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Michael von Grünau, Tomas Matthews, Mikael Cavallet; Covert attention can be captured by an illusory Focus of Expansion. Journal of Vision 2010;10(7):126. doi: 10.1167/10.7.126.
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Purpose: Covert attention can be captured by sudden stimulus onsets and other salient events. It has recently been shown that the focus of expansion (FOE) of a radial flowfield can also capture covert attention (Fukuchi et al., 2009). We were wondering whether an illusory FOE displaced by a linear flowfield (optic flow illusion; Duffy & Wurtz, 1993) could also capture attention. Methods: We measured the illusory FOE displacement with a 2AFC method, and then presented targets at the actual and illusory FOE and at corresponding locations in the other hemifield, with and without the presence of the linear flowfield. This was done for each observer according to the individual illusion strength. We measured the detection response times for targets appearing with different SOAs between flowfield and target, including 20% of catch trials. Results: A majority of participants showed a pattern of responses that suggested that the illusory FOE had captured attention. Some observers showed a different pattern indicating that the actual FOE had continued to capture attention, even in conditions where they had experienced the illusion. The effectiveness of the illusory FOE for capturing attention was not related to the size of the perceived illusion. Conclusion: Covert attention can be captured by both actual and illusory FOEs. This implies that smooth pursuit eye movements or whole world motions can take part in capturing attention. Thus covert attention can exert its effects at different levels. Fukuchi M. et al. (2009). Journal of Vision, 9(8), 137a; Duffy C. & Wurtz R. (1993). Vision Research, 33(11), 1481.
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