The return-sweep in reading.
Authors: Parker, A.
Return-sweeps are saccadic eye movements that take a reader’s fixation from the end of one line to the beginning of the next. Our current understanding of return-sweeps is limited to a description of their physical characteristics. Moving beyond these descriptive characteristics, this thesis examined how lexical processing is influenced by return-sweep execution in both adults and children.
Following a review of the existing eye movement literature in chapter 1, chapter 2 examined the basic characteristics of return-sweep saccades. The reported data indicates that return-sweeps follow one of two trajectories: they land close enough to their target to enable readers to begin a rightwards pass or they are followed by a corrective saccade towards the left margin. When return-sweeps are accurate, the resulting line-initial fixation is longer in duration than intra-line reading fixations. Undersweep-fixations, those preceding corrective saccades, are shorter in duration than intra-line reading fixations. Chapter 3 examined a candidate explanation for longer accurate line-initial fixations; that binocular coordination processes are responsible for inflated fixation times following a return-sweep. Yet, the reported data lend no support for such an account. Instead, it is argued that longer line-initial fixations result from a lack of parafoveal preprocessing.
Chapter 4 directly examined the influence of return-sweep execution on lexical processing at the very start of the line. The studies detailed within chapter 4 indicate that when readers land accurately, lexical processing continues as it would during a left to right reading pass. However, when readers make an undersweep- fixation, they appear able to extract information from the word to the left of fixation such that reading times are shorter on line-initial words following an undersweep- fixation compared to cases in which they are fixated directly after a return-sweep. Chapter 5 further reflects readers’ ability to extract information at the point of an undersweep-fixation as indexed by increased skipping rates and reduced gaze durations for words receiving an undersweep-fixations during a subsequent rightwards pass. Together, these findings challenge the widely held view that undersweep-fixations are uninvolved in lexical processing.
Chapter 6 examined return-sweep saccades in developing readers. Relative to adults, children appear to fixate more extreme positions on a line when reading for comprehension. This likely reflects their reliance on foveal processing to encode written information. Furthermore, like adults, children appear able to extract information at the point of, and to the left of, an undersweep-fixation.
Collectively, the findings from this thesis characterise return-sweep saccades in both skilled and developing readers and consider the implications of return-sweep execution on lexical processing. Generally, it seems that readers continue processing information at the start of the line as they do when reading from right-to-left, except they must wait until this information becomes available in (para)foveal vision as it is unavailable for preprocessing.