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Masaki Fukuchi, Christof Koch; The focus of expansion acts as a cue for visual attention. Journal of Vision 2008;8(6):880. doi: 10.1167/8.6.880.
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© ARVO (1962-2015); The Authors (2016-present)
In everyday vision, human observers sequentially shift focal attention as well as their gaze across the scene. It is well known that a number of low-level, task-independent cues, such as intensity, color, orientation and motion, as well as top-down, task-dependent information drive covert and overt attention. The extent to which qualitative features of the optical flow field, in particular the focus of expansion (FOE), are salient and thereby attract attention is not known. This is an important question as the visual cues on our retina in daily life, especially while walking or driving, contain global motion fields. To study this, we recorded eye-movements in human observers at 1000 Hz using an Eyelink1000 tracker while subjects viewed image sequences and performed associated tasks. In the first experiment, subjects viewed dynamic natural scene and were asked to rate their preferences for the images. The entire image started zooming toward one of four predefined points, FOEs, on the screen for 1 sec following stimulus onset. Subsequently, the image remained static for another 1 sec. We observed an immediate and a significant attentional bias toward the FOE in all the subjects. The bias peaked at around 300 msec and persisted throughout the entire 2 second trial with decay. In the second experiment, subjects viewed a search screen which contains a target letter, T, and 47 distracter letters, L's, and were asked to find the target letter. Even under this demanding eye-movement task, a significant attentional bias toward the FOE was observed. The bias was less persistent than the letter search trial but also peaked at around 300 ms. These results suggest that the FOE, a qualitative feature of global motion fields, plays a role as a cue for human attention mechanisms and strongly biases our attention.
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