Peripheral filling in causes illusory afterimages

In a uniformity illusion, participants experience that peripheral stimuli appear identical to the central stimulus even though they are different. The uniformity illusion generally occurs after prolonged central fixation. The uniformity illusion thus seems to evoke illusory peripheral perceptions of colour, shape, size, and even movement. This could be the result of a passive process where the periphery is unattended and ignored, resulting in erroneous reporting of peripheral stimulus properties. The current experiment, however, points to an active filling-in process that resulted in an actual percept of the periphery by showing that the illusory periphery is "sticky": Even after the central stimuli inducing the illusion were removed, the peripheral illusion persisted, and continued to influence perceptual reports of the participants. Participants viewed displays featuring colour or size variations between the center and periphery for a set time to induce the uniformity illusion, reporting if they experienced a uniform screen. Subsequently, the central patch was altered to match the original periphery, creating a truly uniform display. Participants then evaluated whether the new display appeared uniform and reproduced the size or colour of the peripheral texture. Reaction time and reproduction accuracy revealed that experiencing an illusory periphery interfered with processing subsequent physical stimuli, especially in trials where participants explicitly reported the illusion. These findings suggest that the uniformity illusion can produce a persistent illusory periphery, which disrupts the perception of the actual peripheral stimulus even seconds after the original display has been modified. The results underscore the active, hierarchical nature of perceptual reconstruction in visual processing.