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)
Eodiscina surface. The interlensar sclera is not deeper than the lenses. This type of eye is called abatochroal. A second type of eye, called schizochroal, is unique to the Phacopina suborder, and has up to several hundreds of relatively large lenses (0.05-0.5 mm), that do not touch either, but the corneal membrane extends into the sclera outside the lens, and the sclera is deeper than the lens. The most usual type of trilobite eye, called holochroal, has usually thousands of small hexagonal lenses without an interlensar sclera, and a common cornea. Many later Eodiscina however, lost their visual organs altogether, and