We first demonstrated the left hemisphere’s unique drive to interpret the world around it using the simultaneous concept test on a split-brain patient [61] . Patient P.S. was shown simultaneously a chicken claw to the speaking left hemisphere and a snow scene to the silent right hemisphere. Patient P.S. was then instructed to pick out the picture most related to the scene he just saw from a set of eight choices, using both hands. His left hand (controlled by his right hemisphere) chose a snow shovel, while his right hand chose a chicken. When asked why he chose those particular pictures, P.S. replied, ‘ Oh, that’s simple. The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed ’ . While the speaking left hemisphere can easily explain that he chose the chicken with his right hand because it was picture most related to the chicken claw that he saw, the speaking left hemisphere did not see the snow scene so it must concoct a rational and reasonable explanation for why his left hand chose the snow shovel as well.
As demonstrated in the simultaneous concept test above, the left hemisphere quickly interprets the actions of its left hand controlled by the disconnected right hemisphere in a way that makes sense for the patient. It has no internal representation available to explain why he is moving his left hand in that way. Yet, to the patient, the movement seems perfectly plausible once its actions have been interpreted. Interestingly, this does not always happen instantly for the patient. Sometimes it takes the patient’s left hemisphere as long to figure out what its left hand is doing as it would an outside observer. For example, in one session we presented the word phone to the right hemisphere of patient J.W. and asked him to verbalize what he saw. Of course, J.W. was speaking from his left hemisphere and his left hemisphere did not see the word ‘ phone ’ , and his right hemisphere was mute. Therefore, he said he did not see anything. However, when we put a pen in his left hand and asked him to draw it, J.W. immediately started drawing a phone. For the outside observers who did not see the word ‘ phone ’ displayed, it took some time to make out what J.W. was drawing. J.W.’s left hemisphere was in the same boat. Fortunately for us, J.W. tends to articulate what he is thinking (a great trait for a research subject). He was quite confused by what he was drawing, and started making guesses about what he saw. It was not until the picture was almost complete that outside observers, including J.W.’s left hemisphere got what his left hand was drawing. At which point, J.W. exclaimed, ‘ Duh, it’s a phone ’ . The communication between the hemispheres happened out on the paper and not within his head. In the meantime, his interpreter struggled to find an explanation for his actions. Usually, the interpreter’s explanations come much more readily. For example, if we flash the command ‘ stand up ’ to J.W.’s right hemisphere, he will stand up. But if we ask him why he is standing up, he doesn’t respond, ‘ well, you just told me to ’ because that command is not available to his left hemisphere. Instead, J.W. will say something like, ‘ I just felt like getting a coke ’ . His left hemisphere is compelled to concoct a story that provides an explanation, or interpretation, of his actions after they have already occurred.
