Normally, the pineal gland governs a person's sleep-wake

Question

Normally, the pineal gland governs a person's sleep-wake cycle by secreting melatonin in response to the daily cycle of light and darkness as detected by the eye. Nonetheless, many people who are totally blind due to lesions in the visual cortex of the brain easily maintain a 24-hour sleep-wake cycle. So the neural pathway by which the pineal gland receives information from the eye probably does not pass through the visual cortex.

For purposes of evaluating the argument it would be most useful to establish which of the following?

(A) Whether melatonin supplements help people who have difficulty maintaining a 24-hour sleep cycle to establish such a pattern

(B) Whether the melatonin levels of most totally blind people who successfully maintain a 24-hour sleep-wake cycle change in response to changes in exposure to light and darkness

(C) Whether melatonin is the only substance secreted by the pineal gland

(D) Whether most people who do not have a 24-hour sleep-wake cycle nevertheless have a cycle of consistent duration

(E) Whether there are any people with normal vision whose melatonin levels respond abnormally to periods of light and darkness

ChrisLele · Accepted Answer

Normally, the pineal gland governs a person's sleep-wake cycle by secreting melatonin in response to the daily cycle of light and darkness as detected by the eye. Nonetheless, many people who are totally blind due to lesions in the visual cortex of the brain easily maintain a 24-hour sleep-wake cycle. So the neural pathway by which the pineal gland receives information from the eye probably does not pass through the visual cortex.

For purposes of evaluating the argument it would be most useful to establish which of the following?

The argument: the pineal gland secretes hormones according to changes in light and dark. Blind people still react to normal sleep-wake cycle, therefore the pineal gland must not go through the visual cortex. We need an extra piece of information that will help us determine the soundness of the argument.

(A) Whether melatonin supplements help people who have difficulty maintaining a 24-hour sleep cycle to establish such a pattern

Here we are only dealing with people whose sight has not been impaired. In order to evaluate the argument, we need to understand how blind people's pineal glands react to changes in light.

(B) Whether the melatonin levels of most totally blind people who successfully maintain a 24-hour sleep-wake cycle change in response to changes in exposure to light and darkness

If the pineal gland is indeed responsible for mediating the sleep wake cycle, then blind people have to be responding to light and dark (that's how the pineal gland works). True, it is not via their visual cortex, but somehow the pineal gland of blind people must be able to detect light and darkness. Therefore (B) helps us determine that blind people do notice changes in light and darkness. If they didn't, then we could not conclusively say that the pineal gland is responsible for their ability to maintain sleepless, and we could not conclude that the pineal gland does not pass through the visual cortex.

(C) Whether melatonin is the only substance secreted by the pineal gland

This is tempting, but even if we find out that there is another substance that neither strengthens nor weakens the contention that the pineal gland bypasses the visual cortex.

(D) Whether most people who do not have a 24-hour sleep-wake cycle nevertheless have a cycle of consistent duration

Here the focus is shifted away from blind people and to those who do not have normal sleep wake cycle.

(E) Whether there are any people with normal vision whose melatonin levels respond abnormally to periods of light and darkness

Again, a shift away from blind people. That is we are trying to understand how the pineal glands of blind people work.

Tough question

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samusa · Answer

Situation-

Daily cycle of ligth and darkness is detected by eye.Pineal gland maintains sleep wake cycle.The pineal gland secrets melatonin in response to this cycle of detection to maintain sleep wake cycle!
BUT blind people ( due to lesions in the visual cortex) also maintain the same rhythm or sleep wake cycle.

Conclusion-

So the neural pathway by which the pineal gland receives information from the eye    probably   does not pass through the visual cortex.

Evaluation-

The author is not sure about the mechanism.He has given us a PROBABLE explanation. We need to help him confirm or reject his conclusion.
We need to make it more probable or less probable.
We need to a help him find a piece of information that will help to find whether the neural pathway passes through visual cortex .

POE

(A) Whether melatonin supplements help people who have difficulty maintaining a 24-hour sleep cycle to establish such a pattern

We do not need to comfirm whether melatonin helps to maintain a 24 hour sleep wake cycle.We already know for a fact that melatonin does affect the sleep wake cycle.
Also the main point of the argument is about people who maintain normal sleep cycle.

(B) Whether the melatonin levels of most totally blind people who successfully maintain a 24-hour sleep-wake cycle change in response to changes in exposure to light and darkness

A yes answer to the above option will help confirm that pineal gland does respond to light and darkness cycles NOT detected by the eye.Hence, the neural pathway does not pass through the visual cortex.
A no answer to the above option will help confirm that the neural pathway does pass through the visual cortex.

(C) Whether melatonin is the only substance secreted by the pineal gland

That is besides the point. It may release many other substances but we are only interested in the melatonin and the associated mechanism.

(D) Whether most people who do not have a 24-hour sleep-wake cycle nevertheless have a cycle of consistent duration

The duration of the cycle is not so much of an issue as is the mechanism behind the sleep wake cycle.

(E) Whether there are any people with normal vision whose melatonin levels respond abnormally to periods of light and darkness

This does no help us understand the mechanism or the pathway behind the sleep cycle.The reasons for abnormal levels may be varied.
This option just tells us that melatonin levels change with light and darkness but does not answer whether the neural pathway passes through the visual cortex.

Hope the above helps!

manimgoindown · Answer

1. Normal-Pineal gland releases melatonin in response to day and night
2. But wait, Blind people with lesions still mantain a consistent sleep cycle too
Conclusion: The pathway to get dark/light info from the eye skips the visual cortex 
Key inferences/implications: 1. meltaonin regulates our sleep pattern in both blind and 'can see' people 2. Even in 'can see' people the pineal gland's pathway to producing melatonin skips the visual cortex

Pre-think- I see one possible and likely problem in this already, what if there was another way for the body to produce that melatonin consistently other than from light and darkness information?

Another important thing to notice that would have practical applications. None of the answer choices mention anything about a visual cortex, so even more justification not to not look to strengthen that link to any other part of the problem. Let's just focus on melatonin production then

A Meltaonin regulates sleep patterns. It's a fact in the prompt. We shouldn't doubt this which is what A is trying to do
B 
C All we know about meltaonin is it regulates our sleep and is the only relevant hormone in the prompt. We could care less about other hormones OOS
D Prompt only talks about 24 hour sleep cycle OOS
E What does a spike or lack of meltanin have to do with anything? I'm not a scientist and this prompt doesn't tell me what an abundance or dearth of melatonin will do to my sleep cycle. We just want to know why a certain consistency of meltonin helps keep a regulated sleep pattern in both blind and 'can see' people

POE B

Let's look at B
(B) Whether the melatonin levels of most totally
blind people who successfully maintain a
24-hour sleep-wake cycle change in response to
changes in exposure to light and darkness

This question would answer the pre-think I had. If it is true that, say blind people can get means to produce meltatonin without detecting light, somehow regularly,they can still mantain a sleep cycle. Also agrees with prompt and constricts it to blind people and 24 hour sleep cycle. Doesn't make the errors of other answer choices.

manojkumarmatala · Answer

hidden assumption is: Blind people are similar to normal people when it comes to melatonin secretion.

B: Correctly evaluates this assumption by gauging melatonin levels when blind are expose different conditions. If they are respond then they are similar to normal people.

abrakadabra21 · Answer

Premise : normal person -> melatonin govern sleep - wake cycle. --> pineal gland
blind peopple : leison in visual cortex -> still have functioning sleep-wake cycle.

conclusion : ok, then visual cortex doesn't come in between of melotinin path.

Prethinking :

1> what if blind people develops different pathway then normal path of melotinin ? as it's given (in normal condition)

(A) Whether melatonin supplements help people who have difficulty maintaining a 24-hour sleep cycle to establish such a pattern => we can negate this as comparison is between normal and blind people. not anything about people who have difficulty in sleeping.

(B)   Whether the melatonin levels of most totally blind people who successfully maintain a 24-hour sleep-wake cycle change in response to changes in exposure to light and darkness - so something changes in case of blind people, aligned with prethinking.  
 
(C) Whether melatonin is the only substance secreted by the pineal gland - not relevant

(D) Whether most people who do not have a 24-hour sleep-wake cycle nevertheless have a cycle of consistent duration - not the point here.

(E) Whether there are any people with normal vision whose melatonin levels respond abnormally to periods of light and darkness - not the point here.

felippemed · Answer

Depending on the stage of Critical Reasoning, it is good to try to think like a test maker.

by P.O.E. process

a)  Changes of m also change S-W cycle  ------> This option doesn't tackle the connection urging for an explanation (L-D) captured by P.G.  OUT!

c)  P.G. produces element "X"  ----> who guarantees this element is an alternate explanation for S-W cycle regulation?  OUT!

d)  Duration of S/W Cycle vary with/out eye   -----> This option doesn't tackle the connection urging for an explanation (L-D) captured by P.G.  OUT!

e)  One element with eye varies melatonin abnormally regardless Light and Dark   --------->  One single element can't be representative of a whole hypothesis  This test could be helpful only if constantly we get this results from other individuals and if blind individuals also present the same result  OUT!

The three reasons for why choosing B
 
1st) The main point of the hypothesis, which is the connection between Light-Darkness and P.G., is being fully assessed by the test. From the diagram below it is easy to see why this is the best option.

2nd) The test is being conducted in a controlled group (blind people), which would dismantle the hypothesis if proved the other way round. (the melatonin doesn't change in the abscence of an eye)

3rd) Differently from e), the question considers many individuals and not only one to be tested

Here is the logic.

Hope it helps

adkikani · Answer

Hi Experts, 
Can you help me to understand pre-thinking and underlying assumption to evaluate answer choices?
I tend to make statements in arguments causal to help bridge gap between premises and conclusion in order to find assumptions while attempting evaluate Q type.
For eg: 
cause: variations in response to daily light as detected by eye
effect: PG gland governs person's sleep cycle by secreting M.
Final conclusion: NP by which PG receives information from eye does not pass through VC.
Supporting premise for conclusion: People who are totally blind due to defect in VC maintain 24 hours sleep cycle. This premise counters general principle in first sentence.

GMATNinjaTwo · Answer

adkikani , that is a very thorough analysis of the passage! As you've written, the author is saying that the eye detects the daily cycle of light and darkness and that the pineal gland secretes melatonin in response to that cycle. The author than cites the example of totally blind people who still maintain a 24-hour sleep-wake cycle despite having lesions in the visual cortex to conclude that the information sent from the eye to the pineal gland probably does not pass through the visual cortex (since the visual cortex has lesions and thus is most likely defective). This argument rests on the assumption that the sleep cycle of those totally blind people is dependent on the information from the eye, but what if that weren't the case? What if there was some other source of information regulating melatonin levels in those blind people? Or that the sleep cycles of those totally blind people were regulated by something other than melatonin? In that case, those blind people could maintain a 24-hour sleep-wake cycle even if the information from the eye does pass through the visual cortex (since, in that case, the information from the eye is not required). If the evidence suggested by choice B were established, we could better assess the validity of that assumption.

I hope that helps!

madhukaramar · Answer

Normally, the pineal gland governs a person's sleep-wake cycle by secreting melatonin in response to the daily cycle of light and darkness as detected by the eye. Nonetheless, many people who are totally blind due to lesions in the visual cortex of the brain easily maintain a 24-hour sleep-wake cycle. So the neural pathway by which the pineal gland receives information from the eye probably does not pass through the visual cortex.

What are we looking for - So, due to the lesions in the visual cortex , blind person can't detect the light , but still maintains the sleep and wake cycle. It is a fact that pineal gland secretes something to maintain the sleep/wake cycle. So we are thinking that pineal gland must have received the info of light/darkness by a way not via visual cortex (which is blocked in blind folks). So can we looking for details which can give us answer as yes / no.

For purposes of evaluating the argument it would be most useful to establish which of the following?

(A) Whether melatonin supplements help people who have difficulty maintaining a 24-hour sleep cycle to establish such a pattern
-- Irrelevant. We are not talking about supplements.

(B) Whether the melatonin levels of most totally blind people who successfully maintain a 24-hour sleep-wake cycle change in response to changes in exposure to light and darkness
-- If we say Yes - We can infer yes there must a way to pineal gland which doesn't go via visual cortex, which is blocked.
-- If we say No - We can infer there is no way. The only way is by pineal gland.This is the reason melatonin levels are not getting changed.There must be something else, which is controlling the sleep-wake cycle.
-- So this is the answer.

(C) Whether melatonin is the only substance secreted by the pineal gland
-- Even if there are other substances, there is no relation shown with sleep-wake cycle, so Irrelevant.

(D) Whether most people who do not have a 24-hour sleep-wake cycle nevertheless have a cycle of consistent duration
-- Irrelevant.

(E) Whether there are any people with normal vision whose melatonin levels respond abnormally to periods of light and darkness
-- There can be multiple reasons of this issue. Out of scope.

CAMANISHPARMAR · Answer

Official Explanation:

Argument Evaluation 
 Situation   - Normally, a person’s sleep‐wake cycle is governed by the pineal gland secreting melatonin in response to the daily cycle of light and darkness as detected by the eye. Yet many people who are totally blind due to lesions of the visual cortex easily maintain a 24‐hour sleep‐wake cycle.

Reasoning  - What additional information would be most helpful in evaluating the argument? The argument’s conclusion is that the neural pathway by which the pineal gland receives information probably does not pass through the visual cortex. This is suggested by the fact that people without a well‐functioning visual cortex (e.g., people with a certain type of blindness) can nonetheless maintain a 24‐hour sleep‐wake cycle. Is it by the pineal gland’s secretion of melatonin that they do so? The argument tells us that normally (i.e., in sighted people), this is the mechanism for sleep regulation. But the argument depends on assuming that a similar mechanism is operating in people who are blind but have well‐regulated sleep cycles. The best choice will be the one that helps us decide whether that assumption is correct.

A This question would not give us an answer that would help in evaluating the argument. A “no” answer would not clarify whether the pineal gland‐melatonin mechanism operates in people who are blind. A “yes” answer would do no better. The question refers only to people who have sleep dysfunctions (which the argument does not address).

B Correct.  Answering this question would provide the most useful information for evaluating the argument. A “yes” answer would help confirm a key assumption of the argument: that blind people rely on the pineal gland‐melatonin mechanism for sleep regulation. A “no” answer would help disconfirm that assumption.

C Whether or not there are other substances secreted by the pineal gland makes no difference to the reasoning. The argument relies on the premise that the pineal gland governs the sleep cycle by secreting melatonin . For example, if the pineal gland sometimes secreted adrenaline, that would still have no bearing on the argument.

D The consistency or inconsistency of the duration of some people’s sleep patterns has no relevance to the reasoning. Their sleep patterns could be due to any of a number of factors.

E This does not help, for there could be sighted people whose melatonin levels respond abnormally simply because of a pineal‐gland abnormality.

Bikki · Answer

Understanding the passage 
 
 Normally, the pineal gland governs a person's sleep-wake cycle by secreting melatonin in response to the daily cycle of light and darkness as detected by the eye.
 
• Usually, the sleep-wake cycle of a person is controlled by the pineal gland.
• The pineal gland secretes melatonin when the eyes of a person detect the cycle of light and darkness.
• Process: Eyes detect the cycle of light and darkness and send signals to the pineal gland to secrete melatonin.

Nonetheless, many people who are totally blind due to lesions in the visual cortex of the brain easily maintain a 24-hour sleep-wake cycle. 
 
• Many people are completely blind because of lesions in the visual cortex of the brain.
• These completely blind people are also able to maintain the 24-hour-sleep-wake cycle.

So the neural pathway by which the pineal gland receives information from the eye probably does not pass through the visual cortex.
 
• Thus, the neural pathway through which the pineal gland receives signals from the eye probably does not pass through the visual cortex.

Conclusion:  The neural pathway through which the pineal gland receives signals from the eye probably does not pass through the visual cortex.

Pre-thinking

Falsification scenario

In what scenario  – will the neural pathway through which the pineal gland receives signals from the eye probably pass through the visual cortex?
 Given that: 
(i) For people who are not blind, the pineal gland controls their sleep-wake cycle.
(ii) Eyes detect the cycle of light and darkness and send signals to the pineal gland.
(iii) The pineal gland secretes melatonin, which helps control a person's sleep-wake cycle.
(iv) Many people who are completely blind due to lesions in the visual cortex of the brain, easily maintain a 24-hour sleep-wake cycle.

Thought process

The pineal gland controls the sleep-wake cycle in a person who is not blind by secreting melatonin when eyes detect the daily cycle of light and darkness. However, people who are completely blind are also able to maintain this sleep-wake cycle. Therefore, the author concludes that the neural path through which the pineal gland receives signals from the eye most likely does not pass through the visual cortex.

Falsification scenario 1:  What if melatonin secretion in blind people is different from normal people?
If the blind people can detect the cycle to light and darkness with their eyes differently, then it would mean that the neural pathway through which the pineal glands receive information does indeed pass through the visual cortex. This scenario breaks the author's conclusion.

Assumption 1:   Melatonin secretion in blind people is similar to normal people.

Falsification scenario 2:  What if blind people have other unusually developed senses which allow them to detect the cycle of light and darkness?
In this scenario, the neural pathway can pass through the visual cortex with attaining any information from the visual cortex, since the visual cortex of blind people is damaged. This scenario would break the author's conclusion.

Assumption 2:   Blind people do not have other unusually developed senses which allow them to detect the cycle of light and darkness.

Answer Choice Analysis

(A) Whether melatonin supplements help people who have difficulty maintaining a 24-hour sleep cycle to establish such a pattern   INCORRECT  
• This option does not talk about blind people specifically. This option only talks about people in general who have difficulty maintaining a 24-hour sleep cycle taken melatonin supplements. Therefore, this choice is incorrect.

(B) Whether the melatonin levels of most totally blind people who successfully maintain a 24-hour sleep-wake cycle change in response to changes in exposure to light and darkness   CORRECT  
• The answer to this question will help us determine whether melatonin secretions in blind people are affected in response to signals of light and darkness.
• Variance test
o Yes - the melatonin levels of most of the totally blind people who successfully maintain a 24-hour sleep-wake cycle CHANGE in response to changes in exposure to light and darkness.
o This proves that the neural pathway does not pass through the visual cortex because blind people are also able to receive information regarding the cycle of light and darkness. This strengthens our belief in the conclusion.
o No - the melatonin levels of most of the totally blind people who successfully maintain a 24-hour sleep-wake cycle DOES NOT change in response to changes in exposure to light and darkness.
o This would weaken our belief in the conclusion because it would mean that the pathway for the neural information does pass through the visual cortex, which is why blind people are unable to detect the cycle of light and darkness.
• Hence, this option is the correct choice.

(C) Whether melatonin is the only substance secreted by the pineal gland   INCORRECT  
• This evaluation question, when answered, will bring information that is completely irrelevant for the passage. The passage is concerned about the neural pathway.
• Therefore, this option is incorrect.

(D) Whether most people who do not have a 24-hour sleep-wake cycle nevertheless have a cycle of consistent duration   INCORRECT  
• This option provides information that is not pertinent to the passage because this option talks about people in general and not blind people specifically. 
• Also, the information from this evaluation question will not affect the conclusion.
• This choice is incorrect.

(E) Whether there are any people with normal vision whose melatonin levels respond abnormally to periods of light and darkness   INCORRECT  
• The comparison is between people with normal vision and people who are totally blind and if their melatonin levels respond differently from one another.
• This option presents information that is outside the scope of the passage and has no impact on the conclusion. Therefore, this option is incorrect.

LoneSurvivor · Answer

Conclusion is about whether melatonin passes through visual cortex but C is saying something that melatonin level changes according to the sunlight. I find there is a gap. Can someone explain .

egmat · Answer

I guess you are talking about the correct choice, which is B, not C.

B says  Whether the melatonin levels of most totally blind people who successfully maintain a 24-hour sleep-wake cycle change in response to changes in exposure to light and darkness

From the passage, we know that the detection of light and darkness from the eye is what controls melatonin production in the pineal gland.

If the neural pathways that carry this information pass through the visual cortex, then people who are blind due to lesions in the visual cortex should not be responding with a change in melatonin production if the light-darkness exposure pattern changes.

If the exposure pattern changes but the melatonin production does not change, we can see that it is  not  the eye- brain connection that has the control here. But if it is indeed a neural pathway that connects the light exposure in the eye to the brain, not via the visual cortex, then artificially induced changes in the light exposure pattern on the eyes should also reflect in the melatonin production. If it is through the visual cortex, obviously it will not affect the blind.

Elite097 · Answer

ThatDudeKnows   avigutman  not clear on what choice B is doing and its variance analysis. Not sure how a yes indicates that it does not pss through the visual cortex and no indicate the opposite.

avigutman · Answer

Elite097 , This argument describes a surprising phenomenon (how come blind people easily maintain a 24-hour sleep-wake cycle, even though the daily cycle of light and darkness  as detected by the eye  indirectly governs a person's sleep-wake cycle. Then, the argument attempts to explain this surprising phenomenon by suggesting that blind people are still able to detect the daily cycle of light and darkness by some other means (the relevant neural pathway probably does not pass through the visual cortex).
Let's look at a simpler, analogous story. Let's imagine that fathers ring a bell to call their children home for supper, and that surprisingly, this works for deaf children as well. If you want to test whether these deaf children are somehow able to *hear* the bell, what kind of experiment would you run? The first experiment I'd think of is to change supper time and see if they still come home when I ring the bell.

jabhatta2 · Answer

Hi Experts -  ChiranjeevSingh   AnishPassi   RonTargetTestPrep   avigutman

Arent there 2 issues with (b) ?

(i) 
For one, (B) has the word " Most ". So (B) doesnt even relate to  all  the people who are totally blind (who successfully maintain a 24-hour sleep-wake cycle)

So (B) could be referring to only 50.01 % of the folks who are blind with successful sleep-wake cycles.

What about the 49.99 % of folks who are blind with successful sleep-wake cycles ?

49.99 % of any group IS a SIGNIFICANT percentage (albeit minority)

The bigger issue with (B) is (ii) below

jabhatta2 · Answer

(ii) the variance tree is not throwing up  binary  strengthen / weakener as expected

(B) - Yes

vs

No

avigutman · Answer

Agreed, (B) doesn't offer us full information on ALL totally blind people (who successfully maintain a 24-hour sleep-wake cycle). That's probably to allow for edge cases for whom the proposed experiment might yield misleading results. I'll try to explain what I mean by that. Let's imagine that indeed the neural pathway by which the pineal gland receives information from the eye does not pass through the visual cortex, but instead passes through the XYZ cortex.
Now, imagine a totally blind person who, in addition to lesions in the visual cortex of his brain, has a problem with his XYZ cortex. How does this person successfully maintain a 24-hour sleep-wake cycle? Maybe he uses sleeping pills and alarm clocks. This person would "fail" the experiment (his melatonin levels won't change in response to changes in exposure to light and darkness), and his failure may lead researchers to the wrong conclusion. Their hypothesis was correct, but this particular individual's results indicate otherwise.
So, I would argue that testing whether *most* (rather than *all*) blind people respond in a manner consistent with the hypothesis is just best practice in medical research in general.

Your analysis above is incorrect,  jabhatta2 . It seems that you're ignoring the most important part of answer choice (B), which I will boldface below:

jabhatta2 · Answer

Hi  avigutman  - i am afraid i dont see it.

Want to point out that the yellow highlight in option (b) is NOT REFERRING to blind people (who have lesions in the visual cortex) ONLY.

The yellow highlight in Option (B) is referring to  another group  of blind people

Option (B) is referring to blind people (who successfully maintain a 24-hour sleep-wake cycle)

So option (B) can be referring to ANY OF THESE 3 groups.

(Group 1) Blind people,because of lesions in the visual cortex, who successfully maintain a 24-hour sleep-wake cycle
(Group 2) Blind people,because of birth defects, who successfully maintain a 24-hour sleep-wake cycle
(Group 3) Blind people,as a result of injuries, who successfully maintain a 24-hour sleep-wake cycle

Normally, the pineal gland governs a person's sleep-wake

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GMAT Critical Reasoning (CR) Questions

Normally, the pineal gland governs a person's sleep-wake

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