The book is saying that the left hemisphere answers incorrectly, in both cases! As I said, this is surprising.
That’s not just surprising, that’s absurd. I can absolutely believe the claim that the left hemisphere always takes what’s written for granted, and solves the syllogism formally. But the claim here is that the left hemisphere pays careful attention to the questions, solves them correctly, and then reverses the answer. Why would it do that? No mechanism is proposed.
I looked at the one paper that’s mentioned in the quote (Deglin and Kinsbourne), and they never ask the subjects whether the syllogisms are ‘structurally correct’; they only ask about the truth. And their main conclusion is that the left hemisphere always solves syllogisms formally, not that it’s always wrong.
If you’ve heard the bizarre stories about patients confabulating after strokes (eg “my limb isn’t paralyzed, I just don’t want to move it) this is almost unilaterally associated with damage to the right hemisphere.
Interesting, I didn’t know this only happened with the left hemisphere intact.
the claim here is that the left hemisphere pays careful attention to the questions, solves them correctly, and then reverses the answer.
Fwiw I also think that that is an absurd claim and I also think that nobody is actually claiming that here. The claim is something more like what has been claimed about System 1, “it takes shortcuts”, except in this case it’s roughly “to the left hemisphere, truth is coherence; logical coherence is preferred before map coherence, but both are preferred to anything that appears incoherent.”
I looked up the source for the “However” section and it’s not Deglin and Kinsbourne but Goel and Dolan, 2003). I looked it up and found it hard to read but my sense is that what it’s saying is:
An general, people are worse at answering the validity of a logical syllogism when it contradicts their beliefs. (This should surprise nobody.)
Different parts of the brain appear to be recruited depending on whether the content of a syllogism is familiar:
A recent fMRI study (Goel, Buchel, Frith & Dolan, 2000) has provided evidence that syllogistic reasoning is implemented in two distinct brain systems whose engagement is primarily a function of the presence or absence of meaningful content. During content-based syllogistic reasoning (e.g. All apples are red fruit; All red fruit are poisonous;[All apples are poisonous) a left hemisphere frontal and temporal lobe system is recruited. By contrast, in a formally identical reasoning task with arbitrary content (e.g. All A are B; All B are C;[All A are C) a bilateral parietal system is recruited.
(Note: this is them analyzing what part of the brain is recruited when the task is completed successfully.)
This 2003 study investigates whether that’s about [concrete vs abstract content] vs [belief-laden vs belief neutral content] and concludes that it’s about beliefs, and also < something new about the neuroanatomy >.
I think what’s being implied by McGilchrist citing this paper (although it’s unclear to me if this was tested as directly as the Deglin & Kinsbourne study) is that without access to the right hemisphere, the left hemisphere’s process would be even more biased, or something.
I’d be interested in your take if you read the 2000 or 2003 papers.
That’s not just surprising, that’s absurd. I can absolutely believe the claim that the left hemisphere always takes what’s written for granted, and solves the syllogism formally. But the claim here is that the left hemisphere pays careful attention to the questions, solves them correctly, and then reverses the answer. Why would it do that? No mechanism is proposed.
I looked at the one paper that’s mentioned in the quote (Deglin and Kinsbourne), and they never ask the subjects whether the syllogisms are ‘structurally correct’; they only ask about the truth. And their main conclusion is that the left hemisphere always solves syllogisms formally, not that it’s always wrong.
Interesting, I didn’t know this only happened with the left hemisphere intact.
Fwiw I also think that that is an absurd claim and I also think that nobody is actually claiming that here. The claim is something more like what has been claimed about System 1, “it takes shortcuts”, except in this case it’s roughly “to the left hemisphere, truth is coherence; logical coherence is preferred before map coherence, but both are preferred to anything that appears incoherent.”
I looked up the source for the “However” section and it’s not Deglin and Kinsbourne but Goel and Dolan, 2003). I looked it up and found it hard to read but my sense is that what it’s saying is:
An general, people are worse at answering the validity of a logical syllogism when it contradicts their beliefs. (This should surprise nobody.)
Different parts of the brain appear to be recruited depending on whether the content of a syllogism is familiar:
(Note: this is them analyzing what part of the brain is recruited when the task is completed successfully.)
This 2003 study investigates whether that’s about [concrete vs abstract content] vs [belief-laden vs belief neutral content] and concludes that it’s about beliefs, and also < something new about the neuroanatomy >.
I think what’s being implied by McGilchrist citing this paper (although it’s unclear to me if this was tested as directly as the Deglin & Kinsbourne study) is that without access to the right hemisphere, the left hemisphere’s process would be even more biased, or something.
I’d be interested in your take if you read the 2000 or 2003 papers.