Tuesday, August 16, 2011

More Autistic Strengths: Symmetry-Spotting

ResearchBlogging.orgEXECUTIVE 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.

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.


Michelle Dawson said...

Not sure I'm allowed to comment here, but this study was done in Armando Bertone's lab.

Also, the Wikipedia page for Raven's Progressive Matrices (which you link to) has false information about our published work.

Lindsay said...

Sure, you can comment here!

I have no idea why your comment went into the spam folder; maybe because of the link.

I'll get rid of that link; found an interactive version of the test online that I will use instead.

Lindsay said...

(Er, "that link" referring to the Wikipedia page with false information on it, not the one in your comment).

Anonymous said...

The sample seems very small.

And what kind of "people" were they testing? I would expect visual skills like this to be well developed in artists and designers, less so among accountants or programmers. 3D perceptual skills are a similar set which have to be developed for certain occupations.
Developing mental skills of this type is one of the things people do on degree courses.

Lindsay said...

Hi, Anon!

It is a small sample, but sample sizes for this sort of psychological study are usually pretty small.

As to the study participants, they were recruited from a patient database kept by the Rivière-des-Prairies Hospital in Montreal. If you look at the demographic data in Table 1 in the article, you can see that the average age for both groups is pretty young --- and younger for the non-autistic group than for the autistic group. (Mean age for the autistic group is about 24 years, compared with about 20 and a half for the non-autistic group.) With a mean of 20, you can guess that maybe half of the non-autistic group is made up of teenagers; the autistic group is older overall and has more variability by age, but they are also pretty young. So I don't think higher education, job training or work experience would play too much of a role with this group. Good question though!

(Also, you can see that one of the authors of the study has commented here, too --- you could go to her blog and ask her if you have other questions, or if you want to know more about the study participants than what's in the article about them.)