Factors of Visual Symmetry

    We had the pleasure of having Nicholas Baker present a seminar on what factors play a role in shape detection. The research article, “The role of vertical mirror symmetry in visual shape detection” speaks to one of the elements in shape detection, that being symmetry. This test, unlike others that came beforehand, used Gabor arrays. Gabor arrays are mathematically created and allow for control over interference and the constraints of the symmetry. This ensured that other grouping cues like proximity or connectedness did not interfere. The data showed that participants detected images with symmetry at a higher rate than controls. The results concluded that vertical symmetry does act as a cue for perceptual organization. As later explained, it helps humans detect figures against a background. Nicholas Baker’s presentation went on to talk about grouping cues in shape detection. The grouping cues, especially when presented with shapes constructed with dots, played a larger role in shape detection than symmetry. While symmetry proved to be important in shape detection, this was only during static scenes.

    A research paper published in 2017, named “The role of motion and number of element locations in mirror symmetry perception,” focuses on how motion and position affect symmetry perception. This study used dots to construct symmetry, and tested positional symmetry, symmetrical motion and their relationship. Two images, one containing symmetry and one without, were shown after each other for 400ms and with a gap of 400ms. In both symmetrical and non-symmetrical images, random dots were introduced to reduce the impact of grouping cues. An analysis of variation (ANOVA) was made to compare all the results of the different scenarios. The study finds that static symmetry has a significantly higher detection threshold than symmetrical motion or static symmetry that flickers. Additionally, symmetry detection thresholds were higher than motion thresholds, meaning symmetry is harder to detect than motion. Seeing that life typically happens in motion, whether relative or absolute, it is critical to analyze how symmetry not only works in static scenes but also when in motion.

    Both these articles discuss visual symmetry and its role in shape detection. Visual symmetry has long been thought to play a role in shape and object detection. While these studies are helpful, vision isn’t static; what is seen is seen in color and motion. That is to say, actual vision includes color, motion, and depth that aren’t present in static Gabor or dot images. The second research paper suggests that symmetry may play a larger role in shape detection in real scenarios, as most scenarios in life are in motion.  It is difficult to quantify the impact of a system like symmetry in non-lab conditions when there are so many variables that can impact detection. I think further research has to be done to understand what brain systems are responsible for each factor in symmetry. That is, the different brain areas are responsible for processing symmetrical color, symmetrical motion, symmetrical depth, among others. It could very well be that in some cases symmetry isn’t used at all in shape detection while in others, it is heavily relied on. 

References: 

Machilsen, B., Pauwels, M., & Wagemans, J. The role of vertical mirror symmetry in visualshape detection. Journal of Vision, 9(12), 11–11 (2009). https://doi.org/10.1167/9.12.11

Sharman, R., Gheorghiu, E. The role of motion and number of element locations in mirror symmetry perception. Sci Rep 7, 45679 (2017). https://doi.org/10.1038/srep45679