Eye Movements in Reading

Based on the eye-mind hypothesis proposed in 1976, Just and Carpenter (1980) proposed two other assumptions for the relationship between eye movements and reading comprehension. The first was the immediacy assumption: readers immediately process the fixated word so that information processing is not deferred but happens immediately upon fixation. The second assumption was that eyes remain fixated on a word as long as the word is being processed. Also, the time needed to process a newly fixated word is directly indicated by fixation duration.

Based on these two assumptions, eye movements can, to some extent, indicate the mental processes that take place in reading.

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Over the past few decades, the general characteristics of eye movements during reading have been studied in great depth. These characteristics are reviewed summarily below: English reading first, followed by Chinese reading.

2.2.3.1 English Reading

During English reading, eyes rest in fixation for approximately 200-250 ms.

Saccades between fixations span an average about 2 degrees of visual angle, or it is better expressed in terms of a span of 7 to 9 spaces of English letters. The chances of an individual word being fixated on vary according to whether it is a content word (85%) or a function word (35%), and in relationship to the length of the word, with 2-3 letter words being skipped 75% of the time, but 8 letter words fixated almost always. Eye movements also vary as a function of the syntactic and conceptual difficulty of the text.

Moreover, although readers typically move their eyes forward when reading, approximately 10-15% of saccades move backward, fixating previous letters or words.

Many regressions tend to be only a few letters long and could be due to the reader making too long of a saccade, in which case a short saccade to the left may be necessary to direct the eyes to where the reader really wants to pay attention to.

Short within-word regressive saccades may also be due to problems that the reader has encountered while processing the currently fixated word. Longer regressions (more than 10 letter spaces back along the line or to another line) occur because the reader did not understand the text. In such cases, good readers are very accurate in sending their eyes to that part of text that caused difficulty, whereas poor readers engage in more backtracking through the text. These regressive saccades are thought to be related to difficulties in processing an individual word, or difficulties in processing the meaning or structure of a sentence (Rayner, 2009).

Take one reading comprehension study as an example (Rayner et al., 2006).

Sixteen native English speakers read 32 passages with different levels of difficulty.

The results showed significance in positive correlation between difficulty rating and average fixation duration, number of fixations, as well as total reading time. In other words, the harder the passage is, the longer the average fixation duration and total reading time and more number of fixations. Another experiment in this study examined the effect of inconsistency in text on eye movements. Its data suggested that when there was an inconsistency, readers fixated longer on the region where the inconsistency occurred. In both experiments, the probability of making a regressive eye movement increased as well.

In short, as text gets more difficult, fixations get longer, saccades get shorter, and

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more regressions are made. Typographical variables such as font difficulty can also influence eye movements. Fonts that are more difficult to encode yield longer fixations, shorter saccades, and more regressions. Where level of proficiency is concerned, beginning readers have longer fixations, shorter saccades, and more regressions than skilled readers.

Compared with normal reading, which is reading silently, eye movements for reading aloud somewhat differ, as previously shown in Table 1. When reading aloud, mean fixation durations are longer than in silent reading, and the eyes tend to get ahead of the voice.

2.2.3.2 Chinese Reading

Chinese is considered the most different writing system from English. First, English is alphabet-based whereas Chinese is character-based. An English word is only meaningful when its building blocks—the alphabets—are arranged in the right order.

Each alphabet standing alone has no meaning. By contrast, a Chinese word can be composed of one character or more. Each standalone Chinese character already conveys certain meaning and different combinations of the same characters may express different meanings. Therefore, the same amount of messages can usually be expressed with fewer Chinese words than English words, making Chinese a more

“compact” language. Second, English only makes sense when it is read from left to right while Chinese characters can be arranged either vertically or horizontally. In Chinese, depending on how the characters are arranged, a text can be meaningful by being read either from top down or from left to right. Due to these distinct differences, it is not surprising that eye-movement literature focusing on Chinese reading is also in abundance as English reading.

Chinese reading studies have shown that the mean fixation duration is about 220-230 ms, not much different from English reading. Their regression rate does not differ dramatically either. Where they do differ is that Chinese readers’ average saccade length is much shorter than that of English readers as they typically move their eyes only for the span of 2-3 characters, which makes sense given that linguistic information in Chinese is more densely packed than in English (Tsai et al., 2005).

Regarding the layout, as early as in 1925, studies showed that readers’ mean fixation duration was shorter while reading Chinese horizontally (294 ms) than vertically (305 ms). However, they used more fixations in each horizontal line than vertical line. The average number of regressive fixations during horizontal reading also outnumbered that in vertical reading, 2.51 and 1.16 respectively. Researchers, therefore, concluded that reading Chinese texts of vertical alignment was easier than horizontal alignment

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(Miles & Shen, 1925; Shen, 1927). Nonetheless, another study (Sun et al., 1985) found readers more skillful in reading the horizontal format. During vertical and horizontal reading, the fixation durations were 290 and 260 ms respectively; saccade distance 1.2 and 2.6 characters; and reading speed 260 words and 580 words per minute. One explanation of such discrepancies in these studies many be due to the fact that a majority of Chinese printing shifted from a vertical-line format to a horizontal-line format in the 60-year time span. Readers became much less adept at reading vertically (Tsai et al., 2005)

Another study conducted by Tsai et al. (2000) found that Chinese reading speed is significantly faster while reading horizontally (753 words/min) than vertically (713 words/min). Such difference can be mainly attributed to the fact that readers fixate fewer times in each horizontal line (4.8 times) than vertical line (5.2 times). This result also suggested that visual acuity is superior while reading horizontally than vertically as readers were able to extract sufficient information in fewer fixations while reading horizontally. In addition, saccade distance was longer (3.9 characters) while reading horizontally than vertically (3.6 characters). The subjects switched between lines faster in a horizontal-reading context than a vertical-reading context.

However, the mean fixation durations did not differ significantly in the two situations (214 ms and 221 ms respectively for horizontal and vertical reading). These results implied that although readers extract less information in one fixation while reading vertically due to inferior visual acuity, their eyes could still obtain as much necessary information as in a horizontal reading context by increasing the number of fixations and shortening saccades to compensate for the less than ideal information gathering capability while reading vertically.