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Start position strongly influences fixation patterns during face processing: Difficulties with eye movements as a measure of information use.

Arizpe, JM; Kravitz, DJ; Yovel, G; Baker, CI; (2012) Start position strongly influences fixation patterns during face processing: Difficulties with eye movements as a measure of information use. PLoS One , 7 (2) , Article e31106. 10.1371/journal.pone.0031106. Green open access

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Abstract

Fixation patterns are thought to reflect cognitive processing and, thus, index the most informative stimulus features for task performance. During face recognition, initial fixations to the center of the nose have been taken to indicate this location is optimal for information extraction. However, the use of fixations as a marker for information use rests on the assumption that fixation patterns are predominantly determined by stimulus and task, despite the fact that fixations are also influenced by visuo-motor factors. Here, we tested the effect of starting position on fixation patterns during a face recognition task with upright and inverted faces. While we observed differences in fixations between upright and inverted faces, likely reflecting differences in cognitive processing, there was also a strong effect of start position. Over the first five saccades, fixation patterns across start positions were only coarsely similar, with most fixations around the eyes. Importantly, however, the precise fixation pattern was highly dependent on start position with a strong tendency toward facial features furthest from the start position. For example, the often-reported tendency toward the left over right eye was reversed for the left starting position. Further, delayed initial saccades for central versus peripheral start positions suggest greater information processing prior to the initial saccade, highlighting the experimental bias introduced by the commonly used center start position. Finally, the precise effect of face inversion on fixation patterns was also dependent on start position. These results demonstrate the importance of a non-stimulus, non-task factor in determining fixation patterns. The patterns observed likely reflect a complex combination of visuo-motor effects and simple sampling strategies as well as cognitive factors. These different factors are very difficult to tease apart and therefore great caution must be applied when interpreting absolute fixation locations as indicative of information use, particularly at a fine spatial scale.

Type: Article
Title: Start position strongly influences fixation patterns during face processing: Difficulties with eye movements as a measure of information use.
Open access status: An open access version is available from UCL Discovery
DOI: 10.1371/journal.pone.0031106
Publisher version: http://dx.doi.org/10.1371/journal.pone.0031106
Language: English
Additional information: This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Funding: This work was supported by the Intramural Program of the National Institutes of Mental Health and by the United States-Israel Binational Science Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Keywords: face processing, eye movements, eye tracking, inverted face, facial recognition
UCL classification: UCL
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences
URI: https://discovery.ucl.ac.uk/id/eprint/1350080
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