THE STRENGTH OF A VISUAL ILLUSION MEASURED BY A RELATED ILLUSORY PHENOMENON
Quantifying perceptual illusions leads to estimate the endogenous dynamics underlying perceptual processing. In the present research we consider the illusory enhancement in brightness occurring when one approaches a blurred white area, a phenomenon called & Stubbs (2006). We test the strength of the brightness variation by means of a grey sharp-boundary disk superimposed on the blurred white region. When approaching the stimulus the blurred area was perceived brighter and simultaneously the grey disk darker. Two experiments demonstrate a causal relationship between the increase in brightness due to the BLI and the darkening of the superimposed disk. Importantly, the increment of achromatic contrast of the disk superimposed on the blurred area indirectly quantifies the BLI effect.