Just seeing an eye… and only the eye is enough to establish the first components of neural facial recognition. In this interesting paper by Elias B. Issa and James J. DiCarlo, the authors found using a combination of functional magnetic resonance imaging (fMRI) that the first stage in the primate visual/face processing circuitry is tuned to regions in images containing eyes. Even a single eye is enough to trigger recognition pathways.
fMRI and electrophysiological recording work in facial processing has established that the facial processing network possesses six areas that are extensively interconnected and the anatomical analysis suggests a nested, hierarchical layout where signals progressing through the system become more established. This of course begs for a true connectomics analysis which will be difficult at the large scale, but tractable at the mesoscale. It turns out that this is an interesting computational problem as identification of isolated components of images that connate larger meaning is difficult. Discovering how neural systems unravel this will have substantial importance to diverse applications.