The effect of the target size on the detection of luminance and chromaticity flicker and gratings was studied. Discrimination ellipses in a luminance–chromaticity plane were determined with square test areas subtending from to 1°. Pure luminance modulation thresholds and pure chromaticity modulation thresholds were obtained for square targets subtending from 1/16° to 2°. 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 × 8 periods; the integration area for detecting flicker is more than 1° × 1°. 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.
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