Box 1 | Visual fading outside the laboratory: Troxler's effect

From the following article:

The role of fixational eye movements in visual perception

Susana Martinez-Conde, Stephen L. Macknik & David H. Hubel

Nature Reviews Neuroscience 5, 229-240 (March 2004)

doi:10.1038/nrn1348

Although perfect retinal stabilization is most easily achieved under laboratory conditions, fading of objects in our visual periphery occurs often in normal vision. Peripheral fading of stationary objects was first noticed by Troxler in 1804. Troxler reported that, under voluntary fixation, stationary objects in the periphery of vision tend to fade and disappear106. In the late 1950s, Clarke made a connection between Troxler's fading and the fading of stabilized images in the laboratory1, 2, and attributed both phenomena to neural adaptation107, 108, 109, 110. The simplest explanation for Troxler's peripheral fading is that receptive fields in the periphery of our vision can be considerably larger than fixational eye movements (especially as accurate fixation tends to eliminate microsaccades56, 57, 58, 59). Drifts and tremor, being smaller than the peripheral receptive fields, do not provide effective visual stimulation to prevent peripheral visual fading, especially in the case of low-contrast stimuli. The figure is a demonstration of Troxler's effect. To experience it, fixate precisely on the red spot, while paying attention to the bluish annulus. After a few seconds of careful fixation, the annulus will disappear, and the red spot will appear to be surrounded by a completely white field. Movements of the eyes will immediately bring the blue annulus back to perception.

The role of fixational eye movements in visual perception