PrepTest 125, Section 4, Question 7
In an experiment, biologists repeatedly shone a bright(79 more words not shown)
Which one of the following(7 more words not shown)
- AAll sea snails(16 more words not shown)
- BSea snails are(15 more words not shown)
- CThe sea snail(20 more words not shown)
- DThe appearance of(15 more words not shown)
- ETensing of the(16 more words not shown)
Reading the argument
Did the snail learn to tense up when the light appeared, or did light make it tense up all along?
At first, the researchers shine the light and shake the tank together. Two things happen at once, so the snail's response doesn't tell us which one caused it to tense its foot. Later, the researchers use the light without the shaking, and the snail still tenses up. That fits a learned association, but it also fits a snail that would have reacted to the light before any training.
Think of pairing a bell with food until an animal begins reacting to the bell alone. To show that the pairing taught it something, we need to distinguish the new response from one it already had. The same concern applies to the snail. What did light alone do before these repetitions?
There's another possible concern: perhaps the snail associated the researchers' arrival with the shaking. The light might not be the cue that mattered.
What we’re looking for
But the necessary-assumption question doesn't require one answer to eliminate every possible objection. We need something the argument depends on. Ruling out an ordinary, unlearned reaction to the light would address the most basic problem with calling this response learned.
Working the answers
- A
The conclusion concerns this snail, not every sea snail. Other snails could react differently to turbulence while this one learned the proposed association. We don't need a universal rule about the species to explain this individual animal's behavior.
- B
How often snails encounter bright lights is different from how this snail ordinarily responds to one. A snail could encounter light often and still learn a new association during the experiment. Or it could rarely encounter light and tense up naturally whenever it does. B doesn't supply the baseline response we need.
- C
A representative snail would matter if we were using this experiment to draw a conclusion about the species. We aren't. This snail could be unusual in many ways and still learn to associate the light with the shaking. Its similarity to other snails is not required for that conclusion.
- DCorrect
Ordinarily, light alone would not produce this response. Without that assumption, the snail's behavior after the repetitions could be exactly what it would have done beforehand. The evidence would give us no basis for saying the pairing taught it to associate light with shaking. D removes that problem; it doesn't claim to settle every other question about the experiment.
- E
Read what the response is to: ocean turbulence. Tensing up in response to turbulence could be instinctive while tensing up in response to light is learned. Those can both be true. The argument depends on what the snail learned about the light, not on whether its original reaction to moving water was itself learned or instinctive.
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