PrepTest 159, Section 1, Question 5
Researchers gave each of eighteen subjects a playing(62 more words not shown)
Which one of the following(8 more words not shown)
- AExisting methods of(12 more words not shown)
- BThe majority of(9 more words not shown)
- CThe amount of(23 more words not shown)
- DTelling a carefully(10 more words not shown)
- EStress reactions in(22 more words not shown)
Reading the argument
What happens when someone tells the truth while hooked up to the same scanner?
Picture the task: you're holding the ace of spades, but you tell the computer it's the king of hearts. The scan shows activity in brain regions associated with stress. That is an observation worth investigating. It still doesn't tell us whether the stress comes from lying, being scanned, or participating in an unfamiliar experiment.
I might also wonder whether lying to a computer produces the same response as lying to a person. But the more immediate problem is the missing comparison. If truthful subjects show the same stress response, how will the machine tell them apart from liars?
What we’re looking for
We're asked to weaken the idea that this result supports a useful lie detector. I'd look for evidence that truth-telling can produce the same signal. Detecting stress won't distinguish lies from truth if both can look alike on the scan.
Working the answers
- A
The unreliability of an existing method doesn't establish that a different technology will fail. The researchers are proposing a new basis for lie detection. We'd need a problem with the evidence for this method, not merely a disappointing history for other methods.
- B
Thinking the lie is unethical might help explain why a subject feels stressed. But we're not deciding whether the experiment is morally acceptable. We need to know whether the observed brain activity distinguishes lying from telling the truth, and this belief about ethics doesn't settle that comparison.
- C
Different amounts of stress don't necessarily defeat the proposed detector. Suppose one person's lie produces a large response and another person's lie produces a small but detectable response. A scanner might still detect both. C raises a complication, but it doesn't show that the stress patterns fail to distinguish truth from lies. The stronger objection is that a truthful person could produce a similar pattern.
- D
Less stress isn't the same as no detectable stress. A carefully prepared lie could produce a weaker signal that a sufficiently sensitive scanner still identifies. The conclusion concerns the technology's eventual prospects, so we shouldn't dismiss D simply because the particular card lie is simple. The problem is that a difference between two kinds of lies doesn't establish the crucial overlap between lying and truth-telling.
- ECorrect
Truthful subjects show stress reactions similar to those of subjects who lie. That gives us the missing comparison and undermines the interpretation of the observed signal: seeing that reaction doesn't tell us which kind of subject we're looking at. This doesn't prove that no future fMRI method could ever work. It shows why the stress response reported in this study is inadequate support for the proposed detector.
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