Researchers conditioned a group of flies to associate a particular odo

Question

Researchers conditioned a group of flies to associate a particular odor with a weak electric shock. Twenty-four and forty-eight hours later the researchers conducted tests on the flies, both individually and in groups, to determine whether the flies retained the conditioning. When tested individually, the flies were significantly less likely to avoid areas marked with the odor. The researchers hypothesized that in the presence of the odor, a fly that retains the conditioned association gives off an alarm signal that arouses the attention of any surrounding flies, retriggering the association in them and thereby causing them to avoid the odor.

The researchers' hypothesis requires which of the following assumptions?

The researchers' hypothesis requires which of the following assumptions?

A. The flies do not give off odors as alarm signals.
B. Flies that did not avoid the odor when tested individually were not merely following other flies' movements when tested in a group.
C. Flies that did not avoid the odor when tested individually were less likely than the other flies to avoid the odor when tested in a group.
D. Prior to their conditioning, the flies would likely have found the odor used in the experiment to be pleasant.
E. An electric shock was used during the flies' conditioning and during the later tests.

CR47931.01

GMATIntensive · Accepted Answer

The Story     
 Researchers conditioned a group of flies to associate a particular odor with a weak electric shock.  - A group of flies were conditioned to associate an odor with an electric shock.

Twenty-four and forty-eight hours later the researchers conducted tests on the flies, both individually and in groups, to determine whether the flies retained the conditioning.  - The flies were then tested to check whether they retained the conditioning. Two sets of tests were conducted - 24 and 48 hours after the conditioning. The flies were tested individually and in groups.

When tested individually, the flies were significantly less likely to avoid areas marked with the odor.  - Individual flies were less likely to avoid odor-marked areas. (“less likely” indicates a comparison. Less likely than whom? Logically, individual flies were less likely to avoid odor-marked areas than flies in groups.)

The researchers hypothesized that in the presence of the odor, a fly that retains the conditioned association gives off an alarm signal that arouses the attention of any surrounding flies, retriggering the association in them and thereby causing them to avoid the odor.  - Based on their findings (previous statement), the researchers have come up with a hypothesis. They hypothesize that a fly that still has the conditioning gives off an alarm signal in the presence of the odor. This alarm signal grabs the attention of the surrounding flies. The surrounding flies’ association gets retriggered. And that’s why the other flies in the group also avoid the odor. (A fairly long-ended hypothesis.)

Gist:  
Flies in groups avoid odor-marked areas more than individual flies. Why? The researchers came up with a hypothesis.
A fly that retains the association gives off an alarm signal.
An alarm signal leads to retriggering of the association. A retriggered association leads to flies’ avoiding odor.

The Gap     
 1. What if the other flies avoided the odor-marked area simply because a fly gave off an alarm signal and they sensed something was amiss. The other flies need not have had the association retriggered in them. 
2. What if there wasn’t even an alarm in the first place? Or, even if there was an alarm, what if the flies did not change course because of an alarm? There could have been some other reason that led to the other flies’ change of course.

The Goal     
We have already discussed a couple of gaps in the above section. Each pertains to an assumption. There could, of course, be other assumptions as well.

The Evaluation     
 A. The flies do not give off odors as alarm signals.  
  Incorrect  . Does the argument rely on what KIND of alarm signals the flies give off? Not at all. Moreover, even if the flies did give off odors as alarm signals, the hypothesis still holds as is.

B. Flies that did not avoid the odor when tested individually were not merely following other flies' movements when tested in a group. 
  Correct  . This is in line with the second gap we discussed above. The hypothesis requires this assumption. If flies avoided the odor simply because they were following other flies, the researchers’ hypothesis falls flat. This would mean that the other flies did not change their course because of an alarm signal. They were simply following other flies when tested in groups.

C. Flies that did not avoid the odor when tested individually were less likely than the other flies to avoid the odor when tested in a group. 
  Incorrect  . Let’s first understand what this statement is saying. Let’s say that ‘flies “did not avoid” the odor’, implies flies flew into the odor. And, let’s try to tackle the way-too-many negatives in the sentence. We can rewrite the statement as: 
Flies that flew into the odor when flying individually were more likely to fly into the odor when flying in groups than flies that avoided the odor when flying individually.

The sentence is essentially dividing the flies into two segments and then comparing the likelihoods of the two segments to fly into the odor. Now, we can understand that the flies that flew into the odor when flying individually needed some external trigger (such as an alarm signal) to avoid the odor. But after they got the trigger, do we really care whether they avoided more, less, or equally the odor compared with the other segment of flies? The argument is based on an overall likelihood of flies to fly into the odor, not likelihoods of different segments of flies. Thus, this option does not have an impact.

D. Prior to their conditioning, the flies would likely have found the odor used in the experiment to be pleasant. 
  Incorrect  . How flies found the odor prior to the conditioning is irrelevant to the hypothesis.

Even if somehow we do not see the irrelevance, we can see that it is not necessary for the flies to have found the odor pleasant prior to the conditioning for the hypothesis to hold. The hypothesis would hold as is even if the flies did not find the odor pleasant before their conditioning.

E. An electric shock was used during the flies' conditioning and during the later tests. 
  Incorrect  . We already know that an electric shock was used during the flies’ conditioning. Thus, the new information that this option gives is that an electric shock was used during the later tests as well. If in the later tests an electric shock was used, we start to wonder whether the flies responded the way they did because of their conditioning towards the odor, or because of the electric shock used? If an electric shock was used during the later tests, it is possible that, while in groups, a fly that got the shock gave an alarm signal to others. In this case, the fly that gave off the alarm signal had not retained any conditioned association and the alarm signal just warned the other flies and not retriggered their association. Thus, this option rather weakens the argument and thus cannot be an assumption.

Additional Notes

SC Notes:

Let’s break down the last sentence of the passage to understand the modifiers better.

The researchers hypothesized that (Main Clause)
 1. in the presence (Prepositional Phrase modifying the verb “gives off”)
  of the odor, (Prepositional Phrase modifying “presence”) 
2. a fly (Subject of the ‘that’ clause)
  that retains the conditioned association (Another ‘that’ clause modifying ‘fly’)  
3. gives off an alarm signal (“gives off”: verb for the subject ‘fly’
  that arouses the attention (‘that’ clause modifying ‘alarm signal’)
  of any surrounding flies, (Prepositional Phrase modifying “attention”) 
 retriggering the association in them (Comma+Verb-ing modifier modifying the previous clause ‘that arouses…’) 
 and thereby causing them (Comma+Verb-ing modifier modifying the previous clause ‘that arouses…’)
  to avoid the odor. (Infinitive Phrase modifying “causing”)

If you have any doubts regarding any part of this solution, please feel free to ask.

gmatt1476 · Answer

Official Explanation

Argument Construction

This question asks us for an assumption required by the hypothesis.

The researchers noted that the flies that had been conditioned to associate a particular odor with an electric shock were much less likely to avoid the odor when they were tested individually than when they were tested as a part of a group.

Based on this fact, the researchers hypothesized that the flies that had retained the conditioning would give off an alarm when they detected the odor. This alarm would then retrigger the association among the other flies, leading them to avoid the odor.

We must consider whether there is some other fact that could explain why the flies were more likely to respond to the odor in a group than when they are alone. If there were, that alternative explanation would severely call into question the researchers' hypothesis. The hypothesis therefore requires that any such alternative explanation be false.

A. It is possible that the flies do in fact give off odors as an alarm signal. Because the nature of the flies' alarm signal is not specified by the hypothesis, this is entirely consistent with the hypothesis and would not undermine it. Therefore, the hypothesis does not require that flies do not give off odors as alarm signals.

B. Correct. Suppose that the flies that did not avoid the odor when tested individually were more likely to avoid the odor when in groups. This may be simply because these flies were following the movements of the flies that were triggered. That is, the signal did not cause the other flies' reactions. Instead, the movements of the triggered flies did. It follows that this possibility must be ruled out in order for the hypothesis to be plausible, and this answer choice does precisely that.

C. The hypothesis would actually be more plausible if this statement were false. That is, the hypothesis would be more plausible if the flies that did not avoid the odor when tested individually were just as likely, when they were tested in a group, to avoid the odor as the other flies in the group.

D. The hypothesis is perfectly compatible with the assumption that, prior to their conditioning, the flies were entirely indifferent to the odor.

E. The principle of association—that the shock is associated with the odor even when the shock itself is not present—actually requires that this statement be false.

The correct answer is B.

ArtVandaley · Answer

B.IF theyy were merely following others, the conclusion stands invalid.

gvij2017 · Answer

Luckily I got it correct. But I appreciate detailed explanation for selecting B among other options.

syedmohammad211 · Answer

gvij2017

The reason why B is the correct answer is pretty straightforward:

"  The researchers hypothesized that in the presence of the odor, a fly that retains the conditioned association gives off an alarm signal that arouses the attention of any surrounding flies, retriggering the association in them  "

As is evident from the above text that the hypothesis was based on the ability of the flies to detect the alarm signals given by other members of their group.

By assumption negation option B says that the flies were merely following other flies and did not infact detect signals. This option throws the hypothesis out the window if negated , hence is the correct answer

santorasantu · Answer

Understanding the sentence: 
Researchers basically trained a group of flies to connect with a particular smell with an electric shock. After some hours, researchers tested the flies both individually and in groups. This test was done to determine if the flies still retained the training. 
Individual test result: Flies would not avoid the areas with smell
Theory of researchers: When smell is there, a fly that is trained sends a signal to the other flies like a warning and these flies would then avoid the smell.

A. The flies do not give off odors as alarm signals.
--> This answer is irrelevant on the assumption of the researchers

B. Flies that did not avoid the odor when tested individually were not merely following other flies' movements when tested in a group.
This is the right assumption that makes the hypothesis/theory stand. If the flies tested in the group are merely following the movements of the other flies, then the signal thing which researchers assume does not hold.
Therefore, this is the right assumption.

C. Flies that did not avoid the odor when tested individually were less likely than the other flies to avoid the odor when tested in a group.
This does not tell anything as the statement is trying to compare the flies that did not avoid individually vs other flies in the group that would avoid the smell.

D. Prior to their conditioning, the flies would likely have found the odor used in the experiment to be pleasant.
Irrelevant as the kind of smell is not discussed in the passage

E. An electric shock was used during the flies' conditioning and during the later tests.
Also not relevant for the hypothesis as the theory basically deals with the signal sent by induvial flies

Researchers conditioned a group of flies to associate a particular odor with a weak electric shock. Twenty-four and forty-eight hours later the researchers conducted tests on the flies, both individually and in groups, to determine whether the flies retained the conditioning. When tested individually, the flies were significantly less likely to avoid areas marked with the odor. The researchers hypothesized that in the presence of the odor, a fly that retains the conditioned association gives off an alarm signal that arouses the attention of any surrounding flies, retriggering the association in them and thereby causing them to avoid the odor.

The researchers' hypothesis requires which of the following assumptions?

The researchers' hypothesis requires which of the following assumptions?

A. The flies do not give off odors as alarm signals.
 B. Flies that did not avoid the odor when tested individually were not merely following other flies' movements when tested in a group. 
C. Flies that did not avoid the odor when tested individually were less likely than the other flies to avoid the odor when tested in a group.
D. Prior to their conditioning, the flies would likely have found the odor used in the experiment to be pleasant.
E. An electric shock was used during the flies' conditioning and during the later tests.

aniket16c · Answer

Passage explanation:
Let us consider there are 6 flies. Now researches trained the flies such that whenever they smell a particular odor (say smell of a nice pie), the flies would associate that smell with a shocking sensation and tend to avoid that area.

Now they conducted two types of tests:
1. Lets say they kept a freshly baked pie in an area. Now out of 6 flies, say 2 flies (A and B) went and sat on pie. They did not recall the shocking sensation on smelling the pie. A and B sat on pie in 7 out of 10 trials and rest sat on pie only in 2 out of 10 trials

2. Now they conducted a similar test with 6 flies. The two flies, A and B, sat on the pie only in 4 out of 10 trials.

Hypothesis: The other flies(other than A and B) sent an alarm signal when they smelled the pie. This alarm signal triggered a shock response in A and B, and hence A and B avoided sitting on the pie

Question type - Assumption
It could be a case, that the other flies did not send a signal. Instead in a group, there generally an alpha fly who the other flies obey. So consider a case, that the shock response was triggered in the alpha fly and it simply moved away from pie. Thus the other flies also followed the fly and moved away from the pie. This suggests that there was no alarm signal.

A. The flies do not give off odors as alarm signals.
The argument does not mention the form of alarm signal. It could be a wink, an odor, a sound anything. So this option does not affect the conclusion

B. Flies that did not avoid the odor when tested individually were not merely following other flies' movements when tested in a group.
Exactly what we thought. It the flies were merely imitating the alpha fly the alarm was never triggered, the shock response was never generated and the hypothesis falls apart  Correct answer

C. Flies that did not avoid the odor when tested individually were less likely than the other flies to avoid the odor when tested in a group.
This suggests that the flies A and B, sat on pie less number of times than the other flies in the case when tested in the group than when tested in individually. Okay good. That is supporting the argument but it is not an assumption. The information does not shed any light on why they sat less number of times. Is it because they were merely following the leader or the shock sensation was triggered.

D. Prior to their conditioning, the flies would likely have found the odor used in the experiment to be pleasant.
This is irrelevant. We are trying to find if the odor triggers the sensation. The type of odor does not affect the argument

E. An electric shock was used during the flies' conditioning and during the later tests.
This means that we do not know if the results of the action were because of odor triggering the sensation or because of the physical shocks.

Please correct me if I have misunderstood anything!

TrungTiger · Answer

Dear  GMATNinjaTwo

I was not able to pick a right one between Choice B&C because I did not understand what they said. Now It seems that I can understand what they wrote:

Choice B:  Flies that did not avoid the odor when tested individually were not merely following other flies' movements when tested in a group.
mean:
Flies (let say X) that did not avoid the odor  when tested individually were merely  following other flies' movements 
BUT
Flies X  when tested in a group were NOT merely  following other flies' movements

Choice C:  Flies that did not avoid the odor when tested individually were less likely than the other flies to avoid the odor when tested in a group.
mean:
Flies (let say X) that did not avoid the odor  when tested individually were likely  the other flies to avoid the odor
BUT
Flies X  when tested in a group were LESS likely  than the other flies to avoid the odor.

I therefore pick B.
Please correct me if I am wrong in my interpretation from the original statement.

mSKR · Answer

It seems you are trying to make sense but have not understood completely. I guess you might have read these options several times and then trying to figure out what are they saying. Then connect with the right answer to make sense out of it. 
In this way, you won't be able to use this learning in next question .
( btw, this is my guess based on some hints: E.g. you said: Flies (let say X) that did not avoid the odor  when tested individually were merely   following other flies' movements  . When individual why would they follow other flies' movements. It makes no sense)

So how to make simple understanding and avoid multiple times reading.

Let's see what C says first: 
I know it's a bit confusing in my reading. It wil be more confusing if you try to get everthing in first shot. 
Here is : How i tacked its meaning:
Flies that did not avoid the odor -- which flies? ok the flies that actually got the shock
when tested individually --ok so these flies were tested invidually. 
were less likely than -comapre with whom? I guess the ones that didn't get shock
the other flies -yup as i guessed, but comparison in what?
to avoid the odor when tested in a group. --> i see, to avoid the shock when these flies were tested in group.
So it means:
2 flies: X. flies that get shock Y. the flies that didn't shock .
X are less likely to avoid shock when tested in group. 
I see, so when flies are in group , these flies still get shock. 
So when the flies are in group, ,  retriggering the association in them and thereby causing them to avoid the odor.  doesn't work.
It mean it weakens the claim.

Now I can analyze more based on my logic reasoning:
If these flies could avoid shock when in group then it would have strengthen the claim. 
( or i can say opposite of C: flies when in group are equally likely to avoid odour when tested in group with the flies that did avoid the odour. 
In other words , opposite of B says: X and Y are equally likely to avoid shock when in group. But when X and Y are individually then X is less likely to avoid ( or can say X is more likely to get shock)

I hope you can handle B now.

You try it again what B says.

FOr your reference here is the meaning:
X when tested individually were not just following movements . 
X--> that did not avoid the odor
Think: If they were not just following and still they didn't get shock. So it maybe possible that these flies avoid the odor because other flies might have helped due to retriggering of the association. 
So now B make sense and you can see how it fits in the argument.

Key point is: Take the meaning and use logic in your own words. Forget the wording and just see how logic fits in the argument.

I hope it was helpful:)

jabhatta2 · Answer

hi  avigutman  - a quick question. While I agree that (B) is the OA (because the argument is assuming, there is NO ALTERNATIVE EXPLANATION to the hypothesis proposed by the author)

As part of my pre-thinking, I was actually focussed on coming up with "Things that need to be true" for the  hypothesis to be true . So for example -

I think (option F)   also   is   another   necessary assumption in order to conclude the hypothesis.

(F) is different from (B) because (F) is focussed on the author's hypothesis whereas (B) is focussed on "other hypothesises"

Just curious on your thoughts

avigutman · Answer

Let's see,  jabhatta2 : the hypothesis suggested that 
Does that require that flies can communicate with each other?
It requires that flies be capable of giving off an alarm signal, and that flies be capable of noticing said alarm signal. I'm not sure this rises to the level of "communicating with one another". If it does, then yeah, (F) is required. I can't imagine the GMAT offering such an answer choice, though.

agrasan · Answer

Hi  GMATNinja   IanStewart   KarishmaB   egmat

Option B was spot on to me when I read the passage, however, just to eliminate all options, I am facing a problem with option C.

My understanding is - option C is irrelevant as its negated version is "Flies that did not avoid the odor when tested individually were EQUAL OR MORE likely than the other flies to avoid the odor when tested in a group", and conclusion can still follow as original C/negated C is just a comparison and doesn't provide us necessary info for researchers' hypothesis to hold true.

Please correct me if I am wrong or if there is a simple logic without negation to understand this better.

KarishmaB · Answer

Premises:

Researchers conditioned a group of flies to associate a particular odor with a weak electric shock. 
Later the researchers conducted tests on the flies, both individually and in groups, to determine whether the flies retained the conditioning. 
When tested individually, the flies were significantly less likely to avoid areas marked with the odor.

Hypothesis:   The fly that remembers (smart fly) signals the others (slow ones).

What is the assumption here?

A. The flies do not give off odors as alarm signals.
  
We don't know what kind of an alarm signal the flies give. They could give out special odors indicating danger or emit a sound or flap their wings with a particular frequency etc. There is no assumption made about the means of sending out the alarm signal.

B. Flies that did not avoid the odor when tested individually were not merely following other flies' movements when tested in a group.
  
The researcher is concluding that the smart fly gives a signal to the slow flies to stay away from the odor. That is why in a group, they stay away from odors but when alone, they fly everywhere. To conclude this, it must be true that the slow flies are not just following the smart flies around. What if the smart flies gave no signal and the slow ones just followed them and since the smart ones avoided odor areas, the slow ones also avoided them in the group. This would explain the observation in a very different way and then we will not be able to hypothesize what the researchers have hypothesized. Correct.

C. Flies that did not avoid the odor when tested individually were less likely than the other flies to avoid the odor when tested in a group.
  
This option says that in a group, slow flies were less likely than smart flies to stay away from the odor. It is talking about observation during the experiment. It is written on the same lines as the result of the experiment: When tested individually, the flies were significantly less likely to avoid areas marked with the odor.

We don't need this to be true for our conclusion. We are given that as a group, they were avoiding the odor places much more. 
In the group, perhaps the slow flies were copying the very smart ones or got signal from them and hence completely avoided the odors while the smart ones avoided them but not completely. Perhaps the slow flies avoided odors as much as the smart ones. Perhaps the slow flies stayed away from the odors a bit more than before but not as much as the smart ones. The point is that whether the slow flies paid full heed to the signal given or to a large extent or somewhat only, is irrelevant to the conclusion. We know that there was a marked difference in their behavior in the group than their behavior individually.

D. Prior to their conditioning, the flies would likely have found the odor used in the experiment to be pleasant.

Irrelevant. They were conditioned and the argument revolves around what happened afterwards.

E. An electric shock was used during the flies' conditioning and during the later tests.
  
Electric shock was used during the flies' conditioning, not later tests. Ignore.

Answer (B)

Researchers conditioned a group of flies to associate a particular odo

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Researchers conditioned a group of flies to associate a particular odo

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