When my kids were small, I had them draw a self-portrait on each birthday. Here's what their early pictures looked like:
None of us have any trouble recognizing that this is a picture of a little person, yet the head and hands are drawn too big. When my daughter drew one of her first self-portraits, I watched her as she carefully counted her fingers and then drew each hand with five finger lines. No other part of her body was given this kind of attention.
My children were not drawing what they saw in the mirror. Instead they were drawing how they sensed the world. The head with its eyes and mouth got a big representation (although the ears were often missing). The hands loomed large. Their pictures looked much more like the "somatosensory homunculus" in our brain than a real child.
The somatosensory homunculus is based on the map of our body which is repeated several times in a part of the brain called the somatosensory cortex. This part of the cortex, located toward the top of the head, processes input from touch, temperature, and pain receptors throughout the body. The input is organized in a "somatotopic" fashion meaning that input from, let's say, the hand is mapped next to input from the arm which is mapped next to input from the shoulder. However, the body map is distorted. Areas of the body that receive more input have a bigger representation in the somatosensory map. Here is a picture of the somatosensory cortex showing where the different body areas are represented. Next to it is a homunculus drawn from the somatosensory map.
