Stare-in-the-crowd effect evolved from a necessity for fast and accurate gaze perception for complex social interactions (Emery 2000). According to this model, an eye direction detector (EDD) mechanism - a neurocognitive system responsible for the rapid detection of eyes in the environment and their gaze direction – arose as a function of the geometry created by a dark circular iris relative to the white sclera (Baron-Cohen 1994). Specifically, it is contended that the increased ratio of exposed sclera in the eye outline of humans serves to enhance the velocity and acuity of gaze direction perception (Kobayashi and Kohshima 2001). Baron-Cohen, S. (1994)
Arthropod eye more complex schizochroal eye was found only in one sub-order of trilobite, the Phacopina (Ordovician-Silurian). It has no modern counterpart. The eye has up to 700 larger lenses with individual sclera separating each lens. Each lens has a cornea. Schizochroal eyes developed from holochroal ones and were more powerful with overlapping visual fields. They were particularly useful for nocturnal vision and possibly for colour and depth analysis. The lenses of the eye were constructed from single calcite crystals. Early schizochroal eye designs were rather haphazard and irregular, though constrained by the geometrical requirements of packing identical sized lenses on a