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Mr Evans, are you still with us? It’s alright. What was I saying?

Yes, sleep may also have a vital physiological function in helping the brain to process memories. One researcher gave various learning tasks to students and then internipted their sleep during the deep, or REM, phase. He found that memorising complex materiał, such as stories, was greatly impaired by the sleep loss, while simpler tasks such as memorising lists of words were not much affected.

One ąuestion still remains: how much sleep do we really need? Opinion is divided on this matter. While some suggest that we get too much — one researcher claims that beyond five or six hours, the rest is mere self-indulgence — others say that as a society we are severely sleep-deprived, and that accidents such as the Exxon Valdez oil spili and the cxplosion of the space shuttle Challenger involved people who were short of sleep. Of course, the need for sleep varies quite considerably with age — older people generally sleep fewer hours than younger people — but what stands out clearly is that sleep is essential. Now, if you could tum to page 248 in your textbook ...