I know where you are secretly attending!

A remarkable study has just been published in the cognitive science journal Vision Research which may be the first genuine demonstration of brain scan ‘mind reading’.

The study focuses on visual attention and particularly what is called ‘covert visual attention’ – the ability to mentally focus on something without moving your eyes.

For example, take the phrase ‘cat x dog’. I want you to fix your eyes on the ‘x’ and keep them there, but then alter your concentration so you mentally focus on ‘cat’ and then ‘dog’ and back again.

Your eyes aren’t moving but you can concentrate on different things in the scene you’re looking at just by shifting your attention. This is called ‘covert’ visual attention because there is no obvious (‘overt’) bodily movement associated with it, it’s a hidden (‘covert’) mental process.

Since the time of William James, attention has been thought of like a spotlight in that you just ‘shine’ it on an area to make it mentally clearer.

The authors of this new study wondered whether attention was really this selective and decided to use a nifty brain imaging method to test this out.

They relied on the fact that every point in your retina is literally mapped in the brain. Each point in the visual scene has a corresponding area of the visual cortex which is laid out in the same way – in something called a retinotopic map

We know that visual attention selectively boosts activity in the visual cortex, so when you switch between ‘cat’ and ‘dog’ in our example above, the brain increases activity in the visual areas that corresponds to each word.

In other words, it’s possible to measure the effect of visual attention by looking at where changes in visual cortex activity occur.

After doing some tests to make sure they’d verified the exact layout of each of the participant’s retinotopic map, the researchers asked participants in the scanner to systematically focus on specific parts of a circular area cut into segments, with inner, middle and outer rings – all while keeping their eyes fixed in the centre.

They then mapped activity from the visual cortex back into the visual scene to create a ‘heat map’ of where attention was spread.

You can see an example in the image on the right. The ‘x’ never appeared in the actual experiment, I just added those to make the diagram clearer, but they illustrate where the participants were instructed to concentrate.

Overall, the results showed that attention was not tightly focussed like a spotlight. In fact, when we direct our concentration to the outer ring of vision, large areas of the visual scene are flooded with activity.

This happened to a lesser extent with the very inner ring of vision, with visual scene enhancement typically extending outwards as well.

But with the middle ring of vision, the enhancement was pretty tight, being restricted to just that area.

This is an amazing finding in itself, but the ‘mind reading’ part is quite a finale.

The researchers also had a section of their study where they asked the participants to randomly focus on parts of the circle. Remember, they weren’t moving their eyes (and this was checked with a monitor), just changing their internal focus of concentration.

By solely looking at the patterns of brain activation, the researchers worked out where the participants were concentrating with 87% accuracy.

In many previous ‘mind reading’ experiments, researchers have shown people different sorts of pictures and then worked out which ones they were looking at by analysing brain activity.

It’s a largely passive process and relies on distinguishing different physiological reactions. If you measured blood flow to the penis you could probably distinguish whether men were looking at pictures of furniture or people having sex – but you probably wouldn’t call this ‘mind reading’. These previous studies just measured the brain to do something similar.

While such studies are often over-hyped, this new experiment does take the process a step further.

It’s still a very limited task but the participants are voluntarily engaging in a purely internal mental process and the brain scans tell us where their focus of concentration is.

The researchers had no knowledge of where this was beforehand and the same thing couldn’t have been worked out through watching participants’ behaviour.

Link to study.
Link to PubMed entry for same.