When a picture of a human face appears, an area at the back of the first volunteer's brain lights up. The second volunteer, who suffers from autism, records no difference in brain activity - whether he is looking at a face... or at a teacup.
For the OU's Steve Swithenby, Dean of Science and one of the few UK researchers carrying out this kind of non-invasive brain scan, these results not only take us a step further in our understanding of autism, but add yet one more piece to the complex jigsaw which represents what we know about how the brain works.
It is precisely because of these differences in the way an autistic brain processes information that studying it may provide information about the way a 'normal' brain works.
As Steve explains: "We are not just trying to understand autism: it is a very good 'probe' of the normal brain.
"For example, we know autistic people have a problem recognising and projecting emotion. If you can find some marker which is different in the autistic brain in tasks which are emotionally laden then you've got a fighting chance that those markers reveal something about normal brains."
Unlike scanners found in hospitals, the Helsinki imaging records information on the time-course of brain activity, which makes it well-suited to studying cognitive activity.
One result of the study, which is being funded by the OU with small grants from the Medical Research Council and Leverhulme Trust, has been to establish unambiguously where face-specific activity in the brain occurs.
The surprise, perhaps, has been how large this area is.
Steve says: "You put up a picture and, in a normal brain, about 140 milli- seconds later there's a bit of the brain at the back and at the right that 'lights up'.
"The activity is much stronger when there's a face than any other sort of image - an indication that the normal brain has evolved in such a way that it has devoted a large part of its resources to looking at faces.
"That's terribly important: we need to make all sorts of judgments instantly. If someone walks through the door with a face like thunder you don't want to have to think about it too hard!"
For those with autism, their friends and families, the knowledge that there is no apparent area of the brain dedicated to face-specific activity is an important clue to behaviour - and is also prompting Steve to begin looking for other evidence that an autistic brain may be less specialised.
"If you consider a face to be about as important as a teacup in terms of your brain circuits, presumably you process it in this same general way. You lack this specific adaptation for things which are terribly important to you, and that may give us important clues about why autistic behaviour is as it is.
"What I observe is that the handling of the condition requires a great deal of understanding of all those involved.
"If we can explain to the sufferer, and the sufferer's family, what is going on, it may help temper the worst aspects of the condition."