Abstract
As a contribution to the mysteries of human symmetry perception, reaction time data were collected on the detection of symmetry or repetition violations, in the context of short term visual memory studies. The histograms for reaction time distributions are rather narrow in the case of symmetry judgments. Their analysis was performed in terms of a simple kinetic model of a mental process in two steps, a slow one for the construction of the representation of the images to be compared, and a fast one, in the 50 ms range, for the decision. There was no need for an additional ‘mental rotation’ step. Symmetry seems to facilitate the construction step. I also present here original stimuli showing a color equalization effect across a symmetry axis, and its counterpart in periodic patterns. According to a “folded sheet model”, when a shape is perceived, the brain automatically constructs a mirror-image representation of the shape. Based in part on the reaction time analysis, I present here an alternative “transparent sheet” model in which the brain constructs a single representation, which can be accessed from two sides, thus generating simultaneously a pattern and its mirror-symmetric partner. Filtering processes, implied by current models of symmetry perception could intervene at an early stage, by nucleating the propagation of similar perceptual groupings in the two symmetric images.
Highlights
Symmetry invited itself on several occasions while I was performing psychophysical work on a number of topics, including unpublished work on geometrical illusions, and work on visual short term memory
What did we gain other than elegance, in presenting a new metaphorical explanation? In agreement with Jan Koenderink [30], I feel that there is virtue in pursuing theoretical ideas for their own sake, not trying to look for an immediate quantitative fit with the data. It turns out, as I will attempt to show in the Discussion, that quite unexpectedly, both the transparent sheet model and the color equalization effect may throw some light on my first data set—that on reaction times in short term memory experiments
The work presented here was, at the beginning, an extension of work on short term visual memory experiments, so it used patterns, tools and concepts that were developed in the memory experiments, and are unusual in the field of symmetry perception
Summary
Symmetry invited itself on several occasions while I was performing psychophysical work on a number of topics, including unpublished work on geometrical illusions, and work on visual short term memory. In the latter, I measured the time to detect the difference between two nearly symmetric patterns. There are fiber systems in the brain which are able to compare and establish the identity or non-identity of symmetrical points of the visual field. While most psychophysical studies on symmetry perception involve stimuli presentations in the 100 ms time scale, my own data or observations were made in situations of free inspection without time limitation
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