Influência da luminância de fundo em estímulos pseudoisocromáticos sobre a discriminação de cores

Abstract

Color perception is one of the most complex attributes of the human sensory system and contributes to survival in the expression of eating, reproductive, sexual, surveillance, and other behaviors. Pseudo-isochromatic stimuli are widely used for color vision assessment of humans and other primates. Despite the pervasive use, there are no norms for its application, each developer of these tests using varied stimulus configurations. The present study aims to evaluate the effects of background luminance on color discrimination in humans using pseudo-isochromatic stimuli. Ten trichromatic subjects of both sexes, aged 26 to 54 years (32.3 ± 8.3 years of age), normal visual acuity and no history of previous diseases that potentially affected the visual apparatus and / or nervous system were tested. To evaluate the influence of background luminance on color discrimination, a pseudo-isochromatic stimulus with spatial noise of size and luminance (luminance noise between 5 and 35 cd / m2) was used, with a background of 0 cd/m² illumination, 7.5 cd/m², 15 cd/m², 22.5 cd/m² and 30 cd/m 2. The target was composed of a set of central circles that formed a letter C, which presented different chromaticity in relation to the mosaic field in eight different chromatic axes (0º, 45º, 90º, 135º, 180º, 225º, 270°, 315°) around a chromaticity point of the CIE 1976 diagram (u '= 0.219; v' = 0.48). The color discrimination thresholds on each axis were estimated using a 4-alternative forced choice method and a staircase of 21 reversals, with a 2-hit rule for 1 error, and the threshold was calculated as the average of the last 15 reversals. The variation of color discrimination thresholds as a function of background luminance was dependent on the angle being studied. At angles 0°, 45°, 180° and 225°, the size of vectors in threshold perception were higher at 0 cd/m² and decreased sharply by 7.5 cd/m², where they reached their lowest values and remained low in conditions with higher background luminances. At angle 90°, the vector size was minimal in background luminance condition of 7.5 cd/m² and increased to higher and lower background luminance values. On vectors of angle 135°, 270° and 315° the color discrimination did not change significantly as a function of change background luminance. The area of color discrimination ellipse varied as a function of luminance stimulus background with a minimum value of 7.5 cd/m². The results show that the color discrimination is influenced by modification of luminance background of pseudoisochromatic stimulus. Activation of a red-green opposing mechanism and two blueyellow opposing mechanisms may explain the different influences of background variation in stimulus on discrimination of chromaticity in different axes. The results are important in understanding the physiology of perception of pseudo-isochromatic stimuli and search for a standardization use of these stimuli in clinical practice to facilitate comparison of results between different studies.