Evidence for cognitively controlled saccade targeting in reading

Evidence for cognitively controlled saccade targeting in reading Klinton Bicknell 1 (kbicknell@ucsd.edu), Emily Higgins 1 (ehiggins@ucsd.edu), Roger Levy 2 (rlevy@ucsd.edu), & Keith Rayner 1 (krayner@ucsd.edu) 1 Department 2 Department of Psychology, UC San Diego, La Jolla, CA, USA of Linguistics, UC San Diego, La Jolla, CA, USA Abstract of the center, and Rayner initially suggested that readers may intentionally send their eyes to this position because it is the most efficient location from which to process the word (cf. O’Regan, 1981). However, Rayner, Well, Pollatsek, and Bert- era (1982) found evidence from a display change paradigm in which they controlled the amount of preview – visual infor- mation available about the next word – by replacing some letters with Xs that readers send their eyes further into the following word when they had received more preview. They suggested a cognitive account of character-level saccade tar- geting, in which readers target a position further into a word when they have already processed more of the word. For ex- ample, if readers are able to identify initial letters in a word, they no longer need visual information about those letters, and it is an efficient reading strategy to target the eyes at the latter, still-unidentified part of the word (Rayner, McConkie, & Zola, 1980). However, it is possible that Rayner et al.’s (1982) results do not reflect normal reading behavior, and may instead reflect an experiment-specific strategy, e.g., mak- ing shorter saccades when the next word contains more Xs. It is generally assumed that the character position targeted within a particular word is not under direct cognitive con- trol, but is rather determined by oculomotor processes sensi- tive only to word length and distance. An alternative view is that readers target more distant characters in words when they have parafoveally processed these words more. These possibil- ities are difficult to distinguish because the actual landing site within a word has large effects on subsequent word processing measures. In two experiments, we decoupled the targeted loca- tion from the actual landing site by shifting the text 3 charac- ters during the saccade into a target word. Results show that subsequent word processing time given a particular landing site was lower/higher when the eyes would have landed further forward/backward in the word. This effect remains significant in some cases when controlling for saccade launch site. These data provide evidence against the oculomotor theory and sup- port a cognitive account of saccade targeting. Keywords: eye movements; reading; display change Introduction Reading is a complex process that requires the combination of language processing with visual information to make de- cisions about when and where to move the eyes. These deci- sions are made very rapidly: saccades in reading take around 150 ms to program (Rayner, Slowiaczek, Clifton, & Bert- era, 1983), yet fixation durations in reading are around 200– 250 ms, leaving only 50–100 ms to decide when and where to send the eyes next. Given these temporal requirements, one central question of reading research is the extent to which these decisions are made by the cognitive system – and thus are sensitive to ongoing linguistic processing – or made by faster, low level oculomotor heuristics. Much of this debate has focused on how readers decide when to make a saccade, e.g., investigating the sensitivity of the distribution of fixation durations to the linguistic properties of a fixated word such as its frequency or predictability (Staub, White, Drieghe, Holl- way, & Rayner, 2010; Staub, 2011; Feng, 2009b). It is gen- erally assumed, however, by researchers on both sides of this debate that it is via oculomotor heuristics that readers decide where within a word to target their eyes. 1 In this paper, we provide evidence against this view, suggesting that character- level saccade targeting decisions are under cognitive control, and thus supporting a view in which even the fine details of eye movements are sensitive to ongoing linguistic processing. McConkie, Kerr, Reddix, and Zola (1988) investigated this issue with an analysis of the effect of preview on saccade tar- geting in a corpus of naturalistic reading. To assess the ef- fect of preview, McConkie et al. investigated the effect on landing position of launch site, the distance of the previous fixation from the beginning of the word. Because the quality of visual information rapidly decreases away from the fovea, nearer launch sites would be expected to yield more pre- view, and – under Rayner and colleagues’ cognitive account – landing positions further into the word. McConkie and col- leagues’ results confirmed this prediction, showing that the modal landing position was more rightward for nearer launch sites. However, McConkie et al. presented analyses suggest- ing that this result was not best explained by the cognitive account. Specifically, they presented evidence that the rela- tionship between launch site and modal landing position was linear, and argued that an account that explains the shift in modal landing position in terms of parafoveal preview should predict a non-linear relationship. Because readers only ob- tain significant information about letter identities from 7 or so characters away (Underwood & McConkie, 1985), they argued that a preview account would predict that the effect of launch site on landing site should asymptote by launch sites of 7 characters. McConkie and colleagues presented evidence that the shift in modal landing position was well modeled as a linear function of launch sites from 1 to 7 characters, with no evidence of becoming smaller near 7 characters. Neverthe- Character-level saccade targeting It has been known since Rayner (1979) that the eyes’ modal landing position in (medium and long) words is slightly left 1 This is specifically the case for decisions about where within a word to target the eyes. The control of decisions about which word to target is known to reflect cognitive processing.