) -was found to be reinforced by the acquisition of literacy [36].…”

Music and words in the visual cortex: The impact of musical expertise

“…Proverbio et al (2013) found that left fusiform activations to words were about one centimeter more anterior in musicians than in controls, without assessing the significance of this difference and using the spatially imprecise method of event-related potentials. Another example of interaction between categories of visual objects in defining the layout of cortical specialization was reported by Dehaene et al (2010), who showed that literacy was correlated with a shrinking of face-selective areas contiguous to the VWFA, and an increase in face-induced activation in the right FFA (see also Plaut and Behrmann, 2011;Pegado et al, 2014). Srihasam et al (2014) showed that when monkeys learned a second symbol set, activations induced by a first-learned set moved away slightly, again suggestive of competition between categories for cortical space.…”

“…knife, hair-dryer) presented in a normal orientation. The faces, tools, and houses images used here were used in previous studies in order to map category selectivity in the occipitotemporal cortex (Gaillard et al, 2006;Thirion et al, 2007;Dehaene et al, 2010;Pegado et al, 2014;Pinel et al, 2015). Music notation corresponded to one bar of classical piano music (G and F clefs), containing no alphabetic symbol.…”

Sex differences of hemispheric lateralization for faces and Chinese characters in early perceptual processing

“…For example, the face-response displacement effect: as literacy increases, face-induced functional magnetic resonance imaging (fMRI) responses in the left fusiform face area (FFA) become slightly smaller but increase substantially in the classical right FFA [26]. This effect was replicated in an fMRI study on children [27] and ERP studies on children and adults [28,29]. Moreover, there were some overlaps of neural selectivity between faces and words in early perceptual processing [30].…”