■Human
symmetry detection exhibits reverse eccentricity scaling.
■The
influence of stimulus dimensionality and viewing orientation on detection of
symmetry in dot patterns.
■Display
symmetry affects positional specificity in same-different judgments of pairs
of novel visual patterns.
■On the role
of symmetry in visual search.
■Surfaces
versus features in visual search.
■Discriminating
mirror symmetry in foveal and extra-foveal vision.
Human
symmetry detection exhibits reverse eccentricity scaling.
Tyler, Christopher W.
Visual Neuroscience. 1999 Sep-Oct Vol 16(5) 919-922
To evaluate the eccentricity scaling function for human symmetry processing, threshold width-integration functions were measured for static bilateral symmetry around an axis set at various distances from the fovea. As in previous work, the bilateral symmetry around a vertical axis in random dot fields was masked by a random strip of various widths centered on the symmetry axis. Human symmetry detection in dense patterns exhibits a spatial integration range that becomes narrower with distance of the symmetry axis from the fovea. This narrowing violates the general properties of eccentricity that have been found for all previous visual cortical areas, tasks, and assessment techniques. This reverse eccentricity scaling may, in conjunction with the long-range matching properties for symmetry described by C. W. Tyler and L. K. Hardage (1996), imply that symmetry is processed by a specialized cortical area with non-retinotopic neural architecture.
The influence of stimulus dimensionality and viewing orientation on detection of symmetry in dot patterns.
Locher, Paul; Smets, Gerda
Bulletin of the Psychonomic Society. 1992 Jan Vol 30(1) 43-46
Tested whether depth and visual motion contribute to detection of the global percept of mirror symmetry in briefly exposed masked dot patterns viewed orthogonally and nonorthogonally by 6 Ss. Neither depth nor motion provided perceptually useful information about a pattern's symmetry beyond that contained in a 2-dimensional view, suggesting that these processing modules can be ignored when modeling the perceptual properties of symmetric dot displays. Results reveal significantly lower levels of detectability for nonorthogonal vs orthogonal regard.
Display symmetry affects positional specificity in same-different judgments of pairs of novel visual patterns.
Dill, Marcus; Fahle, Manfred
Vision Research. 1999 Nov Vol 39(22) 3752-3760
Investigated whether global pattern display symmetry and properties of individual pattern stimuli can influence performance in same-different discrimination of symmetrical dot cloud stimuli. 10 observers participated. Patterns were small dot-clouds that could be mirror-symmetric or asymmetric. Translations were displacements of the visual pattern symmetrically across the fovea, either left-right or above-below. Results show that same-different discriminations were worse (less accurate and slower) for translated patterns, to an extent which in general was not influence by pattern symmetry, or pattern orientation, or direction of displacement. However, if the displaced pattern was a mirror image of the original one (along the trajectory of the displacement), then performance was largely invariant to translation. Both positional specificity and its reduction in symmetric displays may be explained by location-specific pre-processing of the visual input.
Surfaces versus features in visual search.
He, Zijiang J.; Nakayama, Ken
Nature. 1992 Sep Vol 359(6392) 231-233
Seven observers participated in a study in which binocular disparity was manipulated to degrade visual search, so that otherwise identical features became parts of surfaces through perceptual completion, rendering them less clearly distinguishable as targets and distractors. Results suggest that binocular disparity plays a large part in the slowing down of visual search, but only in cases where it facilitates surface completion behind an adjoining occluder. Visual search appears to be applied at a much higher level of visual representation than is feature detection.
On the role of symmetry in visual search.
Wolfe, Jeremy M.; Friedman-Hill, Stacia R.
Psychological Science. 1992 May Vol 3(3) 194-198
It is known that the efficiency of visual search for a target item among distractor items increases when distractors are similar to each other and decreases when target and distractors are similar. Two experiments with naive Ss show that symmetry relations between targets and distractors can alter search efficiency. When distractors formed a background texture symmetrical about a vertical axis, search was easier than when they did not. In contrast, when some distractors were symmetrical with the target, search was more difficult than when they were not. Results suggest that (1) symmetry relations are processed in parallel and can help distinguish a target from a distracting background and (2) stimulus similarity can have several components even for a single feature (e.g., orientation).
Discriminating mirror symmetry in foveal and extra-foveal vision.
Barrett, B. T.; Whitaker, D.; McGraw, P. V.; Herbert, A. M.
Vision Research. 1999 Nov Vol 39(22) 3737-3744
ABSTRACT Examined the ability to discriminate perfect from imperfect mirror symmetry at the fovea and at eccentricities out to 10 deg. in the nasal visual field. A 2-AFC method of constant stimuli was employed in which a bilaterally symmetric pattern was resented in one interval and a degraded version of this symmetric pattern in the other. The S's task was to decide which interval contained the perfectly symmetric pattern. Pattern size was varied by changing the viewing distance. Probit analysis reveals the degree of asymmetry corresponding to 75% correct performance. Given sufficient size scaling, perfectly symmetric stimuli were discriminated from degraded symmetric stimuli in extra-foveal vision. Spatial scaling with an E2 value similar to that for positional acuity was successful in removing the eccentricity dependence for the task. An appendix of self-scaling vs spatial scaling is presented.