With only 26 letters to represent all possible words, it is inevitable that words overlap considerably with each other. The more words that children can read, the more likely it is that a word will overlap in letters with other words, meaning that sensitivity to both letter identity and letter position is critical. Relatively little is know about how children learn to process letter position information. We asked ReadOxford visitor Dr Yvette Kezilas to tell us more.
Reading a passage of text requires the mind to be somewhat sensitive to the position of letters within words. Without sensitivity to letter position information, words would frequently be misread. Stop might be misread as “pots”, “post”, “tops” or “opts”, making the experience of reading unenjoyable at best, and incomprehensible at worst. Whilst letter position processing needs to be sensitive enough to enable the fine discrimination between words that look similar, words like smile and slime for example, it is also flexible, enalbing tehse wrods to be raed with apparenlty litlte congitive effrot. This fine balance between precise and flexible letter position processing is thought to be a hallmark feature of skilled reading.
Mastering this balance between precise and flexible letter position processing does not always come easily. It’s normal for young children to occasionally shuffle letters when they read, but some children do so far more frequently than their peers. This reading profile is known within the research community as “letter position dyslexia” (LPD), and is thought to be caused by a hyper-flexibility in the processing of letter positions within words (Friedman & Rahamim, 2007; Kezilas, Kohnen, McKague, & Castles, 2014; Kohnen, Nickels, Castles, Friedmann, & McArthur, 2012). As a result, children with LPD frequently misread anagrams. For example, they might misread diary as “dairy”, or vice versa. This can compromise comprehension, if the word diary is interpreted as “something that comes from a cow”.
At present, there is a lot of confusion as to what exactly goes wrong in LPD. This is because it is yet unclear as to how children in general process letter position, and how this might change as they transition from novice to skilled readers. In fact, there are two somewhat contradictory developmental patterns within the literature. Some research suggests that letter position processing in typical readers becomes less flexible with development (Acha & Perea, 2008; Castles, Davis, Cavalot, & Forster, 2007; Kezilas, McKague, Kohnen, Badcock, & Castles, in press; Perea & Estevez, 2008); whereas other research suggests that letter position processing becomes more flexible with development (Lété & Fayol, 2013; Ziegler, Bertrand, Lété, & Grainger, 2014).
The aim of my research is to resolve these mixed findings within the literature, and hence to clarify how letter position processing typically changes over the course of reading development. The hope is that this information will then provide us with critical insights into how and why children with LPD struggle to deal with letter position.
One potential reason for the mixed findings is that changes in letter position processing over the course of development are driven by changes to more than one component of the reading system. Most studies that have found a developmental change in letter position processing have concluded that this is driven by a change in the visual encoding of letter position information (e.g., Perea & Estevez, 2008; Ziegler et al., 2014). However, visual encoding does not occur in isolation. In fact, the reading system is highly dynamic – not only does visual encoding have ‘bottom-up’ effects on later processes in the system such as word retrieval, but later processes also have ‘top-down’ effects on the visual encoding of text (e.g., Reicher, 1969; Wheeler, 1970; see here for discussion of the word-superiority effect, nicely illustrating top-down influences). It could therefore be the case that changes in letter position processing over the course of development are driven, at least in part, by changes in components of the reading system that occur after the initial encoding of letter position information.
A specific hypothesis that we have recently tested is that changes in letter position processing might be influenced by changes in the size of a child’s written word vocabulary. When a child encounters a word for the first time (e.g., cat), they must sound out the letters that make up the word in order to retrieve its meaning (e.g., /c/-/a/-/t/). As the child becomes more and more familiar with the word, an orthographic representation (or memory trace) for the written word is formed, and the word can then be recognised more automatically. As children’s reading vocabulary increases, the letters (and position of letters) within a reader’s orthographic representations must become better specified in memory to ensure that words do not get confused with one another.
One possibility is that older readers code letter position more accurately than younger readers because they have well-specified orthographic representations that they can draw upon to aid them in accurate letter position coding. To test this hypothesis, we looked at how children and adults code letter position within words (e.g., slime), and pseudowords (e.g., blire; see Kezilas, Kohnen, McKague, Robidoux, & Castles, in press, for a full description of the task). If a person’s orthographic representations assist them in letter position coding, then letter position should be coded more accurately for words (for which people have orthographic representations) than for pseudowords (which do not have orthographic representations).
In our study, we found that children were equally good at coding letter position in words and pseudowords, indicating that their orthographic representations had no influence on their ability to code letter position. In contrast, we found that adults were far better at coding letter position information in words than in pseudowords. These findings indicate that changes in letter position processing observed over the course of development are driven, at least in part, by the development of well-specified orthographic representations.
The results from this study are just one small piece of the puzzle. By continuing to isolate the various components of the reading system that are thought to be involved in letter position processing, I hope to provide a clearer understanding of how letter position processing develops in typical readers. Only once we have this information will we be able to fully understand why letter position processing develops atypically in children with LPD.
About the Author
Dr Yvette Kezilas completed her doctorate at Macquire University’s ARC Centre of Excellence in Cognition and its Disorders. She is now a Research Fellow in the School of Psychological Sciences at Melbourne University. She’s currently an Academic Visitor with ReadOxford, working on several experiments to explore the development of letter position coding further. With Ascen Pagan and Kate Nation, she’s exploring letter position processing in silent text reading, by monitoring children’s eye movements. With Yaling Hsiao and Kate, she’s using the Oxford Children’s Corpus to identify developmentally sensitive orthographic neighbourhood statistics. Her visit is made possible by study awards to Yvette from the UK Experimental Psychology Society and the CCD, and a grant to Kate from St John’s College. We thank the EPS, the CCD and St John’s College for supporting our collaboration.