Edge influences on suprathreshold white brightness perception.

Edge plays special role in spatial perception and in determining the lightness information of the surface within borders. The aim of our study was to measure suprathreshold brightness in different levels of edges hardness. Steven's Power Law for circles modulating in luminance were estimated for 10 subjects (mean age 25 SD 3, 5 female). Stimuli and psychophysical procedures were built using Psyknematix software (v1.4.3, KiberVision, Montreal, Canada) installed in iMAC OS 10.8 X (Apple Inc., USA). Stimuli were presented on the iMAC display using 11 bit graphic board and consisted of two circles of 3 degrees of visual angle, separated by 10 degrees. We tested 7 levels of Michelson contrast: 7, 8, 10, 15, 26, 50, 100. Three edge filtering was tested ( 0.3, 0.8 and 1.5 degrees of smoothing). The subject task were to judge the brightness of the edge filtered circle compared with the circle of hard edge which was considered the Modulus and received an arbitrary level of 50, representing the amount of brightness perception. If the bright was perceived as two times more intense, the subject had to give a number 100. . If the bright was perceived as two times less intense, the subject had to give a number 25 and so on. In each trial, the same contrast level was presented in both circles. Five judgments were performed for each contrast level in each edge filtering. We found an increase in the Power Law exponent as the increase of filtering (for sigma of 0.3 = 0.37, sigma of 0.8 = 0.55, and sigma 1.5 = 1.03). All power function fitting had a correlation coefficient higher than 0.95. We conclude that there is a progressively increase in brightness perception as increase the edge filtering and a full performance in suprathreshold contrast perception is achieved with a half size stimulus smoothing. Meeting abstract presented at VSS 2015.