Sleep Deficit

Judging from recentsurveys,most experts in sleep behavior agree that there is virtually anepidemic（流行病）of sleepinessin the nation."I can't think of a single study that

hasn't foundAmericans getting less sleep than they ought to,"says Dr.David.Even peoplewho think they are sleeping enough would probably be better off with more rest.

The beginning of oursleep-deficit（睡眠不足）crisiscan be traced to the invention of the light bulb a century ago.From diaryentries and other personal accounts from the

18th and 19thcenturies,sleep scientists have reached the conclusion that the average personused to sleep about 9.5 hours a night."The best sleep habits once wereforced on

us,when we hadnothing to do in the evening down on the farm,and it was dark."By the1950s and 1960s,that sleep schedule had been reduced dramatically,to between7.5

and 8 hours,and mostpeople had to wake up to an alarm clock."People cheat on their sleep,andthey don't even realize they're doing it,"says Dr.David."They thinkthey're

okay because theycan get by on 6.5 hours, when they really need 7.5,8 or even more to feelideally vigorous."

Perhaps the mostmerciless robber of sleep,researchers say,is the complexity of the day.Wheneverpressures from work,family,friends and community mount,many people

consider sleep theleast expensive item on his programme.In our society,you're considered dynamicif you say you only need 5;5 hours, sleep.If you've got to get 8.5

hours,people thinkyou lack drive and ambition.

To determine theconsequences of sleep deficit,researchers have put subjects through a set ofpsycho-logical and performance tests requiring them,for instance,to add columns

of numbers or recalla passage read to them only minutes earlier."We've found that if you're insleep deficit,performance suffers,"says Dr.David."Short-term memoryis

weakened,as arc abilitiesto make decisions and to concentrate."The word"subjects"(Line 1,Para 4)refers to______.

A.the performance tests used in the study of sleep deficit

B.special branches of knowledge that are being studied

C.people whose behavior or reactions are being studied

D.the psychological consequences of sleep deficit