Inaworldperfumedbyfreshlypoppedpopcornandexhaustfumes,whereseabreezescanminglewiththescentsofsweetflowersorwetpaint,newresearchshowsthathumansarecapableofdiscriminatingatleastonetrilliondifferentodors.HowardHughesMedicalInstitute(HHMI)scientistsdeterminedthatoursenseofsmellispreparedtorecognizethisvastolfactory（嗅觉的）palette（调色板）aftertestingindividuals'abilitytorecognizedifferencesbetweencomplexodorsmixedinthelaboratory.Ithasbeensaidfordecadesthathumansarecapableofdiscriminatingbetween10,000differentodors.Thenumberiscitedinscientificliteratureandappearsinpopularmagazines."It'sthegenerallyacceptednumber,"saysHHMIinvestigatorLeslieVosshall,whostudiesolfactionattheRockefellerUniversity."Ouranalysisshowsthatthehumancapacityfordiscriminatingsmellsismuchlargerthananyoneanticipated."VosshallandhercolleaguespublishedtheirfindingsMarch21,2014,inthejournalScience."Ihopeourpaperwilloverturnthisterriblereputationthathumanshavefornotbeinggoodsmellers,"shesays.Vosshallhadlongbeenbotheredbytheideathathumanswerelimitedtosmelling10,000odors--anestimatethatwasmadeinthe1920s,andnotbackedbyanydata."Objectively,everybodyshouldhaveknownthatthat10,000numberhadtobewrong,"shesays.Foronething,itdidn'tmakesensethathumansshouldsensefarfewersmellsthancolors.Inthehumaneye,Vosshallexplains,threelightreceptorsworktogethertoseeupto10millioncolors.Incontrast,thetypicalperson'snosehas400olfactoryreceptors.Butnoonehadtestedhumans'olfactorycapacity."Weknowexactlytherangeofsoundfrequenciesthatpeoplecanhear,notbecausesomeonemadeitup,butbecauseitwastested.Wedidn'tjustmakeupthefactthathumanscan'tseeinfraredorultravioletlight.Somebodytookthetimetotestit,"Vosshallsays."Forsmell,nobodyevertookthetimetotest."VosshallandAndreasKeller,aseniorscientistinherlabatRockefellerUniversity,knewtheycouldn'ttestpeople'sreactionsto10,000ormoreodors,buttheyknewtheycouldcomeupwithabetterestimate.Theydevisedastrategytopresenttheirresearchsubjectswithcomplexmixturesofdifferentodors,andthenaskwhethertheirsubjectscouldtellthemapart.Theyused128differentodorantmoleculestoconcocttheirmixtures.Thecollectionincludeddiversemoleculesthatindividuallymightevokegrass,orcitrus,orvariouschemicals.Butwhencombinedintorandommixturesof10,20,or30,Vosshallsays,theybecamelargelyunfamiliar."Wedidn'twantthemtobeexplicitlyrecognizable,somostofourmixtureswereprettynastyandweird,"shesays."Wewantedpeopletopayattentionto'here'sthisreallycomplexthing--canIpickanothercomplexthingasbeingdifferent?'"Thescientistspresentedtheirvolunteerswiththreevialsofscentsatatime:twomatched,andonedifferent.Volunteerswereaskedtoidentifytheonescentthatwasdifferentfromtheothers.Eachvolunteermade264suchcomparisons.Vosshallandhercolleaguestalliedhowoftentheir26subjectswereabletocorrectlyidentifythecorrectoutlier.Fromthere,theyextrapolatedhowmanydifferentscentstheaveragepersonwouldbeabletodiscriminateiftheywerepresentedwithallthepossiblemixturesthatcouldbemadefromtheir128odorants."It'slikethewaythecensusworks:tocountthenumberofpeoplewholiveintheUnitedStates,youdon'tknockoneverysingledoor,yousampleandthenextrapolate（推断）,"sheexplains."That'showIliketothinkofthisstudy.Weknockedonafewdoors."Inthisway,theyestimatedthattheaveragepersoncandiscriminatebetweenatleastonetrilliondifferentodors."Ithinkwewereallsurprisedathowridiculouslyhigheventhemostconservativelowerestimateis,"Vosshallsays."Butinfact,therearemanymorethan128odorants,andsotheactualnumberwillbemuch,muchbigger."Vosshallsaysshedoubtsindividualsareexposedtoatrillionsmellsonadailybasis."ButIliketothinkthatit'sincrediblyusefultohavethatcapacity,becausetheworldisalwayschanging,"shesays.Plantsareevolvingnewsmells.Perfumecompaniesaremakingnewscents.Youmightmovetosomepartoftheworldwhereyou'veneverencounteredthefruitsandvegetablesandflowersthatgrowthere.Butyournoseisready.Withasensorysystemthatisthatcomplex,wearefullyreadyforanything,"shesays.More：面试英语学习资料wwspiikers/study-interviehtml
