Researchers have found that emoticons, though they obviously resemble little faces, aren't actually processed in our brain the same way. Instead, the smiley symbols have more in common with logographs, or symbols used to represent words, like some Chinese characters.
The study, performed by neuroscientists at Flinders University and the University of South Australia, compared the cortical response of the ":-)" emoticon to pictures of smiling human faces and to a meaningless series of characters — "*/."
There is a certain pattern on the electroencephalogram called the "N170 event-related potential" that is helpful in telling whether a visual stimulus is being processed "featurally," which is how you perceive most objects, or "configurally," for familiar things like faces that are best understood in a certain arrangement — eyes on top, nose in the middle, mouth below, for instance.
By watching when and how this pattern appeared, the researchers could tell whether emoticons were perceived the same way faces were or not. Their finding was that, while emoticons are understood as being faces, they don't actually go through the same neural process to reach that point. Like faces, emoticons have a "canonical" orientation, left-to-right, and are processed configurally. But the powerful facial recognition hardware in your brain is not actually used to interpret the ":-)".
What the researchers suggest is that emoticons are more like logographs used in East Asian written languages: symbols that incorporate some parts of the object they represent (like a wavy line for water) but are not actually seen the same way as the object itself would be. Instead, the emoticon or symbol is more like shorthand for the idea it represents — a smiling face, a crying face, a kiss — and although we associate them with each other, the paths they take through our brains are very different.