Logical Reasoning

PT159 · S1 · Q5 Researchers gave each of eighteen subjects

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Researchers gave each of eighteen subjects a playing card, then offered them money to lie to a computer about the identity of the card while undergoing a scan by functional magnetic resonance imaging (fMRI).

Conclusion (this supports the idea)

fMRI can eventually form the basis of an effective lie detector.

Evidence

When 18 subjects lied about a playing card, fMRI scans showed increased activity in regions of the brain known to be stimulated by stress.

Evaluate

The evidence tells us that the fMRI picked up on activity in stress-related brain regions. The conclusion i s claiming the fMRI is detecting a lie.

So we need to assume that activity in these regions clearly signals a lie. The author seems to be thinking,

But does lying cause stress? If not, this test could provide false negatives, because people would be lying but it wouldn't detect them.

And what if other things cause stress, even though the person is telling the truth? Or what if other things besides stress cause these brain regions to light up? If so, this test could provide false positives, because it might look like they're lying even though they aren't.

Goal

Since we want to weaken, let's look for a way to say that this test wouldn't be reliable. It would provide false negatives or false positives.

Which one of the following would, if true, most weaken the argument above?

Existing methods of lie detection,
No Impact
The fact that other lie-detection methods are unreliable does not bear on whether fMRI in particular can become an effective lie detector. We're judging this method on its own merits, not based on whether other methods succeeded or failed.
1% picked this
The majority of people regard
No Impact
What people think about the ethics of lying in experiments is irrelevant to whether fMRI can detect lies.
0% picked this
The amount of stress that
Unclear Impact
This might mean that we sometimes have false negatives, because certain people in certain circumstances might have low enough stress when they lie for the test to detect them. But this doesn't provide nearly as much punch as the correct answer.
9% picked this
Telling a carefully planned lie
Weaker Impact
You could possibly stretch this into a story about false negatives, where the lie detector doesn't pick up on carefully planned lies because those lies don't cause enough stress to be detected. But this isn't nearly as incriminating as the correct answer.
3% picked this
Correct
Stress reactions in the brains
Why this is right
This hurts the most. How could this test, which is trying to detect lies based on stress reactions in the brain, be a reliable indicator of lying, if you get the same stress reactions when you tell the truth? The signal it's looking for doesn't at all differentiate between truth-tellers and liars!
Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.
87% picked this

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