Jun 26, 2015
- 1. AI Philosophy: Computers and Their Limits G51IAI Introduction to AI Andrew Parkes http://www.cs.nott.ac.uk/~ajp/
2. Natural Questions
- Can a computer only have a limited intelligence? or maybe none at all?
- Are there any limits to what computers can do?
- What is a computer anyway?
3. Turing Test
- The test is conducted with two people and a machine.
- One person plays the role of an interrogator and is in a separate room from the machine and the other person.
- The interrogator only knows the person and machine as A and B. The interrogator does not know which is the person and which is the machine.
- Using a teletype, the interrogator, can ask A and B any question he/she wishes. The aim of the interrogator is to determine which is the person and which is the machine.
- The aim of the machine is to fool the interrogator into thinking that it is a person.
- If the machine succeeds then we can conclude that machines can think.
4. Turing Test: Modern
- Youre on the internet and open a chat line (modern teletype) to two others A and B
- one is a machine trying to imitate a person (e.g. capable of discussing the X-factor?)
- If you cant tell the difference then the machine must be intelligent
- Or at least act intelligent?
5. Turing Test
- Often forget the second person
- Informally, the test is whether the machine behaves like it is intelligent
- This is a test ofbehaviour
- It is does not ask does the machine really think?
6. Turing Test Objections
- It is too culturally specific?
- If B had never heard of The X-Factor then does it preclude intelligence?
- What if B only speaks Romanian?
- It tests only behaviour not real intelligence?
7. Chinese Room
- a human, who only understands English
- a rule book, written in English
- One stack of paper is blank.
- The other has indecipherable symbols on them.
- the rule book is the program
- the two stacks of paper are storage devices.
- The system is housed in a room that is totally sealed with the exception of a small opening.
8. Chinese Room: Process
- The human sits inside the room waiting for pieces of paper to be pushed through the opening.
- The pieces of paper have indecipherable symbols written upon them.
- The human has the task of matching the symbols from the "outside" with the rule book.
- Once the symbol has been found the instructions in the rule book are followed.
- may involve writing new symbols on blank pieces of paper,
- or looking up symbols in the stack of supplied symbols.
- Eventually, the human will write some symbols onto one of the blank pieces of paper and pass these out through the opening.
9. Chinese Room: Summary
- Simple Rule processing system but in which the rule processor happens to be intelligent but has no understanding of the rules
- The set of rules might be very large
- But this is philosophy and so ignore the practical issues
10. Searles Claim
- We have a system that is capable of passing the Turing Test and is therefore intelligent according to Turing.
- But the system does not understand Chinese as it just comprises a rule book and stacks of paper which do not understand Chinese.
- Therefore, running the right program does not necessarily generate understanding.
11. Replies to Searle
- The Brain Simulator Reply
12. Blame the System!
- The Systems Reply states that the system as a whole understands.
- Searle responds that the system could be internalised into a brain and yet the person would still claim not to understand chinese
13. Make Data?
- The Robot Reply argues we could internalise everything inside a robot (android) so that it appears like a human.
- Searle argues that nothing has been achieved by adding motors and perceptual capabilities.
- The Brain Simulator Reply argues we could write a program that simulates the brain (neurons firing etc.)
- Searle argues we could emulate the brain using a series of water pipes and valves. Can we now argue that the water pipes understand? He claims not.
15. AI Terminology
- machine can possiblyactintelligently
- machines can actuallythinkintelligently
- AIMA: Most AI researchers take the weak hypothesis for granted, and dont care about the strong AI hypothesis(Chap. 26. p. 947)
16. What is a computer?
- In discussions ofCan a computer be intelligent?
- Do we need to specify the type of the computer?
- Does the architecture matter?
- Matters in practice: need a fast machine, lots of memory, etc
- But does it matter in theory?
17. Turing Machine
- A very simple computing device
- storage: a tape on which one can read/write symbols from a list
- processing: a finite state automaton
18. Turing Machine: Storage
- Storage: a tape on which one can read/write symbols from some fixed alphabet
- tape is of unbounded length
- you never run out of tape
- move to next cell of the tape
19. Turing Machine: Processing
- The processor can has a fixed finite number of internal states
- there are transition rules that take the current symbol from the tape and tell it
- whether to move the head left or right
- which state to go to next
20. Turing Machine Equivalences
- The set of tape symbols does not matter!
- If you have a Turing machine that uses one alphabet, then you can convert it to use another alphabet by changing the FSA properly
- Might as well just use binary 0,1 for the tape alphabet
21. Universal Turing Machine
- This is fixed machine that can simulate any other Turing machine
- the program for the other TM is written on the tape
- the UTM then reads the program and executes it
- C.f. on any computer we can write a DOS emulator and so read a program from a .exe file
22. Church-Turing Hypothesis
- All methods of computing can be performed on a Universal Turing Machine (UTM)
- Many computers are equivalent to a UTM and hence all equivalent to each other
- Based on the observation that
- when someone comes up with a new method of computing
- then it always has turned out that a UTM can simulate it,
- and so it is no more powerful than a UTM
23. Church-Turing Hypothesis
- If you run an algorithm on one computer then you can get it to work on any other
- as long as have enough time and space thencomputers can all emulate each other
- an operating system of 2070 will still be able to run a 1980s .exe file
- Implies that abstract philosophical discussions of AI can ignore the actual hardware?
- or maybe not? (see the Penrose argument later!)
24. Does a Computer have any known limits?
- Would like to answer: Does a computer have any limit on intelligence?
- Simpler to answer Does a computer have any limits onwhat it can compute?
- e.g. ask the question of whether certain classes of program can exist in principle