title: Influence of the target size on the deterction threshold for luminance and chromaticity contrast.
abstract: The effect of the target size on the detecton of luminance and chromaticity flicker and gratings was studied. Discrimination ellipses in a luminance-chromaticity plane were determined with square test areas subtending from 1/4 degree to 1 degree. Pure luminance modulation thresholds and pure chromaticity modualtion thresholds were obtained from square targets subtending from 1/16 degree to 2 degree. Square-wave stimuli were presented on a color television monitor; the mean color of the screen was yellow, the average retinal illuminance was 350 td. The main effect of enlarging the field size is that the threshold for any luminance-chromaticity combination decreases monotonically except when spatial frequencies are high. The summation area for detecting a fine bar pattern is at least 8 x 8 periods; the integration area for detecting flicker is more than 1 degree x 1 degree. This holds for any luminance-chromaticity mixture. For a fixed spatial or a fixed temporal frequency the change in sensitivity sometimes depends strongly on the ratio of luminance modulation to chromaticity modulation. The main conclusion of this study is that if a target is predominantly yellow the target size has similar influence on the sensitivity to both luminance and chromaticity contrast.
mesh_terms: D000328:Adult; D003118:Color Perception / Q000502:physiology*; D004192:Discrimination, Psychological; D006801:Humans; D008027:Light; D008297:Male; D011601:Psychophysics; D012684:Sensory Thresholds; D013997:Time Factors; D014796:Visual Perception / Q000502:physiology*