Читать книгу The Science of Reading - Группа авторов - Страница 85

Theoretical models propose that readers map orthographic representations onto meaning via two pathways. One pathway relates orthographic representations to semantic representations directly, while the other achieves this mapping via phonological representations (Harm & Seidenberg, 2004; see Seidenberg, this volume). Meta‐analyses of neuroimaging data are consistent with these models, revealing dorsal (spelling‐sound‐meaning; see Figure 5.1) and ventral (spelling‐meaning) pathways for reading (Taylor, Rastle, & Davis, 2013; see also Hoffman, Ralph, & Woollams, 2015; Yeatman, this volume). Though there is wide agreement that phonological decoding plays a vital role in the computation of meaning (particularly during the initial stages of learning to read), it is also recognized that skilled reading ultimately requires rapid, direct computation of meaning from a printed stimulus. The acquisition of this spelling‐meaning mapping is sometimes called orthographic learning (Castles & Nation, 2006; Castles & Nation, this volume).

Figure 5.1 Dual pathway model of reading.

Our understanding of the nature of the spelling‐meaning mapping and its acquisition is relatively poor (Nation, 2009; Nation, 2017; Taylor et al., 2015), perhaps because it has been difficult to find a clear behavioural measure of this pathway (Seidenberg, 2011). Behavioral and electrophysiological data suggest that semantic information is activated rapidly in visual word recognition (Balota et al., 2004; Carreiras, Armstrong, Perea, & Frost, 2014), although these semantic effects may be at least in part driven by processing along the phonological pathway (van Orden, 1987). However, there is also evidence that by the age of 7, children activate semantic information from subword orthographic patterns in reading, irrespective of whether those subword patterns share pronunciation with the carrier word (e.g., the crow in crown; Nation & Cocksey, 2009). These data provide evidence for a direct mapping between spelling and meaning.

Neural models conceptualize the ventral (spelling‐to‐meaning) pathway as supporting reading expertise (Dehaene‐Lambertz, Monzalvo, & Dehaene, 2018; McCandliss, Cohen, & Dehaene, 2003). Likewise, longitudinal data suggest that sensitivity along this pathway continues to develop into adolescence (Ben‐Shachar, Dougherty, Deutch, & Wandell, 2011) as reliance shifts from the dorsal pathway to the ventral pathway (Pugh et al., 2000). More recent neuroimaging research has revealed a hierarchical posterior‐to‐anterior gradient whereby representations of visual symbols become increasingly invariant as they are transformed to meaningful information (Taylor, Davis, & Rastle, 2019).

Morphology brings an important dimension to thinking about the nature of the spelling‐meaning mapping. Recent estimates suggest that the average 20‐year‐old English speaker recognizes around 71,400 printed words (Brysbaert, Stevens, Mandera, & Keuleers, 2016). If the spelling‐meaning mappings were wholly arbitrary, this would require children to learn over 12 new printed words each day (assuming that learning to read begins at age 4); surely, an unfeasible task. However, if we remove inflectional variants of stems (e.g., cleans, cleaning, cleaned), this reduces the learning challenge to 42,000 printed words. If we go further and remove derivational variants (e.g., unclean, cleanliness, cleanly), this reduces the learning challenge to 11,100 stems (Brysbaert, et al., 2016; see also Nagy & Anderson, 1984), or to just under two new words each day. Though this figure seems more feasible, it is still over double the number of distinct spellings required for full literacy in Chinese (Katz & Frost, 1992), providing an indication of the difficulty of acquiring the spelling‐meaning mapping. Crucially, these revised figures also presume that the learner has sufficient knowledge of morphological relationships to recognize that printed words such as cleanly, unclean, cleanliness, and cleaned are variations of clean.

The previous discussion suggests that acquiring knowledge of morphological relationships may be a vital part of developing a direct mapping between spellings and meanings. Strong causal evidence for this hypothesis is lacking. However, neural evidence using MEG (Lewis, Solomyak, & Marantz, 2011; Solomyak & Marantz, 2010), fMRI (Devlin, Jamison, Matthews, & Gonnerman, 2004; Gold & Rastle, 2007), and diffusion tensor imaging (Yablonski, Rastle, Taylor, & Ben‐Shachar, 2019) converge in suggesting that morphological computations engage ventral (spelling‐meaning) pathway regions of the reading system (Rastle, 2019a).