Abstract
A right-hemispheric superiority has been shown for spatial symmetry perception with mono-dimensional stimuli (e.g., bisected lines). Nevertheless, the cerebral imbalance for bi-dimensional stimuli is still controversial, and the aim of the present study is to investigate this issue. Healthy participants and a split-brain patient (D.D.C.) were tested in a divided visual field paradigm, in which a square shape was presented either in the left or right visual field and they were asked to judge whether a dot was placed exactly in the center of the square or off-center, by using the left/right hand in two separate sessions. The performance of healthy participants was better when the stimuli presented in the left visual field (LVF) were on-center rather than off-center. The performance of D.D.C. was higher than chance only when on-center stimuli were presented in the LVF in the left hand session. Only in this condition did his accuracy not differ with respect to that of the control group, whereas in all of the other conditions, it was lower than the controls’ accuracy. We conclude that the right-hemispheric advantage already shown for mono-dimensional stimuli can be extended also to bi-dimensional configurations, confirming the right-hemispheric superiority for spatial symmetry perception.
Highlights
Symmetry is detected by the visual system, and the way in which humans and other animals process visual symmetry is a central issue both in psychology and neuroscience
In support of the first point of view, it has been shown that patients with hemispatial neglect (“blind” for the left visual field as a consequence of a right-hemispheric lesion) show a preference for symmetrical arrangements in both visual fields, confirming that preattentive processes are responsible for figure-ground organization [8,9,10]
In contrast to that study, in the present study we presented geometrical shapes, for which no comparison with a “model” is required, and we aimed at investigating the pure hemispheric imbalance in symmetry detection
Summary
Symmetry is detected by the visual system, and the way in which humans and other animals process visual symmetry is a central issue both in psychology and neuroscience. Several models have been proposed in the attempt to explain how symmetry is detected and analyzed by the brain (e.g., [1,2,3,4,5,6,7]). Among the most acknowledged models, the perceptual rules proposed by Gestalt psychologists suggested that our preference for symmetric configurations (“symmetry bias”) could be considered as a consequence of the perceptual preference for regularity and balance, compared to randomness and imbalance, by the human visual system. In support of the first point of view, it has been shown that patients with hemispatial neglect (“blind” for the left visual field as a consequence of a right-hemispheric lesion) show a preference for symmetrical arrangements in both visual fields, confirming that preattentive processes are responsible for figure-ground organization [8,9,10]. Other important results in this context come from those patients who have undergone surgical resection of callosal fibers, in the attempt to Symmetry 2017, 9, 76; doi:10.3390/sym9050076 www.mdpi.com/journal/symmetry
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