Gray bananas look more yellow than equally gray non-bananas. Your conceptual categorization of a stimulus as a banana has something to do with the perceptual appearance of the stimulus. But what more can be said about this “having something to do with” stuff? More later.
Fig. 1. These bananas are bluer than they seem.
We asked human observers to adjust the color of natural fruit objects until they appeared achromatic. The objects were generally perceived to be gray when their color was shifted away from the observersâ€™ gray point in a direction opposite to the typical color of the fruit. These results show that color sensations are not determined by the incoming sensory data alone, but are significantly modulated by high-level visual memory.
I saw Gegenfurtner demonstrate some of this in a talk he gave at the Pasadena Neurophilosophy conference in June ‘05. Gray bananas did indeed look more yellow than their equally gray non-banana counterparts.
So, what’s going on here? One hypothesis, call it the “phenomenal hypothesis” is that the activation of “high-level visual memory” influences, but is in no way constitutive of, the appearance. Another, call it the “conceptual hypothesis” is that the activation of high-level visual memory partially constitutes the appearance. I favor the latter hypothesis. Why? More later. Which do you favor? Why?
Reference: Hansen, T., Olkkonen, M., Walter, S. & Gegenfurtner, K.R. (2006). Memory modulates colour appearance. Nature Neuroscience, DOI:10.1038/nn1794.