The left hemisphere of split-brain subjects has been shown to have to come up with random reasons for things the right hemisphere does
The left hemisphere tends to be stubbornly certain, whereas the right acknowledges ambiguity and is always uncertain. There are numerous examples of this phenomenon. A split-brain subject, to whose right hemisphere a photograph of a nude in a suggestive pose is projected, becomes flustered and laughs in an embarrassed fashion. When the experimenter asks her why, her verbal left hemisphere has no idea. She therefore makes something plausible up—someone in the room is upsetting her.
But a famous example, reported by Micheal Gazzaniga and Joseph LeDoux, illustrates the most important point here. The experimenters show a split-brain patient a picture projected to one or other hemisphere and ask him to pick a card connected with the scene. For example, they show a snow scene to the right hemisphere and ask him to choose an appropriate picture from an array of cards, with either hand. He cannot say what it is that he has seen, because the right hemisphere cannot speak, but he is able with his left hand to go straight to the picture of a shovel. However, since the left hemisphere did not see anything, his right hand chooses at random, and scores no better than chance.
Then they make things a bit more interesting. At the same time that they flash a picture of the snow scene to the right hemisphere, they flash a picture of a chicken claw to the left hemisphere. Each hemisphere has knowledge of only one image, and in each case it is different. When they ask the patient to choose an appropriate card, again his left hand chooses a shovel (because the right hemisphere has seen the snow), but the right hand chooses a picture of a chicken (because what the left hemisphere has seen is the chicken claw). When asked why his left hand had chosen the shovel, his verbal left hemisphere, which has to respond to the question, but knows nothing of the snow scene, the real reason for choosing the shovel, is not in the least abashed. He explains that he saw a chicken,’ and of course chose the shovel because ‘you need that to clean out the chicken shed’.
The really interesting finding here, as the authors themselves put it, is that ‘without batting an eye’ the left hemisphere draws mistaken conclusions from the information available to it and lays down the law about what only the right hemisphere can know: ‘yet, the left did not offer its suggestion in a guessing vein but rather [as] a statement of fact …’
References
- Mcgilchrist, Iain. (2010). The Master and His Emissary Chapter 2 What Do the Hemispheres Do (p. 163). London, UK: Yale University Press.
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Type:🔴 Tags: Biology / Neuroscience / Neuropsychology Status:☀️