Effects of a gap between the central and surrounding regions with luminance gradients on the feeling of being dazzled.

The feeling of being dazzled is evoked by images consisting of an achromatic uniform center, surrounded by regions with luminance gradients. As the perceptual distinctness of the central region has been suggested to contribute to the feeling of being dazzled, we examined the effects of a gap between the central and surrounding regions on the feeling of being dazzled. The stimulus comprised a disk with uniform luminance surrounded by an annulus, of which the luminance was decreased from the inner boundary to the periphery. Three luminance profiles (linear, logistic, and inverse-logistic) of the surrounding luminance ramps were used. The distinctness of the disk decreased in the order of logistic, linear, and inverse-logistic profiles. The luminance of the disk, the maximum luminance of the annulus, and the gap size were also varied. When the luminance continuously transitioned from the disk to the annulus, the feeling of being dazzled was stronger for the inverse-logistic annulus luminance profile, compared with the logistic and linear profiles without a gap; however, it was not different for the three profiles with a gap. Further, the feeling of being dazzled increased when a gap was introduced for the logistic and linear profiles, but not for the inverse-logistic profile. These results suggest that the feeling of being dazzled was reduced by the perceptual indistinctness of the central disk for the logistic and linear annulus luminance profiles, while the gap restored the feeling of being dazzled by making the central disk perceptually distinct.