Pupillometry: Psychology, Physiology, and Function.

And, even if in some animals (such as humans) the PLR may confer but little advantage, “one should bear in mind that seemingly trivial advantages may become extremely significant in a competitive situation; thus an animal whose pupil can dilate a little more may acquire a distinct competitive edge at dusk, and this could make the difference between starvation and plenty.” ( Barlow, 1972, p. 3 ).

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