BioEd Online

Our perception of colours can depend on whether we view them from the left or the right, scientists have found. They say this demonstrates how language can alter the way we see the world.

The idea that language can affect cognition is not new. In the 1930s, the American linguist Benjamin Lee Whorf proposed the controversial hypothesis that the structure of language affects the way people think. Later studies have hinted that this may be true in some circumstances (see ' Tribes without names for numbers cannot count'). But whether language affects our perception of the world has remained an open question.

Richard Ivry of the University of California, Berkeley, and colleagues suspected that separating out the effects of visual input to the right and left brain hemispheres might yield some clues. Language is processed mainly in the left hemisphere of the brain, which also deals with signals from the left side of the retinas in both our eyes.

Because light from objects to our right falls mainly into the left-hand area of our retinas, the researchers hypothesized that colours to the right would feel the influence of language more keenly. Conversely, objects on our left side activate the right hemisphere of the brain, so the effect of language would be minimal.

Field of green

To test their idea, they showed a series of people a picture of green squares arranged in a circle. They measured how long it took each person to pick out a single square of a different colour, which was situated on the right or left side.

The oddball square was either a different shade of green from the rest of the squares, or it was blue. If this square was positioned on the left, people detected both the blue and green square in the same amount of time. But if the square was on the right, the subjects took longer to identify the green square than the blue one.

The researchers say this is because the colour blue has a distinct name, and so the language-loving left hemisphere could perceive the colour difference faster than it could a square with a different shade of green.

"You get this language-based enhancement of differences or similarities," says Ivry. "But you only get that in one half of the brain."

Memory game

Ivry and his colleagues went on to test their theory by asking the subjects to memorize a series of words during the visual tests. With their left brain's language centre otherwise occupied, there would be less opportunity for it to influence visual perception, and so, as expected, the subjects picked out blue or green squares on the right-hand side of the picture in the same time.

"This suggests that the effect was indeed due to language," says Michael Corballis at the University of Auckland, New Zealand. The results appear in the Proceedings of the National Academy of Sciences USA¹.

The findings are fascinating, says Ian Davies, a psychologist at the University of Surrey in Guildford, UK. Davies says his own experiments on human subjects have recently yielded similar results.

Ivry's team is now investigating whether the same effect is seen with everyday objects, such as cats or cars, rather than colours. Early results suggest that we do indeed see these everyday objects differently depending on their position and our vocabulary for them. Ivry adds that it would be interesting to examine paintings to find out whether artists use colours differently on the left and right sides of the canvas.