Methodological differences across studies can contribute to
Methodological differences across studies can contribute to explain these different patterns of results. Neuroimaging studies on adults highlight the strong impact of literacy on spoken word responses when people perform explicit tasks (e.g., rhyming, repetition, lexical decision tasks; Castro-Caldas et al., 1998; Dehaene et al., 2010; Dehaene, 2011). Importantly, they did not report cloprostenol changes during passive listening (Dehaene et al., 2010). Similarly, a neuroimaging study where children were passively listening to sentences did not systematically report reading-induced changes (Monzalvo and Dehaene-Lambertz, 2013). Variations in neural correlates of spoken sentences relative to foreign sentences were reported after few months of reading instructions (6 years old), but not after years (6–9 years old; Monzalvo and Dehaene-Lambertz, 2013; see also Simos et al., 2000 for a similar null effect). Apart from the task, the contrast of interest might also contribute to explain the different patterns of results. In Monzalvo and Dehaene-Lambertz (2013) significant differences in the speech network were observed between 6 and 9 years of age only when responses to native and foreign sentences were grouped, but not when they were compared against each other. Similarly, Pugh et al. (2013) reported an enhancement of left temporal responses after combining activity from words and pseudowords (Pugh et al., 2013). However, results concerning the direct contrast between words and pseudowords were not reported. Altogether, these findings show that the impact of reading acquisition on the left spoken language network is evident only under specific experimental circumstances. Both the task and the contrast of interest might influence the final pattern of results (Dehaene et al., 2010; Monzalvo and Dehaene-Lambertz, 2013; Pugh et al., 2013). Given the paucity of studies on literacy and reading development it is difficult to draw definitive conclusions on this issue. Based on the available findings, we can claim that reading expertise does not have strong effects on auditory processes involved in passive listening. This questions a consistent automatic access to orthography during auditory word processing (Perre et al., 2011) and highlights that, at least in children, orthographic representations are not always activated by the passive listening to the corresponding words. In addition, reading acquisition does not seem to affect processes that are specifically related to the analysis of meaningful words and sentences compared to other auditory controls (i.e., scrambles, foreign sentences). Other auditory subdomains might be more affected by the experience of reading. Behavioural and electrophysiological studies seem to suggest that the processing of prosodic contours (Goswami et al., 2009; Molinaro et al., 2016), syllabic boundaries (Hornickel et al., 2009; Lizarazu et al., 2015; Morais et al., 1986) and phonological cues (Morais et al., 1979; Morais et al., 2007; Woodruff et al., 2014; for a review see Huettig and Mishra, 2014) might be more affected by reading expertise as compared to lexical analysis. Brain responses to visual objects differ from those to scrambles over posterior sites (200–500ms). The distribution and the timing of this effect are consistent with those reported in previous electrophysiological studies for recognition and semantic encoding of visual objects (Friedman et al., 1988, 1992; He et al., 2015). Importantly, we observed changes of these responses as a function of reading scores and picture naming scores, with increased left responses to objects relative to scrambles as reading and verbal decoding of visual images improves. The lack of clear differences between poor and skilled readers in the between-group comparisons might suggest that these brain changes gradually happen over time. These findings show for the first time that neural correlates of children’s object recognition change as they become more expert readers. Reading acquisition is associated with the activation of the left language network during children’s object recognition. One possible explanation of the present finding is related to the linguistic decoding of visual material. This effect can be interpreted as reflecting a more efficient access to lexical codes through visual configurations after reading acquisition. As children learn to read they get trained to associate symbolic visual material (e.g. letters) with phonological, lexical and semantic content (Kolinsky et al., 1990; Reis et al., 2006). This training would influence the interaction between the visual and the language systems (for a similar proposal see Hoving et al., 1974; Reis et al., 2006) and it would enable the left language network to be activated by different types of visual representations.