Sleep Deficit

Judging from recentsurveys,most experts in sleep behavior agree that there is virtually anepidemic（流

行病）ofsleepiness in the nation."I can't think of a single study that hasn'tfound Americans getting less

sleep than theyought to,"says Dr. David.Even people who think they are sleeping enoughwould probably

be better off withmore rest.

The beginning of oursleep-deficit (睡眠不足）crisiscan be traced to the invention of the light bulb a

century ago.Fromdiary entries and other personal accounts from the 18th and 19thcenturies,sleep scien-

tists have reachedthe conclusion that the average person used to sleep about 9.5 hours anight."The best

sleep habits oncewere forced on us,when we had nothing to do in the evening down on the farm,andit 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'redoing it,"says Dr. David."They think they're okay because they canget by on 6.5 hours,

when they reallyneed 7.5,eight or even more to feel ideally vigorous.

Perhaps the mostmerciless robber of sleep,researchers say,is the complexity of the day.Whenever

pressures fromwork,family,friends and community mount,many people consider sleep the leastexpensive

item on hisprogramme.In our society,you're considered dynamic if you say you only need5.5hours'

sleep.If you'ye gotto get 8.5 hours,people think you lack drive and ambition.

To determine theconsequences of sleep deficit,researchers have put subjects through a set ofpsycho-

logical andperformance tests requiring them,for instance,to add columns of numbers orrecall a passage

read to them onlyminutes earlier."We'ye found that if you're in sleep deficit,performancesuffers,"says

Dr.David."Short-term memory is weakened,as are abilities to make decisionsand to concentrate."People in the 18thand 19th centuries used to sleep about 9.5 hours a night because theyhad_______.

A.no drive andambition

B.the best sleephabits

C.no electric light

D.nothing to do inthe evening