The role of color in symmetry detection - from local to global
Date Issued
2011
Date
2011
Author(s)
Wu, Chia-Ching
Abstract
Symmetry is a higher-order form that requires a complicated computation in the visual system. In a nature scene, symmetric objects or stimuli may come with any combination of color. Hence, human visual system needs to integrate both color and form information to detect chromatic symmetry. In this study, we conducted five experiments to investigate the role of color in symmetry detection. We distinguished two stages, that is, matching and pooling stage, of the symmetry encoder and examined the color selectivity of these two stages of symmetry encoder. Our results showed that these two stages are color-selective. This suggests that there are a band of color-selective symmetry channels in our visual system. We further manipulated the number of the colors in the images to investigate how human visual system integrates the response of these symmetry channels to detect chromatic symmetry. Our results showed that the increment of the number of the colors facilitated the symmetry detection performance, regardless the observers had prior knowledge of the symmetry axis orientation or not. Finally, we examined the symmetry detection in two images sharing the same axis or not, to see whether the segmentation of two images with different colors helps symmetry detection. The results however showed better symmetry detection performance when two symmetric patterns shared the same axis than those did not. All these results can be accounted for by a computational model that incorporated linear symmetry encoding mechanisms, nonlinear transducer response, noise manipulation and a multiple channel based decision making process. The model fitting results suggests that the increment of the number of the color reduces the inhibition of the symmetry channels, and in turn facilitates the symmetry detection performance when the images contain more than one color. In addition, the inhibition between channels responding to the two symmetric patterns sharing the same axis is smaller than that between channels responding to two patterns in different axes, in turn facilitates the symmetry detection performance when the two images shared the same symmetry axis.
Subjects
symmetry detection
higher-order color vision
color and form integration
psychophysics
noise masking
Type
thesis
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