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

Hi avigutman - the conclusion has a negative and this is really throwing me off.




Do you recommend re-phrasing "negative conclusions" to a 'positive conclusion' ?

While your rephrase is technically correct, I don't think I'd recommend this as a strategy for the GMAT. It feels to me like a bandaid solution that fails to address the root cause, allows you to get away with doing less reasoning, and is likely to cost you more time and mental effort than is appropriate for the GMAT. That said, if you find that it works well for you and doesn't take too much time, go for it!
My recommendation is to instead use reasoning to help you digest the meaning of the sentence. Why would the authors conclude that the neural pathway (by which the pineal gland receives information from the eye) probably does not pass through the visual cortex?
Your ability to answer that question will determine success or failure on this problem, and my worry is that having to rephrase the question in the way that you did might indicate that you're not fully engaging with the question of why the authors came to that conclusion.
Again, if my worry is misplaced, go for the rephrasing. It's technically correct, jabhatta2.

Hi avigutman - the screenshot below shows the sequence of events. I have marked it with [1] through [6].

Hypothesis : Amongst blind people, (4) is recieving information about (1) NOT THROUGH (3)

Test - i was hoping for a test to check between the relationship between (1) and (3) or maybe (1) and (4) {[1] and [3] is the best IMO}

Those would be better experiments (do you concur ?)

So a test like :



OR



Tests like the ones aboves are the best to test the hypothesis

Option (B) seems to be checking the relationship between (1) and (5), within the test group

But doing this, you leave big gaps

Just because (1) and (5) are seen among blind people,
- can i really say (3) does not play a part in sending information to (4) ? [which is the hypothesis]

I CANT

Maybe, within the test group, [3] is getting information about [1] through the another organ (Say through touch or feel - it gets cooler when the lights dim, hence you can feel the change in lights)

Once [3] gets information about [1], then [3] is then sending the info to [4], amongst blind people

- can i really say (4) must be causing (5) -- I cant. Maybe among the blind, (4) does not cause (5) at all.

Many gaps if you ask me, testing the relation between [1] and [5]

To me, this seems to go against the premise: "people who are totally blind due to lesions in the visual cortex of the brain." I take that to mean that their visual cortex is unable to detect (1). Do you have a different understanding, jabhatta2?
Sure, this would be great, but I suspect that the only way to check this (I'm not a scientist) is to check the melatonin levels (in other words, maybe we can only check (4) by evaluating (5).
Again, my understanding is that [3] is completely disabled.

So you're saying that even if we have the information that answer choice (B) offers us, we still wouldn't be able to PROVE the hypothesis. Okay, sure. But that wasn't the question. The question was: which of the five answer choices would be most useful for purposes of evaluating the argument.

Hmm avigutman - the yellow DID suprise me.

Just because people are blind because of lesions in the visual cortex, i didnt think it was a premise that [3] cannot talk to [1]

In fact, If [3] cannot detect [1] as per the premise - i cant think of how to weaken the hypothesis /conclusion (in the red font above)

In order to weaken the hypothesis (red font above) - we need something that says

Actually [4] IS probably getting information about [1] THROUGH [3]

It seems that you are taking for granted that the pineal gland receives information from the eye, jabhatta2? I don’t think that fact was provided as a premise

Posted from my mobile device

hmm are you referring with your above statement - are you referring to blind people only or regular people only or both ?

for Regular people - i thought it was a fact that pineal glands ARE GETTING information from the eyes, that was not up for debate when it comes to regular people

I think the main issue is -- i am not clear, what is it that i am evaluating

Is it

(a) Do Pineal Glands govern sleep cycles (for blind and regular people)

OR

(b) Do Pineal Glands get info about [1] thorough [3] (for blind people only) - evaluate the sequence of events specifically

Agreed.
You're not evaluating either of those things. You're presented with a surprising phenomenon (the surprise is indicated by the word "Nonetheless" at the beginning of the 2nd sentence of the argument) which demands an explanation, and you're evaluating the validity of one particular explanation.

So... How is it that many people who are totally blind due to lesions in the visual cortex of the brain easily maintain a 24-hour sleep-wake cycle?

That's the surprising phenomenon that demands an explanation. Wait, why is it surprising? Well, because 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. That's clearly not happening for people who are totally blind due to lesions in the visual cortex of the brain.

Can you think of any explanations, jabhatta2? I can think of a few:
(i) these blind people are surrounded by non-blind people, and they just go to sleep and wake up at the same time as the non-blind people
(ii) these blind people have smart clocks that signal audibly when it's time to go to sleep and wake up
(iii) these blind people have developed super hearing to compensate for their lack of sight, and they go to sleep when they hear the hustle bustle of their surroundings quiet down (and they wake up when the hustle bustle resumes)
.
.
.
(ix) the neural pathway by which the pineal gland receives information from the eye does not pass through the visual cortex

To evaluate the argument about the neural pathway by which the pineal gland receives information from the eye, it would be most useful to establish which of the following:

(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 answer choice addresses the issue of whether the pineal gland in blind individuals still responds to changes in light and darkness, indicating that the neural pathway by which the pineal gland receives information from the eye does not pass through the visual cortex. If blind individuals' melatonin levels still change in response to light and darkness, it would suggest that the neural pathway bypasses the visual cortex. Therefore, this answer choice would be the most useful for evaluating the argument.

Answer choice (A) is not relevant to the argument as it concerns the use of melatonin supplements for individuals who have difficulty maintaining a 24-hour sleep cycle.

Answer choice (C) is not relevant to the argument as it concerns whether melatonin is the only substance secreted by the pineal gland, which is not related to the neural pathway by which the pineal gland receives information from the eye.

Answer choice (D) is not relevant to the argument as it concerns whether most people who do not have a 24-hour sleep-wake cycle have a cycle of consistent duration, which is not related to the neural pathway by which the pineal gland receives information from the eye.

Answer choice (E) is not relevant to the argument as it concerns whether there are any people with normal vision whose melatonin levels respond abnormally to periods of light and darkness, which is not related to the neural pathway by which the pineal gland receives information from the eye in blind individuals.

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 PG 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?

Premise: The Pineal Gland (PG) determines a person's sleep-wake cycle by secreting melatonin in response to the daily cycle of light and darkness as detected by the eye

Counterargument: Blind people easily maintain a 24-hour sleep-wake cycle

Conclusion: So, the pineal gland receives information from the eye and doesn't pass through the visual cortex.

Weakening:
What if the pineal gland receives information from the eye pass through the visual cortex?

(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 question Yes: The melatonin levels CHANGE in response to changes in exposure to light and darkness. That means it must be passed through the visual cortex. Which weakens the argument.

if the question NO: The melatonin levels don't change in response to changes in exposure to light and darkness. That means it doesn't pass through a visual cortex. This strengthens the argument.