Synaesthesia Part II: Language Colors Vision

Richard Ivry's team of researchers at Berkeley have demonstrated a remarkable effect of the laterality of language processing in the human brain.

Because language is mostly processed in the left hemisphere, they hypothesized that light falling on the left side of each retina (which is relayed to the left side of the brain) would be more affected by linguistic cues than light falling on the right side of each retina.

To test this idea, they asked participants to find the square of a different color from a circular arrangement of otherwise identical squares. The square of a different color was either blue or a slightly different shade of green, and was located on the right or left side of the arrangement. If the square was on the right (and hence processed on the left side of the retina), the subjects took longer to identify the slightly-different green square than the blue one; there was no difference in reaction time between blue and green squares when presented on the left. (image © copyright Richard Ivry / PNAS)

Subjects were able to more quickly select the "one that doesn't belong" if its color has a different name than the others, but only if this was presented to the left side of each retina. There was no "color name" advantage when the objects were presented to the right side.

This research shows just one way that we are able to recruit processing power from other cognitive functions to help in a certain task. You would probably see similar influences from spatial processing on mathematical tasks, given that spatial processing is somewhat lateralized to the right hemisphere.