Bacaan
Sleeping With One Eye Open
(1) For most mammals, sleep is an all-or-nothing state: the whole brain slows down together, and the body becomes still and largely unaware of its surroundings. A number of animals, however, have found a way around this risky arrangement. They can let one half of the brain sink into deep sleep while the other half stays awake. Scientists call this unihemispheric slow-wave sleep.
(2) Bottlenose dolphins are the best-known example. A dolphin has to swim up to the surface for every breath, so it cannot simply drift off for hours the way a person does in bed. By resting one half of the brain at a time, a dolphin can keep swimming, surfacing, and watching for danger while still getting the sleep it needs.
(3) Birds use the same trick. In a well-known experiment published in 1999, researchers filmed mallard ducks sleeping side by side in a row and recorded their brain activity. The ducks at the two ends of the row, which were the most exposed, spent much more time sleeping with one half of the brain than the ducks in the middle. They also tended to keep open the eye facing away from the group, the direction from which a predator would most likely come. Each open eye was linked to the half of the brain that was still awake.
(4) Some birds even sleep in the air. In 2016, scientists who recorded the brain activity of great frigatebirds during long flights over the ocean found that the birds slept mostly while circling upward in rising air, often with only one half of the brain at a time. In flight, however, they slept for less than an hour a day in total, compared with more than twelve hours a day once they were back on land.
(5) Humans cannot do anything as dramatic, but traces of the same idea may exist in us. A 2016 study of people sleeping in a laboratory for the first time found that, on the first night, the left half of the brain slept less deeply than the right and responded more strongly to unusual sounds. On the second night, the difference disappeared. The researchers suggested that this "night watch" may help explain why many people sleep poorly in a new place.
Soal 1
Pilih satu jawabanBased on the passage, it can be inferred that sleeping with half of the brain is most useful to an animal when
Lihat kunci & pembahasan
Kunci: A
Kenapa benar
Semua contoh di teks memperlihatkan pola yang sama: separuh otak tidur ketika hewan tetap harus bergerak atau berjaga. Lumba-lumba harus terus berenang ke permukaan, bebek di ujung barisan harus mewaspadai pemangsa, burung frigata harus terus terbang, dan otak manusia lebih waspada di tempat baru. Simpulannya, tidur separuh otak paling berguna saat hewan perlu istirahat sambil tetap bergerak atau waspada.
Langkah
Kumpulkan keadaan setiap contoh: lumba-lumba (harus berenang ke permukaan untuk bernapas), bebek di ujung (paling terbuka terhadap pemangsa), frigata (sedang terbang jauh), manusia (malam pertama di tempat baru).
Cari kesamaan keempatnya: istirahat yang harus dibarengi gerakan atau kewaspadaan.
Uji setiap pilihan dengan semua contoh. Pilihan yang hanya cocok dengan satu contoh, atau bertentangan dengan salah satunya, gugur.
Tips: simpulan yang kuat dari teks eksposisi biasanya menggeneralisasi semua contoh, bukan satu contoh saja.
Kenapa opsi lain salah
- B.
Kebalikan dari teks. Efek "night watch" justru muncul di tempat baru, dan bebek yang lebih aman di tengah barisan lebih jarang tidur separuh otak.
- C.
Burung frigata yang tidur separuh otak saat terbang justru tidur kurang dari satu jam sehari, jauh lebih sedikit daripada di darat.
- D.
Lumba-lumba memang hidup di air, tetapi bebek dan burung frigata juga memakai cara ini. Jadi hidup di air bukan syaratnya.
- E.
Teks sama sekali tidak menyebut makan atau pencernaan.
Konsep
Inferensi dari beberapa contoh: mencari kesamaan keadaan pada semua contoh, lalu menarik simpulan yang tidak bertentangan dengan satu pun contoh.
Jebakan umum
Menyimpulkan dari satu contoh saja (lumba-lumba) sehingga memilih "hidup di air".
Mengira tidur separuh otak membuat hewan tidur lebih lama, padahal data frigata menunjukkan sebaliknya.
Referensi
- Wikipedia, "Unihemispheric slow-wave sleep"
- Rattenborg, Lima & Amlaner (1999), "Half-awake to the risk of predation", Nature 397
- Rattenborg dkk. (2016), "Evidence that birds sleep in mid-flight", Nature Communications 7:12468
- Tamaki dkk. (2016), "Night watch in one brain hemisphere during sleep associated with the first-night effect in humans", Current Biology 26(9)
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