Psychedelia 4
Acrylic on canvas
9" X 12"

Psychedelia 4 shows a phosphene-rich background behind the edge of an orange cylindrically shaped object. It also features a reverse-color aura, such as appears next to every sharp edge a person sees.

Unlike phosphenes, which arise spontaneously within the visual system, auras come from photobleaching of rhodopsin within the rod and cone cells in the retina. Photosensitivity of retinal cells occurs when rhodopsin molecules respond to photons by switching between a light-sensitive conformation and a light-insensitive conformation, releasing energy in the process. Those cells have reduced sensitivity until they "pump" their rhodopsin molecules back up to their light-sensitive conformation.

The auras appear when eye movements shift the image on the retina slightly. In this case, the gaze has shifted slightly upward and to the left, uncovering part of the retina that was previously protected from photobleaching by the dark edge of the orange cylinder. The cells in that area are, therefore, overly sensitive compared to cells that have been looking at the brighter background, and the scene looks lighter there.