Perception of Lightness and Brightness of Achromatic Surface Color and Impression of Illumination

The relationships between lightness and brightness responses under the condition that achromatic "surface color " appears and the relationships between perceived illumination and brightness were examined. The Ss were required to make categorical judgments upon both lightness and brightness of the test patches presented on black and white backgrounds and upon the over-all illumination in the visual field. Conclusion is as follows: the functions of lightness judgments and of brightness judgments are different, and the relation between them depends on the luminance of the background. Brightness responses for a test surface depends not only on the surface luminance but also on the background or the adjacent ield luminance. The similarity of the stimulus correlate of brightness to that of perceived illumination is also argued.