Patient TN was, by his own account, completely blind. Two consecutive strokes had destroyed the visual cortex of his brain, and consequently, his ability to see. Researchers began examining him and discovered that despite his blindness, he had maintained the ability to detect emotion on a person’s face. He responded appropriately — with emotions such as joy, fear, and anger — to a variety of facial expressions. Observed activity in his amygdala — the part of the brain responsible for processing emotions — confirmed the curious results.
TN’s rare condition is known as blindsight. Because his stroke damaged only his visual cortex, his eyes remain functional and as a result can still gather information from his environment. He simply lacks the visual cortex to process and interpret it. Sight has changed for TN from a conscious to a largely subconscious experience. He no longer has a definitive picture of his surroundings, but he has retained an innate awareness of his position in the world. He is, to some degree, able to see without being aware that he is seeing.