Frederick Snyder proposed the idea that rapid eye movement (REM) sleep serves a sort of sentinel function because it is...
GMAT Reading Comprehension : (RC) Questions
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Frederick Snyder proposed the idea that rapid eye movement (REM) sleep serves a sort of sentinel function because it is a state of much neural activity. The hypothesis is that episodes of REM sleep allow an animal to be ready to escape once awake should a predator attack, and that the brief periods of wakefulness associated with REM sleep also serve an antipredator function.
The sentinel hypothesis is appealing in many respects. Mammals in REM sleep are clearly more physiologically prepared for wakefulness than are those in deep slow-wave (SW) sleep. Furthermore, humans and rats can detect and process information to a surprising degree during REM sleep. Paradoxically, however, thresholds for arousal from REM sleep tend to be higher than from SW sleep. Additionally, the brief periods of wakefulness associated with REM sleep may not be frequent enough to have much benefit from an antipredator perspective.
Moreover, the hypothesis has never really been tested, and its predictions are not obvious. One would expect that REM sleep would be more prominent in species that suffer high predation or would become so when the perceived risk of predation increases. However, this prediction does not hold. One would also expect that an increase in predation risk would lead to shorter cycles of REM sleep and thus more arousals to wakefulness.
Ques. 1/3
Based on the information in the first paragraph, it is most reasonable to attribute to Snyder which of the following assumptions?
Solution
1. Passage Analysis:
Progressive Passage Analysis
| Text from Passage | Analysis |
|---|---|
| Frederick Snyder proposed the idea that rapid eye movement (REM) sleep serves a sort of sentinel function because it is a state of much neural activity. | What it says: A researcher named Frederick Snyder thinks REM sleep acts like a guard or watchman function because the brain is very active during REM sleep. What it does: Introduces the main theory we'll be examining Source/Type: Researcher's hypothesis/claim Connection to Previous Sentences: This is our starting point - no previous context yet Visualization: Think of REM sleep as a security guard on duty - brain activity = 90% active vs deep sleep = 20% active Reading Strategy Insight: Note the simple language: "sentinel function" = "guard duty." Authors often use accessible metaphors to introduce complex concepts. What We Know So Far: Snyder's theory: REM sleep = guard function What We Don't Know Yet: How this guard function works, evidence for/against it |
| The hypothesis is that episodes of REM sleep allow an animal to be ready to escape once awake should a predator attack, and that the brief periods of wakefulness associated with REM sleep also serve an antipredator function. | What it says: Snyder's theory explained in simple terms: REM sleep helps animals wake up quickly to escape predators, and the short wake-ups during REM sleep also help avoid predators. What it does: Clarifies and elaborates on the sentinel function concept Source/Type: Elaboration of researcher's hypothesis Connection to Previous Sentences: This is NOT new information! This sentence takes the abstract "sentinel function" from sentence 1 and explains it in concrete, understandable terms. - Sentence 1: "sentinel function" (abstract) - Sentence 2: "ready to escape predators" (concrete) Visualization: Animal in REM sleep = 5 seconds to wake up and run vs Animal in deep sleep = 15 seconds to wake up and run Reading Strategy Insight: Feel relieved here - this is simplification, not new complexity! The author is helping us understand the first sentence. |
| The sentinel hypothesis is appealing in many respects. | What it says: The theory has several attractive or convincing aspects What it does: Provides author's evaluation and signals that supporting evidence will follow Source/Type: Author's opinion/transition statement Connection to Previous Sentences: This builds on sentences 1-2 by introducing the author's stance - they're about to tell us why Snyder's theory makes sense Visualization: Theory scorecard: "Appealing aspects" column is about to be filled with evidence Reading Strategy Insight: Transition signals are your friends! "Appealing in many respects" tells us exactly what's coming next - reasons why the theory is attractive. |
| Mammals in REM sleep are clearly more physiologically prepared for wakefulness than are those in deep slow-wave (SW) sleep. | What it says: Animals in REM sleep can wake up more easily than animals in deep sleep What it does: Provides first piece of supporting evidence for the sentinel hypothesis Source/Type: Factual evidence/scientific observation Connection to Previous Sentences: This directly supports Snyder's theory from sentences 1-2 - Theory predicted: REM sleep helps animals "be ready to escape" - Evidence confirms: REM sleep animals are "more prepared for wakefulness" Visualization: REM sleep readiness = 85% prepared to wake vs Deep sleep readiness = 40% prepared to wake Reading Strategy Insight: This restates the core idea using scientific language. "Physiologically prepared for wakefulness" = "ready to escape" from sentence 2. |
| Furthermore, humans and rats can detect and process information to a surprising degree during REM sleep. | What it says: People and rats can notice and understand things around them even while in REM sleep, more than you'd expect What it does: Provides second piece of supporting evidence with specific examples Source/Type: Factual evidence with concrete examples Connection to Previous Sentences: This builds on sentence 4's evidence by adding another layer of support - Previous evidence: can wake up easily - New evidence: can even detect threats while still asleep Visualization: REM sleep awareness = 60% conscious detection vs Deep sleep awareness = 10% conscious detection Reading Strategy Insight: "Furthermore" signals additive evidence. We're building a stronger case for the sentinel hypothesis with concrete species examples. |
| Paradoxically, however, thresholds for arousal from REM sleep tend to be higher than from SW sleep. | What it says: Surprisingly and contradictorily, it's actually harder to wake someone up from REM sleep than from deep sleep What it does: Introduces first major contradiction to the evidence Source/Type: Factual evidence that contradicts the hypothesis Connection to Previous Sentences: This directly contradicts sentence 4's claim - Sentence 4: REM sleep animals are "more prepared for wakefulness" - Sentence 6: Actually "harder to wake up" from REM sleep Visualization: Wake-up difficulty: REM sleep requires 80 decibel alarm vs Deep sleep requires 60 decibel alarm Reading Strategy Insight: "Paradoxically, however" signals a major shift. The author is now presenting evidence AGAINST the theory. This is still part of a logical argument structure. |
| Additionally, the brief periods of wakefulness associated with REM sleep may not be frequent enough to have much benefit from an antipredator perspective. | What it says: The short wake-ups during REM sleep might not happen often enough to actually help avoid predators What it does: Provides second piece of contradictory evidence Source/Type: Critical analysis/potential weakness in the hypothesis Connection to Previous Sentences: This continues the contradictory evidence theme and specifically challenges the second part of Snyder's theory from sentence 2 - Sentence 2: "brief periods of wakefulness...serve an antipredator function" - Sentence 7: These periods "may not be frequent enough" Visualization: REM wake-ups = 3 times per hour vs Needed for protection = 10 times per hour Reading Strategy Insight: "Additionally" continues the pattern of contradictory evidence. We're systematically examining both parts of Snyder's original theory. |
| Moreover, the hypothesis has never really been tested, and its predictions are not obvious. | What it says: Scientists haven't actually tested this theory properly, and it's not clear what results we should expect from testing it What it does: Points out fundamental problems with the hypothesis beyond contradictory evidence Source/Type: Author's critical evaluation of research methodology Connection to Previous Sentences: This shifts from contradictory evidence (sentences 6-7) to fundamental research problems. The author is building a comprehensive case against the theory. Visualization: Research status: Snyder's theory = 0 proper tests conducted vs Established theories = 50+ tests conducted Reading Strategy Insight: "Moreover" adds a different type of criticism. We've moved from "evidence contradicts this" to "we don't even have proper tests." |
| One would expect that REM sleep would be more prominent in species that suffer high predation or would become so when the perceived risk of predation increases. | What it says: If Snyder's theory were true, animals that face lots of predators should have more REM sleep, and all animals should have more REM sleep when they sense danger What it does: States what the theory predicts should happen in the real world Source/Type: Logical prediction derived from the hypothesis Connection to Previous Sentences: This responds to sentence 8's complaint about unclear predictions by spelling out specific, testable predictions - Sentence 8: "predictions are not obvious" - Sentence 9: Here's what the theory actually predicts Visualization: Pred Theory Prediction: High-predation rabbits = 40% REM sleep vs Low-predation elephants = 20% REM sleep Reading Strategy Insight: The author is helping us by clarifying the theory's predictions. This makes the theory more concrete and testable. |
| However, this prediction does not hold. | What it says: The prediction from the previous sentence is wrong - it doesn't match what actually happens in nature What it does: Immediately contradicts the theoretical prediction with real-world evidence Source/Type: Factual contradiction of theoretical prediction Connection to Previous Sentences: This is the devastating follow-up to sentence 9 - Sentence 9: "One would expect..." (theory predicts) - Sentence 10: "this prediction does not hold" (reality contradicts) Visualization: Reality Check: High-predation rabbits = 20% REM sleep vs Low-predation elephants = 25% REM sleep (opposite of prediction) Reading Strategy Insight: Classic setup-and-knockout pattern. The author gave us the prediction just to immediately show it's wrong. This is decisive evidence against the theory. |
| One would also expect that an increase in predation risk would lead to shorter cycles of REM sleep and thus more arousals to wakefulness. | What it says: The theory also predicts that when predator danger increases, animals should have shorter REM periods with more frequent wake-ups What it does: States a second testable prediction from the sentinel hypothesis Source/Type: Additional logical prediction derived from the hypothesis Connection to Previous Sentences: This continues the pattern from sentences 9-10 by presenting another prediction (presumably to be contradicted) - Following the same structure: state prediction, then show it's wrong Visualization: Theory's Second Prediction: High danger = 10-minute REM cycles vs Low danger = 30-minute REM cycles Reading Strategy Insight: Pattern recognition! The author used this exact structure in sentences 9-10. We can predict this will also be contradicted, showing the theory fails multiple tests. What We Know So Far: Snyder's sentinel theory has supporting evidence but more contradictory evidence, hasn't been properly tested, and its predictions don't match reality What We Don't Know Yet: Whether this second prediction also fails (though the pattern suggests it will) |
2. Passage Summary:
Author's Purpose:
To evaluate the strengths and weaknesses of Frederick Snyder's sentinel hypothesis about REM sleep serving a protective function against predators.
Summary of Passage Structure:
In this passage, the author walks us through a systematic examination of a scientific theory:
- First, the author introduces Snyder's sentinel hypothesis, which claims that REM sleep helps animals stay alert and escape from predators quickly.
- Next, the author presents evidence that initially seems to support this theory, showing that animals in REM sleep are more prepared to wake up and can even detect information while sleeping.
- Then, the author shifts direction and presents several problems with the theory, including contradictory evidence about wake-up difficulty and concerns about insufficient testing.
- Finally, the author examines specific predictions the theory should make about real animal behavior and shows that these predictions fail when tested against actual observations.
Main Point:
While Snyder's sentinel hypothesis about REM sleep protecting animals from predators seems appealing at first and has some supporting evidence, it ultimately fails because the contradictory evidence is stronger and its key predictions about animal behavior don't match what actually happens in nature.
Question Analysis:
This question asks us to identify an assumption that Snyder must have made when proposing his sentinel hypothesis. We need to look at the logical foundation underlying his theory that REM sleep serves a protective function because it involves high neural activity.
Connecting to Our Passage Analysis:
From our passage analysis, we know that:
- Snyder's core theory links high neural activity in REM sleep to a "sentinel function" that helps animals escape predators
- The hypothesis assumes that REM sleep's neural activity makes animals "ready to escape once awake should a predator attack"
- The theory implies that this high neural activity state provides some advantage over other sleep states for survival purposes
The key insight from our analysis is that Snyder's entire theory rests on the premise that neural activity levels during sleep directly impact an animal's ability to respond to threats upon waking.
Prethinking:
For Snyder's theory to make sense, he must assume that sleep states with different levels of neural activity result in different response capabilities when animals wake up. Specifically, he must believe that waking from high neural activity (REM sleep) provides faster, better responses than waking from low neural activity (deep sleep). Without this assumption, there would be no logical basis for his sentinel hypothesis - why would neural activity matter for predator protection if it didn't affect response quality?
Answer Choices Explained
A
Sleep that involves much neural activity is the least restful form of sleep.
This is wrong because Snyder's theory focuses on protective function, not restfulness or sleep quality. The passage never discusses which type of sleep is most or least restful. This confuses the protective benefits of neural activity with sleep restoration.
B
The greater the amount of an animal's neural activity, the sharper its perception of the surrounding environment.
This is wrong because this focuses on perception during sleep, but Snyder's theory is about readiness upon waking. While the passage mentions animals can "detect and process information" during REM sleep, this isn't Snyder's core assumption. The theory emphasizes escape readiness, not environmental perception while asleep.
C
REM sleep occurs in most animal species and serves to protect them against predators.
This is wrong because this states conclusions of the theory rather than underlying assumptions. The passage notes that predictions about species differences "do not hold," contradicting this choice. This describes what the theory predicts should happen, not what Snyder assumed to create the theory.
D
REM sleep generally does not occur in animals except when they fear a high risk of predation.
This is wrong because this suggests REM sleep is rare and only occurs under threat, contradicting the basic premise. Snyder's theory assumes REM sleep is a normal, regular occurrence that provides ongoing protection. The passage discusses REM sleep as a regular sleep phase, not a fear response.
E
Animals waking from sleep during low levels of neuroactivity are unlikely to achieve the fastest possible responses.
This is right because this captures the fundamental assumption underlying Snyder's entire theory. Snyder's logic requires that neural activity levels during sleep affect response speed/quality upon waking. Without this assumption, there would be no reason to think high neural activity provides a "sentinel function".
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