Why do (some) autistic kids struggle to recognise faces?

This week, a guest post from the wonderful Ellie Wilson. Ellie's now at the Institute of Psychiatry in London. But she has the honourable distinction of being my first ever PhD student. The post is about the two studies that book-ended her thesis on face recognition in autism. Take it away, Ellie...

Faces are essentially very similar: two eyes above a nose and a mouth. Yet most people are really good at noticing subtle differences between faces, and interpreting accurately. This helps enormously with social interaction: we can tell who they are, if we know them, we can also tell if they are male or female, roughly what age they are, and what that person might be feeling.

In autism, deficits processing facial expressions are widely acknowledged, but there is an increasing amount of evidence for impaired facial identity recognition from scientific studies as well as personal anecdotes.

Several years ago I worked as an ABA therapist for a little girl, Clare (not her real name). She was profoundly autistic and her quirky ways and bounding energy made her popular with her classmates. Despite her popularity Clare was always getting the names of the other children mixed up. She was unconcerned by her mistakes and paid little attention to repeated corrections. But we were a little worried, figuring that after a while the other kids might be offended that she still couldn’t identify them. So, in an attempt to protect her social reputation, her mother took a photograph of each child and we Clare and I played various ‘who’s this?’ games. She did get better at naming the photographs. But I’m not sure she ever actually got better at naming the kids in real life.

A year later I found myself reviewing literature on face recognition in autism for my PhD. ‘Face recognition’ AND ‘autism’ returns over 600 hits on Web of Science. The experimental methods used in these studies varied hugely. There were memory tests, matching tests, spot-the-difference tasks. Faces were turned upside down, blurred, or shown with all the hair removed. Features were moved around or switched or presented without the face they came from. .. and the results? Some studies reported impairments, some did not.

I was confused.

Image matching

Then it occurred to me that perhaps some tasks allowed participants to do well even though they were not actually very good at facial identity recognition. At this point I got some helpful advice (and pictures of faces) from Prof Mike Burton, who at the time was with the Glasgow Face Recognition Group. The group had done some really interesting work showing that whilst people can easily match the same image of a person, they have a lot more trouble matching different images of the same person when that person is unfamiliar. So – we thought – when autistic participants do well on the face recognition tasks, are they just ‘image matching’?

Examples of two trials. On the left, one of the images on the bottom is the same as the top person. On the right, the bottom left image is the same person but different photo

My first experiment tested this hypothesis. We gave kids two different versions of a simple face-matching task. They’d see one face on a computer screen. Then they’d see two more faces and have to decide which of these was the same person as the first face. In one condition, the correct face would be exactly the same image as the first face. In the other condition, the correct face would be a different image of the same person. Obviously, the second condition is more difficult, but we predicted that the effect of changing the image would be even larger than normal for autistic children because it would prevent them using an ‘image matching’ strategy.

Performance on the test was much better for
identical images than different images, but
the effect was identical for both groups.

Armed with laptops, touch screen monitors, IQ tests, and a generous supply of highly motivational stickers, I visited schools all over Sydney, testing children who varied widely in age (4 – 16years), IQ (60 - 130) and enthusiasm (totally uninterested – wildly keen). The results from over 70 children revealed that the effect of changing the image was almost exactly the same for children with autism as it was for typically developing control kids.

Hypothesis rejected.

Each symbol here represents a single child.
Scores above -1.64 are considered to be age-
appropriate. Roughly half of the autistic kids
were in this "normal" range.

Individual variation

But then we looked again at the results for individual children. Unsurprisingly, older children were better at the task than younger children, so we calculated age-standardized scores to show how well each child performed relative to their age. Results showed that ability level within the autism group varied enormously. Some kids were impaired, some were not and this was not accounted for by differences in intelligence.

The question for the rest of my PhD became: why are some autistic children bad at face recognition? 

Eye-gaze

Probably the most interesting results came from the last study I did where I used an eyetracker to monitor where kids were looking as they did a face recognition test. One idea I tested was that performance on face recognition tasks would be associated with the amount of time participants spent gazing at the eye-region of the faces they were trying to learn. Avoiding eye-contact is a common symptom of ASD and several studies have shown that at least some autistic kids avoid looking at the eyes of people even in movies. This could be detrimental to face recognition because the eye region is thought to be particularly useful for recognising identity [PDF].

However, in our study, we found no correlation between gaze-time on the eyes and performance on the test. Another hypothesis rejected.

Dynamic scanning

So then we looked at distribution of attention across the face. Although most adults focus more on the eyes than other facial features, attention is distributed between core features of the face (eyes, nose, mouth). This is thought to build up a unified percept of the face containing information about individual features as well as their spatial relationships. A failure to distribute attention could impede successful recognition.

Face recognition performance was not predicted by how much people looked at the eyes of the face (a) but it was predicted by (b) the Dynamic Scanning Index

To test this idea, we developed what we called a Dynamic Scanning Index, which indicated the number of times a participant saccaded into, and out of, a core feature interest area. We found that the kids whose eyes moved around the face more were better at recognising faces. This was true of both the autistic and the typical kids.

On average, the autistic kids had much lower Dynamic Scanning Indexes than the typically developing kids. But the autistic kids with normal scores were the ones whose face recognition skills were also OK.

We don't yet know whether there is a causal relationship between identity recognition and dynamic face scanning, and if there is, in which direction. Reduced eye-movements around faces could result in impaired recognition ability. But it's also possible that poor face recognition skills result in an individual developing unusual scan paths for faces.

Where do we go from here? 

The main conclusion from my PhD was that some but not all autistic kids have difficulties with facial identity recognition. We ran several different experiments (not all discussed here) and this was the one clear result that emerged throughout. This serves as a good example of most (if not all) symptoms and characteristics of ASD: variation within autistic participant groups should be expected, and researchers should strive to explain this variation rather than searching only for overall differences between groups.

Some autistic kids did have clear face recognition problems, and a crucial question is whether interventions would be beneficial. For example, training people to move their eyes around the face might improve their recognition skills. There have been a few training studies in the past, but the results haven’t been particularly convincing. This may be because they were training the wrong skills. But it may also be that some of the people they were trying to train didn’t actually have a problem to start with.


Further reading:

An article on face-blindness in non-autistic people by Ellie's other supervisor, Romina Palermo, now at University of Western Australia


References:


Wilson CE, Palermo R, Burton AM, & Brock J (2011). Recognition of own- and other-race faces in autism spectrum disorders. Quarterly journal of experimental psychology, 64 (10), 1939-54 PMID: 21895562 PDF

Wilson CE, Palermo R, & Brock J (2012). Visual scan paths and recognition of facial identity in autism spectrum disorder and typical development. PloS one, 7 (5) PMID: 22666378 Open Access