Ординатура / Офтальмология / Английские материалы / Eye Movements A Window on Mind and Brain_Van Gompel_2007

incongruent sentences, the three-group model may not fit the data as well because of the need of an additional group of saccades to account for cognitive influences.

Models of eye-movement control in reading that posit word-based eye guidance may be able to account for the relationship between launch site and landing site for mediumlength saccades (Engbert et al., 2006; Reichle et al., 2003; Reilly & Radach, 2003, 2006). The assumption of oculomotor range error, that oculomotor aiming errors result from a bias toward the center of the range of saccade lengths in the task, would predict a preference for the same saccade length at different launch sites (Kapoula, 1985; McConkie et al., 1988; Radach & McConkie, 1998). However, these models would have difficulty accounting for three findings in the present experiments. First, both pseudoand normal reading favored an early bias toward saccades of about 7–8 letters (estimated mean length of medium-length saccades), whereas the length of pseudo-words was actually greater than the length of words in normal reading. This result is in contradiction with the prediction of oculomotor range error. Second, the distributions of initial landing sites in words and pseudo-words presented similar shifts over the period of a fixation, suggesting that effects of saccade latency were unrelated to ongoing word-identification processes. Third, the rather small percentage of late-latency (or large-length) saccades in reading and the small percentage of corrective saccades severely question the importance of a saccade-target mechanism in reading. Finally, it should be noted that in this chapter, we favored the C/I model and the distinction between strategy-based and visually based activation, as it accounts for the dissociation between mediumand large-length saccades or between early and late saccades. However, the present findings are also consistent with the assumption that in reading, the eyes move forward in a center-of-gravity manner without aiming for specific target locations (Vitu, 2003). As the launch site moves further away from the beginning of a word, the center of gravity of the peripheral configuration would move accordingly, shifting the distribution of initial landing sites, but producing only negligible changes on the distribution of saccade length (see also Vitu, 1991a–b). It would be only at later times, when visual information becomes more detailed and center-of-gravity influence are reduced (Coëffé & O’Regan, 1987; Findlay, 1982) that the eyes would attempt to reach predefined target locations. However, as suggested by the present data, this would occur only occasionally.

4.2. Word-based gaze guidance

As we have seen above, the term “word-based guidance” can be interpreted from a linguistic or a visual perspective and implemented based on wordor letter-units. Some may consider this chapter as arguing radically against the proposal that eye movements in reading are word-based; this would be a misunderstanding of the C/I model. What the C/I model proposes is that eye guidance is not mainly controlled by the processing of the content of a word, such as its identification; cognitive/linguistic influences may exist but they would come in late and they would be relatively infrequent. The C/I model suggests that the visual configuration of words/letters serves as the basis for visual guidance. The proposal of strategy-based activation does not exclude the use of visual

Coëffé, C., & O’Regan, J. K. (1987). Reducing the influence of non-target stimuli on saccade accuracy: Predictability and latency effects. Vision Research, 27, 227–240.

Dorris, M. C., Taylor, T. L., Klein, R. M., & Munoz, D. P. (1999). Influence of previous visual stimulus or saccade on saccadic reaction times in monkey. Journal of Neurophysiology, 81(5), 2429–2436.

Engbert, R., Nuthmann, A., Richter, E., & Kliegl, R. (2006). SWIFT: A dynamical model of saccade generation during reading. Psychological Review, 112(4), 777–813.

Findlay, J. M. (1982). Global visual processing for saccadic eye movements. Vision Research, 22, 1033–1045. Inhoff, A. W., Radach, R., Eiter, B. M. & Juhasz, B. (2003). Distinct subsystems for the parafoveal processing of spatial and linguistic information during eye fixations in reading. Quarterly Journal of Experimental

Psychology, 56A(5), 803–827.

Jurgens, R., Becker, W., & Kornhuber, H. (1990). Natural and drug-induced variation of velocity and duration of human saccadic eye movements: Evidence for control of the neural pulse generator by local feedback.

Biological Cybernetics, 39, 87–96.

Just, M. A., & Carpenter, P. A. (1980). A theory of reading: From eye fixations to comprehension. Psychological Review, 87(4), 329–354.

Kapoula, Z. (1985). Evidence for a range effect in the saccadic system. Vision Research, 25(8), 1155–1157. Kerr, P. W. (1992). Eye movement control during reading: The selection of where to send the eyes. Unpublished

doctoral dissertation (Doctoral dissertation, University of Illinois at Urbana-Champaign, 1992). Dissertation Abstracts International, #9305577.

Kliegl, R. & Engbert, R. (2003). SWIFT explorations. In J. Hyönä, R. Radach & H. Deubel (Eds.), The mind’s eyes: Cognitive and applied aspects of eye movements (pp. 391–411). Elsevier: Oxford.

Lee, C., Rohrer, W. H., & Sparks, D. L. (1988). Population coding of saccadic eye movements by neurons in the superior colliculus. Nature, 332, 357–360.

May, P. J., Hartwich-Young, R., Nelson, J., Sparks, D. L. & Porter, J. D. (1990). Cerebellotectal pathways in the macaque: implications for collicular generation of saccades. Neuroscience, 36, 305–324.

McConkie, G. W., & Dyre, B. P. (2000). Eye fixation durations in reading: Models of frequency distributions. In A. Kennedy, D. Heller, and J. Pynte (Ed.), Reading as a perceptual process (pp. 683–700). Oxford: Elsevier.

McConkie, G. W., & Yang, S.-N. (2003). How cognition affects eye movements during reading. In J. Hyönä, R. Radach, and H. Deubel (Eds.), The mind’s eye: Cognitive and applied aspects of eye movement research

(pp. 413–427). Oxford, UK: Elsevier.

McConkie, G. W., Kerr, P. W., & Dyre, B. P. (1994). What are ‘normal’ eye movements during reading: Toward a mathematical description. In J. Ygge & Lennerstrand (Eds.), Eye Movements in Reading (pp. 331–343), Oxford, England: Elsevier.

McConkie, G. W., Kerr, P. W., Reddix, M. D., & Zola, D. (1988). Eye movement control during reading: I. The locations of initial eye fixations in words. Vision Research, 28(10), 1107–1118.

Morrison, R. E. (1984). Manipulation of stimulus onset delay in reading: Evidence for parallel programming of saccades. Journal of Experimental Psychology: Human Perception & Performance, 10(5), 667–682.

Nazir, T., O’Regan, J. K., & Jacobs, A. M. (1991). On words and their letters. Bulletin of the Psychonomic Society, 29, 171–174.

O’Regan, J. K. & Levy-Shoen, A. (1987). Eye-movement strategy and tactics in word recognition and reading. In M. Coltheart (Ed.), Attention and performance 12: The psychology of reading (pp. 363–383). Hove, England UK: Erlbaum.

Optican, L. M. & Robinson, D. A. (1980). Cerebellar-dependent adaptive control of primate saccadic system.

Journal of Neurophysiology, 44, 1058–1076.

O’Regan, J. K. (1990). Eye movements and reading. In: E. Kowler (Ed.), Eye movements and their role in visual and cognitive processes (pp. 395–453). Oxford, UK: Elsevier.

O’Regan, J. K. (1992). Optimal viewing position in words and the strategy-tactics theory of eye movements in reading. In K. Rayner (Ed.), Eye movements and visual cognition: Scene Perception and Reading

(pp. 333–354). New York: Springer-Verlag.

O’Regan, J. K., & Jacobs, A. (1992). Optimal viewing position effect in word recognition: A challenge to current theories. Journal of Experimental Psychology: Human Perception and Performance, 18(1), 185–197.

O’Regan, J. K., Lévy-Schoen, A., Pynte, J., & Brugaillère, B. (1984). Convenient fixation location within isolated words of different length and structure. Journal of Experimental Psychology: Human Perception and Performance, 10, 250–257.

O’Regan, J. K. (1979). Eye guidance in reading. Evidence for the linguistic control hypothesis. Perception and Psychophysics, 25, 501–509.

O’Regan, J. K., & Jacobs, A. (1992). Optimal viewing position effect in word recognition: A challenge to current theories. Journal of Experimental Psychology: Human Perception and Performance, 18(1), 185–197.

Radach, R., & Heller, D. (2000). Relations between spatial and temporal aspects of eye movement control. In A. Kennedy, R. Radach, D. Heller, & J. Pynte (Eds.), Reading as a perceptual process (pp. 65–192). Oxford, UK: Elsevier.

Radach, R., & McConkie, G. W. (1998). Determinants of fixation positions in words during reading. In G. Underwood (Ed.), Eye Guidance in Reading and Scene Perception (pp. 77–100). Oxford, UK: Elsevier.

Rayner, K. (1979). Eye guidance in reading: fixation location within words. Perception, 8, 21–30.

Reichle, E. D., Pollatsek, A., Fisher, D. L., & Rayner, K. (1998). Toward a model of eye movement control in reading. Psychological Review, 105(1), 125–157.

Reichle, E. D., Rayner, K., & Pollatsek, A. (1999). Eye movement control in reading: Accounting for initial fixation locations and refixations within the E-Z Reader model. Vision Research, 39(26), 4403–4411.

Reichle, E. D., Rayner, K., & Pollatsek, A. (2003). The E-Z Reader model of eye movement control in reading: comparisons to other models. Behavioral and Brain Sciences, 26, 445–526.

Reilly, R. & Radach, R. (2006). Some empirical tests of an interactive activation model of eye movement control in reading. Cognitive systems research, 7, 34–55.

Reilly, R., & O’Regan, J. K. (1998). Eye movement control in reading: A simulation of some word-targeting strategies. Vision Research, 38, 303–317.

Reilly, R., & Radach, R. (2003). Foundations of an interactive activation model of eye movement control in reading. In J. Hyönä, R. Radach, & H. Deubel (Eds.), The mind’s eye: Cognitive and applied aspects of eye movements. Oxford, UK: Elsevier.

Robinson, D. A. (1975). Oculomotor control signals. In G. Lennerstrand, & P. Bach-y-Rita (Eds.), Basic mechanisms of ocular motility and their clinical implications (pp. 337–374). Oxford: Pergamon Press.

Suppes, P. (1989). Eye-movement models for arithmetic and reading performance. In E. Kowler (Ed.), Eye Movements and their Role in Visual and Cognitive Processes (pp. 455–477), Amsterdam: Elsevier.

Vitu, F. (1991a). The existence of a center of gravity effect during reading, Vision Research, 31(7/8), 1289–1313. Vitu, F. (1991b). Research note: Against the existence of a range effect during reading, Vision Research, 31(11),

2009–2015.

Vitu, F. (2003). The basic assumptions of E-Z reader are not well-founded. Behavioral and Brain Sciences, 26(4), 506–507.

Vitu, F., McConkie, G. W., & Yang, S.-N. (2003). Readers’ oculomotor responses to intra-saccadic text shifts.

Perception, 32, 24.

Vitu, F., McConkie, G. W., Kerr, P., & O’Regan, J. K. (2001). Fixation location effects on fixation durations during reading: An inverted optimal viewing position effect. Vision Research, 41(25–26), 3511–3531.

Vitu, F., O’Regan J. K., & Mittau, M. (1990). Optimal landing position in reading isolated words and continuous text. Perception & Psychophysics, 47(6), 583–600.

Vitu, F., O’Regan, J. K., Inhoff, A., & Topolski, R. (1995). Mindless reading: Eye movement characteristics are similar in scanning strings and reading texts. Perception and Psychophysics, 57, 352–364.

Viviani, P., & Swensson, R. G. (1982). Saccadic eye movements to peripherally discriminated visual targets.

Journal of Experimental Psychology: Human Perception and Performance, 8, 113–126.

Yang, S.-N. & McConkie, G. W. (2004). Saccade generation during reading: Are words necessary? European Journal of Cognitive Psychology, 16(1/2), 226–261.

Yang, S.-N., & McConkie, G. W. (2001). Eye movements during reading: a theory of saccade initiation times.

Vision Research, 41, 3567–3585.

This page intentionally left blank

Abstract

During reading, oculomotor errors not only produce considerable variance of withinword landing positions, but can even lead to mislocated fixations, that is fixations on unintended words. Recently, we proposed a new quantitative approach for the estimation of the proportion of mislocated fixations from experimental data (Nuthmann, Engbert, & Kliegl, 2005). Here, we present an advanced algorithm, which iteratively decomposes observed landing position distributions into mislocated and well-located contributions. The algorithm is checked with numerical simulations of the SWIFT model (Engbert, Nuthmann, Richter, & Kliegl, 2005). Finally, we outline the link between mislocated fixations and the Inverted-Optimal Viewing Position (IOVP) effect.

1. Introduction

Most research on eye movements in reading is based on the implicit assumption that every saccade lands on an intended target word. The validity of this assumption requires that oculomotor errors are small compared to the spatial extension of words. It was noticed early, however, that within-word landing distributions are rather broad and even that preferred viewing locations (Rayner, 1979) show a systematic leftward bias away from word centers. Consequently, McConkie, Kerr, Reddix, and Zola (1988), who showed in an influential paper that saccadic error can be decomposed into systematic and random contributions, suggested more than 15 years ago that “ the combination of systematic and random error in landing site distributions on a word can lead to eye fixations that were destined for one word but are actually centered on another” (p. 1117). Thus, it is surprising that no quantitative approach to the study of mislocated fixations has been proposed so far.1 If there is a substantial contribution of mislocated fixations, this might be a challenge for theories of eye-movement control during reading, which assume that a specific target word is selected for each saccade.

Recently, we proposed a method for the quantitative estimation of the proportion of mislocated fixations during reading (Nuthmann et al., 2005). We became interested in mislocated fixations as a possible explanation of the Inverted-Optimal Viewing Position (IOVP) effect, discovered by Vitu, McConkie, Kerr, and O’Regan (2001): Fixation durations are lowest, rather than highest, near word boundaries – contrary to predictions derived from visual acuity limitations. As first noticed by McConkie et al. (1988; p. 1117), “ mislocated fixations would occur most frequently at the beginnings and ends of words.” Thus, we suggested that – because of the greater frequency of mislocated fixations near word boundaries – an error-correction strategy in response to mislocated fixations which produces shorter than average saccade latencies should selectively reduce average fixation durations at the beginning and end of words. Thus, error-correction of mislocated fixations might be an important source for the IOVP effect.

In this chapter we develop an advanced algorithm for the estimation of the proportion of mislocated fixations based on an iterative approach (Section 2). Since there is currently no means to identify mislocated fixations experimentally, numerical simulations are necessary to check the algorithm. Using the latest version of the SWIFT model (Engbert et al., 2005) we can directly compare the estimated distributions of mislocated fixations with the exact distributions generated in computer simulations (Section 3). Additionally, we perform various analyses on different classes of mislocated fixations and investigate in depth how the SWIFT model responds to these types of oculomotor errors. Finally, we study the relation between mislocated fixations and the IOVP effect for fixation durations (Section 4).

1 However, there were some speculations on the role of mislocated fixations in reading (Rayner, Warren, Juhasz, & Liversedge, 2004).

n − 1 or a failed refixation of word n − 1, while the latter case represents an unintended refixation of word n or a failed skipping of word n. Formally we can write

Using this notation, the probability for a mislocated fixation on letter position x of word n can be approximated by

where p x n n is the well-located landing probability on word n (i.e., word n was intended and realized saccade target). From this quantity, we can compute averages over all words of length L to obtain the desired probability MLx for mislocated fixations on letter x of words of length L,

where L denotes the average over all words of length L.

For numerical calculations, we assume that (i) physical word length L is the only property of a word which modulates its landing probability distribution and that (ii) all landing distributions can be approximated by normal distributions N x with mean L and standard deviation L as a function of word length L. Using these simplifying assumptions, the probability for a well-located fixation at letter position x on word n can be written as

where Ln is the length (i.e., number of letters) of word n. In general, we will observe a mislocated contribution to the landing distribution on word n from a target word m = n, that is

where n mx is a linear transformation of x to move the metric of within-word positions of word m to within-word position of word n. The overlapping contributions pn+−1x and pn−+1x can be estimated by extrapolation of the corresponding landing position distributions from words n − 1 and n + 1,