Chapter 6: Color Vision
6.5 Lightness Constancy
Lightness is the subjective perception of the range of luminance between black and white. Surface lightness is one of the fundamental characteristics of an item, alongside its size and motion. However, our comprehension of the brain’s process for calculating lightness is still lacking. The issue lies in the fact that the perception of an object’s shade of gray is not accurately determined by the amount of light reflected by its surface (reflectance) and the intensity of the lighting. However, the perception of lightness on a surface tends to stay the same even when the lighting conditions vary, this effect is known as lightness constancy. In the real world, lightness constancy can be demonstrated by the fact that our white clothes still look white when we are inside even though they reflect much less light than when we are outside in the sun.
Our perception of brightness is also affected by the presence of shadows and our brains need to figure out whether an apparent change in brightness is due to the presence of the edge of an object or a shadow. In Figure 6.10, you will probably notice that the green cylinder seems to be casting a shadow on the chessboard as we can see some diagonal lines going across some of the squares. Most of us will assume the line is a shadow but not that some of the squares are uneven in their brightness. As a consequence, you probably perceive square A to be darker than square B. In fact, they are the same – but we assume that square A is in a shadow and so we mentally subtract the darkness of the shadow from the actual brightness of the square. You can watch this video https://www.youtube.com/watch?v=RIFXcR2NxcY to see that A and B are actually the same in terms of brightness.
Materials in this Chapter came from:
Dommett, E. (2023). Lighting the world: our sense of vision. In C. Hall (Ed). Introduction to biological psychology. University of Sussex. https://doi.org/10.20919/ZDGF9829
Grose-Fifer, J., Spielman, R. M., Dumper, K., Jenkins, W., Lacombe, A., Lovett, M., & Perlmutter, M. (2021). Introduction to Psychology (A critical approach). CUNY Pressbooks. https://pressbooks.cuny.edu/jjcpsy101/
Cheryl Olman & Mohamed Ahmed, Molly Baugh, Francel Colon-Acosta, Jarod Davis, Kaelyn Dezell, Lucas Gaffney, Madelynn Gibbons, Trevor Graham, Katherine Hebig, Noah Hjelle, and Wanlin Hu (Students of 3031 at the University of Minnesota). https://pressbooks.umn.edu/sensationandperception/
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