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Visuospatial attention and gaze control depend on the interaction of foveal and peripheral processing. The foveal and peripheral regions of the visual field are differentially sensitive to parts of the spatial frequency spectrum. In two experiments, we investigated how the selective attenuation of spatial frequencies in the central or the peripheral visual field affects eye-movement behavior during real-world scene viewing. Gaze-contingent low-pass or high-pass filters with varying filter levels (i.e., cutoff frequencies; Experiment 1) or filter sizes (Experiment 2) were applied. Compared to unfiltered control conditions, mean fixation durations increased most with central high-pass and peripheral low-pass filtering. Increasing filter size prolonged fixation durations with peripheral filtering, but not with central filtering. Increasing filter level prolonged fixation durations with low-pass filtering, but not with high-pass filtering. These effects indicate that fixation durations are not always longer under conditions of increased processing difficulty. Saccade amplitudes largely adapted to processing difficulty: amplitudes increased with central filtering and decreased with peripheral filtering; the effects strengthened with increasing filter size and filter level. In addition, we observed a trade-off between saccade timing and saccadic selection, since saccade amplitudes were modulated when fixation durations were unaffected by the experimental manipulations. We conclude that interactions of perception and gaze control are highly sensitive to experimental manipulations of input images as long as the residual information can still be accessed for gaze control. (C) 2016 Elsevier Ltd. All rights reserved.
Natural vision is characterized by alternating sequences of rapid gaze shifts (saccades) and fixations. During fixations, microsaccades and slower drift movements occur spontaneously, so that the eye is never motionless. Theoretical models of fixational eye movements predict that microsaccades are dynamically coupled to slower drift movements generated immediately before microsaccades, which might be used as a criterion to distinguish microsaccades from small voluntary saccades. Here we investigate a sequential scanning task, where participants generate goal-directed saccades and microsaccades with overlapping amplitude distributions. We show that properties of microsaccades are correlated with precursory drift motion, while amplitudes of goal-directed saccades do not dependent on previous drift epochs. We develop and test a mathematical model that integrates goal-directed and fixational eye movements, including microsaccades. Using model simulations, we reproduce the experimental finding of correlations within fixational eye movement components (i.e., between physiological drift and microsaccades) but not between goal-directed saccades and fixational drift motion. These results lend support to a functional difference between microsaccades and goal-directed saccades, while, at the same time, both types of behavior may be part of an oculomotor continuum that is quantitatively described by our mathematical model. (C) 2015 Elsevier Ltd. All rights reserved.
Serial and parallel processes in eye movement control - current controversies and future directions
(2013)
In this editorial for the Special Issue on Serial and Parallel Processing in Reading we explore the background to the current debate concerning whether the word recognition processes in reading are strictly serialsequential or take place in an overlapping parallel fashion. We consider the history of the controversy and some of the underlying assumptions, together with an analysis of the types of evidence and arguments that have been adduced to both sides of the debate, concluding that both accounts necessarily presuppose some weakening of, or elasticity in, the eyemind assumption. We then consider future directions, both for reading research and for scene viewing, and wrap up the editorial with a brief overview of the following articles and their conclusions.
What theories best characterise the parsing processes triggered upon encountering ambiguity, and what effects do these processes have on eye movement patterns in reading? The present eye-tracking study, which investigated processing of attachment ambiguities of an adjunct in Spanish, suggests that readers sometimes underspecify attachment to save memory resources, consistent with the good-enough account of parsing. Our results confirm a surprising prediction of the good-enough account: high-capacity readers commit to an attachment decision more often than low-capacity participants, leading to more errors and a greater need to reanalyse in garden-path sentences. These results emerged only when we separated functionally different types of regressive eye movements using a scanpath analysis; conventional eye-tracking measures alone would have led to different conclusions. The scanpath analysis also showed that rereading was the dominant strategy for recovering from garden-pathing. Our results may also have broader implications for models of reading processes: reanalysis effects in eye movements occurred late, which suggests that the coupling of oculo-motor control and the parser may not be as tight as assumed in current computational models of eye movement control in reading.
Saccades move objects of interest into the center of the visual field for high-acuity visual analysis. White, Stritzke, and Gegenfurtner (Current Biology, 18, 124-128, 2008) have shown that saccadic latencies in the context of a structured background are much shorter than those with an unstructured background at equal levels of visibility. This effect has been explained by possible preactivation of the saccadic circuitry whenever a structured background acts as a mask for potential saccade targets. Here, we show that background textures modulate rates of microsaccades during visual fixation. First, after a display change, structured backgrounds induce a stronger decrease of microsaccade rates than do uniform backgrounds. Second, we demonstrate that the occurrence of a microsaccade in a critical time window can delay a subsequent saccadic response. Taken together, our findings suggest that microsaccades contribute to the saccadic facilitation effect, due to a modulation of microsaccade rates by properties of the background.
This study investigates the eye movements of dyslexic children and their age-matched controls when reading Chinese. Dyslexic children exhibited more and longer fixations than age-matched control children, and an increase of word length resulted in a greater increase in the number of fixations and gaze durations for the dyslexic than for the control readers. The report focuses on the finding that there was a significant difference between the two groups in the fixation landing position as a function of word length in single-fixation cases, while there was no such difference in the initial fixation of multi-fixation cases. We also found that both groups had longer incoming saccade amplitudes while the launch sites were closer to the word in single fixation cases than in multi-fixation cases. Our results suggest that dyslexic children's inefficient lexical processing, in combination with the absence of orthographic word boundaries in Chinese, leads them to select saccade targets at the beginning of words conservatively. These findings provide further evidence for parafoveal word segmentation during reading of Chinese sentences.
This article introduces a new corpus of eye movements in silent readingthe Russian Sentence Corpus (RSC). Russian uses the Cyrillic script, which has not yet been investigated in cross-linguistic eye movement research. As in every language studied so far, we confirmed the expected effects of low-level parameters, such as word length, frequency, and predictability, on the eye movements of skilled Russian readers. These findings allow us to add Slavic languages using Cyrillic script (exemplified by Russian) to the growing number of languages with different orthographies, ranging from the Roman-based European languages to logographic Asian ones, whose basic eye movement benchmarks conform to the universal comparative science of reading (Share, 2008). We additionally report basic descriptive corpus statistics and three exploratory investigations of the effects of Russian morphology on the basic eye movement measures, which illustrate the kinds of questions that researchers can answer using the RSC. The annotated corpus is freely available from its project page at the Open Science Framework: https://osf.io/x5q2r/.
Saccadic eye movements are frequently followed by smaller secondary saccades which are generally assumed to correct for the error in primary saccade landing position. However, secondary saccades can also occur after accurate primary saccades and they are often as small as microsaccades, therefore raising the need to further scrutinize the processes involved in secondary saccade generation. Following up a previous study, we analyzed secondary saccades using rate analysis which allows us to quantify experimental effects as shifts in distributions, therefore going beyond comparisons of mean differences. We use Aalen’s additive hazards model to delineate the time course of key influences on the secondary saccade rate. In addition to the established effect of primary saccade error, we observed a time-varying influence of under- vs. overshooting – with a higher risk of generating secondary saccades following undershoots. Moreover, increasing target eccentricity influenced the programming of secondary saccades, therefore demonstrating that error-unrelated variables co-determine secondary saccade programs. Our results provide new insights into the generative mechanisms of small saccades during postsaccadic fixation that need to be accounted for by secondary saccade models.
Semantic information extraction from the parafovea has been reported only in simplified Chinese for a special subset of characters and its generalizability has been questioned. This study uses traditional Chinese, which differs from simplified Chinese in visual complexity and in mapping semantic forms, to demonstrate access to parafoveal semantic information during reading of this script. Preview duration modulates various types (identical, phonological, and unrelated) of parafoveal information extraction. Parafoveal semantic extraction is more elusive in English; therefore, we conclude that such effects in Chinese are presumably caused by substantial cross-language differences from alphabetic scripts. The property of Chinese characters carrying rich lexical information in a small region provides the possibility of semantic extraction in the parafovea.