http://www.newscientist.com/news/print.jsp?id=ns99994638

'Mindsight' could explain sixth sense
 
19:00 04 February 04

Exclusive from New Scientist Print Edition. Subscribe and get 4 free issues.

Some people may be aware that a scene they are looking at has changed without being able to identify what that change is. This could be a newly discovered mode of conscious visual perception, according to the psychologist who discovered it. He has dubbed the phenomenon "mindsight".

Ronald Rensink, based at the University of British Columbia in Canada, showed 40 people a series of photographic images flickering on a computer screen. Each image was shown for around a quarter of a second and followed by a brief blank grey screen. Sometimes the image would remain the same throughout the trial; in other trials, after a time the initial image would be alternated with a subtly different one.

In trials where the researchers manipulated the image, around a third of the people tested reported feeling that the image had changed before they could identify what the change was. In control trials, the same people were confident that no change had occurred. The response to a change in image and control trials was reliably different.

Our visual system can produce a strong gut feeling that something has changed, Rensink says, even if we cannot visualise that change in our minds and cannot say what was altered or where the alteration occurred.

"I think this effect explains a lot of the belief in a sixth sense." He has no idea what physical processes generate mindsight, but says it may be possible to confirm it exists using brain scanners.

Attentional mechanism

Mindsight is not simply a precursor to normal visual perception, he argues, because there seems to be no correlation between how long it takes someone to feel the change, and the time taken to identify what it is. The two sometimes happened almost simultaneously, while at other times the subjects did not report seeing any difference until seconds after they were aware of it.

Vision researcher Dan Simons of the University of Illinois in Urbana-Champaign says Rensink's finding "suggests the existence of an interesting and previously unknown attentional mechanism".

He cautions that people can sometimes believe they have perceived something when they clearly have not, pointing out that Rensink's volunteers sometimes reported seeing a change in the image when in fact it remained consistent. But he says Rensink's study is an important first step in distinguishing accurate sensing from believing.

Rensink acknowledges that not everyone seems to sense something, and that the experimental setting might encourage people to simply guess. But he also thinks that people who do not experience mindsight may be screening out what appear to be gut feelings in favour of what appears to be more rational information, while those who do are happy to trust their instincts.

Mindsight may also be at work when someone goes into a room and senses something is different but cannot put their finger on what. "It could well be an alerting system," he says. There is no reason the effect shouldn't operate with other senses too, he says. Knowing someone is behind you may be the auditory equivalent.

Journal reference: Psychological Science (vol 15, p 27)

Helen Phillips