Memory color effect

Memory color is defined as the canonical hue of an object (e.g. sky, leaf, banana, apple) that human observers acquire through their experiences with that object. For example, most human observers know that an apple typically appears in a reddish hue; this knowledge about the canonical color which is represented in memory constitutes a memory color.

Memory color effect is the phenomenon of memory color directly modulating the appearance of the actual color of the object. For example, in a Nature Neuroscience publication researchers discovered that normal human trichromats - when presented with a gray banana - often perceived the gray banana as being yellow - the banana's memory color. In light of this, subjects typically adjusted the color of the banana towards the color blue - the opponent color of yellow, when asked to adjust its surface to gray in order to cancel out the subtle activation of banana's memory color. Subsequent empirical studies have also shown memory color effect on man-made objects (e.g. smurf, German mailbox), effect being uniquely pronounced for blue and yellow objects. To explain this, researchers have argued that because natural daylight shifts from short-wavelength of light (i.e. bluish hue) towards light of longer wavelengths ( i.e. yellowish-orange hue) during the day, the memory color for blue and yellow objects is recruited by the visual system to a higher degree in order to compensate for this fluctuation in illumination, thereby providing a stronger memory color effect.

Significance to the evolution of trichromacy

While objects which possess a canonical hue make up a small percentage of the objects which populate humans’ visual diet, the human visual system evolved in an environment which was populated with objects which possess a canonical hue. This thus suggests that the fruit theory which argues that primate color vision evolved to optimize the ability to detect ripe fruit may be in fact contributed to the emergence of the evolution of color vision in primates.

In perception research

In perception research, memory color effect is cited as evidence in support of the opponent color theory. Researchers have also found empirical evidence which suggest that memory color is recruited by the visual system to achieve color constancy.