The way in which the eyes cross the page during reading. Reading involves a series of rapid shifts along the line of print or writing (known as saccades), followed by periods when the eye rests upon a point in the text. A saccade typically lasts from 20 to 30 milliseconds while a fixation can last from 150 to 500 milliseconds and sometimes longer. Saccades cover no more than about 7–9 characters in reading English– fewer in logographic writing systems and alphabetic systems like Arabic which do not represent vowels. This means that almost every word is fixated. Indeed, processing a long word may sometimes involve two fixations. It is therefore useful to distinguish the duration of the first fixation of a word from the overall gaze duration of the word (all fixations).

 It was once believed that reading efficiency improved if saccades were extended; however, modern methods of tracking eye movements have suggested that good readers do not use fewer fixations than poor ones. What marks out less-skilled reading (and reading in the early stages of acquiring a second language) is a much higher level of regression, where the reader makes a backwards saccade to check information or understanding. For an average reader, regressions only account for about 10–15 per cent of saccades.

 In a skilled reader, forward saccades are mainly driven by lower level processes (i.e. the eye moves on as soon as the currently fixated word is decoded) while regressive saccades usually indicate higher level processing (checking comprehension, integrating incoming information, making anaphoric links). Evidence does not support the much-aired theory that a skilled reader is able to guess ahead and thus substantially reduce the amount of decoding that is necessary. A highly constraining context only leads to a reduction of about 10 per cent in fixation duration.

The reading process varies considerably from text to text. A reader adjusts length of saccade and duration of fixation to reflect the propositional density of the text, the text genre and the type of reading being undertaken. Other factors which determine how long a fixation lasts include the length, frequency and potential ambiguity of the word that is being fixated. Words at the beginning of a line tend to be fixated for longer than words that occur later. Fixation time and amount of regression increase markedly when there is a need to perform an antecedent search (e.g. where there is a pronoun which refers back). There is also an increase in fixation time at clause boundaries, presumably reflecting the need to construct a syntactic representation (see wrap up effects).

 A fixation usually falls on the early part of a word and encompasses a perceptual span of about 31 characters or 15 to either side of the fixation point. Focus is sharpest in the centre of the visual field, the fovea, which provides the fine detail which enables the fixated word to be decoded. However, it appears that characters beyond the foveal area, and especially to the right of it, are also processed at a low level of attention, providing a representation which may involve little more than letter shape and sequence and possibly the length of the next word. This parafoveal preview enables the reader to anticipate certain general features of the next fixation. The effect seems to be to speed up processing– hence the longer fixation times when a new line of text is begun and no pre processing is possible. Parafoveal preview supports word skipping when a short, frequent or highly predictable word lies ahead, and warns of the need for a longer saccade when a long word is in the offing. (Major source: Rayner and Pollatsek, 1989.)

See also: Reading: decoding

Further reading: Just and Carpenter (1987: Chap. 2); Rayner and Pollatsek (1989: Chap. 4)

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