This is the fourth in a series of posts on Visual Processing
Stare at the x in this image for as long as you like:
www.theillusionsindex.org
You might have noticed that features begin to disappear. The entire cat might disappear quickly or slowly, completely or incompletely. The tiniest flick of your eyes brings the cat into view and the process begins again.
This is Troxler Fading. Troxler Fading occurs when items away from the center of your vision are low in contrast, lack lines, and are not moving. Troxler Fading allows you to be aware of the surroundings but specifically facilitates attention away from the location of the effect. Input from the periphery is reduced and simplified, allowing you to focus your attention.
The drawing below uses Troxler fading to emphasize the shell. If you stare directly at the shell, you may perceive that the periphery fades, and the shell appears to float in a void.
Troxler fading is one of the processes that guide the viewer away from less pertinent and unchanging features of your environment. High contrast items with abrupt lines or transitions between form grab your attention. Low contrast items without abrupt lines or transitions will deflect it.
If you try to look at the feet in this drawing, you will feel a force pushing your eyes away from the feet, and pulling you towards the rump. You are pulled to look primarily at the rump, the curve of the lower back, and the upper legs. The rump and lower back are drawn using the most specific and darkest lines, and the greatest contrast within form and between form and background. This portion of the drawing draws in a way that central vision sees.
The arms and legs are drawn with equal care. However, they lack contrast, line, and detail and are drawn against a flatter background. Effects that speak to your peripheral vision are used. You are aware that the lower legs and feet are present. Your minds eye sees them for you in surprising detail. The drawing is relaxing to look at. You know where to look.
The central visual system and peripheral visual system perceive differently using a different set of rules. Drawing every feature with identical contrast and detail can be like writing a song that is always loud or making a movie with nonstop action scenes. It can be noisy and confusing. The unguided viewer is overwhelmed with detail, and may have a difficult time identifying what is important. Although the drawing may be technically impressive, the viewer has the sense of watching passively from a distance, rather than enjoying the pleasure and mystery of participation.