Why readers regress to previous words: A statistical analysis
Why readers regress to previous words: A statistical analysis Klinton Bicknell Roger Levy {kbicknell, rlevy}@ucsd.edu UC San Diego, Department of Linguistics 9500 Gilman Drive #108, La Jolla, CA 92093 0108 USA Abstract of between word regressions (e.g. Reichle, Warren, Mc Connell, 2009; Engbert et al. 2005) that some proportion of them are made in response to overshooting a target word due to motor error, and making a between word regression to re turn to the originally targeted word. Supporting this view is evidence that between word regressions increase following word skipping (Vitu McConkie, 2000) Thus, to better dis tinguish between competing theories of between word regres sions, we focus our discussion here only on cases in which the target of the between word regression was not skipped (about half of all between word regressions in the dataset we exam ine below) The question for the theories then becomes one of why a reader would regress to a previously fixated word. While the major models of eye movement control in reading propose very different mechanisms for the generation of sac cades to previous words, there has been relatively little em pirical data to distinguish these hypotheses. Here we provide a systematic statistical analysis of the factors that elicit these saccades in a corpus of eye movements. We show that the re sults are contrary to the predictions of a number of accounts, and provide new evidence to discriminate among the models. Keywords: eye movements; reading; regressive saccades; lo gistic regression Introduction The control of the eyes during reading is one of the most com plex everyday tasks humans face, as efficient performance requires the rapid integration of complex information from visual, motor, and linguistic sources. In recent decades, our knowledge of the determinants of how readers select saccade targets and decide how long to fixate particular locations has grown immensely (for reviews see Rayner, 1998, 2009) The focus of this work has been on understanding the most com mon ways in which the eyes move through the text: progres sive saccades to a word further in the text and refixations of the current word. As such, our understanding of instances in which the eyes move back to a previous word (between word regressions) is still one of the most poorly developed facets of theories of eye movement control in reading. While not the most common type of saccade, between word regres sions are still a regular property of the eye movement record, consistently occurring on between 1 in 10 and 1 in 20 sac cades (and as high as 30% of all saccades for some read ers, Radach McConkie, 1998) Thus, it is a striking state of affairs that the major models of eye movement control in reading (e.g. Pollatsek, Reichle, Rayner, 2006; Engbert, Nuthmann, Richter, Kliegl, 2005) propose very different reasons for making between word regressions, each of which is intimately tied to the model's view of the nature of eye movements in reading. One of the best ways to tease apart the various models of eye movement control, then, is to gain a better understanding of between word regressions. To date, however, there has been relatively little empirical data analy sis to distinguish these various theories of why a reader would move their eyes to a previous word. Thus, the present work seeks to remedy this situation by providing a systematic anal ysis of the factors that elicit between word regressions, and in so doing to provide a new source of evidence distinguishing among models of eye movement control in reading. While there are many proposals as to why a reader would regress to a previous word, it is a common belief among re searchers who have diverse opinions on the primary cause Theories of between word regressions We consider here five classes of theories of the causes of between word regressions to unskipped words. For each the ory, we highlight the predictions it makes for which variables will influence the rate of between word regressions. For con creteness, we discuss these predictions for the case of a re gression from the nth word in a given sentence (word n) to the previous word n 1. We can group the factors to which regressions are predicted to be sensitive into three categories: (a) properties of word n (i.e. its length, frequency, or pre dictability) (b) those same properties of word n 1, and (c) motor properties (i.e. length of the previous saccade or the position of the eyes on word n or previously on word n 1) Corrective One possibility for most theories is that some between word regressions (even when word n 1 was not skipped) could still be corrective. This could happen if the saccade that landed on word n was intended to be a refixation of word n 1. This is quite plausible since the most common pattern of refixations is that first a word's beginning is fixated and then its end (Rayner, Sereno, Raney, 1996) This account predicts that properties of word n 1 should be relevant, since there should be more regressions when re fixations are more likely (lower frequency or predictability, longer length of word n 1) In addition, motor properties should be relevant: regressions should be more likely when the eyes land closer to the beginning of word n 1 (since re fixations are more likely) and closer to the beginning of word n (since that is where failed refixations would land) Proper ties of word n are not predicted to matter, except insofar as they correlate with properties of the preceding input. Oculomotor strategy Another possibility is that regressive saccades could be initiated as part of an oculomotor strategy (O'Regan Levy Schoen, 1987; Yang McConkie, 2001)
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