Adaptation and Integration of Colour in the Visual System

Perception of colour is not a static translation from wavelength to hue, but a flexible
process which adapts to environmental chromatic properties to maintain stable
colour percepts. Colour adaptation has not been well-investigated between a few
seconds and multiple days, yet the stability of colour perception despite
environmental spectral changes across minutes or hours suggests that adaptation
occurs at this timescale. This thesis aims to investigate the properties of this
‘medium-term’ adaptation, and to localise it within the visual system. Additionally, it
aims to investigate colour processing in the brain, primarily whether visual areas
process colour monocularly or binocularly.

Chapter 3 investigates the effect of the duration and luminance of adapting
environments on changes in colour perception. The results suggest that adaptation
to red and blue filters causes shifts in unique hue settings that endure at least five
minutes post-adaptation. Both the duration and luminance of filters affected the
magnitude of these shifts. Chapter 4 investigates adaptation recovery by comparing
hue settings after 60-minutes post-adaptation either in daylight, or in complete
darkness. The results show that adaptation aftereffects return to pre-adaptation
settings in both conditions, suggesting that colour adaptation recovery is a passive
process. Chapter 5 investigates the transfer of adaptation aftereffects between the
eyes, by adapting participants to the same colour in both eyes, or different colours in
each eye. The results suggest that colour adaptation in one eye does not affect
colour settings made with the other eye. Finally, Chapter 5 investigates cortical
binocular combination of colour, by recording fMRI while participants viewed LM- or
S-cone isolating stimuli in each eye separately, or both eyes together. The results
suggest the existence of some populations of monocular colour neurons in ventral
stream areas. Altogether, these studies contribute to the wider understanding of the
adaptation and combination of chromatic information.