Out of this word: the effect of parafoveal orthographic information on central word processing
The aim of this thesis is to investigate the effect of parafoveal information on central word processing. This topic impacts on two controversial areas of research: the allocation of attention during reading, and letter processing during word recognition. Researchers into the role of attention during reading are split into two camps, with some believing that attention is allocated serially to consecutive words and others that it is spread across multiple words in parallel. This debate has been informed by the results of recent experiments that test a key prediction of the parallel processing theory that parafoveal and foveal processing occur concurrently. However, there is a gap in the literature for tightly-controlled experiments to further test this prediction. In contrast, the study of the processing that letters undergo during word recognition has a long history, with many researchers concluding that letter identity is processed only conjointly with letter ‘slot’ position within a word, known as ‘slot-based’ coding. However, recent innovative studies have demonstrated that more word priming is produced from prime letter strings containing letter transpositions than from primes containing letter substitutions, although this work has not been extended to parafoveal letter prime presentations. This thesis will also discuss the neglected subject of how research into these separate topics of text reading and isolated word recognition can be integrated via parafoveal processing. It presents six experiments designed to investigate how our responses to a central word are affected by varying its relationship with simultaneously presented parafoveal information. Experiment 1 introduced the Flanking Letters Lexical Decision task in which a lexical decision was made to words flanked by bigrams either orthographically related or unrelated to the response word; the results indicated that there is parafoveal orthographic priming but did not support the ‘slot-based’ coding theory as letter order was unimportant. Experiments 2-4 involved eye-tracking of participants who read sentences containing a boundary change that allowed the presentation of an orthographically related word in parafoveal vision. Experiment 2 demonstrated that an orthographically related word at position n+1 reduces first-pass fixations on word n, indicating parallel processing of these words. Experiment 4 replicated this result, and also showed that altering the letter identity of word n+1 reduced orthographic priming whereas altering letter order did not, indicating that slot-based coding of letters does not occur during reading. However, Experiment 3 found that an orthographically related word presented at position n-1 did not prime word n, signifying the influence of reading direction on parafoveal processing. Experiment 5 investigated whether the parallel processing that words undergo during text reading conditions our representations of isolated words; lexical decision times to words flanked by bigrams that formed plausible or implausible contexts did not differ. Lastly, one possible cause of the reading disorder dyslexia is under- or over- processing of parafoveal information. Experiment 6 therefore replicated Experiment 1 including a sample of dyslexia sufferers but found no interaction between reading ability and parafoveal processing. Overall, the results of this thesis lead to the conclusion that there is extensive processing of parafoveal information during both reading (indicating parallel processing) and word recognition (contraindicating slot-based coding), and that underpinning both our reading and word recognition processes is the flexibility of our information-gathering mechanisms.