engleski

Underlying mechanisms of classical and inverted White's effect: a reaction time study

In White’s (1979) illusion of lightness, intermediate luminance patches appear darker when their immediate surround is comprised of black stripes and appear lighter when their immediate surround is comprised of white stripes. In this classical form of White’s illusion, the direction of the induced brightness change does not correlate with the amount of black or white border in contact with the intermediate patch. Some studies have shown that classical White effect arises only when intermediate luminance patch lies between minimum and maximum luminance values of the inducing stripes. With patches either darker or lighter than both inducing stripes, the direction of the brightness effect is reversed. Several theoretical explanations and models have been proposed, ranging from low-level neuronal approaches to complex models of high-level cortical processing. Interestingly, majority of models accounts only for classical White’s effect, leaving inverted variants unexplained. Aim of this study was to test the role of early neural processing in variants of White’s effect, by comparing subjective lightness matches and simple reaction time (SRT) to intermediate luminance patches imbedded in lighter or darker inducing stripe. It is generally assumed that SRT latency represents effect of the stimulus intensity on the latency of early sensory processing. Therefore, if perceived lightness indeed depends on the mechanisms in early visual stages, SRT should be shorter for the luminance patch that is perceived as brighter. Three experiments were performed (1) for classical White’s effect, (2) for double decrement variant of inverted effect (intermediate patch as highest luminance) and (3) for double increment variant of inverted effect (intermediate patch as lowest luminance). Results show that illusion does not invert as expected, and that SRT does not fully correlate with perceived luminance. Results are discussed in terms of existing explanations of White’s effect.

classical White's effect; inverted White's effect; reaction time

nije evidentirano