Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Light stimuli created by the visual system. Although illuminated objects exist apart from observers, visual stimuli do not. Visual stimuli arise only after the evolved properties of the visual system create them by ordering the chaotic flux of photons that reaches the corneal surface at any given moment into ordered patterns whose evolved frequency of occurrence indexes reproductive success.
