PrepTest 121, Section 1, Question 1
The effort involved in lying produces measurable physiological(32 more words not shown)
Which one of the following(8 more words not shown)
- ALie-detector tests can(13 more words not shown)
- BPeople are often(14 more words not shown)
- CLying about past(15 more words not shown)
- DFor people who(24 more words not shown)
- EWhen employers use(16 more words not shown)
Reading the argument
My heart is racing. Does that mean I'm lying? What if I'm just nervous about taking the test?
Accept the connection we're given: lying produces physical reactions that the machine can measure. But a reaction can have more than one cause. Exercise, illness, or stress might also speed up a person's heartbeat. Those are possibilities to investigate, not facts we're adding to the argument. If a truthful person can produce the same signal as a liar, the machine might identify that truthful person as lying.
We might initially wonder about the opposite problem, too: could someone lie so effortlessly that the expected reaction never appears? The passage tells us that lying has these reactions, though. We don't need to dispute that premise. The cleaner objection accepts it and asks whether the reactions can happen without a lie.
What we’re looking for
For the weaken question, that's what I want: another way to produce the signals this test treats as evidence of lying. A test can detect a racing heart perfectly and still get the reason for that racing heart wrong.
Working the answers
- A
We don't need to measure every reaction. Suppose there are five reactions and just one reliably distinguishes lying from telling the truth. Measuring that one could be enough. A limits how much the machine measures without showing that the reactions it does measure are misleading.
- B
Whether people notice their reactions doesn't tell us whether those reactions identify a lie. The machine could measure a change that the person never notices. We need a problem with what the test establishes, not with the person's awareness of their body.
- C
The test is supposed to tell whether someone is lying, not how serious the subject of the lie is. Lies about a crime and lies about a board game could produce equally strong reactions while both remained detectable. A difference between those topics isn't required for the test to work.
- DCorrect
A truthful person can produce the same reactions just from the tension of taking the test. Now the machine can't safely move from “I detected the reaction” to “You lied.” The reaction could be a response to the testing situation itself. That directly challenges the claim that these tests are a sure way to identify lying.
- E
Wanting to lie is different from successfully fooling a lie detector. Highly motivated applicants could lie and get caught every time. This tells us why someone might lie during a particular use of the test, not whether the test accurately identifies the lie.
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