Children’s Eye Movements during Reading (стр. 4 )

With respect to the symmetry of the perceptual span, reading was equally disrupted for participants of all ages when the availability of information to the left of fixation was restricted; the characteristic asymmetrical span for adults is present in children by the age of 7-years. Finally, the data showed very clearly that the window size which allowed maximum reading speed was smaller for more difficult sentences – the perceptual span was reduced when the reader experienced greater processing difficulty. Thus, these experiments showed that several different aspects that characterise the perceptual span in skilled adult readers are established in readers as young as 7-years-old (the acquisition of gross properties of the upcoming text at a greater eccentricity than more specific letter information, and the asymmetry of the perceptual span). Alongside these similarities, some differences were also pared to adults, younger readers have a reduced perceptual span and proportionally more of their processing capacity is devoted to the fixated word. Manipulations of text difficulty with the children supported the argument that, when comparing adults and children, age-related changes in the overall size of the perceptual span were, at least partially, attributable to differences in processing difficulty. Note that increased processing difficulty has also been shown to reduce parafoveal pre-processing in skilled adult readers (Henderson & Ferreira, 1990; White, Rayner, & Liversedge, 2005).

Surprisingly, no research was conducted to extend or challenge these findings for 20 years. A recent study has, however, looked in detail at the development of the letter identity span – the eccentricity from fixation at which readers of different ages can access letter-specific information (Häikiö et al., 2009). Rayner showed that access to some degree of word-specific information was limited to either one or two words to the right of fixation depending on the reader’s age, while word length information was processed at greater eccentricities. Häikiö et al. designed their experiment to examine more closely the level of detail associated with individual letters that readers can access during reading at varying eccentricities.

Letters outside the window were replaced by visually similar characters (i. e., replacing an o with a c), with word boundaries preserved. In this way, readers were able to pre-process both word length and letter feature information outside the moving window, but it was only inside the window that correct letter identities were available. First, the data clearly showed developmental change in the letter identity span. At 8-years, the letter identity span extends five characters to the right of fixation, at 10-years it extends seven characters, and at 12-years and for adults it extends nine characters to the right of fixation. These data were compared to those from Rayner’s experiments and showed that, for all age groups, letter identity span was smallest, with letter feature information available relatively further to the right, and with word length information available further still from fixation. Interestingly, they also compared the letter identity spans of fast and slow readers of the same age. Clear differences were found at all ages, with slower readers having a smaller span than faster readers. These data again suggest that reading skill, rather than chronological age, is responsible for developmental differences in the perceptual span.

Some recent work, also investigating children’s pre-processing of upcoming information in a sentence, has specifically examined whether pre-processing is different between words compared to within words (Häikiö, Bertram, & Hyönä, 2010). Häikiö et al. compared adults’ and 8-, 10-, and 12-year-old children’s pre-processing of the second consituent of compound words (e. g., of “boy” in “cowboy”) to their pre-processing of the second word in adjective-noun pairs (e. g., of “bad boy”) using the boundary paradigm (Rayner, 1975). In this paradigm an invisible boundary was placed before the target word/s. Prior to the reader making a saccade that crossed the boundary, a preview letter string was presented in the target location; in this experiment, the letters of the target word/s were replaced with visually similar letters. When a saccade crossed the invisible boundary, the preview string changed to the target word. Since this change occurred during a saccade, when visual input is suppressed, the change was not noticed by the reader. In all age groups, pre-processing was greater within a compound word than between the words in an adjective-noun pair (see also Juhasz, Pollatsek, Hyönä, Drieghe, & Rayner, 2009). They also found a significant parafoveal-on-foveal effect within the compound words, but not in the adjective-noun pairs, in both adults and children (for a full explanation and discussion of parafoveal-on-foveal effects, see the chapter by Drieghe in the present volume). These data show that from as young as 8-years, the allocation of attention during reading and, thus, pre-processing of upcoming information is determined to a significant degree by the visual cues corresponding to word boundaries (rather than simply extending certain number of character spaces ahead, irrespective of whether this includes one or multiple words).

To summarise, developmental changes have been shown to occur in the pre-processing of three different aspects of text within the perceptual span (word length, letter feature, and letter identity) such that this information can be acquired further to the right from the point of fixation as age increases. Furthermore, these age-related increases in the perceptual span are driven by the underlying improvement in reading skill, reinforcing understanding of the perceptual span as an index of the allocation of attention and processing resources during reading rather than simply being a low-level perceptual restriction on eye movement behaviour. That said, the left-right asymmetry of the perceptual span is established by the age of 7-years; clearly, relatively little experience of processing printed text is necessary to develop one of the key characteristics of visual information processing during skilled adult reading. This asymmetry reflects the allocation of attention to upcoming words for parafoveal pre-processing. In our view, the development of parafoveal pre-processing during sentence reading is an integral aspect of the progression from beginning to skilled reader. The finding that the perceptual span is asymmetric in 7-year-olds is remarkable, given that reading skills at this age are still relatively basic and measures of eye movement behaviour during reading (such as fixation durations and sentence reading times) continue to show developmental change for a further four years, on average, before reaching adult levels of performance. To our knowledge, no research has been conducted to examine developmental changes in sensitivity to specific characteristics of upcoming words in parafoveal pre-processing, despite the large body of literature on this topic for adults (for a review, see Rayner, 1998, 2009). Future research must address how parafoveal pre-processing continues to develop with age and reading skill, as 7-year-olds are still a long way from being skilled readers.

Given that the perceptual span is related to the reader’s cognitive processing of the text, we anticipate that as reading skills improve with age: (1) a beginning reader will become sensitive to increasingly detailed information from the word to the right of fixation; (2) the extent to which they pre-process information from the upcoming word will increase; (3) reading times on directly fixated words will decrease as a consequence of greater parafoveal pre-processing of those words. Through such mechanisms we believe that the process of lexical identification will become quicker and more efficient with age, not only due to more efficient linguistic processing during direct fixation but also, at least partially, due to developmental changes in parafoveal pre-processing. Increased parafoveal pre-processing of upcoming words in sentences will decrease the demand on processing resources necessary to identify that word during direct fixation; this in turn will facilitate parafoveal pre-processing of the next word. This cycle of pre-processing a word and subsequent facilitation of lexical identification during direct fixation will develop with reading skill, and it seems likely that this will be reflected in shorter fixation durations, fewer refixations, and increased word skipping probabilities – an increasingly mature pattern of eye movement behaviour during reading.

5.2. Temporal limitations on visual information extraction.

Recent research has compared children of different ages with adults using the disappearing text paradigm (Liversedge et al., 2004; Rayner, Liversedge, White, & Vergilino-Perez, 2003). This is a gaze-contingent change method, where there are invisible boundaries placed between all the words within the sentence. Each time the reader’s eye crosses a boundary, the newly fixated word disappears after a specified delay while the previously fixated word reappears; there is only one word missing from the sentence at any one moment, but it is the word being fixated by the reader. Critically, a pre-specified delay can be manipulated between the reader’s eye crossing the boundary and the word disappearing, thus restricting the reader’s opportunity to visually encode the word to the initial period (typically 60 ms) of the first fixation on the word. Work with skilled adult readers has demonstrated that they are able to read and understand sentences normally when presented as disappearing text with the word being presented for 60 ms from fixation onset (Liversedge et al., 2004; Rayner et al., 2003). Interestingly, word frequency effects were found upon fixation durations in the disappearing text condition; even when the word was no longer visible, the reader’s cognitive processing determined when they would move their eyes onto the next word in the sentence.