Abstract
Memory colour - the colour associated with familiar objects in memory - is learned over repeated exposure to objects under varying illumination conditions. It is an open question whether distinct memory colours are encoded for distinct illuminations, or whether they are encoded as invariant surface reflectance descriptors from which colour appearance may be computed afresh under novel illuminations. To approach this question, we assessed how memory colour matches vary with the ambient illumination spectrum, for fixed states of chromatic adaptation. Participants (N=7) viewed a naturalistic familiar object (banana, apple, pear, or pepper) in an enclosed chamber containing otherwise achromatic surfaces. Spectrally tuneable lamps provided the sole, immersive illumination. Each trial began with an adaptation period under the reference illumination, with the object hidden. During the following adjustment phase, participants used joystick controls to smoothly alter the illumination along metameric loci, changing its spectral power distribution but preserving the reference chromaticity and lux, thereby maintaining a constant white point. The participant’s task was to select the illumination for which the object appeared most natural. Reference illumination chromaticities were constrained to the daylight locus. Metameric illuminations varied away from broadband daylight spectra, systematically altering the object’s colour appearance. The “memory colour match” is the object’s colour appearance under the selected illumination; accuracy is defined as perceptual distance of the match from colour appearance under broadband daylight of the same chromaticity. Results: Participants were able to perform the task, and generally reported that only the object appeared to change colour, not the illumination. There is a trend for the memory colour match to be most accurate and have the least inter-individual variation for illumination chromaticities closest to neutral, suggesting that memory colour may be represented as colour appearance under typical daylight illuminations, or is more easily accessed for those illuminations.