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Hans Trukenbrod, Ralf Engbert; Using spatial statistics to investigate allocation of attention within single trials. Journal of Vision 2014;14(10):366. doi: https://doi.org/10.1167/14.10.366.
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© ARVO (1962-2015); The Authors (2016-present)
Due to visual acuity limitations of the retina, we need to move our eyes when exploring a visual scene. As a result, we usually observe clusters of fixations in some parts of the image. Both bottom-up (e.g., salience) and top-down factors (e.g., gist of a scene) have been put forward to explain the generation of fixation clusters. Here, we show that target selection is not only a consequence of image properties but also depends on the size of the attentional window – a stimulus-independent mechanism. We demonstrate that the inhomogeneous pair correlation function (PCF) can be used to investigate distributions of fixation locations during single trials, independent of the inhomogeneity generated by images. Our results show that fixations cluster at short length scales (<3°) during single trials. The effect cannot be explained by the overall inhomogeneity of fixations locations generated across subjects. Presenting the same image twice augmented the effect. The PCF can be interpreted as an indicator of the size of the attentional window that decreases during reinspection of images. In general, the limited attentional window reinforces inspection of close fixation locations. We conclude that the PCF is a promising tool to investigate dynamics of target selection during individual trials.
Meeting abstract presented at VSS 2014
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