Understanding the rules of life

Category: Standard Studentships

The physiology of colour afterimages

Project No. 2375


Primary Supervisor

Dr Christoph Witzel – University of Southampton


Dr Jenny Bosten – University of Sussex


Perceptual adaptation is one of the most powerful abilities of the human organism to adapt to a constantly changing environment at short time scales.

In colour perception, chromatic adaptation is fundamental to perceive colours of objects and materials across changes in illumination (colour constancy). Colour afterimages probe the striking effects of chromatic adaptation and are used in every introductory lecture and textbook to illustrate perceptual adaptation. Despite their importance, existing evidence has not established whether colour afterimages arise in cone photoreceptors, retinal ganglion cells, or cortically. This project will determine the physiological origin of colour afterimages through a combination of behavioural, genetic, computational and electrophysiological methods. In a first study, the student will test predictions of computational models of afterimages in both normal trichromats and anomalous trichromats (individuals with 3 cone types that differ from the norm and therefore are predicted to have different afterimages). For anomalous trichomats we will sequence the genes underlying the cone photopigments to generate testable predictions for afterimages in particular individuals. The second study combines steady-state visually-evoked potentials (SSVEPs) gathered using both electroretinogram (ERG) and electroencephalogram (EEG) to identify the locus of afterimages along the visual processing cascade, from the retina (decoded using ERG) to different stages of cortical processing (decoded using phases of EEG SSVEP). The third study exploits the fact that visual information from both eyes is separated before the primary visual cortex. Through dichoptic presentation, the student will investigate interocular transfer of colour afterimages. The student will visit the Sussex Colour Group at the University of Sussex for 3 months to benefit from the group’s infrastructure and expertise on anomalous trichromacy and SSVEP. Behavioural and EEG studies will be conducted in the colour and EEG labs of the Centre of Perception and Cognition in Southampton.