parasena
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
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-thinkingFalsification scenarioIn 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 processThe 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.