Computational Computational FunctionalismFunctionalism

MotivationsMotivations

A functionalist general purpose A functionalist general purpose input-output device certainly sounds input-output device certainly sounds like a computerlike a computer

Mind does informational thingsMind does informational things A machine implementation of A machine implementation of

functionalism is naturalfunctionalism is natural Computational functions are Computational functions are

multiply realisablemultiply realisable

Turing MachineTuring Machine

Turing machines Turing machines consist of:consist of:

an infinite tape an infinite tape divided into squaresdivided into squares

a head that reads from a head that reads from and writes to the tapeand writes to the tape

a finite set of internal a finite set of internal states; states; qq00, …, , …, qqnn

a finite alphabet; a finite alphabet; bb11, , …, …, bbmm

Turing MachineTuring Machine

#    #    1   1    1    #    #    1   1    1    ++    1       1   1   #   # 1   #   # 

qq00

qq00 qq11

11 1R1Rqq00 #Halt#Halt

++ 1R1Rqq00

## #L#Lqq11

Turing MachineTuring Machine

#    #    1   1    1    #    #    1   1    1    ++    1       1   1   #   # 1   #   # 

qq00

qq00 qq11

11 1R1Rqq00 #Halt#Halt

++ 1R1Rqq00

## #L#Lqq11

Turing MachineTuring Machine

#    #    1   1    1    #    #    1   1    1    ++    1       1   1   #   # 1   #   # 

qq00

qq00 qq11

11 1R1Rqq00 #Halt#Halt

++ 1R1Rqq00

## #L#Lqq11

Turing MachineTuring Machine

#    #    1   1    1    #    #    1   1    1    ++     1      1   1   #   # 1   #   # 

qq00

qq00 qq11

11 1R1Rqq00 #Halt#Halt

++ 1R1Rqq00

## #L#Lqq11

Turing MachineTuring Machine

#    #    1   1    1    1    1   #    #    1   1    1    1    1   1   #   # 1   #   # 

qq00

qq00 qq11

11 1R1Rqq00 #Halt#Halt

++ 1R1Rqq00

## #L#Lqq11

Turing MachineTuring Machine

#    #    1   1    1    1    1   #    #    1   1    1    1    1   1   #   # 1   #   # 

qq00

qq00 qq11

11 1R1Rqq00 #Halt#Halt

++ 1R1Rqq00

## #L#Lqq11

Turing MachineTuring Machine

#    #    1   1    1    1    1   #    #    1   1    1    1    1   1   #   # 1   #   # 

qq00

qq00 qq11

11 1R1Rqq00 #Halt#Halt

++ 1R1Rqq00

## #L#Lqq11

Turing MachineTuring Machine

#    #    1   1    1    1    1   #    #    1   1    1    1    1   1   #   # 1   #   # 

qq11

qq00 qq11

11 1R1Rqq00 #Halt#Halt

++ 1R1Rqq00

## #L#Lqq11

Turing MachineTuring Machine

#    #    1   1    1    1    1   #    #    1   1    1    1    1   #   #   # #   #   # 

Halt Halt

qq00 qq11

11 1R1Rqq00 #Halt#Halt

++ 1R1Rqq00

## #L#Lqq11

Turing MachineTuring Machine

#    #    1   1    1    +    1   #    #    1   1    1    +    1   1   #   # 1   #   # 

qq00

qq00 qq11

11 #R#Rqq11 1R1Rqq11

++ 1Halt1Halt

##

Machine FunctionalismMachine Functionalism

The computational functionalist The computational functionalist claim is that the mind can be claim is that the mind can be thought of as a TMthought of as a TM

Mental states of Stephen are to be Mental states of Stephen are to be identified with the internal states of identified with the internal states of Stephen’s TMStephen’s TM

PsychologyPsychology

InstrumentalismInstrumentalismA theory A theory predictspredicts

RealismRealismA theory A theory explainsexplains

DifficultiesDifficulties

IdentityIdentity What does it means for A to have the What does it means for A to have the

same mental state as B?same mental state as B? qq00 is only definable as the triplet: is only definable as the triplet:

{<1, 1R{<1, 1Rqq00>, <+, 1R>, <+, 1Rqq00>, <#, #L>, <#, #Lqq11>}>} Each state is defined in terms of the other Each state is defined in terms of the other

states states Different psychologies can’t even be Different psychologies can’t even be

comparedcompared

DifficultiesDifficulties

SimulationSimulation Do we think that a weather simulation Do we think that a weather simulation

program actually has weather going on program actually has weather going on inside it?inside it?

Turing TestTuring Test

If a machine passes a test that we think If a machine passes a test that we think could only be passed by a thinking could only be passed by a thinking thing then we have no grounds to deny thing then we have no grounds to deny that the machine is thinking.that the machine is thinking.

Have a conversation with A and B, one Have a conversation with A and B, one of them a machine, the other a person. of them a machine, the other a person. If you can’t tell which is the machine If you can’t tell which is the machine then both are thinking.then both are thinking.

The Chinese RoomThe Chinese Room

Searle thought that the idea that Searle thought that the idea that mental states could be identified mental states could be identified with computational states was with computational states was almost demonstrably incorrect.almost demonstrably incorrect.

The Chinese RoomThe Chinese Room

ResponsesResponses SystemSystem

The room + the man + … understandsThe room + the man + … understands

ReplyReply

Let him memorise it allLet him memorise it all

The Chinese RoomThe Chinese Room

ResponsesResponses RobotRobot

Connect the room to the worldConnect the room to the world

ReplyReply

What is the robot really What is the robot really receiving?receiving?

The Chinese RoomThe Chinese Room

ResponsesResponses SimulatorSimulator

Make the room look like the brainMake the room look like the brain

ReplyReply

Where’s computation now?Where’s computation now?

The Chinese RoomThe Chinese Room

Searle thinks that Searle thinks that only only  machines  machines can think, ie. brainscan think, ie. brains, but not by , but not by computingcomputing..