Ramp aftereffect

from “Visual Phenomena & Optical Illusions”

Warning: this is a subtle effect.

Gaze for at least 10 s at the fixation cross in the neighbouring dynamic image. This will adapt your eyes to a brightening patch (above) and a repetitively dimming patch (below). Then move the mouse over the panel to turn it into a steady gray. You should see an aftereffect of apparent dimming (above) and apparent brightening (below). Move the mouse away to re-adapt.

This demonstrates the existence of transient visual pathways selective for gradual changes of luminance.

Source

Steward Anstis’s Demos. Reproduced with kind permission.

*This demo requires that looping of GIF animations is enabled.