Macpherson, F. (2011) Taxonomising the senses. Philosophical studies . ISSN 0031-8116 http://eprints.gla.ac.uk/43551/ Deposited on: 11 November 2010

Enlighten – Research publications by members of the University of Glasgow http://eprints.gla.ac.uk

2

TaxonomisingtheSenses

FionaMacpherson

DepartmentofPhilosophy,

UniversityofGlasgow

fiona.macpherson@glasgow.ac.uk

+44(0)1413308761

3

TaxonomisingtheSenses

FionaMacpherson

Abstract:

Iarguethatweshouldrejectthesparseviewthatthereareorcouldbeonlya

smallnumberofratherdistinctsenses.Whenoneappreciatesthisthenone

canseethatthereisnoneedtochoosebetweenthestandardcriteriathat

havebeenproposedaswaysofindividuatingthesenses–representation,

phenomenalcharacter,proximalstimulusandsenseorgan–oranyother

criteriathatonemaydeemimportant.Rather,onecanusethesecriteriain

conjunctiontoformafine­grainedtaxonomyofthesenses.Wecanthinkof

thesecriteriaasdefiningamultidimensionalspacewithinwhichwecan

locateeachofthesensesthatwearefamiliarwithandwhichalsodefinesthe

spaceofpossiblesensestherecouldbe.

Keywords:senses,perception,experiences,phenomenalcharacter,representation,

proximalstimulus,senseorgan

Thesenses,orsensorymodalities,constitutethedifferentwayswehaveof

perceivingtheworld,suchasseeing,hearing,touching,tasting,andsmelling.But

whatmakesthesensesdifferent?Howmanysensesarethere?Howmanycould

therebe?

Ofanycreaturewecanask:

(1)Howmanytokensensesdoesithave?

(2)Whattypesarethosesenses?

4

Typesaregeneralkindsofthing,andtokensareinstancesoftypes.Forexample,

intheword“sense”therearefourtypesofletterbutfivelettertokens.Thisis

becausetherearetwotokensofthesametype:“s”.

Questions1and2areverydifferentquestions,anditisimportanttokeep

themseparate.Toillustratewhatwewouldbeaskingifweaskedquestion1,

imaginethatwecameacrossacreatureverymuchlikeahumanbutforthefact

thatithadfoureyes—onepairaboveanother.Callthecreature“Four‐Eyes”.

Four‐Eyesmighthaveonesenseofvision,aswedo,withallfoureyes

contributingtoit,asourtwoeyescontributetoours.OrFour‐Eyesmighthave

twodistinctsensesofvision,witheachsetofeyescontributingtoitstwo

differentvisualsenses.Ifthelatterwerethecase,andifFour‐Eyeshadnoother

senses,thenitwouldhaveonlyonetypeofsensorymodality,butitwouldhave

twotokensofthattype.(Ofcourse,forallIhavesaid,Four‐Eyesmightindeed

havethreeorfourtokensofthevisualsensorymodalitytype.1)

InthispaperIwillnotdiscussindetailthequestionofhowweshould

individuatetokensensorymodalities,althoughthisisaninterestingquestionto

investigate.Rather,Iwillfocusonthequestionofhowtotaxonomisetypesof

senses.Whataretheprinciplesweshoulduseforindividuatingthesensesand

howmanyactualorpossiblesensesarethere?

1.WhatTypesofSensesAreThere?

1Grice(1962)considersacreaturelikeFour‐Eyes.However,heputshisimaginedcreaturetodifferentphilosophicalusethanIdohere.

5

Manypeoplehavethoughtthatthereareonlyfivetypesofsenses.Forexample,

Aristotle,inDeAnima, famouslysaidthattherearefiveandonlyfivesenses:

sight,hearing,touch,taste,andsmell.2(Heistalkingherebothaboutthenumber

andkindofsensesthathumanshaveandthenumberandkindthatanimals

have.)Thisviewhasechoeddownthecenturies,advocatedbyanumberof

scholars,mostrecentlyperhapsbyMatthewNuddswhosaysthatitis“obvious”

thathumanshavefivesensesandthattheirhavingthisnumberisatruthoffolk

psychology.Moreover,hethinksthatitisnotthecasethat“common‐sense

embodiesthekindofproto‐scientificunderstandingofthesenseswhichisliable

torevisionorreplacement.”3Therefore,heholdsthatnoamountofextradata

fromsciencecouldchangeourmindsonthequestionofhowmanytypesof

sensesthereare.

Thecommitmenttotheexistenceofonlyarelativelysmall,specifiable

numberoftypesofsenses—typically,butnotnecessarily,five—formspartof

whatIcallthe“sparseview”ofthecountingquestion.Thesparseviewmaintains

thefollowing:

• Thenumberofpossiblesensorymodalitiesisrelativelylimited.

• Thesensorymodalitiesarediscrete.4

2SeebookIII,chapter1.ItisreasonablyclearthatAristotlewasclaimingthatasamatteroffactthereareonlyfivesenses,and,giventhenatureoftheworldashetookittobe(composedofelements,eachofwhichhaddifferentproperties),therecouldbeonlyfivesenses.Thus,hewasclaimingthatitisnomologicallynecessarythatwehaveonlyfivesenses.Hewasnotclaimingthatitismetaphysicallynecessary.3Nudds(2004,35).Onthesamepage,notonlydoeshesaythathehas“notcomeacrossagoodargument”fortheideathatthefolknotionofthesensesisliableforrevision,buthealsosays,“Therehavebeenauthorswhoattempttogivea‘scientific’accountofthesenses,buttheydonothingtoshowthattheyhaven’tsimplychangedthesubject.Whatevertheyaregivinganaccountof,it’snotthesensesaswecommonlyunderstandthem”(fn11).4ItmaybethatnoonehaseverheldthesparseviewthatIoutlinehere,butpartsofithavecertainlybeenavowed,andthepositionservesasausefulstalkinghorse.

6

Tosaythatthemodalitiesarediscreteistosaythatallofthepossiblemodalities

areratherdifferentanddistinctfromeachother(notthatthemodalitiescannot

interact).

Shouldonebelievethesparseview?Ithinknot,fortworeasons.First,

thereisevidencethatmanymorethanfivesensorymodalitiesactuallyexist.

Fromthesecaseswecangoonandextrapolateandthuscometobelievethatthe

numberofpossiblesensorymodalitiesislarge.

Letustakethecaseofhumansfirst.ManysensesbeyondtheAristotelian

fivehavebeenattributedtohumans.Someofthebestcandidatesare:

proprioception–comprisingawarenessofthepositionofthepartsofthe

body,awarenessofmovementofthebodyandofhowmuchforceis

requiredtomoveit5

equilibrioception–thevestibularsenseorsenseofbalance

thevomeronasalsystem–detectspheromonesusingtheJacobson’sorgan

inthenoseandisseparatefromtheolfactorysystem.

Thesearegoodcandidates,because,plausibly,althoughbynomeans

indisputably,theyhavesomefeaturesthatpeoplehavespecifiedasnecessaryor

sufficientforbeingasense,suchashavingadedicatedsenseorgan,producing

experienceswithphenomenalcharactercapableofbeingaccurateand

inaccurate,andbeing,atleastpartly,exteroceptive.6

Candidatesforyetmorehumansensesincludedistinctivepain,

temperatureandpressuresensesinsteadofoneamalgamatedsenseoftouch.

5Theterm“kinesthesia”issometimesusedinterchangeablywith“proprioception”thusdefined.However,sometimes“kinesthesia”isusedexclusivelyasatermforoursenseofawarenessofthemovementofthebody,while“proprioception”isreservedforthesenseofthebody’sposition.6Notethatthevomeralnasalsystemdoesnotproduceexperiencewithphenomenalcharacterbutitdoespossesstheotherfeatures.

7

Scientistshavefoundthattherearedistinctivereceptorsthatdetect

temperature,pressure,andpainfulstimuliandthatthereareseparatespotsin

theskinreceptivetopressure,warmth,cold,andpainfulstimuli.Thishasbeen

themainreasonthathaspersuadedsomepeoplethatthereareseveralsenses

here.However,inadditiontothis,somepeoplehavethoughtthatthe

experiencesofpressure,temperature,andpainarefairlydistinctive;thatis,they

haveratherdifferentphenomenalcharacters.Forexample,itissometimes

claimedthatPlatothoughtthattemperatureperceptionwasasenseseparate

fromthatoftouchandalsothathethoughtpainwasdistinctive,beinga

sensationor“passionofthesoul.”7Moreover,hedidthisnotbecauseheknewof

thedifferencesinphysiologythatweknowoftoday,butdidsoatleastinparton

phenomenologicalgrounds.

Whetherthesearegoodenoughreasonstopostulatemanysensesinthis

caseishighlydisputed.Onemightdoubtthatpain,temperature,andpressure

areparticularlyphenomenologicallydistinct.Thereseems,forexample,tobea

phenomenologicalcontinuitybetweenexperiencesofexcessesofpressureand

temperatureandexperiencesofpain.Wealsohaveevidencethataphysiological

overlapexistsbetweenthesensorsthatdetectpressure,temperature,and

painfulstimuli—inbothnormalandpathologicalconditions.Forexample,pain

seemstobeelicitedbyextremepressureortemperature(bothhotandcold),

suggestingthatthemechanismsunderlyingexperiencesofeacharenotseparate.

However,thisresultmightbeexplainedawaybecauseitishardtostopintense

pressureandtemperaturestimulifromstimulatingadjacentpainreceptorsin

theskin.Nonetheless,thereismorepersuasiveevidenceinfavorofcontinuity.

7SeeClassen(1993,2).

8

Experiencesofcoldorvibrationcaninhibitthefeelingofpain,andtactileacuity

isdiminishedbypainfulheatexperiences.Indeed,thereisevidenceof

“multireceptive”neuronsthatareresponsivetotwooreventhreeofthese

allegedlyseparatemodalities,whichsomecommentatorsclaimindicatethatthe

allegedlyseparatemodalitiesareintegratedcentrallyinthebrain.8

Criticsoftheaforementionedevidencemaythinkthattheseinteractive

phenomenaaremerelysimilartotheMcGurkeffect—andthusthinkofthem

simplyasintermodalinteractionsbetweendifferentsenses.So,unfortunately,

suchevidencedoesnotclearlysettlethematter.Moreover,appealto

phenomenologytosettletheseissuesisnotstraightforwardsincephenomenal

factsarenotoriouslysubjecttodispute.Thus,thereseemstobealargeopen

questionaboutwhetherthereisonesenseoftouchormultiple,distinctivetactile

senses.

Othercandidatesthathavebeenconsideredasbeingadditionalhuman

sensesincludesensesofhunger,thirst,wetanddry,theweightofobjects,

fullnessofthebladder,suffocationandrespiration,sexualappetite,and

lactiferousness.9Indeed,intheirsurveyofthehumansenses,Rivelinand

Gravellehaveconcludedthat,“Fiveisobviouslyjustnotenoughtoaccountfor

thehugerangeofsensorypossibilitiesofwhichthehumanspeciesiscapable;

seventeensensesisprobablyamoreaccuratecount.”10Thisnumbermaybewell

beyondthenumberoneshouldendorse,buttheirsurveygivesanindicationof

thenumberofcandidatesthatonemayhavetoconsider.

8TheevidenceadducedhereabouttouchissummarizedinCraig(1996).Craigclaimsthattemperatureandpainprocessingarecloselycoupledstructurallyinthebrainandthatbrainlesionsrarelyaffectonewithouttheother.Thebrain’sprocessingofpressureisstructurallymoredistinct.9SeeDallenbach(1939).10RivelinandGravelle(1984,17)

9

Outsidethehumansphere,thereareevenmorecandidatesintheanimal

kingdomforbeingsensesinadditiontotheAristotelianfive.Forexample,

pigeonsandotherbirdsseemsensitivetothemagneticfieldoftheEarth,which

givesthemafantasticsenseofdirection.11Ithasalsobeenshownthattroutcan

betrainedtostrikeattargetsdistinguishedonlybytheirpositioninamagnetic

field.Moreover,adistinctivesensoryorganandsensorysystemhavebeen

identifiedintroutthatdetectmagneticfields.Thisevidencehasledpeopleto

thinkthatalloftheconditionsrequiredforpositingamagnetoreceptivesensein

trouthavebeenestablished.12

Manyfishandsharksseemtohaveanelectricsense.Sometimesthis

sensetakesapassiveform,meaningthatthecreaturescandetectelectricfields

thatexistindependentlyofthemintheenvironment.However,thereisanother

activeformofthesensewherethecreaturesproduceanelectricfieldandthen

sensechangestoit.Somefishusethisactiveelectricsensefornavigationandto

detectotherlivingcreatures.13

Afurtherapparentlydistinctiveanimalsenseisinfrared(IR)detection.

Allpitvipersandsomeboidsnakeshavepitsontheirheadsthatcontaincells

thataresensitivetoinfraredlight.Thepitsareorgansdistinctfromthesnakes’

eyesandnostrilsandcanbeusedtoaccuratelydetectpreywhentheeyesare

covered.14

11SeeHughes(1999).12SeeWalkeretal.(1997),reportedinHughes(1999).13SeeHughes(1999).14Seeibid.

10

Fromthisevidence,onecanseethatmanygoodcandidatesexistforbeing

asense,distinctfromtheAristotelianfive.15Evenifwerequiredfurther

informationaboutthesecasesbeforeweconfidentlyassertedthatthey

constitutedsenses,theseexamplessuggestthatthereatleastcouldbesensesof

manydifferentkindsotherthantheAristotelianfive.Theonlywaytoresistthis

thoughtwouldbetoclaim,aswesawNuddsdoearlier,thatthefolk

psychologicalnotionofthesensesissuchthat,accordingtoit,thereareonlythe

fiveAristoteliansensesandthatthisconceptofthesensesissuchthatitisnot

liabletorevisionorreplacementbyscientificdiscovery.Dowehavegoodreason

tobelievethatthefolkconceptionofthesensesisasNuddsclaims?Ithinkthe

answerisno.

Onereasontothinkthatthefolknotionofasenseisnotrestrictedtothe

Aristotelianfiveisthatscientistsaresomeof“thefolk”andthenumberofsenses

thattheyrecognizehasfrequentlybeenaltered.Aswehavealreadyseen,the

debateabouthowmanysensesthereareisapresentconcerntoscientistsbut

thedebateisnotamodernphenomenon.Thenumberofsenseshasbeen

disputedthroughouthistorybybothphilosophersandscientists.SeeDallenbach

(1939).

Anotherreasonisthatitisveryplausibletothinkthatifordinarypeople

heardthefactsaboutothercreatures’sensitivitytothingssuchasmagnetic

fields,andtheyfoundouthowcreaturescanactbecauseofsuchsensitivity,orif

theyheardthefactsabouthumanproprioceptionandequilibrioception,they

15ThereareotherexamplesthatIhavenotdiscussedhere.See,forexample,ibid.andtheessaysinthisvolume.

11

would,Ibelieve,unhesitatinglythinkoftheseassenses.Iamhappytodoso,and,

inmyexperience,theaveragepersonshowsnoresistancetodoingso.

Anevenmoretellingfactinfavoroftheviewthatthefolkconceptofthe

sensesisnotrestrictedtotheAristotelianfiveisthat,inpopularculture,theidea

ofsensesotherthantheAristotelianfiveabounds.Howcouldthisbeunlessthe

folkconceptofasensewassuchthatitcountenancedthepossibilityofadditional

senses?Forexample,infictionthereareaccountsofpossiblesensessuchas

these:

• X‐rayvision

• mind‐readingsense

• sixthsense—theabilitytoperceivethefuture,ghosts,andsoon

• thePredator’sinfraredperception

• theTerminator’sperception,whichcananalyzethecompositionofobjects

• spidersense—theabilitytoperceivedangerviaaspecialtinglinginthe

extremities

Thus,Iseenogoodreasontothinkthatthefolkconceptionofthesensesis

committedtotherebeingfiveandonlyfivesenses.Thus,Iseenoneedtorevise

thefolkconceptioninlightofscientificevidence.Ibelievethatthefolkconceptis

simplysilentwithregardtothequestionofhowmanysensesthereare.16The

numberofsensesseemstobeleftopenbytheconceptofthesensesthatwe

16MatthewNudds(personalcorrespondence)isconcernedthatmyaccountdoesnotexplainwhypeopledosaythattherearefivesenseswhenaskedandwhythishasnotchanged.Ithinkthatitischanging.Somepeopledonotreplythattherearefive.Otherswhodo,quicklyrescindtheviewwhenothercandidatesensesarementionedtothem.Nodoubtmostpeoplehavegiventhequestionlittlethoughtandreplyautomaticallywiththeanswertheylearnedfromtheirpreschoolbooks.

12

have.Thefolkalreadyembracetheideathatthenumberofactualsensesisa

mattertobedeterminedbyempiricalfindings,andtheyembracetheideathat

thenumberofpossiblesensesisgreaterthanthis.Thus,Ibelieve,thefolk

conceptissuchthatwhennewempiricalevidenceoftherightkindisbroughtto

light,thatwhichistakentofallundertheconceptofthesensescaneasilybe

enlargedwithoutchangingorrevisingtheconcept.This,togetherwiththefacts

mentionedearlier,givesusgoodreasontothinkthatthereare,andcouldbe,

manymoresensorymodalitiesthantheAristotelianfive.Howmanyactually

existisaquestionthatonlyprogressinscience,togetherwithphilosophical

investigationintotheconditionsrequiredfortheexistenceofsensorymodalities,

willbeabletoshedlighton.

Canwesayanythingfurtheraboutthequestion:Howmanysensescould

therebe?Theanswerdependsinpartonthequestionthatformsthemaintopic

ofthenextsection.Therefore,Ireturntothisquestionafterconsideringhowto

individuatethesenses.

2.WhatMakesaTokenSenseanInstanceofOneTypeRatherThan

Another?

Whatdeterminesthatasensorymodalityistheparticularmodalitythatitis,

ratherthananother?Toanswerthisquestiononewouldneedtohavea

principleforindividuatingthesenses.Thatis,youwouldneedtobeabletosay

whatestablishesthatasenseisvisual,say,ratherthanauditory,tactile,

gustatory,orolfactory.

13

Thisindividuationquestionhasbeenthefocusofmuchoftheworkin

philosophyconcerningthesenses.Asnotedattheendofthelastsection,thereis

anobviousrelationshipbetweenthisquestionandthatofhowmanysenses

thereare.Ibelievethatanexplicitoratacitacceptanceofthesparseviewabout

howmanysensestherearehasinfluencedwhatpeoplehaveoftensaidaboutthe

individuationquestion—inadetrimentalfashion.Afterelucidatingthestandard

answerstotheindividuationquestion,Isuggestanotheranswerthatrejectsthe

sparseviewandsuggeststhatthenumberofactualandnomologicallypossible

sensesisratherlargerthanmanyhavethought.

Therearefourmainphilosophicalapproachestoindividuatingthe

senses.17Importantversionsofthefirsttwoarebroadlyexperientialapproaches,

holdingthatwhichsenseisbeingusedisdeterminedbywhichfeaturesthe

perceptualexperiencesproducedbythesensehave.Theothertwoarebroadly

physicalapproachesthatholdthatwhichphysicalfactorsareatplayintheuseof

asensedeterminewhichsenseisbeingused.Idiscusstheminturn.

2.1.TheRepresentationalCriterion

Onepredominantlyexperientialapproachisthatasenseisindividuatedby

whichobjectsandpropertiestheexperiencesinthatmodalityrepresent.The

classicAristotelianviewisonevarietyofthisapproach.AccordingtoAristotle,

thereare“commonsensibles”—objectsorpropertiesthatcanbedetectedby

morethanonesense.Forexample,shapeisacommonsensibleasitcanbe

17SeeGrice(1962).

14

detectedbybothsightandtouch.Othersincludemotion,rest,magnitude

number,andunity.Therearealso“propersensibles”—objectsorpropertiesthat

canbedetectedbyonlyonesense.Withoneexception,eachsensehasitsown

propersensible,andrepresentationofitiswhatmakesthesensethesensethat

itis.Forexample,thepropersensiblesofhearing,tasting,smelling,andseeing

aresound,flavor,odor,andcolor,respectively.Touchistheoddmanoutasithas

multiplepropersensibles,whichAristotlethinksarereducibletofourbasic

ones:dry,fluid,hot,andcold.

Therearemanyvariantsoftherepresentationview.Forexample,one

mightthinkthatthereareanumberoffeatures,representationofwhichis

necessaryorsufficientorbothforasensetobethesensethatitis.Forexample,

onemightthinkthatvisionessentiallyinvolvesrepresentationoftheshapeand

sizeofobjectsinthree‐dimensionalspaceatadistancefromone’sbody,aswell

ascolorandshadesoflightanddark.Onemightthinkthattouchessentially

involvestherepresentationoftheshapeandsizeofobjectsthatareincontact

withone’sbodyandmustinvolvetherepresentationoftemperature,pressure,

andtexture.Whatexactlyonespecifiesforeachofthesesenseswilldependon

thinkingthroughalargenumberofexamplesofinstancesofsightandtouch.

Anothervariantoftherepresentationviewwouldinsistthatthe

representationthatweshouldconsiderwhenindividuatingasenseshouldnot

be,orshouldnotjustbe,whatisrepresentedinexperienceattheconscious,

personallevelbutwhatisrepresentedbyunconscious,subpersonalbrainstates

ormechanisms.Inotherwords,theywouldinvokeaninformation‐processing

15

notionofrepresentationwhereinoneattributescontentto(perhaps)

unconsciousbrainstatesinvolvedinperceptualprocessing.

Somepeoplewillthinkthatwhatiscrucialinindividuatingasenseisthe

behaviorthatthesenseallowsacreaturetoengagein.Forexample,asense

mightallowacreaturetonegotiatethroughitsenvironment,avoidingobstacles

atadistancefromitsbody,oritmightallowthecreaturetodetermineits

positionwithrespecttogravityortomagneticfields.Itisnotunreasonableto

includepositionsthatmakeessentialreferencetobehaviorunderthe

representationalcriterion.Thisisbecausewhenweaskhowacreaturecan

behave,theanswerwillverylikelydependonwhatitknowsorbelievesabout

theenvironment—inshort,howitrepresentstheenvironmenttobe.Some

peoplemightresistthisbecausetheyholdaviewofperceptionthatdeniesthat,

inperception,representationsarecreatedinone’smindorone’sbrain.Rather,

whenperceiving,acreaturedirectlyrespondseithertotheworldortothe

patternoflightinspaceandtimethatdirectlystimulatesit.18However,although

theseviewsdenythatrepresentationsareinvolved,onecanarguethatthereis

alwaysatleastaminimalsenseinwhichperceptualstatesarerepresentational.

Thisisbecause,attheveryleast,experiencesorotherperceptualstatesofthe

creaturecanbeassessedforaccuracy,andtheconditionsinwhichthe

experienceorstatewouldbeaccuratecanbetakentospecifywhat

representationisinvolved.19Alternatively,onecouldclaimthattheaccurate

descriptionoftheactionsinvolvedcanbeusedtogenerateasetofobjectsand

18Somedisjunctivists,followersofJ.J.Gibson’secologicalapproach,aswellassensorimotortheorists,holdsuchaposition.19ThishasbeenarguedforbySusannaSiegel(2010),whereaccuracyiselucidatedastheconditionsinwhichthereisfreedomfromerror.

16

propertiestakentospecifyarelevantrepresentationalcontent.Forexample,ifa

creaturecan“avoidtheobstacletoitsleft”or“battheball,”thenthese

descriptionsofactionsinpartspecifywaystheworldisorcouldbeandthus

couldbetakenasdescriptionsofrepresentationsrelevanttodeterminingthe

senseinvolved.

Nodoubtsomephilosopherswouldprefertokeepseparatea

representationalcriterionandabehaviororactioncriterion.However,nothing

ofimportturnsonthisformypurposes.Aslongasoneisclearaboutwhatform

ofrepresentation,behaviour,oractiononeisusingtoindividuatethesenses,it

doesnotmatterwhetheronecallsthistypeofcriterionarepresentationalone,a

behaviouralone,oranactionone.

2.2.ThePhenomenalCharacterCriterion

Asecondexperientialapproachistothinkthatwhatmakesasensethetypeof

senseitiswillbethenatureofthephenomenalcharacteroftheexperiencesthat

thesenseproducesorinvolves.Immediately,however,oneisfacedwiththe

questionofhowonemightspecifythesortofphenomenalcharacterthatallof

theexperiencesofonesensorymodalitymusthave.Itseemsthatwhenwe

specifythephenomenalcharacterofanexperience,wealmostalwayssaywhatit

wasanexperienceasof—thatis,whattheexperiencerepresented,whetheror

notthatrepresentationwasaccurate.Soonemightspecifyaclassofexperiences

withacertainphenomenalcharacterbyspecifyingaclassthatrepresentscertain

things.Inthisrespect,thephenomenalcharactercriterioncouldturnouttolook

17

verymuchliketherepresentationalcriterion.(Indeed,whetherthenatureofthe

phenomenalcharacterofanexperiencecanbefullyspecifiedjustintermsof

whattheexperiencerepresentsisapointmuchdisputedinthephilosophyof

mind.20)Forthosephilosopherswhothinkthatthephenomenalcharacterof

experiencecanbeidentifiedwiththerepresentationalcontentofexperience,the

representationalcriterionandthephenomenalcharactercriterionwillbethe

same,butforthosephilosopherswhodenythis,theywillbedistinct.

Anotherwayonemightspecifythesortofphenomenalcharacterthatall

theexperiencesofonesensemusthaveistospecifyonetypeofexperienceand

thenciteagroupofexperiencesrelatedtoit.Animportantandinfluentialwayof

doingthisistodefineclassesofexperiencesusinganotionofglobal

indiscriminability.21Thehopeisthatwecoulddefinesimilarityclasses

correspondingtoallandonlythoseexperiencesthatweintuitivelywouldthink

ofasexperiencesineachdifferentsensorymodality.Onemightthendefineeach

ofthesensorymodalitiesasbeingtheonethatproducestheexperiencesinthe

appropriatesimilarityclass.

2.3.TheProximalStimulusCriterion

Aphysicalapproach,andonequiteunliketheexperientialapproachessofar

considered,istoindividuatethesensesbythenatureoftheproximalphysical

stimulithataffectthesenseorgan.Theproximalstimulusisthatwhichdirectly

impingesonthesensoryorganofthesense.Forexample,onemightthinkthat20Tye(1995)andDretske(1995),amongothers,arguethatitis.I(2003,2005,2006),amongothers,arguethatitisnot.21Formoreinformationonthismethodologyseeibid.

18

electromagneticwavesofbetween380and750nanometersaretheproximal

stimuliofvision,forthosearewhatdirectlystimulatethecellsintheeye.Onthis

view,oneisseeingifandonlyifone’smethodofperceivingtheworldinvolves

thedirectstimulationofone’ssensoryorganbysuchelectromagneticwaves.

Onemightthinkthatpressurewavesinamediumaretheproximalstimuli

associatedwithhearing.Thus,onewouldbehearingifandonlyiftheproximal

stimulithataffecttheorganthatoneisusingtoperceivearepressurewavesin

somemediumsuchasairorwater.Onemightthinktheproximalstimuliofsmell

arethemembersofaclassofairbornechemicals.Onecouldsimilarlyidentify

proximalstimuliforeachsense.

2.4.TheSense­OrganCriterion

Thesecondphysicalapproachistoindividuatethesensesbythenatureofthe

senseorganthatoneisusingwhenperceiving.Onemightthinkthatifeyesare

used,thenoneisseeing;ifears,thenoneishearing;andsoon.However,itwould

seemincumbentononetothengiveanaccountofwhatmadesomethinganeye,

anear,andsoon.

Onetemptingwaytodothiswouldbetospecifythenatureofthesensory

organsbyspecifyingthenatureoftheproximalstimulusthataffectedthem.For

example,perhapsonemightdefineaneyeasbeinganorganthatdetectslight

wavesandearsasorgansthatdetectpressurewaves,andsoon.Ifone

proceededinthisway,thenthedifferencebetweenthisapproachandthe

previousonewouldessentiallycollapse.

19

Onecouldalsodefinethesensoryorgansinphysicalways.Thus,the

physicalmakeupoftheorganwouldbeimportant.Indeed,onemightnotonly

wanttomentionthephysicalmakeupofjustthesensoryorganbutalsoinclude

aspartofthecriterionthephysiologyofthewholesensorysystem,suchasthe

natureofthenervesleadingtothebrainandeventherelevantpartsofthebrain

itself,inparticularthecorticalregionstowhicheachsensorysystemprojects.

WhenIspeakofsense‐organapproaches,Iincludeapproachessuchasthesethat

includethewholesensorysystem.

2.5.TheStandardViewsandtheAristotelianSenses

Muchofthephilosophicalliteratureonindividuatingthesensesinvolves

presentingreasonstofavoroneoftheseviewsoveranother.Forthemostpart,

thefiveAristoteliansensesdifferfairlymarkedlyonallfourapproachesfrom

eachotherwhentheyareoperatingnormallyandinoptimalconditions.Those

whosupportthesparseviewofthesenseswouldclaimthatthisisevidencefor

theirviewthatthesensesareverydifferentanddiscrete.Toillustratethis,see

thefollowingtable,whichdisplayshowonemightthinktheAristoteliansenses

differonallfourcriteriasuggestedbythetheories.22

Vision Touch Hearing Taste Smell

Representation Colour,shapeandmovementatadistance

Temperature,pressure,shapeand

Sounds,volume,pitch,

Flavours(sweet,salty,bitter,

Odourslocatedeitherin

22Ofcourse,therearesomereasonstoquestionthisneatdichotomy,evenfortheAristoteliansenses,aswewillseeinduecourse.Inparticular,itturnsoutthatdistinguishingtasteandsmellisparticularlydifficult.

20

fromourbodyinfrontofoureyes

movementatthesurfaceofourbody

objectsbeingstruckorvibratedatlocationsinandatdistancefromandallaroundourbody

sour,umami)inthemouthoronthetongueorinthefoodtouchingthetongue

thenoseorintheairaroundthenose,perhapscomingfromacertaindirection

Phenomenal

Character

Visualexperiences

Tactileexperiences

Auditoryexperiences

Tasteexperiences

Olfactoryexperiences

Proximal

Stimulus

Electromagneticwaves

Mechanicalpressureandtemperature

Pressurewavesinamediumsuchasairorwater

Chemicalsthataffectreceptorsonthetongue

Volatilemoleculesthataffecttheepithelium

SenseOrgan Eyes,particularlytheretina

Skinorreceptorsintheskin

Ears,particularlythecochlea

Tongue,particularlythetaste‐budsonthetongue

Nose,particularlythenasalepithelium

However,thefollowingcreatehavocwiththisneattaxonomy:

(1)non‐Aristoteliansenses

(2)tamperingwiththeAristoteliansenses

(3)malfunctionoftheAristoteliansenses

(4)theAristoteliansensesoperatinginoddenvironments

Thesecasesshow(aswillshortlybeillustrated)thatnoneofthefourcriteria

allowustoneatlycategorizeeachofthesensesasbeingoneoftheAristotelian

sensesorasbeingoneofasmallnumberofdiscretesenses.Furthermore,the

fourcriteriapullusindifferentdirectionswhenwetrytodeterminewhichtype

ofsenseagivensenseis.Thisisonereasonthatpeoplehavethoughtthatone

hastochoosebetweenthefourcriteriaforindividuatingthesenses—theyhave

thoughtthatonehastopickthebestoutofthecompetingtheoriesfor

21

individuatingthesenses.However,afteroutliningfourexamplesthatbringto

lightthemostimportantproblemsthesetheoriesface,Isuggestanalternative

approachtoindividuatingthesenses.Iclaimthat,inlightoftheseexamples,we

havereasonnottobesparsetheoristsandthat,oncewegiveupthat

commitment,wecancometoseethefourcriteriainanewlight.Theyarecriteria

thatcanbeusedtogethertoallowustoaccurately,nonarbitrarily,andinafine‐

grainedmannertaxonomizetheactualandpossiblesenses.

2.6.TheStandardViewsandBatEcholocation

Batssendoutahighfrequency“chirrup”andlistenforthereturningecho.Both

thetimeittakesforthesoundtobounceoffobjectsandreturntothebatandthe

directionfromwhichthesoundisreturned(determinedbythedifferenttimesat

whicheachearisstimulatedbythereturningecho)areusedtodeterminethe

size,shape,andpositionofobjectsatadistanceinfrontofthebat.Thismeansof

perceptionallowsbatstonegotiatethroughtheirenvironmentskillfullyand

quickly,dodgingobstaclesandcatchingmothsandotherpreyinthedark.23

Whatdoyourintuitionssayaboutthissense?

(1)Batshaveanincredibleformofhearing.

(2)Batscanseeinthedarkusingthismechanism.

(3)Batshaveasensethatwedonot:echolocation.

23Furtherdetailsofthebat’secholocation,togetherwithexcellentinformedspeculationontherepresentationalandphenomenalnatureofthebat’sexperience,isgiveninAkins(1993).

22

Theproximalstimulusandsense‐organcriteriatendtosuggestthatthebathasa

formofhearingbecausetheproximalstimulusispressurewavesandthe

sensoryorganisanear,oratleastsomethingmorelikeourearsthananyother

organ.However,thefrequenciesthatbatscanheararedifferentfromthosethat

wecanhear.So,tojudgethatthebatishearingistothinkthathearinginvolves

thedetectionofanyfrequencyofpressurewave,asopposedtojustthosethat

humanscandetect.Similarly,thebat’searsarenotphysicallyexactlylikeours.In

addition,ifwithinthesense‐organcriterionwewishtoincludethebrain

mechanismsthatprocessthesignalscomingfromtheear,thenbecauseabat’s

brainreceivesorcalculatessomuchmoreinformationfromitsauditorysignal

comparedtohumans,therearenumerousdifferencesbetweenthebat’sbrain

andours.Sothebat’ssensoryorgansaresomewhatlikeours,butsomewhatnot.

Inshort,whiletheproximalstimulusandsense‐organcriterionmostnaturally

suggestthatthebatishearing,onecouldholdthattheproximalstimulusandthe

senseorganaredifferentenoughfromoursthatthebatshouldbecounted,on

applicationofthesecriteria,ashavingasensethatwedonot.

Therepresentationalcriterionyieldsunclearresults.Onemightthinkthat

itwillyieldtheresultthatthebatisseeingbecause,usingthissense,thebatcan

detectthree‐dimensionalobjectsatadistancefromitsbody,whichhumanscan

dowiththeirsenseofsight.However,thebatdoesnotdetectcolor,andsome

peoplehavethoughtthatperceptionofcolorisrequiredforseeing.So

alternatively,onemightthinkthatthebatreallyhasasenseofhearing,forsurely

thebat’sexperienceswillrepresentthesoundthatbouncesbackintheformof

theecho.Andindeed,onemightquestionwhetherthebat’sexperiences

23

representwhereobjectsareatadistancefromitsbody.Onemightthinkthat

instead,postperception,thebatjudgeswheretheseobjectsareonthebasisof

thingsthatithears.24Alternativelyagain,onemightbeinclinedtothinkthatthe

bat’sexperiencesrepresentbothsoundandobjectsatadistancefromitsbody.If

thisisright,thenperhapsthebatbothseesandhearswiththeonesensory

organ.Orperhapsitwouldbebesttosaythatithasadifferentsensealtogether

fromanyoftheonesthatwehave.

Thephenomenalcharactercriterionisunhelpfulinthiscase.Tothe

extentthatwecanimaginewhatitisliketobeabatonemightthinkthattheir

experiencessharesomeauditoryandvisualcharacteristicswithhuman

experiencesandperhapshavesomeunlikeeitherofthese.25

Sowhatshouldwedecide?Inpartweareignorantofsomefacts,knowledgeof

whichmighthelpusdeterminewhichsensethebathas.However,Ibelievethat

evenifweknewalloftherelevantfacts,ourintuitionsandcriteriawouldtellus

thatthebat’ssenseislikeourvisioninsomerespectsandlikeourhearingin

othersandlikeneitherinsomerespects.Beforeexploringwhatweshoulddoin

thefaceofthis,considertheothercases.

2.7.TheStandardViewsandBee“Vision”

24Whetherwecandrawasharplinebetweenperceptualcontentandjudgmentisahighlydebatablematter.25Famously,philosophershavethoughtthatonecannotknowwhatitisliketobeabat.(SeeNagel[1974].)However,Akins(1993)persuasivelyclaimsthatwecanknowquitealotaboutwhatitislike,evenifnoteverything.

24

Beesaresensitivebothtowhatwecallvisiblelightandalsotoultraviolet(UV).If

welookatmanyflowersinvisiblelight,theyoftenlookliketheflowerontheleft

ofthediagram(Fig.1)—theyhaveasmalldarkcenterandthenauniformcolor

onthepetals.However,ifwephotographthemusingacamerasensitiveto

ultravioletlight,thentheflowersoftenlookliketheflowerontherightofthe

figure.Theextramarkingsthatcanbedetectedusingultravioletarecalledthe

“nectarguide”pattern,andtheyguidethebeestothesourceofthenectar.

Fig.1Diagramoftypicalmarkingsonflowers:invisiblelightontheleft,andin

ultravioletlightontheright

Itisnaturaltosaythatbeeshavevision—aformofvisioninwhichboth

thehumanvisiblespectrumandultravioletlightaredetectedbythebees’eyes.

Butshouldwe?

Ifwethinkthatbee“vision”reallyisvision,andwethinkweshould

individuatethesensesbytheproximalstimuluscriterion,thenonemustthink

thattheproximalstimulusofvisioniswiderthanthevisiblespectrumandalso

includesultravioletelectromagneticwaves.However,ifoneiswillingtoextend

theproximalstimulusbeyondvisiblelight,thenshouldoneextendittothe

25

wholeelectromagneticspectrum?Onemightthinkthatoneoughtto.Afterall,

onemightthinkthatalltheelectromagneticwavelengthsformanaturalkind.

Whatmakesthemdifferentismerelytheirwavelength.However,ifonedoes

that,thenonewouldbecommittedtothinkingthatacreaturethatdetectedonly

radiowaveswasseeingandthatonethatdetectedonlygammarayswasseeing.

Nevertheless,itisfarfromobviousthatcreatureswithsuchdetecting

mechanisms,evenifwewereconfidentthattheyweresenses,wouldreallybe

onesthatwewouldwanttocountasvision.Icertainlywouldwanttoknowalot

moreaboutthesenseinquestion,suchasthenatureofthesenseorgan,whatthe

subject’sexperiencesrepresented,andwhattheirphenomenalcharacterwas

beforeIwouldfeelconfidentthatthesensewasvision.

Alternatively,perhapsweshouldlimittheproximalstimulusofvisionto

encompassjustvisiblelight.Inthatcase,thebeewouldeitherhavevisionplus

someothersense,anultravioletsense,orjustsomesenseotherthanvision—one

thatdetectedbothultravioletandvisiblelight.(Afurthercaseforthethought

thatweshouldlimittheproximalstimulusofvisionisoutlinedwhenwecometo

discusssnakeinfraredperceptionlater.)

Thesense‐organcriterionyieldsunclearresults.Wedoclassifythebees’

organsthatdetectvisiblelightandultravioletlightaseyes.Nonetheless,bee

eyesareverydifferentfromhumaneyes.Beeshavetwolarge,compoundeyes

andthreesmall,simpleeyes(called“ocelli”)arrangedinatriangleontheir

forehead.Whenwelearnjusthowdifferenttheorganofthebees’“vision”isto

ours,itisnotcompletelyobviousthatweshouldthinkofbeesashavingeyes.

26

Therepresentationalcriterionperhapsdeliverstheclearestverdictthat

beeshavevision.Theywouldseemtorepresentwhatwerepresent—three‐

dimensionalobjectsatadistancefromourbodies.Perhapstheyrepresentallof

thequalitiesthatwerepresenttheworldashaving,plussomeothersvisibleonly

tothosewhocandetectultraviolet.Still,ifthatisright,thenperhapsweshould

thinkthattheyhavetheirownspecialvision‐plus‐ultravioletsense.Thisismade

allthemoreplausiblewhenweconsiderthatitisnotclearthatbeessimply

representmorethanus—someextraultravioletfacts.Humanshavethreetypes

ofcellsintheireyesthatareresponsivetolong,medium,andshortwavelengths

ofvisiblelight.Thenatureofthesecells,plussubsequentprocessing,determines

thekindofcolorvisionthatwehave.Beeshavethreekindsofreceptor,too,but

theirsspanboththevisibleandtheultravioletranges.Thus,thekindof“color

vision”thatbeeshaveisratherdifferentfromours.Beesdonotseethecolors

thatweseeplussomeothercolors.Theydonotsee,forexample,howtheflower

lookstousundervisiblelightandhowitappearstousinapicturetakenbya

camerasensitivetoultravioletlight.Rather,theyseetheflowerinjustoneway,

determinedbyboththereflectanceofvisiblelightandultravioletlightandbythe

natureoftheirlight‐sensitivecells.Becauseofthis,itistemptingtodescribethe

caseasoneinwhichbeesdonotseecolors—orattheveryleastdonotseethe

colorswedo.Andthenif,withAristotle,wethoughtthatwhatmadeasense

visionwastherepresentationofthecolors—oratleasttheoneswesee—it

wouldberighttoconcludethatthebeesdonotsee,althoughtheydosomething

similar.

27

Finally,thinkaboutthephenomenalcharactercriterion.Ofcourse,itis

hardtoknowwhatthephenomenologyofbeeexperienceislike,butourbest

guesswouldbethattosomeextentitisthesameandtosomeextentdifferent

fromhumanvision.26Thefactsthatmakeusthinkthatwhatthebees’experience

representspartiallyoverlapswithhumanvisualexperienceandpartlydoesnot

motivatesthisthought.Here,amixtureofourignoranceandourbestguess

leavesusunsureastohowtoclassifybee“vision.”Itissomewhatlikeourvision

andsomewhatnot.

Thus,althoughafewcriteriasuggestthatbeeshavevision,thesensethey

haveissufficientlydifferentfromourvisionthatonemightthinkitadifferent

sense,evenifitismostlikeourvision.Thiscaseshowsthatforeachproposed

criterionforindividuatingthesenses,itwillbedifficulttodecideuponthe

necessaryandsufficientconditionsthatittakestohaveaparticularsense.We

willseethisproblemmanifestitselffurtherinthenextexample.

2.8.TheStandardViewsandSnakeInfraredPerception

Itisinterestingtocontrastandcomparethecaseofbeevisionwiththatofsnake

infraredperception.Somesnakes,suchaspitvipersandboidsnakes,have

organsseparatefromtheireyesthatdetectinfrared.Theseorgansaresituated

onthefrontofthesnakes’faces,belowtheeyesandclosetothesnakes’nostrils.

Theyconsistofpitslinedwithinfrareddetectingcells.27Usingthissensealone,

26Somepeoplemightevenwonderwhetherbees(andotheranimals)arethesubjectsofanystateswithphenomenalcharacter.27SeeHughes(1999).TherelevanceofthiscasetoindividuatingthesensesisalsodiscussedbyGray(2005).

28

snakescandetectpreyinfrontofthemanddiscriminatetheshapeoftheprey

enoughtoallowthemtomakeprecisestrikesonvulnerablepartsoftheprey’s

body.(Thisabilityhasbeendocumentedinacongenitallyblindrattlesnake.28)Is

thisaformofvisionornot?Letusrunthroughthelistofcriteriaagain.

Theproximalstimuluscriterionisunclear.Aswithbee“vision”wefacea

decisionastowhetherweshouldextendtheproximalstimulusofvisionbeyond

thatofhumanvisiblelight,thistimetoincludenotultravioletbutinfrared

radiation.Ifonethinksthatoneshoulddoitforultraviolet,thenitwillbehardto

findprincipledgroundsonwhichtoexcludeanextensiontoinfrared.Thenagain,

thequestioncomesup:shoulditbeextendedtoincludedetectionofanypartof

theelectromagneticspectrum,includinggammaorradiowavesevenif,

intuitively,thedetectionofthesewaveswouldnotyieldasenselikevision?

Thesense‐organcriteriondoesnotyieldperspicuousresults,either.The

snakes’pitsarelikeoureyesinsomerespectsbutnotverymany.Theobvious

questionfacingthiscriteriononconsiderationofthisexampleis,Whatisitfor

somethingtobeaneye?Rightawaywecanseethatanycriteriaforbeinganeye

willbeverymalleable.Forexample,isaneyeanyelectromagneticdetectoror

justadetectorofallandonlyvisiblelightorsomethingelse?

Anotherinterestingquestionthatthesnakeinfraredsenseraises,in

additiontothatofwhichsenseitis,iswhetheritisaseparatesensefromwhatis

commonlytakentobethesnake’svisualsense.Certainlytheeyesandthe

infraredpitsaredifferentsensorysystemstotheextentthatwethinkofthemas

formedbyjustthephysiologicalstructuresnearthesurfaceofthesnake’shead.

28SeeKardongandMackessy(1991).

29

However,ifwethinkofthesenseorgansascomposingthewholephysiological

structureleadingfromthecellsthatlightandinfraredimpingeupontothe

centralpartsofthebrain,whichprocesstheinformationgatheredbythosecells,

theissueisfarfromclear.Ithasbeenfoundthatthemaplikevisualandinfrared

representationsoftheworldinthesnake’sbrainarepartlyoverlaidintheoptic

tectum.Someneuronsinthetectumrespondonlytovisualstimulationoronlyto

infraredstimulation;othersrespondtoeithervisualorinfraredstimulation;still

othersrespondonlytoacombinationofvisualandinfraredstimulation.There

maybeenoughoverlapthatoneistemptedtothinkthatbothsetsoforgans(the

snakes’eyesandinfraredpits)arereallyorgansoftheonesenseinthewayour

twoeyesareorgansoftheonesense.

Thequestionofwhetherthesnakehasonevisible‐light‐plus‐infrared

senseortwotokensenses—eithervisionandaninfraredsenseortwotoken

sensesofvision—muddiesthewaterinconsideringthenatureofthesnake’s

senses.Fortherestofthissection,Iassumethattherearetwotokensensesand

addressthequestionofwhetherthesensethatdetectsinfraredisasenseof

visionornot.

Whatdoestherepresentationalcriteriontellus?Itisareasonable

assumptionthatthree‐dimensionalobjectsatadistancefromthesnake’sbody

arerepresentedonaccountoftheprecisetargetingofpreybysnakesusingonly

thissense.Theinfraredsensethensharesarepresentationalaspectwithhuman

vision.Nonetheless,thesnake’sinfraredsensedetectsheatanddoesnotdetect

thecolorpropertiesthatwedetect,sothereareconsiderabledifferenceswith

regardtorepresentation,too.Theserepresentationalsimilaritiesanddifferences

30

suggestthatthephenomenalcharacterofthesnake’sinfraredsensemaybe

somewhatlikeourvisionbutsomewhatdifferent.Itishardtosayverymuch

morethanthis.

Insummary,thesnakeinfraredsenseissomewhatlikeourvisionand

somewhatnot.Unlikethecaseofbee“vision,”whichinvolvesdetectionofthe

partoftheelectromagneticspectrumhumanscandetectplusanadditionalpart,

snakeinfraredperceptiondoesnotinvolvedetectionofapartofthe

electromagneticspectrumthathumanscandetect,merelydetectionofshorter

wavelengths.

2.9.TheStandardViewsandTactile­VisualSensorySubstitution

Tactile‐visualsensorysubstitution(TVSS)devicestrytoreplacethesenseof

sightbyexploitingthesenseoftouch.Acameraimagedrivesagridofvibrating

pinsthatpressagainstthebackorothersuitableexpanseofskin.Areasofthe

cameraimagecorrespondtoisomorphicareasofthegridofpins,andpressure

andvibrationagainsttheskincorrespondtothelightlevelsthecameradetects.

Withpractice,subjectscanusethesystemtoskillfullynavigatetheirway

throughtheworldandidentifythree‐dimensionalobjectsatadistancefrom

theirbody.29

Atfirst,subjectsreportthattheyareawareofthesensationsontheirskin,

butastheycontinuetousethesystemtheystoppayingattentiontoornoticing

thetactilestimulation,atleastassuch,andinsteadattendtoornoticewhat

29SeeBach‐y‐Rita(1972).

31

seemstothemtobetheobjectsintheworldinfrontofthem.Reportsaboutsuch

subjectssuggestthattheirexperienceshavemuchincommonwithvisual

experiences,particularlywithregardtotheirspatialnature.Forexample,

NicholasHumphreyreportsthefollowing:

Bymakinguseofinformationintheimageaboutperspectiveandmotionparallax,

theblindsubjectscametoperceiveexternalobjectsasbeinglocatedinastable

three‐dimensionalworld.Theydidnotlocateobjectsaslyingupagainsttheir

skin—anymorethanwewithnormalvisionlocateobjectsaslyingupagainstthe

retinaofoureyes—butimmediatelyperceivedthemasbeingoutthereinspace.

(1993,59)

ArepeoplewhouseTVSSdevicesseeing,feeling,orperceivinginsome

differentway?Thatis,arewereplacingtheirvision,orareweextendingtheir

existingsenseoftouchtoallowthedetectionofobjectsandpropertiesitusually

cannotdetect,orarewecreatingabrandnewsense?Thesensory‐organ

criterionwouldyielddifferentanswersdependingonwhatwesaythesense

organhereis.Ifitisthecamera,thenperhapsweshouldthinkthatthesenseat

playisvision.Ifitistheskin,thenweshouldthinkittouch.Ifitisthecamera

plustheskin,thenperhapsthesenseisneithervisionnortouchbutanew

sensorymodality.Theproximalstimuluscriterionisopentojustthesamesort

ofspeculation.Isthestimulusthepressureontheskin,lightonthecamera,or

both?Whichonedecidesuponwilldeterminewhetherthesenseistouch,vision,

orneither.

Whatdoestherepresentationalcriteriontellus?Certainlyatfirst,when

usingtheTVSSsystem,thereisarepresentationofthepinstouchingthebody.

32

ThissurelyremainsovertimeasthesubjectgetsusedtotheTVSSsystem,even

ifitisnotthemainfocusofsubject’sattention.Thesubjectalsoseemstoacquire

arepresentationofobjectsinthree‐dimensionalspaceinfrontofthem.Tothis

extenttheirexperiencesseemtorepresentinpartwhatvisualexperiencesdo

(minuscolor).Thenagain,ifthesubjecthasexperienceswithbothvision‐like

andtouch‐likerepresentationalcharacteristics,thenperhapsthesubjecthasa

sensethatordinaryhumansdonot.Thephenomenalcharactercriterionyields

muchthesameresulthere:oneimaginestheexperiences,phenomenally

speaking,tobepartlyliketouch,partlylikevision,andpartlydistinctive.

Thus,peoplewhouseaTVSSsystem,atleastoncetheyhaveadaptedtoit,

areusingasensepartlylikevision,partlyliketouch,andpartlyunique.

2.10.RejectionoftheSparseViewandHowtoIndividuatetheSenses

Thecriteriaandourintuitionstellusthatineachofthefollowingcases:

•echolocation

•UVvision

•IRvision

•tactilevision

thesenseinvolvedisinsomerespectslikeourvisionandinsomerespects

different—sometimeslikeanotheroneofoursensesandsometimesdifferent

altogether.Isuggestthattheseexamplesandothersshowthattheactualandthe

possiblesensescannotbeclearlydividedintoalimitednumberofdiscretekinds.

33

Thedifferencesbetweenthesensesamountsmoretoadifferenceofdegree

ratherthanadifferenceofkind.

Ratherthantrytopigeonholeallofthesensesintoasmallnumberof

discretecategoriesweshouldsimplynotewhateachsenseislikewithregardto

eachofthefourcriteriaproposedbyphilosophers:

•proximalstimulus

•representation

•phenomenalcharacter

•senseorgan

(andperhapsothersiftheyarerequiredtofullycapturealloftheimportant

aspectsofthesenses).Foreachcriterionwecannotehowdifferentorsimilar

eachsenseistooneofthefiveAristoteliansensesifwelike,butthatisrelatively

unimportant.Weshouldstoptryingtoartificiallydetermineorstipulatewhich

Aristoteliansenseanysenseis—ortoshoehorneachsenseintooneofasmall

numberofdiscretekinds.Itisbecausepeoplehavetriedtodothisandbecause

thefourcriteriapullindifferentdirectionsinproblemcasesthatpeoplehave

thoughtthattheyhavetochooseamongthefourcriteria—ratherthanembrace

themall.

Forexample,MatthewNuddshassuggestedthatourchoiceofwhichof

thestandardcriteriaweusetoindividuatethesensesshouldbedeterminedby

theirsignificance.Thisseemslikeagoodmethodology.Weshouldask,Whydoes

distinguishingthesensesmattertous?Nudds’sownansweristhat,“In

34

distinguishingdifferentsenseswearedistinguishingdifferentwaysof

perceiving”(2004,45).Hegoesontoexplainthatdifferentwaysofperceiving

willinvolveperceivingdifferentrangesofproperties.TellingyouwhichsenseI

amusingtoperceivesomethingletsyouknowthetypeofpropertiesthatI

(normally)knowabout.

However,Ithinkthatdistinguishingthesensesmatterstousbecausewe

careaboutallofthefollowing:

•representation

•proximalstimulus

•phenomenalcharacter

•senseorgan

Philosophershavearguedoverwhichisimportant,butwhynotthinktheyall

are?Allcanmatterpractically,andallcanmatterfordeterminingboth

philosophicalandscientificissues.

Iholdthatthefourcriteriaarerelativelyindependentdimensionsalong

whichdifferentpossiblekindsofsensescouldtakedifferentvalues.Wecanthink

ofthesefourcriteriaasdefiningamultidimensionalspacewithinwhichwecan

locateeachoftheAristoteliansenses,thefourexamplesofunusualsenses

discussedearlier,andanyothersense.Thus,humanvision,bee“vision,”snake

infraredperception,andTVSSperceptionwouldeachbelocatedatadifferent

placeinthemultidimensionalspace.Indeed,thismultidimensionalspaceisa

wayofdelineatingthespaceofallpossiblesenses.Allpossiblesenseswill

35

occupyaplaceinthespace.30(Theactualsenseswilloccupyasmallnumberof

theseplaces.31)

Plottingtheactualsensesinthisspacewillallowonetoseethe

similaritiesandconnectionsbetweenthemyet,atthesametime,toindividuate

thetypesofsenseinanonsparse,fine‐grainedmanner.Whenwedosucha

plottingfortheactualsenses,wecoulddoitforeachtokeninstanceofasense,or

wecoulddoitforidealizedversionsofthesensesineachspecies.Ifwedidthe

former,thenmysenseofvisionmightturnouttobeadifferentsensefromyours,

forImaybemuchmorenearsightedthanyou.Ifwedidthelatter,thenwewould

havethesamesense,forweeachhavetokensoftheidealizedsenseofvisionin

humans.Also,ifwedidthelatter,wemightfindthattheactualsensesaretobe

foundinclustersinthisspace.Forwewillfind,forexample,thathumanvision

andbee“vision”areclosertogetherinthisspacethanhumanvisionandbat

echolocation.PerhapstheseclusterswouldcorrespondtotheAristoteliansenses

ortheAristoteliansensesplusafewothers.Isuspectthismightbethecase.This

wouldshowusthatthefolkweretryingtoreflectcomplexfactsaboutthetypes

ofsensesthatwefindintheworldusinganoversimplisticmodel,butonewhose

originisexplicablegiventhefacts.However,iftwosensesareclosetogetherin30Intheactualworldtherewillofcoursebecontingentconnectionsbetweenthecriteria.Forexample,theproximalstimulusandthesenseorgan/physiologyofthesenseprobablypartlydeterminetherepresentationalpropertiesandthephenomenalcharacterofperceptualexperience.Theextenttowhichanynecessaryconnectionsexistamongthecriteriaisadifficultquestionandone’sanswertoitwilldependonone’sviewson(atleast)thefollowing:thenatureofphenomenalcharacter,whattypesofmetaphysicallypossibleworldsthereare,andwhetherasensemustgenerateconsciousexperiences.Thus,onemightholdthatwhileeachpossiblesensewilloccupysomeplaceinthemultidimensionalspace,noteverypositioninthespaceisaplacethatapossiblesensecouldoccupy.31Ofcourse,whenfacedwithcertainsenseswemaybeignorantofthenatureofthosesenseswithregardtothefactspertainingtooneormoreofthecriteria,butthatismerelyourunfortunateepistemicsituation.Whenweembraceallfourcriteriaandresistshoehorningallofthesensesintoafewdiscretekinds,wecansimplynote,foreachcriterion,allofthefactsweknow.Forexample,inassessingthenatureofthesensoryorganinTVSSweshouldmentionboththecameraandtheskinofthesubjectandtheconnectionbetweenthem.

36

thisspace,weshouldnotconcernourselveswiththequestionofwhetherthey

arethesamesense.Oncewehaveplottedtheirlocationinthespaceandnoted

theirsimilaritiesanddifferences,wehavesaideverythingweneedtosayabout

thesenses.Thatiswhenweshouldceasetoaskhowtoindividuatethesenses.

3.Conclusion

Ihavearguedthatweshouldrejectthesparseviewthatthereareorcouldbe

onlyasmallnumberofratherdistinctsenses.Whenoneappreciatesthisthen

onecanseethatthereisnoneedtochoosebetweenthestandardcriteriathat

havebeenproposedaswaysofindividuatingthesenses–representation,

phenomenalcharacter,proximalstimulusandsenseorgan–oranyothercriteria

thatonemaydeemimportant.Rather,onecanusethesecriteriainconjunction

toformafine‐grainedtaxonomyofthesensesthattakeseachcriterioninto

account.Wecanthinkofthesecriteriaasdefiningamultidimensionalspace

withinwhichwecanlocateeachofthesensesthatwearefamiliarwithand

whichalsodefinesthespaceofpossiblesensestherecouldbe.32

Acknowledgements

VersionsofthispaperhavebeengivenattheConsciousnessattheBeach3

Workshop,CentreforConsciousness,AustralianNationalUniversity,Kioloa

Campus;aninterdisciplinaryworkshoponthesensesarrangedbythe

PhilosophyDepartment,UniversityofTorontoattheÉcoleNormaleSupérieure

32Perhapswithadditionalrestrictionsofthekindoutlinedinfootnote30.

37

inParis,Francein2009;andatthePacificAPAinSanFranciscoin2010.Iwould

liketothanktheparticipantsandinaddition,MichaelBrady,JonBird,Barry

SmithandSusannaSiegel.Thematerialinthispapercomprisesaportionofmy

“Introduction:IndividuatingtheSenses”forthcominginF.Macpherson(ed.)The

Senses:ClassicalandContemporaryPhilosophicalPerspectives,OxfordUniversity

Press.

References

Akins, K. 1993. What Is It Like to Be Boring and Myopic? In Dennett and His

Critics, ed. B. Dahlbom, pp. 124–160. Cambridge, Mass.: Blackwell.

Bach-y-Rita, P. 1972. Brain Mechanisms in Sensory Substitution. New York:

Academic Press.

Classen, C. 1993. Worlds of Sense: Explaining the Senses in History and across

Cultures. London: Routledge.

Craig, A. D. 1996. Pain, Temperature, and the Sense of the Body. In Somesthesis and

the Neurobiology of the Somatosensory Cortex, ed. O. Franzén, R. J. Lars, and

Y. Terenius, pp. 27–39 Basel: Birkhäuser.

Dallenbach, K. M. 1939. Pain: History and Present Status. American Journal of

Psychology 52(3): 331–47.

Dretske, F. I. 1995. Naturalizing the Mind. Cambridge, Mass.: MIT Press.

Gray, R. 2005. On the Concept of a Sense. Synthese 147(3): 461–75.

Grice, H. P. 1962. Some Remarks about the Senses. In Analytical Philosophy, first

series, ed. R. J. Butler, 133–53. Oxford: Blackwell.

Hughes, H. C. 1999. Sensory Exotica. Cambridge, Mass.: MIT Press.

38

Humphrey, N. (1993) A History of the Mind, London: Vintage.

Kardong, K. V., and S. P. Mackessy. 1991. The Strike Behaviour of a Congenitally

Blind Rattlesnake. Journal of Herpetology 25(2): 208–11.

Macpherson, F. 2003. Novel Colours and the Content of Experience. Pacific

Philosophical Quarterly 84(1): 43–66.

———. 2005. Color Inversion Problems for Representationalism. Philosophy and

Phenomenological Research 70(1): 127–52.

———. 2006. Ambiguous Figures and the Content of Experience. Noûs 40(1): 82–

117.

———. Forthcoming. Cognitive Penetration of Color Experience: Rethinking the

Issue in Light of an Indirect Mechanism. Philosophy and Phenomenological

Research.

264(5588): 746–48.

Nagel, T. 1974. What Is It Like to Be a Bat? Philosophical Review 83: 435–50.

Nudds, M. 2004. The Significance of the Senses. Proceedings of the Aristotelian

Society 104(1): 31–51.

Rivelin, R., and K. Gravelle. 1984. Deciphering the Senses: The Expanding World of

Human Perception. New York: Simon and Schuster.

Siegel, S. 2010. Do Visual Experiences Have Contents? In Perceiving the World, ed.

B. Nanay. New York: Oxford University Press.

Stephens, J. C. 1982. Temperature Can Sharpen Tactile Acuity. Perception and

Psychophysics 31: 57–80.

Tye, M. 1995. Ten Problems of Consciousness: A Representational Theory of the

Phenomenal Mind. Cambridge, Mass.: MIT Press.

Walker, M., C. Diebel, C. Haugh, P. Pankhurst, J. Montgomery, and C. Green. 1997.

39

Structure and Function of the Vertebrate Magnetic Sense. Nature 390: 371–

76.