Studies of eye movements in reading alphabetic writing system languages, such as English, suggest that the optimal viewing position (OVP), the most effective target in each word that allows fastest word processing, is the word centre. In alphabetic languages with spaces between the words, research has shown that readers' preferred viewing location (PVL) is to the left of the OVP. It appears that spaces between words is the most salient low-level visual processing cue to guide the eyes during reading, for when the spaces are removed from the text of alphabetic spaced languages, reading rate decreases by approximately 35% and the PVL shifts dramatically from the word-centre towards the word-beginning. Although these finding are widely accepted, it is unclear how well such results generalize to languages without spaces between words "" scriptio continua alphabetic languages. Thai is a good model of a scriptio continua language in which to investigate eye movements during reading, not only because it is written without spaces between words but because its orthography is also quite complicated in terms of visual information. In brief, characters such as vowels, tones, and other diacritics or even some parts of the consonants can be written above or below the main horizontal line. Reilly et al. (2003) surprisingly found that Thai adult readers also target the word centre during saccadic eye movements, even though there is no spacing to help indicate word boundaries. They suggested that the relative position-specific frequency of occurrence of final and initial characters serve as visual cues to guide eye movements of Thai readers. Analysis of the frequency of initial and final characters calculated for the texts used in their experiment confirm their suggestion that participants' landing site location tended to be closer to the word centre if the position-specific frequency of the initial and especially final characters are relatively high. The aim of this thesis was to test the effects of low-level visual distinctive features in Thai orthography "" namely i) the relative frequency of occurrence of characters in the initial and final positions, and ii) spaces between words "" on reading time, eye movement patterns and control, and fixation patterns of native Thai readers, both children and adults. Experiment 1 involved studies of reading time with a group of adults and four groups of children (1st, 2nd, 5th and 6th Graders, with half in each group being good and half being poor readers). This experiment focussed particularly on the start and end characters of words. It was found that relative frequency of occurrence of characters in the word-start and word-end positions had significant effects on reading time and reading accuracy of Thai participants across all ages. Higher frequency characters, especially word-start characters helped reduce reading time and spacing between words facilitated reading in general as indicated by shorter reading times, especially for poor reader young children. Differences due to groups and spacing decreased as the age of participants increased and their reading skills improved. Experiments 2 and 3 involved precise measurements of eye movements using the EyeLink II apparatus and followed up on the effects found in Experiment 1, those of position-specific frequency of word-start and word-end characters. In Experiment 2, adults of lower and higher education levels were tested on unspaced and spaced text reading either silently or aloud. It was found that Thai readers' PVL was at or near the word centre in all conditions. The presence or absence of spaces between words did not cause any dramatic changes to this PVL, like those found in the eye movements of English language readers presented with the unusual unspaced text. That is, for Thai readers reading normal unspaced text and unusual spaced text, the oculomotor patterns were the same in contrast to the dramatic change in English readers' eye movements when faced with the unusual unspaced text (Rayner et al., 1998). Nevertheless, in concert with the Experiment 1 reading time studies, spaces between words did allow faster reading in Thai readers; there were shorter first fixations and gaze durations for spaced than unspaced text. In addition, for reading aloud the PVL was closer to word start than for silent reading, and first fixation and gaze duration were longer for reading aloud. Relative frequency of characters especially at word-start position had significant effects on landing site location of Thai adults (skilled readers), i.e., higher start character frequency allowed participants to land their eyes at the PVL. Word-end character frequency had less effect on landing site but stronger effects on fixation time of the participants; both first fixation and gaze durations on words with higher end character frequency were shorter than those with the lower frequency. In Experiment 3, with two groups of children the results were similar although the landing site of the younger child participants was a bit further to the left of the word centre than it was for older children and adults, but still too far into the word to be designated as the word-initial area. Unlike the results of the adults' eye movements, spaces between words had significant effects on landing site location especially in younger children. Spaces facilitated young children's oculomotor controls and assisted in lading their eyes closer to the OVP. There were no significant main effects of character frequency on landing site location of Thai children on the target words. However, frequency of characters in both word-start and word-end positions were used by younger child readers if there were no visible visual cue, i.e., spaces, available. Thus younger children relied on low-level visual information such as spaces between words more when reading. This may be because literacy teaching in Thai starts with spaced texts therefore younger children were more familiar with spaced text and try to use this information to locate word boundaries first before moving to the next resource such as the characters at word-start and word-end position. Generally the results of this thesis show that Thai readers, child and adult, use the same oculomotor controls when reading spaced and unspaced text. Adding spaces into the text does not change the PVL which remains near the OVP at or near word centre and similar to that of native readers of spaced alphabetic languages; however spacing does facilitate the landing site of younger children to be closer to the OVP. The developmental trend of eye movements in reading Thai seems to be that Thai readers rely less on visible visual cue as their reading skills increase at which point spaces between words facilitate reading time (first fixation and gaze duration) of skilled readers. Such results show that spaces between words are not essential for optimal eye movements in Thai. However, as spaces between words result in a decrease in reading time, spaces may aid in word recognition. These results have important implications for models of eye movements in reading which, at present, do not explicitly account for reading in scriptio continua languages. Additionally, two more reading time studies were conducted to investigate other distinctive features of Thai orthography (and details are given in Appendix C). In Experiment A, the focus was the feedback consistency versus inconsistency of initial and final characters. Similar results to Experiment 1 were found in terms of spacing conditions of the texts. Feedback inconsistent grapheme-phoneme relationships between letters and sounds slowed reading time for both initial and final consonants but there were more errors for final consonants, possibly due to significantly fewer final phonemes in the Thai phonological system. In Experiment B, the transparency of tone realisations was investigated. It was found that participants read words with transparent tone realisations faster and made fewer errors than for words with opaque tone realisations. Together these results show that reading time is sensitive to the influence of features of particular characters (frequency, grapheme-phoneme consistency, transparency of tone realisation) and also to spacing between words. Even though these features had some significant effects on reading time and reading accuracy of Thai readers, we still did not know if they would have any effects on eye movements of Thai readers or not. The results of these two additional reading time experiments provide the bases and hypotheses for further eye movement experiments; the effects found there need to be followed up in further studies. On the other hand the results of the reading time (Experiment 1) and eye movement (Experiment 2 and 3) studies of word-start and word-end character frequencies provided definitive evidence that the PVL in Thai, a scriptio continua language, is near the OVP at word centre as for spaces alphabetic languages. This finding should be further investigated in other scriptio continua languages such as Khmer (Cambodian) and Lao.
| Date of Award | 2011 |
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| Original language | English |
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