LSAT Explanation PT 44, S2, Q5: The corpus callosum—the thick band of
LSAT Question Stem
Which one of the following is an assumption on which the argument depends?
Logical Reasoning Question Type
This is a Necessary Assumption question.
Correct Answer
The correct answer to this question is A.
LSAT Question Complete Explanation
Let's first analyze the argument in the passage and identify its structure. The argument presents the following information:
Premise: The corpus callosum of a musician is, on average, larger than that of a nonmusician, with particularly striking differences when comparing adult musicians who began training around age seven to adult nonmusicians.
Conclusion: Therefore, musical training, particularly when it begins at a young age, causes certain anatomic brain changes.
The author is concluding that there is a causal relationship between musical training and anatomic brain changes. However, the evidence provided only shows a correlation between the two variables. To better understand this, let's use a simple example: Imagine a study that finds people who wear glasses tend to read more books than those who don't. We cannot conclude that wearing glasses causes people to read more books, as there might be other factors at play, such as poor eyesight leading to both wearing glasses and reading more books.
An "Evaluate" question for this argument could be: "Is there any other factor that could influence the size of the corpus callosum in both musicians and nonmusicians?"
Now, let's discuss the answer choices for the question, which asks us to identify an assumption on which the argument depends.
a) The corpora callosa of musicians, before they started training, do not tend to be larger than those of nonmusicians of the same age.
- This is the correct answer choice. If we negate this statement, it would say that musicians' corpora callosa were already larger before they started training, which would weaken the argument. Therefore, the argument assumes that the corpora callosa of musicians and nonmusicians were initially similar in size.
b) Musical training late in life does not cause anatomic changes to the brain.
- This answer choice is not necessary for the argument, as the argument focuses on the effect of early musical training on brain anatomy. The argument does not assume that late-life musical training has no effect on the brain.
c) For any two musicians whose training began around the age of seven, their corpora callosa are approximately the same size.
- This answer choice is not necessary for the argument, as the argument compares musicians to nonmusicians. The size of the corpus callosum among similarly trained musicians is not relevant to the argument.
d) All musicians have larger corpora callosa than do any nonmusicians.
- This answer choice is not necessary for the argument, as the argument specifically states that the corpus callosum of a musician is, on average, larger than that of a nonmusician. The argument does not assume that all musicians have larger corpora callosa than any nonmusicians.
e) Adult nonmusicians did not participate in activities when they were children that would have stimulated any growth of the corpus callosum.
- Negating this answer choice would result in the statement, "adult nonmusicians did participate in stimulating activities when they were children." This negated version does not weaken the author's argument, so this choice does not reflect an assumption required by the argument.
In conclusion, the correct answer choice is (a), as it represents an assumption on which the argument depends.