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Matthew S. Mould, Kinjiro Amano, David H. Foster, John P. Oakley; Constancy of the functional visual field across natural scenes. Journal of Vision 2010;10(7):1323. doi: 10.1167/10.7.1323.
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When an observer is engaged in visual search, the region within which detection of a target is possible is known as the functional visual field. The extent of this region can be affected by search conditions, such as the density of distractors in search arrays and whether eye movements are permitted [B. C. Motter and D.A. Simoni, Vis. Res., 48:2382-2393 2008]. This dependence suggests that the size of the functional visual field might also vary in search over natural scenes. To test whether this is so, observers' gaze was monitored with a video eye tracker while they searched, with free eye movements, for a neutral grey target (Munsell N7) randomly located in a natural scene presented on a calibrated colour monitor, angular subtense 17x13 deg. The mean luminance of the target was matched to its local surround. Each trial lasted one second, after which the observer signalled with a mouse whether they had detected the target, and each image was viewed a total of 260 times, with the target present in half of the trials. Five observers participated and they viewed 20 near and far natural scenes. The closest fixation made to the target during trials in which the target was undetected was used to define an upper limit on the functional visual field. A routine ANOVA suggested systematic effects of both scenes and individual observers. But there was limited variation in the actual value of the average upper limit on the functional visual field i.e. from 4.9 to 6.2 deg over observers and from 5.1 to 6.2 deg over scenes. Although a more detailed analysis of observers' search patterns revealed marked individual differences, it seems that, despite the variety of visual attributes in the scenes, the size of the functional visual field was almost constant from fixation to fixation.
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