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1、VisionandArt-TheBiologyofSeeingbyMargaretLivingstoneChapter2:TheEyeandColorVisionThevertebrateeyeissocomplexthatitwas(andsometimesstillis)usedasanargumentagainstevolutionandinfavorofdivineintelligence:howcouldarandomprocesslikeevolutionproducesomethingsointricateandbeautiful?Iti
2、scommonlythoughtthattheeyeislikeacamera,andthatitsfunctionistosendahighresolutionimageofthevisualworldtothebrain.Somepeopleeventhinkoftheentirevisualsystemasakindoffancycamera,.Thismisperceptionissocommonthatithasaname:thehomunculusfallacy.(HomunculusisGreekfor“littleman.”)Thefa
3、llacyistheideathatwhenweseesomething,asmallrepresentationofitistransmittedtothebraintobelookedatbyalittleman.Thefactis,ofcourse,thatthereisnolittlemaninthebraintolookatthatoranyotherimage.Thefunctionofthevisualsystemisreallytoprocesslightpatternsintoinformationusefultotheorganis
4、m.Theeyeinitiatesthisprocessoftheextractionofinformation.LightLightpassesthroughthepupil;thelensfocusesanimageontheretinapassesthroughtheopeningintheatthebackoftheeye,andtheretinaperformsthefirstcalculationsontheimagebeforetransmittingitssignalstothebrain.Forpeoplewithfrontofthe
5、eye,thepupil,andthenormalvisionlookingatdistantobjects,thelensgivesasharpfocuslensfocusestheimageontheretina,whenitisinitsflatteststate.Toseeobjectsthatareonlyafewfeetorasheetoflayersofneuraltissuelessaway,thelensmustbecomeroundertogiveasharpfocus.Todothis,theciliarymuscle,acirc
6、ularmusclethatsurroundsthelens,thatlinesthebackoftheeyeball.contracts.Asweage,ourlensesbecomelesselastic,soweneedglassesThefirstlayersaretheganglion,tobringcloseobjectsintofocus.Manypeoplethinkwegetfarsightedandhorizontalcells;thecellsthataswegetolder,butwhatactuallyhappensistha
7、twelosetheabilitytofocusupclose.responddirectlytolight,thephoto-receptors,are,surprisingly,intheoutermostlayer.Thephotoreceptorscontainlight-absorbingchemicals,thatgenerateaneuralsignalwhentheyabsorblight.Thesignalspasstowardtheeyeballthroughthebipolarandhorizontalcellstothegang
8、lioncells,whichsendsignalsfromtheeyeviatheoptic
