More Autistic Strengths: Symmetry-Spotting

EXECUTIVE SUMMARY: A recent study has added to the list of cognitive strengths peculiar to autism: in this study, a group of autistic teens/young adults and a group of age-, IQ-, sex- and eyesight-matched control subjects were shown a series of paired images, all of them different arrangements of lots and lots of tiny black-and-white dots, and determine which of the two images has some of the dots arranged in a symmetric pattern. Consistently, the autistic young people were able to pick out the symmetrical images at lower signal-to-noise ratios (i.e., with smaller proportions of the dots possessing mirror images) than their non-autistic peers.
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Michelle Dawson and Laurent Mottron have done lots of research on perception and cognition in autism --- particularly visual processing. (Morton Ann Gernsbacher is another frequent collaborator, but she didn't participate in the research I'm about to describe).

Their research has identified several cognitive strengths* specific to autism: enhanced sensitivity to pitch; enhanced sensitivity to, and recall of, details (without any corresponding loss of ability to see the big picture); ability to switch between different strategies (big-picture vs. small details) as needed; . Autistic people also do a lot better on one particular IQ test, Raven's Progressive Matrices, than you would predict based on their scores on other IQ tests (e.g., various Wechsler tests).

A new skill has just been added to this constellation: the ability to quickly determine whether a complex pattern is symmetrical or not.

In a study published this past spring in PLoS ONE, a group of Canadian researchers --- Mottron and Dawson, along with three others: Audrey Perreault, Rick Gurnsey and Armando Bertone --- had participants look at very complicated, visually "busy" patterns of small dots arranged on a video screen and determine, in the very short time the pattern remained onscreen (250 milliseconds), whether it was symmetrical or not. (They were shown two different patterns, one symmetrical and one not, and they had to identify the symmetrical one.)

Here's an example of the kind of image they would have to categorize:
(If it looks obvious to you, remember they only got a fraction of a second to look at it!)

The images were all just black and white, except for the one colored dot in the center, where the participants were told to focus their attention. In the above image, which is 100% symmetrical, each dot has a twin, the same size and color, placed so that they would lie one on top of the other if you printed the image out and folded it along its axis of symmetry. In that image, you can see that the vertical axis is the axis of symmetry; some images are symmetrical along the horizontal axis, and others are symmetrical along an oblique axis, the line y = x in a Cartesian coordinate plane with the colored dot at the origin.

These shapes are symmetrical about the horizontal (x) axis:
These shapes are symmetrical about the vertical (y) axis:

The pink and green curves are symmetrical to each other about the line y = x (blue)

Some of the images were also only partially made up of symmetrically-paired dots; the study participants were supposed to identify which of the two images shown to them had any degree of symmetry at all. (It was always just one; I guess you could design an experiment where both of the images had some degree of symmetry and the participants had to determine in which the degree of symmetry was greater, but that would be harder than just picking out which one had any degree of symmetry at all.)

The two groups whose performance was compared in this study were a group of 14** autistic young people (ages 14 to 35) and 15 typically-developing young men matched with the autistic subjects for age, IQ and visual acuity.

The criterion used to compare the two groups was "symmetry detection threshold", or the proportion of dots in a symmetrical design that had to have mirror images before a given person could identify the symmetrical design 75% of the time. Average detection thresholds were compared across groups, and also across what type of symmetry the image displayed. Both groups did best at spotting symmetry along a vertical axis, and both groups did the worst at spotting it across the line y = x.

But for all of these conditions, the autistic people had lower detection thresholds --- they correctly found symmetry more often in patterns that had less of it, relative to background noise --- than their non-autistic peers.

The study authors see this as indicative of our (autistic people's) ability to look at things more than one way simultaneously. (Another recent study, not referenced in this one, also found something suggestive of that: autistic people were better able to reproduce "ambiguous figures," or line drawings that look like they could be one of two things, depending on how you look at them). They also see their results as incompatible with the "weak central coherence" theory of autism, which explains our relatively keen collective eye for detail as a deficit in big-picture thinking. But this symmetry-spotting task requires both processes at once --- local-level, small detail perception for checking individual dot pairs to see if they really are exactly symmetrical, and also larger-scale, "gestalt" perception of whole shapes created by all the dots together.

Perreault, A., Gurnsey, R., Dawson, M., Mottron, L., & Bertone, A. (2011). Increased Sensitivity to Mirror Symmetry in Autism PLoS ONE, 6 (4) DOI: 10.1371/journal.pone.0019519

*Other, earlier research has also identified autistic strengths: as early as 1983, Amitta Shah and Uta Frith discovered that autistic children did especially well at disembedding figures; those two researchers were also the ones who identified the other really well-known "islet of ability", in the Block Designsection on various IQ tests.

**There were originally 17 people in that group, but three of them couldn't do the experimental task, so they did not contribute any data.