Troxler

Troxler fading, also known as Troxler's fading or Troxler's effect, is an optical illusion affecting visual perception. When one fixates on a particular point, surrounding stationary images presented away from the point of fixation will seem to slowly fade away and eventually disappear. This is due to the brain's adaptive mechanisms reducing neural activity in response to unchanging stimuli.

The effect is named after Swiss physician and philosopher Ignaz Paul Vital Troxler, who first described the phenomenon in 1804.

The physiological explanation for Troxler fading lies in the fact that the brain prioritizes processing new or changing information. Neurons in the visual system, particularly those involved in processing peripheral vision, adapt to constant stimulation over time. This adaptation leads to a reduction in neural firing, effectively making the constant stimulus less noticeable and eventually causing it to fade from conscious perception. Factors that can influence the strength and duration of the effect include the contrast and size of the surrounding stimuli, the stability of fixation, and individual differences in neural processing.

While Troxler fading often occurs with stationary stimuli, it can also be observed with slowly moving or blurred images. The illusion is more pronounced when the stimuli are low in contrast and located further away from the fovea, the central part of the retina responsible for high-resolution vision.

Troxler fading demonstrates the brain's remarkable ability to adapt to its environment and filter out irrelevant information, allowing it to focus on more important and dynamic aspects of the visual scene. It highlights the constructive nature of visual perception, where what we perceive is not simply a passive reflection of the external world, but rather an active interpretation shaped by neural processing and adaptation.