Why were both groups tested two days later?

Researchers who study memory have long suspected that sleep plays an active role in learning. In one experiment, two groups of students learned a list of word pairs in the evening. One group slept normally, while the other stayed awake all night. Two days later, both groups were tested after they had recovered. The students who had slept recalled noticeably more word pairs. The researchers concluded that sleep helps the brain to stabilise new information, although they warned that the sample was small and that further studies would be needed before firm advice could be given to students preparing for examinations.

Answer and explanation

Correct answer: B. So that tiredness would not affect the test results of the group that stayed awake.

  1. Step 1: The passage says they were tested 'after they had recovered'. Step 2. The delay removes the effect of simple tiredness, so the result reflects memory. Answer: So that tiredness would not affect the test results of the group that stayed awake. Why not the others: Forgetting on purpose is not mentioned; no extra study time is described; the awake group, not the sleeping group, needed to recover.

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