Christopher W. Tyler and Lani Hardage
Size-scaled random Gaussian blobs were used to determine the range of pattern matching involved in human perception of mirror symmetry and to evaluate the relative sensitivity of local (linear receptive field) or long-range (polarity-insensitive pattern-matching) mechanisms as a function of retinal eccentricity. Observers were able to perform symmetric pattern matching with presentations shorter than 100 msec across as much as 64º of visual angle. Sensitivities to opposite-polarity symmetry and low-density patterns suggest that this performance was mediated predominantly by polarity-insensitive mechanisms at all eccentricities. The results militate against a pattern-matching process based solely on local processing and implicate the involvement of long-range connections spanning the visual cortex. Outside the fovea, eccentricity scaling for all symmetry tasks was a close match to the self-scaling used for the stimuli in our experiments.
Fig. 1. Scaled Symmetry detection is a flat function of eccentricity both when the symmetry axis is present (vertical) and when it is blanked out (horizontal), when detection must use long-range pattern matching.