PrepTest 117, Section 2, Question 5
The corpus callosum—the thick band of nerve fibers(59 more words not shown)
Which one of the following(8 more words not shown)
- AThe corpora callosa(20 more words not shown)
- BMusical training late(10 more words not shown)
- CFor any two(17 more words not shown)
- DAll musicians have(7 more words not shown)
- EAdult nonmusicians did(18 more words not shown)
Reading the argument
Did music change their brains, or did their brains help them become musicians?
The unfamiliar name isn't the hard part. The corpus callosum connects the brain's two halves, and the passage says it's larger on average in musicians. That gives us a difference between the groups. It doesn't yet tell us how the difference arose.
Maybe children with a larger connection find music easier, enjoy it more, and keep playing. Other children might try an instrument and then stop. If that's what happened, adult musicians could have larger connections even if practicing music hadn't enlarged them. The especially striking difference among musicians who started young doesn't settle that problem. Those children might have started with the advantage too.
What we’re looking for
The author concludes that training causes physical changes in the brain. For the necessary-assumption question, I'd look for a defense against our objection: the musicians didn't tend to have the larger connection before training began. We need that initial difference ruled out as the explanation for the comparison, not a claim that every musician's brain is identical.
Working the answers
- ACorrect
Before training, the musicians' connections did not tend to be larger than those of nonmusicians the same age. That blocks the alternative we were considering: perhaps the brain difference came first and helped determine who became a musician.
If the future musicians already tended to have larger connections, finding a difference later wouldn't establish that training produced it. A is necessary to this inference from the group comparison. It doesn't, by itself, prove that training caused the difference; defending against this objection isn't the same as eliminating every possible objection.
- B
The argument says training causes changes, particularly when started young. It doesn't require late-life training to have no effect. Both early and late training could cause changes, with earlier training producing a more striking difference. B needlessly rules out the later effect.
- C
Musicians can differ from one another. One could have a moderately large connection and another a much larger one, while the group average still exceeds the nonmusicians' average. The argument needs an explanation of the difference between groups, not uniformity within the musician group.
- D
An average is not a rule about every individual. Some nonmusician could have a larger connection than some musician without overturning the comparison of averages. D demands that every musician exceed every nonmusician, which the causal argument doesn't need.
- E
Nonmusicians could have done other activities that stimulated some growth. Perhaps an activity such as studying mathematics had that effect; that's a hypothetical, not a fact we're assuming about brains. Musical training could still produce additional growth in musicians. The author needn't assume that nothing in the other group's childhood affected this part of the brain.
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