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ArtificialIntelligenceinMedicine(2008)44,119—137
http://www.intl.elsevierhealth.com/journals/aiim
Philosophical foundations of
artificial consciousness
Ron Chrisley*
Centre for Research in Cognitive Science and Department of Informatics,
University of Sussex, Brighton BN1 9QH, United Kingdom
Received2May2008; received in revised form28 July 2008; accepted29July 2008
KEYWORDS Summary
Artificial
Objective: Consciousness is often thought to be that aspect of mind that is least
consciousness;
amenabletobeingunderstoodorreplicatedbyartificialintelligence(AI).Thefirst-
Machineconsciousness;
personal, subjective, what-it-is-like-to-be-something nature of consciousness is
Prostheticartificial
thoughttobeuntouchablebythecomputations,algorithms,processingandfunctions
intelligence;
ofAImethod.SinceAIisthemostpromisingavenuetowardartificialconsciousness
Synthetic
(AC),theconclusionmanydrawisthatACisevenmoredoomedthanAIsupposedlyis.
phenomenology;
The objective ofthis paperis toevaluate thesoundness ofthis inference.
Interactiveempiricism;
Methods: Theresultsareachievedbymeansofconceptualanalysisandargumentation.
Heterophenomenology
Results and conclusions: It is shown that pessimism concerning the theoretical pos-
sibilityofartificialconsciousnessisunfounded,basedasitisonmisunderstandingsof
AI, and a lack of awareness of the possible roles AI might play in accounting for or
reproducing consciousness. This is done by making some foundational distinctions
relevant to AC, and using them to show that some common reasons given for AC
scepticismdonottouchsomeofthe(usuallyneglected)possibilitiesforAC,suchas
prosthetic,discriminative,practicallynecessary,andlagom(necessary-but-not-suffi-
cient) AC. Along the way three strands of the author’s work in AC — interactive
empiricism, synthetic phenomenology, and ontologically conservative heteropheno-
menology—areusedtoillustrateandmotivatethedistinctionsandthedefencesofAC
theymakepossible.
#2008ElsevierB.V.Allrightsreserved.
1. Introduction replicated by artificial intelligence (AI). The first-
personal, subjective, what-it-is-like-to-be-some-
Consciousness is often thoughtto be that aspect of thing nature of consciousness is thought to be
mindthatisleastamenable tobeingunderstoodor untouchable by the computations, algorithms, pro-
cessing and functions of AI method. Since AI is the
most promising avenue toward artificial conscious-
* Tel.:[phone];fax:[phone].
E-mailaddress:[email protected]. ness (AC), the conclusion many draw is that AC is
0933-3657/$—seefrontmatter#2008ElsevierB.V.Allrightsreserved.
doi:10.1016/j.artmed.2008.07.011
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120 R. Chrisley
even more doomed than AI supposedly is. In what andintelligenceinvolvesconsciousness,mostorall
follows I hope to show that this pessimism is ofAIwouldseemtofallundertheACrubric:ifACisa
unfounded, based as it is on misunderstandings of subsetofAI,itisanearlyexhaustiveone.Buteven
AI, and a lack of awareness of the possible roles AI whenconcernedwithmentalcapacitiesthatusually
might play in accounting for or reproducing con- involve consciousness in humans, AI typically pro-
sciousness.Iaimtodothisbymakingsomefounda- ceeds in a way that downplays the distinctly phe-
tionaldistinctionsrelevanttoAC,andusingthemto nomenological aspects of those capacities. True
showthatsomecommonreasonsgivenforACscep- AC, on the other hand, is as much concerned with
ticismdonottouchsomeofthe(usuallyneglected) explainingphenomenologicalreports,andeventhe
possibilities for AC, such as prosthetic, discrimina- limitations of consciousness and attention, as it is
tive, practically necessary, and lagom (necessary- with getting systems to perform cognitive tasks. AI
but-not-sufficient)AC.AlongthewayIwillusethree typicallyfocusesonthoseaspectsofmentalitythat
strandsofmyownworkinAC—interactiveempiri- do not require one to confront the problems of
cism, synthetic phenomenology, and ontologically consciousness head-on, while AC bravely confronts
conservative heterophenomenology — to illustrate the consciousness-rich residue. Except that for AC
andmotivatethedistinctionsandthedefencesofAC researchers, consciousness is not as peripheral as
they make possible. the term ‘‘residue’’ suggests; it is central to men-
Prima facie, it might seem easy to distinguish AI tality.
from AC: AI is the attempt to create artefacts that There is no firm consensus as to how to charac-
are intelligent,1 and AC is the attempt to create terisethespecificallyconsciousaspectsofmentality
artefacts that are conscious. But things are more that consequently distinguishes AC. An indicative
complicated than that, for two reasons. First, con- example, however, can be based on [1] (see also
sciousness and intelligence are not so clearly dis- [2]):
tinguishable. For example,in most cases where we ‘‘[A] successful explanation of phenomenal con-
would say that a task requires intelligence, we sciousness... should (1) explain how phenomenally
would also say that it requires consciousness. Sec- conscious states have a subjective dimension; how
ond, the field of AI, in its broadest sense, is poorly they have feel; why there is something which it is
served by the name ‘‘artificial intelligence’’. This like to undergo them; (2) why the properties
term hides the fact that despite an early emphasis involved in phenomenal consciousness should seem
on problem solving, the field has always had more totheirsubjectstobeintrinsicandnon-relationally
than justintelligenceinitssights. That is,AI isthe individuated; (3) why the properties distinctive of
attempttocreateartefactsthathavementalprop- phenomenal consciousness can seem to their sub-
erties, or exhibit characteristic aspects of systems jectstobeineffableorindescribable;(4)whythose
that have such properties, and such properties properties can seem in some way private to their
include not just intelligence, but also those having possessors;and(5)howitcanseemtosubjectsthat
todowith,e.g.,perception,action,emotion,crea- wehaveinfallible(asopposedtomerelyprivileged)
tivity,and consciousness. In thissense, ACis asub- knowledgeofphenomenallyconsciousproperties.’’
fieldofAI.Butthereisreasontobelievethatitisa (SeealsoAleksander’s‘‘axioms’’andMetzinger’s
sub-field that, because of the very nature of its ‘‘constraints’’, discussed by Clowes and Seth, this
topic, will have to use at least some methods that issue.)
aresubstantialdeparturesfromthosetypicallyused Inadditiontothesequitegeneralexplananda,AC
in AI. researchers often aim to explain particular data,
Thecombinationoftheprecedingtwopointshas introspective or more traditionally behavioural,
thefollowingupshot:Inthatmostorallofmentality thathavetodowithwhatitisliketoperformsome
cognitive achievement. For example, some AC
1 Althoughthelasthalf-centuryorsohasseentheintroduction researchers in robot navigation and planning
ofvariousnewapproachestoAI,includingconnectionism/neural (e.g., Tom Ziemke, Dan-Anders Jirenhed and Ger-
networks, dynamical systems engineering, embodied/situated mund Hesslow; cf [3—5]) are as concerned with
robotics,andartificiallife,theterm‘‘artificialintelligence’’is
exploring the extent to which the processes the
oftenusedmorenarrowly,torefertoapproachesthatemphasize
robot employs can be usefully viewed as instances
symbolic computation. Indeed, it was this particular approach
thatwasdominantamongthosewhofirstusedtheterm‘‘AI’’to of imagination and the existence of an ‘‘inner
describetheirwork(asiswell-known,JohnMcCarthycoinedthe world’’, as they are in actually getting the robot
termin1956),asituationthatarguablycontinuestothisday.To to avoid collisions, find its way to a goal location,
avoid confusion in what follows, the term ‘‘symbolic artificial
etc.OtherACresearchexplicitlyconcernedwiththe
intelligence’’ (or ‘‘symbolic AI’’) will be used to refer to this
phenomenologicalaspectsofimaginativeandcoun-
specificapproach,and‘‘artificialintelligence’’(or‘‘AI’’)tothe
generalendeavour. terfactual reasoning includes [6—11].
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Foundations of Artificial consciousness 121
2. Varieties of artificial consciousness of systems that, when implemented, are thereby
instantiations of (are sufficient for) consciousness.
To understand the full range of possibilities for AC, For example, a symbolic AI approach to strong AC
andtomakecleartheconnectionswith,anddiffer- maintains that an appropriately programmed com-
ences from, AI, we can make some distinctions for puter actually is aware, is conscious, has experi-
AC that parallel distinctions made for AI. To high- ences, etc.
lightthefundamentalissuesatstake,however,the Betweenthesetwoextremesisaneglectedzone
distinctionswillnotbetheusualonesbasedonthe of possibility that might be termed lagom AC.
various models, theories, and technologies used by ‘‘Lagom’’ is a Swedish word with no direct English
different AI approaches(e.g., symbolic vs.connec- equivalent,whichmeanssomethinglike‘‘perfection
tionist vs. situated robotics vs. ...). Rather, the through moderation’’ (and is thus reminiscent of
distinctions will be more generic, emphasizing dif- Aristotle’sgoldenmean).ThelagomACview,unlike
ferences in goals and aims, rather than technical weakAC,claimsthatthemodellingrelationholdsasa
means. How these distinctions inter-relate will be resultofdeeper,explanatorypropertiesbeingshared
summarized in a table at the end of the Section. bythetechnologyandconsciousmentalphenomena.
However,unlikestrongAC,lagomACdoesnotgoonto
2.1. Scientific vs. engineering claimthatinstantiatingthesecommonpropertiesis
alone sufficient for instantiating consciousness–—
As with AI, a distinction can be made between two somethingelsemightberequired.Itwouldbenatural
related,butdistinct,goalsinpursuingAC.Engineer- tosaythatwhilestrongACaimstodiscoversufficient
ingACisprimarilyconcernedwithcreatingartefacts conditionsforconsciousness,lagomAConlyaimsto
that can do things that previously only naturally discover(someofthe)necessaryconditionsforit.But
conscious agents could do; whether or not such that’snotquiteright.Itwouldbeiftherewereonly
artificial systems perform those functions or beha- onewayofbeingaconsciousthing.Butalthoughthat
viours in the way that natural systems do is not maybethecase,itmayinsteadbethatthereismore
considered a matter of primary importance. Of than one way to be conscious. If so, then what is
central (sole?) concern are the functional capabil- important,evennecessary,forbeingconsciousinone
ities of the developed technology: what functional ofthesewaysmightnotbenecessaryforbeingcon-
benefits can accrue from making a system behave sciousinanotheroneoftheseways.SolagomACin
morelikeaconsciousorganism?Whetherornotthe generalcansucceedevenifitonlyfindssomeofthe
system so developed is really conscious is not an necessary conditions for some way of being con-
issue.ScientificAC,however,isprimarilyconcerned scious. But let’s put things in perspective: this kind
with understanding the processes underlying ofsuccesswoulditselfbeamomentousachievement,
consciousness, and the technologies provided by and would contribute greatly to understanding how
engineering AC, however impressive, are only con- consciousnesscanbepartofthenaturalworld,even
sidered of theoretical relevance to the extent that ifitwerenotthewholestory,andevenifitwerenot
theyresembleorotherwiseilluminatetheprocesses partofthestoryofhowspecificallyhumanconscious-
underlying consciousness. nessispartofthenaturalworld.Thatsaid,itshould
bestressedthatthereisaparticularkindoflagomAC
2.2. Strong vs. weak (vs. lagom) thatdoestrytodiscoverthenecessarycomputational
conditionsforhumanconsciousness,anditisthissub-
Within scientific AC, further distinctions can be speciesthatisofmostinteresttothemajorityofthe
made concerning the relation that is believed to peoplewhothinkabouttheissuesbeingconsideredin
hold between the technology involved in an AC thisessay.
system and consciousness. Adapting terminology ThepointofraisingthepossibilityoflagomACis
from [12], weak AC is any approach that makes no that many of the arguments against AC have the
claim of a relation (e.g., necessary and sufficient implicit form:
conditions)betweenthe technology andconscious-
ness. This would be a use of technology for under- (1) AC is either strong or weak.
standingconsciousnessinawaysimilartotheuseof (2) Weak AC isn’t interesting.
computationalsimulationsofhurricanesinmeteor- (3) Strong AC is false because of X (for different
ology: understanding can be facilitated by such values of ‘‘X’’).
simulations,butnoonesupposesthatthisisbecause (4) Thus, no interesting form of AC is possible.
hurricanes are themselves computational in any
substantive sense. At the other extreme, strong Theacknowledgementofthepossibilityoflagom
ACisanyapproachwhoseultimategoalisthedesign ACinvalidatestheseargumentsbydenyingthefirst
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122 R. Chrisley
premise.Ofcourse,littlewouldchangeifitturned (cid:2) Causalrequirementshavetodowiththekindsof
outthatlagomACcouldbedismissedasuninterest- software,hardware,userinterfaces,etc.thatwe
inginthesamewaythatweakACcan.Thisdepends, willneedtohelpusachieveAC.Nodoubtsophis-
obviously,onwhatismeantby‘‘interesting’’.Inthe ticated,‘‘intelligent’’,computationaltechnology
case of arguments concerning AC, it usually means notyetinventedwillbeneededtohelpuscollect,
the same thing as is meant in similar debates con- mineandprocesstheenormousquantitiesofdata
cerningAI:anAI(orAC)positionisinterestinginthe we can anticipate to acquire over the next dec-
relevant sense if its truth implies that the mind is ades(centuries?)concerningtheoperationsofthe
computational. The claim that the mind is compu- brainandbodythatunderlieconsciousness.Simi-
tational itself comes in varying strengths, but to laradvancesintechnologicalAIwillalsolikelybe
keepthingsbrief,theupshotcanbeputasfollows. needed to assist in the design of any system
The claim that some computational concepts are complexenoughtobeacandidateforanartificial
partoftheexplanationofsomementalphenomena, consciousness.
whilemuchweaker(andthushardertodefeat)than (cid:2) Conceptual requirements have to do with the
the claims that opponents of AI usually argue kindsofsystemswewillneedtohaveexperience
against, is still interesting in the relevant sense: ofbuilding,andthe kinds oflearning/creativity/
it implies that computation has a role to play in perceptual/performance enhancing technologies
understanding the mind, and not just in the weak wewillneedtodevelop,inordertogetourselves
way that computational technology plays a role in into the right conceptual/knowledge state for
understanding hurricanes. The analogous claim for achieving AC (cf [14]).
anAIapproachtoACwouldbe:somecomputational
concepts are part of the explanation of some con- Itislikelythatbothsortsofpracticallynecessary
sciousphenomena.ToargueagainstthiskindofAC, technologies will have an articulated trajectory.
onehastoshowthatnocomputationalconceptsare That is,therewill likely be many technologies that
ever a useful part of explaining any kind of con- are not themselves part of an AC we will build in
sciousness. Doing this is a tall order, and to my some distant future, nor even part of the technol-
knowledge, no one has done so. For example, to ogieswewillneedatthattimetobuildthatAC,but
refutethisformofACitisnotenoughtoarguethat are part of a long chain of antecedent practical
instantiating the computational processes C requirements for getting to that final stage.
employed in the AC explanation of some conscious This might seem very ‘‘uninteresting’’, in the
phenomenon P are not sufficient for P (e.g., that sense discussed above; as practically necessary
there is an ‘‘explanatory gap’’ [13] between C and some forms of weak AC may be, by the definition
P). This form of AC already concedes that C might ofweakAC,theirpropertieshavenobearingonthe
notbesufficientforP;itdoesnotfollowthatCisnot natureofmind.Inparticular,evenifsuchsupporting
(partially) explanatory of P. technologies were thoroughly computational, this
wouldnotimplythatconsciousnessitselfiscompu-
2.3. Constitutively necessary vs. tational.Althoughthisisso,thepracticalupshot,in
practically necessary terms of what technologies and concepts research-
ers (and thus students!) in AC, or perhaps even
Inasense,weakAI(andweakAC)hasbeengivenshort consciousness studies in general, need to have a
shriftinphilosophicaldiscussions.Theplausibilityof mastery of, remains the same. It makes no differ-
lagomACliesinitrestrictingitsambitionstoneces- ence whether the understanding, designing and
saryconditionsforachievingartificialconsciousness; building of computational systems turns out to be
weakACmayalsoaspiretonecessaryconditionsfor a constitutive or a practical requirement for
achievingartificialconsciousness,albeitofadiffer- advances in a science of consciousness (if it does);
ent sort. Even if they do not model the processes itwouldbearequirementnonetheless.Facilitywith
underlyinghumanintelligenceorconsciousness,cer- non-constitutiveweakACmaybeasfundamentalto
tain artificial intelligence technologies may be a achieving lagom or strong AC as skill at building
practicalrequirementforachievingAC,beitofthe telescopes and grinding lenses was to the develop-
engineeringorthescientificvariety.UnlikelagomAC, ment of modern astronomy.
thenecessityinvolvedisnotaconstitutivematterof
whatpropertiestheartificialagentmusthaveforit 2.4. Constitutive vs. discriminative
tobeconscious,butratherapracticalmatterofwhat
toolsandconceptswemusthavetobeabletobuildit. Adistinctionrelatedtothepointsmadeconcerning
Thesepracticalrequirementsarethemselvesoftwo lagom scientific AC has to do with the form of the
sorts:causalandconceptual. explanatory ambitions involved. The explanatory
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Foundations of Artificial consciousness 123
form that gets the most attention with respect to However, prosthetic AC aims to make a distinct
consciousness is the constitutive form: an account contribution. What is special about prosthetic AC
of what makes something conscious, as opposed to isthatitcreatesnewexperiencesnotbyalteringthe
not being conscious. An alternative explanatory objects of experience, but by altering the (trans-
formisthediscriminativeform:forsomethingthat parent3)agent-basedprocessesthatenableexperi-
is already known (or presumed) to be conscious, ence. In this sense, it shares its aims, if not its
what makes it the case that it is in this kind of methods, with a diverse set of activities: medita-
conscious state as opposed to that kind? (cf. tion, certain rituals, some psychoactive drug use,
[10,11]). some forms of biomorphic art (e.g., the work of
Once one makes this distinction, it should be Stelarc), etc. (In fact, some AI-based AC practi-
clear that a particular scientific AC research pro- tioners find the phrase ‘‘artificial consciousness’’
gramme might contribute to discriminative expla- soevocativeofthesealternativemeansofachieving
nations of consciousness, even if it does not altered states of consciousness that they prefer to
contribute to a constitutive explanation of con- use the term ‘‘machine consciousness’’ to describe
sciousness.Indeed,itmaydosoevenifitisimpos- what they themselves do.) Prosthetic AC, on the
sible for scientific AC in general to provide on its otherhand,wouldmorelikelyinvolveimplantsand
own,orevencontributeto,aconstitutiveexplana- complex sensory—motor interfaces than it would
tionofconsciousness.ThiskindofdiscriminativeAC drugs or chanting. That said, scientific prosthetic
is a kind of lagom scientific AC: it does not provide ACwouldbedistinctfromtheothermeansofalter-
sufficient conditions for consciousness, but none- ing consciousness mentioned above not just in the
thelesscontributestoexplanationsofconsciousness technology involved, but in that the goal of produ-
byofferingmechanismsthatallowasubjecttomeet cingthesealternativeformsofexperiencewouldbe
somenecessaryconditionsforbeinginsomekindsof subsidiary to the goal of understanding conscious-
experiential state. An example of such lagom, dis- ness in a scientific way. The idea is that AC might
criminative AC work will be given in Section 3.2.3. contributetoourunderstandingofconsciousnessas
muchbysystematicallyalteringorextendingitasby
2.5. Autonomous vs. prosthetic replicating it.
There are two sub-kinds of prosthetic AC: con-
Most AC research is autonomous, in that it aims to servative and radical. The former seeks to create
create a self-standing, individual artificial con- alternative material bases for extant kinds of
sciousness. Much less frequently discussed is the experience; the latter seeks to create alternative
possibility of prosthetic AC: ‘‘artificial conscious- material bases that result in novel kinds of experi-
ness’’ as a phrase parallel in construction to ‘‘arti- ence. To elaborate, let us first consider radical
ficial leg’’ rather than ‘‘artificial light’’. Prosthetic prosthetic AC, as it is easier to see the value of
ACwouldseektoextend, alter oraugmentalready its contributions. The controlled, systematic gen-
existing consciousness rather than create it anew.2 erationandobservationofnovel ways ofproducing
It is a misunderstanding to think that creating or familiarphenomenacanallowonebettertoseethe
discovering more instances of a phenomenon to be
explained only increases the problem; rather, the
3 Eveninthespecialcaseofauto-cerebroscopesandthelike,
consideration ofnew instancesisawayto increase
the enabling processes are still transparent in the sense that
the robustness of one’s models and theories. Of althoughtheyhappentobetheobjectsofconsciousnessinsuch
course,we cangeneratenovel experiences inrela- cases,theyarenotsoquaenablingprocesses;theyarenotsoby
tively mundane ways: travel to a foreign location, virtue of being enabling processes. So a silicon visual implant
wouldcontinuetobeakindofprostheticACevenifitwerefitted
listen to a new kind of music, taste an exotic dish.
with a monitor that somehow let the owner of the implant to
Thesearemundaneinthattheyalterexperienceby
inspectthestatesoftheimplant,thusrenderingitanobjectof
altering the objects of experience (the environ- experience.Ontheotherhand,itsstatusasprosthesisaschar-
ment). Despite being mundane, the method of sys- acterised here would be in question if the use of said monitor
tematic variation of the environment and were essential for the implant to provide its functionality. An
aside:itisforthisreason,asIargueinapaperentitled‘‘Cog-
observation of the concomitant changes in experi-
nitiveProvenanceandtheExtendedMind:WhyOtto’sBeliefsare
enceisanimportantpartofconsciousnessscience.
notinhisNotebook’’(toappearinGallagher,S.andMenary,R.
(editors), Cognition: Embodied, Embedded, Enactive, and
Extended(NewYork:Palgrave-Macmillan)),thatthecaseofOtto
2 ThisparallelsasimilardistinctioninAI,althoughprostheticAI andhisnotebookdescribedin[16]isnotacaseofprosthesis,is
hadmoreprominenceinthatfield’searlyyearsthanitdoesnow. notacaseofOtto’smindextendingintohisnotebook;unlikethe
For example, Ross Ashby, a venerated pioneer in the field of casesunderconsiderationhere,Ottocanonlyusethenotebook
dynamicalAI,proposeda‘‘designforanintelligenceamplifier’’ for information retrieval by virtue of it being an object of
[15]. perceptionforhim,atleastorginally.
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124 R. Chrisley
underlying structure of how said phenomena are constituent variables. Keeping these differing
produced in the normal case. Radical prosthetic values fixed, then attempt to manipulate the rest
AC,however,seekstoconferonthesubjectexperi- ofthevariablesintoastateS00suchthatS00produces
ences of a fundamentally different kind than the O. In short, if you can get a balsa wood wing to do
subject had enjoyed before, such as a new sense roughly the same thing as a paper wing, then per-
modality,orthatofusinganewlimb.Oneneednot haps you have learned something about aerody-
look far to find examples of such prostheses. On namics that you would not easily have learned
some accounts (e.g. [17]) sensory substitutions just by generating different kinds of paper wing.
devices (e.g., TVSS [18]) do not, per their name Soalso,then,forprostheticAC:ingettingthesame
andconventionalwisdom,substituteexperiencesin experiences to be realised in different hardware,
onesensemodalityforexperiencesinanother(e.g., one might acquire insights not easily gained by
visionfortouch);rather,theyconferonthesubject trying to generate radically different experiences
sui generis, novel forms of sensory experience. If prosthetically.
this is right, such devices make possible contribu- PerhapsmostexcitingisthatprostheticACcould
tions that gowellbeyondpassive collection ofnew be truly first-personal; if the theorist is also the
data on extant modalities, by allowing active personwhose experiential states are beingtechno-
exploration of the space of possible conscious logically modified, then some fundamental worries
experience via experimental intervention. Such abouttheabilityofACtoaccountforthesubjective
active variation and consideration of new kinds of aspectsofexperiencecanbefinessed.Inparticular,
phenomena is the heart of the experimental scien- prosthetic AC seems well suited to be a kind of
tific method. discriminative AC, as just discussed in Section 2.4.
ConservativeprostheticACseekstoreproducein In this sense, prosthetic AC has similarities with
us experiences similar to those that we already synthetic phenomenology (Section 3.2.3).
enjoy, just with a different material base. Techni-
cally,hearingaids,glasses,ablindperson’scane,or 2.6. Human (or biological) vs. general
evenahammerwouldcountas(simplistic)formsof
conservative prosthetic AC. And consideration of An important distinction within AC has to do with
such prostheses can and has informed more than whether one is attempting to reproduce/explain
onetheoryofperceptualexperience(e.g.[16,19]p human (or biological) consciousness in particular,
67; [20] p 143; [21]). But more interesting possibi- orwhetheroneisattemptingtoreproduce/explain
lities include those offered by the aforementioned consciousnessmore generally. The quest for gener-
sensorysubstitutiondevices,evenontheconserva- alitycanbeeithermoreambitiousormoremodest.
tiveassumptionthatsuchdevicesmerelyallowone For example, in the case of constitutive scientific
standard sensory modality to be substituted for AC,generalitywouldbemoreambitiousifonewere
another(e.g.,visionfortouch,inthecaseofTVSS). attempting to explain, for any possible conscious
A digression into the philosophy of science will agent, why that agent is conscious. A more modest
help illustrate the value of conservative prosthetic formofgeneralitywouldbemerely(!)attemptingto
AC. Often in science we perform experimental explain how it is that some particular non-human
investigations in terms of a set of independent (non-biological) physical thing is also a conscious
variables (‘‘input’’), over which we have direct thing.
control; and dependent, observational variables Even if one’s ultimate goal is to explain human
(‘‘output’’), over which we only have indirect con- consciousness,thethoughtgoes,understandinghow
trol,viatheindependentvariables.Astandardway someparticularartificialsystemiscapableofbeing
ofincreasingone’sunderstandingofaphenomenon conscious might assist completing that task. As
is to fix most of the independent variables, and Fodor states [22], ‘‘Nobody has the slightest idea
manipulate the remainder of them in such a way how anything material could be conscious. Nobody
as to create a large variation in the dependent even knows what it would be like to have the
variables. We could call this ‘‘depth-first explora- slightest idea about how anything material could
tion in input space’’. A complementary way to beconscious.’’Anunderstood,non-humanACwould
explore the relation between the independent give us much more than a slight idea of how some-
anddependentvariablesis‘‘depth-firstexploration thing material could be conscious. In fact (some
inoutputspace’’.Thatis,takeanobserved(depen- would say), it might even be a mistake to spend
dentvariable)phenomenonOthatisproducedbyall much time investigating the specifics ofthe human
of the independent variables being in a particular case(e.g.,humanneurophysiology)atthiscurrent,
stateS.PuttheindependentvariablesintoastateS’ inchoate stage of consciousness science. Doing so
that differs from S in the value of, say, half of all would be like trying, e.g., to understand flight by
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Foundations of Artificial consciousness 125
looking at bird’s feathers under a microscope. necessity(lagom),practicalnecessityornorelation
Instead, the analogy (cf. [23—26]) continues, we (weak). However, lagom AC is not a distinguishable
onlycametounderstandnaturalflightbyachieving sub-kind of prosthetic AC, which renders the suffi-
artificialflight,andweonlysucceededindoingthat ciency/necessity distinction moot. Similarly, while
oncewestoppedtryingtoslavishlycopythesuper- strong and lagom autonomous AC can be further
ficialcharacteristicsofbiologicalflyers,andinstead distinguishedbywhethertheyaimtoexplainwhatit
sought to create artefacts that allowed systematic istobeconscious(constitutive)orwhethertheyaim
isolation and identification of the relevant aerody- to explain which experiential state an agent
namic forces and factors. As for flight, so also for assumed to be conscious is in (discriminative),
consciousness, according to this view. strong prosthetic AC, in that it presupposes the
Similar points can be made for discriminative consciousness being augmented, may only play a
accounts of consciousness. For an artificial system discriminative explanatory role.
that is believed to be conscious, even if one could Obviously, trying to express such complex rela-
notexplainwhyitisso,adiscriminativeaccountof tions in a two-dimensional diagram will introduce
its various experiential states would be of value, distortions and hide inter-relations. For example,
even if one did not thereby have a discriminative the diagram makes many of the distinctions seem
account that applied to the human case. dichotomous, whereas in reality the very same
Althoughtheabovediscussionhasfocussedonthe researchcanbe,e.g.,bothscientificandengineer-
autonomous case, the distinction also applies to ingAC.Anexampleofsomeinter-relationsthatare
prosthetic scientific AC: one may ambitiously not depicted concerns weak prosthetic AC. Such
believeoneisinvestigatingconsciousnessingeneral work may be practically necessary in the construc-
when one does such work, or one may take such tion of autonomous, strong AC. Or it may be that
work to only reveal insights into how biological or autonomous, strong AC is impossible, but weak
human (or one’s own!) conscious states depend on prostheticACmaybepracticallynecessaryforpro-
the material world. ducing a non-AC explanation of consciousness. Yet
these possibilities are not displayed in the table.
2.7. Putting it all together Despitetheselimitations,itishopedthatthefigure
makes clear some gross features ofthe distinctions
Agraphicalrepresentationoftherelationsbetween madeinthissection.Thesedistinctionswillbeused
the varieties of AC just described is presented in inthefollowingsectionstodiscussthemotivations,
Table 1. difficulties, and prospects for different kinds of AC
The main, crosscutting distinctions are scientific research.
vs. engineering AC, and autonomous vs. prosthetic
AC. Both main kinds of scientific AC have further
sub-kinds,dependingonthestrengthoftherelation 3. Motivations for AC
that is meant to hold between the AC technology
andconsciousness:sufficiency(strong),constitutive Why might one think that AC is achievable? The
variety of AC research goals documented in the
previoussectionsuggeststhattherewillbenosingle
Table1 Varietiesofartificialconsciousnessresearch
answer to this question. This section, therefore,
goals
detailsspecificmotivationsforengineeringAC,gen-
Scientific Engineering
eralscientificAC,andtwospecifickindsofscientific
Autonomous AC (strong autonomous AC and weak conceptually
Strong Constitutive Discriminative necessary AC).
Lagom Constitutive Discriminative
Weak Practically Non-necessary 3.1. Motivations for engineering
necessary
autonomous AC
(Causally or
Conceptually)
The plausibility of engineering prosthetic AC lies in
Prosthetic (Conservative orRadical) thefactthatwehavealreadysucceededinmaking
Strong Discriminative
some conservative achievements. This makes
Weak Practically Non-necessary
further conservative prostheses, and more radical
necessary
ones, appear achievable. Motivations for scientific
(Causally
prosthetic AC have already been given in Section
or Conceptually)
2.5. The plausibility of engineering autonomous AC
Notshown:the‘‘Humanvs.General’’distinction.
cannot derive from extant success in such a direct
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126 R. Chrisley
way. One general motivation, then, comes from a requiremind—planning,provingtheorems,playing
belief intheuniversalityofnatural laws. Whatever chess, diagnosing blood diseases, handwriting
laws are responsible for the natural occurrence of recognition, speech recognition, etc. — have been
some phenomenon must inprinciplebe exploitable replicated by computers. So why not all of mental-
by humans to make an artificial occurrence of that ity? Why not consciousness, or at least the beha-
phenomenon.4 Conscious humans, are, after all, viours normally thought to require it? For it is only
physical things: if one kind of physical thing can the latter with which engineering AC is explicitly
be conscious, why not another? If we can produce concerned.
new conscious beings through childbirth, why not
through some other means that affords us more 3.2. Motivations for scientific AC
control over the outcome? That the resource cost
(e.g., materials, time and energy) of doing so may Ingeneral,motivatingscientificACistwiceashard
be practically prohibitive will, however, make the asmotivatingengineeringAC.First,inawaysimilar
more cautious engineer seek firmer foundations. to the case of engineering AC, one has to motivate
More rigorous reasons for believing that specifi- thepossibilityofthetechnologybeingabletoimple-
cally computation-based engineering AC is possible ment some competence associated with or indica-
lie in results from computability theory that pre- tive of consciousness. But beyond that, one has to
date AI and computer technology itself. Turing’s givesomereasontobelievethatthiswillilluminate
introduction of a set of formal models of digital, consciousness in some way; that such replication
algorithmiccomputationisthekeynotionhere.Now can also serve as an explanation. Before looking at
calledTuringmachines,theseautomataaregivena specific motivations for specific kinds of scientific
symbol string (usually interpreted as an integer) as AC, it will be useful to see how AC-based explana-
an input, and produce a symbol string (also usually tion is meant to proceed.
interpreted as an integer) as the output for that A central component of AC-based explanation,
input.Inthiswaysuchmachinescanbeunderstood likethatofAI-based explanation ingeneral,isthat
tobecomputingfunctionsovertheintegers.Turing ofcomputationalmodelling.Modelling,inparticular
proved that there exist Universal Turing machines computational modelling, confers several benefits
that can simulate the action of any other Turing on scientific investigation [28], including allowing
machine. This, coupledwiththeassumptionthat if one to:
any function can be computed at all, it can be
computed by a Turing machine (an assumption (1) State theories precisely;
roughlyequivalent to the ‘‘Church-TuringThesis’’), (2) Test theories rigorously;
yieldsthe result that a Universalmachine can, in a (3) Encounter unforeseen consequences of one’s
sense, compute anything that is computable at all. theories;
In particular, many take this to establish that a (4) Constructdetailedcausalexplanationsofactual
Universal machine can compute any function a events.
human can compute. If one then adds the assump-
tion that human behaviour, or at least the mental Thus even at its weakest, AI methodology can
processesthatgiverisetoit,canbeconceptualized offer these benefits to the understanding of men-
asmathematicalfunctionsoftherelevantsort,then tality(compareClowesandSeth,thisissue).Moving
it follows that any Universal machine can, in prin- from mere (weak) simulation toward strong AI/AC
ciple, be programmed to exhibit behaviour func- presumably multiplies these benefits, especially 2
tionally equivalent to that of any human being–— and3(cf.[29]).Somemightwonderhow2and3can
includingbehaviourwewouldnormallysayrequires apply, particularly in the case of autonomous AC.
consciousness. Given the subjective nature of consciousness, how
These mathematical considerations have appar- could one test a theory of it in an AC? What would
ently borne fruit in everyday life, resulting in a count as confirmation (or falsification)? This is a
general technological optimism concerning the common, general worry about AC: ‘‘how would
assimilation of the mental to the computational. you ever know if you succeeded?’’ Although the
More and more behaviours that were thought to overall structure of this essay dictates that this
point should be addressed in Section 4, responding
to it brings up some points about the nature of AC
4 Althoughthisbeliefis,inmoderntimes,usuallyaccompanied explanation that are best mentioned here.
with a belief in materialism (the denial of a separate mental
Thefirstthingtonoteisthatthequestionisonlya
worldorsubstance),Ihaveelsewherequestionedwhethermate-
problemforsomekindsofAC.Pragmaticallyminded
rialismpersemakesAIorACanymoreplausiblethanitisunder
dualism([27],vol.1,p12). engineering AC will not care whether a duck is
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Foundations of Artificial consciousness 127
‘‘really’’ conscious or not as long as it looks, swims the epistemological bar so high that one calls into
and quacks like a conscious duck. Neither is the question one’s knowledge that other humans are
question a problem for prosthetic scientific AC, conscious.
since the recipient of the experiential prosthesis
will be in a position to confirm its success (or 3.2.1. Motivating strong autonomous AC
failure). Onecouldtransformthecomputability-basedmoti-
Autonomous scientific AC, on the other hand, vations for engineering AC into motivations for
does have to face the question. But so does any scientific AC with some behaviourist assumptions
third-personalnaturalisticexplanationofconscious- about the nature of mind. For example, if one
ness. Any such account faces the problem of con- assumes that all there is to mind is a capacity to
firming or falsifying the underlying theory’s claims producecertainformsofbehaviour,thenexplaining
concerning the presence (constitutive theories) or how a system has a capacity for such behaviour
kind(discriminativetheories)ofconsciousnessasso- would be an explanation of why it is conscious.
ciatedwithagivenphysicalsystem.Sothisproblem But,despitedistractionssuchastheso-called‘‘Tur-
cannot serve as a critique of AC in particular. ing Test’’, most AI (and AC) researchers are not
But more can be said in defence of autonomous tempted by behaviourism; quite the contrary. AC
scientific AC against this criticism, which usually has its roots in AI, which (at least the symbolic
assumesasimplisticvisionofhowanAIexplanation variety) in turn has its roots in anti-behaviourist
ofconsciousnessmightproceed.Infact,thereareat cognitivism. This is the view that cognition (more
least three ways AI methodology can be applied to narrowly: thinking; more broadly: all mentality)
explaining consciousness such that the question actually is (or at least involves; cf. the discussion
‘‘how would you know if you succeeded?’’ can be of lagom AC in Section 2.2) a kind of (symbolic)
answered: computation.Aprimarymotivationforthisviewisa
beliefinthemultiple-realisabilityofmentalstates,
(cid:2) One can attempt to model the physical system itselfmotivatedby,e.g.,thoughtexperimentscon-
underlying consciousness, at various levels of cerningcreatures(‘‘Martians’’)thatbehavejustlike
abstraction (e.g., a connectionist model is humans,buthaveaverydifferentphysiology.Since
pitched at a lower, more hardware-dependent it would be politically incorrect in the extreme to
level of abstraction than is a typical symbolic deny mental states to these Martians, it must be a
model). mistake to think that mental states can only be
(cid:2) One can attempt to model conscious processes implemented in biological states such as those of
directly,e.g. byusing introspectiontonote their humans and animals on Earth. The question then
causal structure, and them implementing this arises: what do Martians and Earthlings have in
structure in an AI system (usually symbolic). commonbyvirtueofwhichtheybothenjoymental
(cid:2) One can attempt to model the behaviour of a lives? The cognitivist answer is not behaviour, but
system known or believed to be conscious, with- abstract causal organisation, which is describable
out any direct knowledge of the underlying phy- using computational formalisms such as Turing
sical or phenomenological structure, in the hope machines. The belief that it is this abstract causal
that reproducing both actual and counterfactual organisationthatconstitutesorindividuatesmental
behaviour is sufficient to ensure that the states is called functionalism. A strong version of
same consciousness-producing causal structure functionalism would maintain that instantiating a
is thereby implemented. particular causal organisation is sufficient for
instantiating that mental state, while a lagom ver-
These models can then be used to predict and sion would only make it a necessary condition. It
explain phenomena in the usual way. follows from strong functionalism that mentality,
SomewillstillinsistthatforanyAIsystemthatis especially thinking, is at root a formal activity:
supposedly conscious, one can always imagine it unlike, say, a rainstorm, if you computationally
being built and behaving the same way and yet simulate thinking, you actually recreate it. The
not being conscious. So what exactly has been upshot of this is that, according to either version
explained? In Section 3.2.2 it will be argued that of functionalism, showing how a physical system
such ‘‘modal intuitions’’ may be the result of an instantiates the causal organisation characteristic
unhelpful, faulty conception of consciousness that ofaconsciousstatewouldcountasanexplanation,
engaging in AC itself may help to repair. In the if only a partial one, of how it is that the physical
meantime, one constraint can be noted: in arguing system is in that conscious state.
that we would not ever be able to know that an AI A compelling reason for believing that this form
systemisconscious,oneshouldbecarefulnottoset of explanation is possible for at least some mental