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Self-consistent estimation of mislocated fixations during reading.

Engbert R, Nuthmann A - PLoS ONE (2008)

Bottom Line: During reading, we generate saccadic eye movements to move words into the center of the visual field for word processing.Our approach is based on iterative computation of the proportions of several types of oculomotor errors, the underlying probabilities for word-targeting, and corrected distributions of landing positions.These results show that fixation probabilities are strongly affected by oculomotor errors.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, University of Potsdam, Potsdam, Germany. Ralf.Engbert@uni-potsdam.de

ABSTRACT
During reading, we generate saccadic eye movements to move words into the center of the visual field for word processing. However, due to systematic and random errors in the oculomotor system, distributions of within-word landing positions are rather broad and show overlapping tails, which suggests that a fraction of fixations is mislocated and falls on words to the left or right of the selected target word. Here we propose a new procedure for the self-consistent estimation of the likelihood of mislocated fixations in normal reading. Our approach is based on iterative computation of the proportions of several types of oculomotor errors, the underlying probabilities for word-targeting, and corrected distributions of landing positions. We found that the average fraction of mislocated fixations ranges from about 10% to more than 30% depending on word length. These results show that fixation probabilities are strongly affected by oculomotor errors.

Show MeSH
Distributions of within-word landing positions for words of length 7 (as an example).Letter position 0 is the space to the left of the word. Experimentally observed distributions (blue) are modulated by the distance of the launch site (the panels show distances between –7 and 5). Positive launch sites indicate refixations of the same word, which often lead to bimodal distributions (e.g., launch site = 3, 4). Estimated distributions (red) show a reduced standard deviation due to subtraction of mislocated fixations.
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pone-0001534-g001: Distributions of within-word landing positions for words of length 7 (as an example).Letter position 0 is the space to the left of the word. Experimentally observed distributions (blue) are modulated by the distance of the launch site (the panels show distances between –7 and 5). Positive launch sites indicate refixations of the same word, which often lead to bimodal distributions (e.g., launch site = 3, 4). Estimated distributions (red) show a reduced standard deviation due to subtraction of mislocated fixations.

Mentions: When you read these lines of text, you generate saccadic eye movements with an average rate of 3 to 4 per second [1] to enable efficient word processing in the center of the visual field (the fovea). Many words are skipped during reading, so that foveal processing is not necessary for all words, while some words need more than a single fixation, which causes refixations on the same word. For saccades, within-word landing positions (Fig. 1) show a pronounced peak near the word center [2], but distributions are rather broad and additionally modulated by word length as well as launch-site distance [3]. Landing position distributions can be approximated by normal distributions, however, these distributions are truncated at word boundaries, suggesting that some of the fixations observed experimentally on a particular word were in fact intended for an adjacent word [3]. Such fixations are mislocated due to saccadic errors.


Self-consistent estimation of mislocated fixations during reading.

Engbert R, Nuthmann A - PLoS ONE (2008)

Distributions of within-word landing positions for words of length 7 (as an example).Letter position 0 is the space to the left of the word. Experimentally observed distributions (blue) are modulated by the distance of the launch site (the panels show distances between –7 and 5). Positive launch sites indicate refixations of the same word, which often lead to bimodal distributions (e.g., launch site = 3, 4). Estimated distributions (red) show a reduced standard deviation due to subtraction of mislocated fixations.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2211408&req=5

pone-0001534-g001: Distributions of within-word landing positions for words of length 7 (as an example).Letter position 0 is the space to the left of the word. Experimentally observed distributions (blue) are modulated by the distance of the launch site (the panels show distances between –7 and 5). Positive launch sites indicate refixations of the same word, which often lead to bimodal distributions (e.g., launch site = 3, 4). Estimated distributions (red) show a reduced standard deviation due to subtraction of mislocated fixations.
Mentions: When you read these lines of text, you generate saccadic eye movements with an average rate of 3 to 4 per second [1] to enable efficient word processing in the center of the visual field (the fovea). Many words are skipped during reading, so that foveal processing is not necessary for all words, while some words need more than a single fixation, which causes refixations on the same word. For saccades, within-word landing positions (Fig. 1) show a pronounced peak near the word center [2], but distributions are rather broad and additionally modulated by word length as well as launch-site distance [3]. Landing position distributions can be approximated by normal distributions, however, these distributions are truncated at word boundaries, suggesting that some of the fixations observed experimentally on a particular word were in fact intended for an adjacent word [3]. Such fixations are mislocated due to saccadic errors.

Bottom Line: During reading, we generate saccadic eye movements to move words into the center of the visual field for word processing.Our approach is based on iterative computation of the proportions of several types of oculomotor errors, the underlying probabilities for word-targeting, and corrected distributions of landing positions.These results show that fixation probabilities are strongly affected by oculomotor errors.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, University of Potsdam, Potsdam, Germany. Ralf.Engbert@uni-potsdam.de

ABSTRACT
During reading, we generate saccadic eye movements to move words into the center of the visual field for word processing. However, due to systematic and random errors in the oculomotor system, distributions of within-word landing positions are rather broad and show overlapping tails, which suggests that a fraction of fixations is mislocated and falls on words to the left or right of the selected target word. Here we propose a new procedure for the self-consistent estimation of the likelihood of mislocated fixations in normal reading. Our approach is based on iterative computation of the proportions of several types of oculomotor errors, the underlying probabilities for word-targeting, and corrected distributions of landing positions. We found that the average fraction of mislocated fixations ranges from about 10% to more than 30% depending on word length. These results show that fixation probabilities are strongly affected by oculomotor errors.

Show MeSH