Figure 114

The perceptual span in reading.

Eye movements in reading

We feel that our eyes move smoothly across the page while reading. In fact, however, they actually move in rapid jerks (known as saccades). Saccades are ballistic (once initiated their direction cannot be changed). There are fairly frequent regressions in which the eyes move backwards in the text, accounting for about 10% of all saccades. Saccades take about 10-20 milliseconds to complete, and are separated by fixations lasting for about 200-250 milliseconds. The length of each saccade is about eight letters or spaces. Information is extracted from the text only during each fixation, and not during the intervening saccades (Latour, 1962).

The amount of text from which useful information is obtained in each fixation has been studied by using the "moving window" technique (see Rayner & Sereno, 1994). Most of the text is mutilated except for an experimenter-defined area or window surrounding the reader's point of fixation. Every time the reader moves his or her eyes, different parts of the text are mutilated to permit normal reading only within the window region. The effects of different-sized windows on reading performance can be compared.

The perceptual span (effective field of view) is affected by the difficulty of the text and the size of the print. It usually extends three or four letters to the left of fixation and 15 letters to the right (see Figure 11.4). This asymmetry presumably occurs because the most informative text lies to the right of the fixation point. The form of the asymmetry is clearly learned. Readers of Hebrew, which is read from right to left, show the opposite asymmetry (Pollatsek, Bolozky, Well, & Rayner, 1981).

Rayner and Sereno (1994) concluded that there are three different spans:

• The total perceptual span (the total area from which useful information is extracted); this is the longest span.

• The letter-identification span (the area from which information is obtained).

• The word-identification span (the area from which information relevant to word-identification processes is obtained); this is the shortest span.

The size of the perceptual span means that parafoveal information (outside the central or foveal region) is used in reading. Some of the most convincing evidence comes from use of the boundary technique. In this technique, there is a preview word just to the right of the point of fixation. As the reader makes a saccade to this word, it changes into the target word. However, the reader is unaware that it has been changed. The length of fixation on the target word is less when that word is the same as the preview word than when it differs (see Reichle et al., 1998). Reading time on the target word is less when the preview word is visually or phonologically similar to the target word, suggesting that visual and phonological information can be extracted from parafoveal processing. However, the processing of information at the parafoveal level does not reach the semantic level (Rayner & Morris, 1992).

E-Z Reader model

Reichle et al. (1998) explained the pattern of eye movements during reading in their E-Z Reader model (the name makes more sense in American English, where Z is pronounced "zee"!). About 80% of content words (nouns, verbs, and adjectives) are fixated, and Reichle et al. argued that it is important to identify the factors determining the length of fixation on such words. Only about 20% of function words (articles, conjunctions, prepositions, and pronouns) are fixated, and we need to identify the factors leading some words to be "skipped" or not fixated at all.

It will be useful to start by listing facts the model was designed to explain (see Reichle et al., 1998):

• Rare words are fixated for longer than common words.

• Words that are more predictable in the sentence context are fixated for less time.

• Words that are not fixated tend to be common, short, or predictable.

• The fixation time on a word is longer when it is preceded by a rare word: the "spillover" effect.

What would be the most obvious kind of model? One might assume that readers fixate on a word until they have processed it sufficiently, after which they move their eyes immediately to the next word. However, there are two major problems with such an approach. First, it takes about 150-200 milliseconds to execute an eye-movement program. If readers behaved according to this simple model, they would waste time waiting for their eyes to move. Second, it is hard to see how readers could skip words on this model, because they would know nothing about the next word until they fixate it.

How can we get round these problems? Reichle et al. (1998) argued that the next eye movement is programmed after only part of the processing of the currently fixated word has occurred. This greatly reduces the time between completion of processing on the current word and movement of the eyes to the next word. Any spare time is used to start processing the next word. If the processing of the next word is completed rapidly enough, then it is skipped.

Reichle et al. (1998) emphasised several general assumptions in their E-Z Reader model:

1. Readers check the familiarity of the word they are currently fixating.

2. Completion of frequency checking of a word is the signal to initiate an eye-movement program.

3. Readers also engage in the task of lexical access, which "refers to the process of identi fying a word's orthographic and/or phonological pattern so that semantic information can be retrieved" (Reichle et al., 1998, p. 133). This task takes longer to complete than does frequency checking.

4. Completion of lexical access is the signal for a shift of covert (internal) attention to the next word.

5. Frequency checking and lexical access are completed faster for common words than for rare ones, and this is more so for lexical access than for frequency checking.

6. Frequency checking and lexical access are completed faster for predictable than for unpredictable words.

These theoretical assumptions lead to various predictions concerning the effects of word frequency on eye movements (see Figure 11.5). Assumptions (2) and (5) together predict that the time spent fixating common words will be less than the time fixating rare words, which is consistent with the evidence. According to the model, readers spend the time between completion of lexical access to a word and the next eye movement in parafoveal processing of the next word. The amount of time spent in such parafoveal processing is less when the fixated word is rare than when it is common (see Figure 11.5). Thus, the word following a rare word

The effects of word frequency on eye movements according to the E-Z Reader model. Adapted from Reichle et al. (1998).

Helping Your Child Learn To Read

Helping Your Child Learn To Read

When parents help their children learn to read, they help open the door to a new world. As a parent, you can begin an endless learning chain: You read to your children, they develop a love of stories and poems, they want to read on their own, they practice reading, and finally they read for their own information or pleasure. They become readers, and their world is forever expanded and enriched.

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