Attention! Now what do you see?
Vision test Our brain's primary visual cortex probably focuses our attention rather than recognising what we see, a new study has found.
An international group of scientists led by Associate Professor Masataka Watanabe from the University of Tokyo investigated a key part of the visual cortex called V1, which is the first region of brain cortex to process information from the eyes.
Their work is described in this week's Science .
Like the rest of the visual cortex, V1 lies at the back of the brain in the occipital lobe.
"Its default processing is 'edge detection' as in software like Photoshop", says Watanabe.
At some level of processing vision we actually become aware of what we see, and some scientists have suspected that the V1 area plays a role in this process.
But Watanabe's study suggests the processes of seeing an object and focusing attention on that object are not necessarily connected.
To examine what role the VI area plays in awareness and attention, Watanabe and colleagues scanned the brains of seven people while they looked at a screen. The participants had to gaze at a point straight ahead while a rippled pattern was displayed slightly off-centre.
The researchers were able to make the ripple pattern either visible or invisible to the subjects, using a perceptual trick known as binocular suppression, in which images of the ripple pattern are rapidly flashed into the same or different eyes.
At the same time, the researchers manipulated the participants' attention. Either their attention was focused to the ripple pattern (by being asked to say whether or not it was visible) or it was focused away from the ripples.
Scans taken of the V1 areas of their brains during the experiment showed no change when the ripples were visible or invisible. So what they were seeing did not seem to make a difference. Watanabe believes this rules out awareness happening in V1.
"The kick to our finding was that there was no awareness effect", he says.
On the other hand, there was increased activity in the area whenever they were asked to pay attention to the ripples — even when the ripples were actually invisible to them.
Watanabe believes this shows that the V1 area is concerned with paying attention to visual objects and that we become aware that we can see an object at some other level in the visual cortex.
Spotlight on attention
Professor Mark Williams of Macquarie University says the work corroborates separate studies of attention and awareness done by other researchers, including his own team, but this is the first study to look at both aspects simultaneously.
"You can think of attention like a spotlight", says Williams. "If you put your keys on the table and you are looking for them, you don't see them until the spotlight of attention falls on them."
"I agree with their conclusions", he says, "that awareness probably doesn't happen in V1."