Mixing Memory

One of the things that I love the most about cognitive science is that it's always challenging our intuitions about the world and how we perceive it. Think, for example, of all the classic Gestalt illusions, such as my all time favorite, the Kanizsa Triangle. What these illusions, and many other findings over the history of the study of visual perception show is that perception doesn't simply represent the world "as it is." Instead, perception is a fundamentally creative process, relying on inference, subtraction, and all sorts of other alterations of incoming sensory data. Spend a little time in a cognitive science lab, and you will quickly be disabused of any inclinations towards naive realism.

I bring this up because there's another example of the creative nature of visual perception in the November issue of Nature Neuroscience. The paper, by Hansen et al1, describes an experiment in which color memory changes the way we perceive colors. Participants were first presented with images of fruit in their normal color against a gray background (like the banana). They were able to change the color of the object in any direction, and were told to manipulate the color until the fruit looked gray like the background. When adjusting the color of the banana, for example, to gray, participants actually overadjusted in the direction away from the banana's normal color. For the banana, this means that the participants treated a slightly blueish banana (blue is yellow's opponent color). This suggests that their memory for the normal color of the banana affected how they perceived the color gray for bananas. As Hansen et al. put it:

[M]emory seemed to have a direct top-down effect that continuously modulated the incoming sensory data and changed basic color sensations.

¹Hansen, T., Olkkonen, M., Walter, S., Gegenfurtner, K.R. (2006). Memory modulates color appearance. Nature Neuroscience, 9, 1367-1368.