Adults’ skill in face perception is facilitated by their ability to rapidly detect that a stimulus is a face, a task that is associated with neural markers that distinguish the processing of faces from the processing of non-face objects. Functional MRI (fMRI) studies indicate that some brain areas, e.g. middle fusiform gyrus, inferior occipital gyrus, and superior temporal sulcus, respond more to faces than to non-face objects. Electrophysiological studies indicate that the distinction between faces and non-face objects is observable within 200 ms of a stimulus being presented.
Face detection is facilitated by the fact that all faces share the same ordinal relations of features: the two eyes are aligned with each other and positioned above the nose, which is above the mouth. As a result, and unlike other object categories, faces can be superimposed and the resulting composite retains a face-like structure.
When you see a circle, two dots and a line, you involuntarily see a face. You just can’t help it!
Picture from the book “Understanding Comics”: