Abstract
A common problem in eye-tracking research is vertical drift—the progressive displacement of fixation registrations on the vertical axis that results from a gradual loss of eye-tracker calibration over time. This is particularly problematic in experiments that involve the reading of multiline passages, where it is critical that fixations on one line are not erroneously recorded on an adjacent line. Correction is often performed manually by the researcher, but this process is tedious, time-consuming, and prone to error and inconsistency. Various methods have previously been proposed for the automated, post hoc correction of vertical drift in reading data, but these methods vary greatly, not just in terms of the algorithmic principles on which they are based, but also in terms of their availability, documentation, implementation languages, and so forth. Furthermore, these methods have largely been developed in isolation with little attempt to systematically evaluate them, meaning that drift correction techniques are moving forward blindly. We document ten major algorithms, including two that are novel to this paper, and evaluate them using both simulated and natural eye-tracking data. Our results suggest that a method based on dynamic time warping offers great promise, but we also find that some algorithms are better suited than others to particular types of drift phenomena and reading behavior, allowing us to offer evidence-based advice on algorithm selection.
Highlights
Reading is a fundamental skill for navigating modern society and, as such, is subject to intense study in the cognitive and language sciences
Sentence reading experiments have been essential in revealing the cognitive processes behind different levels of written language processing, from the width of the perceptual span (e.g., Blythe et al, 2009; Rayner, 1986) to the effects that word length and frequency have on eye movements (e.g., Joseph et al, 2009; Tiffin-Richards & Schroeder, 2015), as well as the effects of syntactic (e.g., Frazier & Rayner, 1982; Pickering & Traxler, 1998) and lexical (e.g., Sereno et al, 2006) ambiguity
We wanted to systematically evaluate the various vertical drift correction algorithms that have been reported in the literature in order to provide guidance to researchers about how they work, when they should be used, and what their limitations are
Summary
Reading is a fundamental skill for navigating modern society and, as such, is subject to intense study in the cognitive and language sciences. Among the many tools that researchers use to investigate reading in the laboratory, eye tracking occupies a prominent position. Using this technique, participants’ eye movements may be recorded as they read written material, providing a window into the relevant cognitive processes as they unfold. Sentence reading experiments have been essential in revealing the cognitive processes behind different levels of written language processing, from the width of the perceptual span (e.g., Blythe et al, 2009; Rayner, 1986) to the effects that word length and frequency have on eye movements (e.g., Joseph et al, 2009; Tiffin-Richards & Schroeder, 2015), as well as the effects of syntactic (e.g., Frazier & Rayner, 1982; Pickering & Traxler, 1998) and lexical (e.g., Sereno et al, 2006) ambiguity
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