For example, consider the above apple tree earlier in the year when the apples were still green and bitter:
Believing each receptor’s response to the photons’ wavelength information at sunset, a simple creature might think the apples had suddenly ripened:
But we are not fooled. Processing the entire spectral scene holistically, our brain estimates the prevailing level and spectral distribution of the lighting conditions. Then automatically corrects the color balance
Lest we think too highly of ourselves, goldfish can do this too.21
Photons can also fool your photometer p. 65
A photometer will tell you that the two squares in the center are equally bright (as measured in terms of luminance – see page 81). How have the photons managed to fool the photometer?
Just like photons’ varying effectiveness when it comes to wavelength, again the “fault is in our stars”. It seems that by using holistic processing our own visual system deceived us. How come this flaw was not “weeded out” by evolution?
Actually it is not a “flaw”. It reveals that our visual system has a higher priority than informing us accurately about what is “out there.”
That higher priority is making us more aware of what is going on even if it means using deception to enhance details that otherwise we might not notice. (After all, we are continually fooled by all the colors we see.)In this case the visual system has exaggerated the differences in brightness to make the small squares easier to see in an otherwise dull scene – brightness contrast processing.