Abstract
In the present paper, I review evidence for the universality of the global effect, i.e. the general tendency to move the eyes towards the centre of gravity of the peripheral configu-ration, and show that the effect is strongly constrained by the retinal location of the stimuli. First, stimuli that are displayed in a central foveal region of a 1-1.5° radius fail to deviate the eyes in a centre-of-gravity manner; this is referred to as the foveal dead zone. Second, the stimuli that are too eccentric relative to the saccade target and/or the main stimulation site are filtered out. These limitations reflect physiological constraints and the dynamics of the patterns of activity in a visual saliency map. They form the basis for a low-level centre-of-gravity type account of eye guidance in natural perceptual tasks such as reading.
Highlights
In the present paper, I review evidence for the universality of the global effect, i.e. the general tendency to move the eyes towards the centre of gravity of the peripheral configuration, and show that the effect is strongly constrained by the retinal location of the stimuli
Coren and Hoenig (1972) were the first to show that saccadic eye movements are much less accurate when the saccade target stimulus is simultaneously presented with one or several distractors than when the target is presented in isolation; in the former case, the eyes are deviated towards an intermediate location between the distractor(s) and the target
These data show that the global effect is not an oculomotor reflex-like response to visual transients, and that it may well be at work in natural perceptual tasks such as reading
Summary
I review evidence for the universality of the global effect, i.e. the general tendency to move the eyes towards the centre of gravity of the peripheral configuration, and show that the effect is strongly constrained by the retinal location of the stimuli. In Findlay and Brown’s (2006) study, averaging responses occurred after the initial saccade, while participants scanned an unchanging set of randomly-arranged ring stimuli and silently counted the number of target elements (i.e. a ring that contained a specific letter); the initial saccade in a trial always took the eyes to the upper left corner of the display where the identity of the target letter was indicated These data show that the global effect is not an oculomotor reflex-like response to visual transients (see Findlay & Blythe, in press), and that it may well be at work in natural perceptual tasks such as reading. I will further develop this key assumption below, but I will first review evidence for a differential role of distractor stimuli depending on their position on the retina
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