2Thinking MachinesA computer can do some things better --and certainly faster--than a human can:Adding a thousand four-digit numbersCounting the distribution of letters in a bookSearching a list of 1,000,000 numbers for duplicatesMatching finger prints
3Thinking MachinesBUT a computer would have difficulty pointing out the cat in this picture, which is easy for a human.Artificial intelligence (AI) The study of computer systems that attempt to model and apply the intelligence of the human mind.Figure A computer might have trouble identifying the cat in this picture.
4Thinking MachinesArtificial: humanly contrived often on a natural modelIntelligence: the ability to apply knowledge to manipulate one's environment or to think abstractly as measured by objective criteriaClearly, intelligence is an internal characteristic. How can it be identified?
5In the beginning…In 1950 Alan Turing wrote a paper titled Computing Machinery And Intelligence, in which he proposed to consider the question “Can machines think?”But the question is “loaded” so he proposed to replace it with what has since become known as the Turing Test.
6The Turing TestThe important question for Turing wasn’t “Can machines think?” but “How will we know if they can?”The Turing test is used to empirically determine whether a computer has achieved intelligence.
7The Imitation Game The 'imitation game' is played with three people: a man (A)a woman (B)and an interrogator (C) who may be of either sex.The interrogator stays in a room apart from the other two.The object of the game for the interrogator is to determine which of the other two is the man and which is the woman.
8The Imitation GameThe interrogator is allowed to put questions to A and B.It is A's object in the game to try and cause C to make the wrong identification.The object of the game for the third player (B) is to help the interrogator.
9The Imitation Game We now ask the question: 'What will happen when a machine takes the part of B in this game?'Will the interrogator decide wrongly as often when the game is played like this as he does when the game is played between a man and a woman?
10The Turing TestFigure In a Turing test, the interrogator must determine which respondent is the computer and which is the human
11The Turing TestThere are authors who question the validity of the Turing test .The objections tend to be of 2 types.The first is an attempt to distinguish degrees, or types of equivalence.
12The Turing TestWeak equivalence: Two systems (human and computer) are equivalent in results (output), but they do not arrive at those results in the same way.Strong equivalence: Two systems (human and computer) use the same internal processes to produce results.
13The Turing TestThe Turing Test, they argue, can demonstrate weak equivalence, but not strong. So even if a computer passes the test we won’t be able to say that it thinks like a human.Of course, neither they nor anyone else can explain how humans think!So strong equivalence is a nice theoretical construction, but impossible in reality.
14The Turing TestThe other objection is that a computer might seem to be behaving in an intelligent manner, while it’s really just imitating behaviour.This might be true, but notice that when a parrot talks, or a horse counts, or a pet obeys our instructions, or a child imitates its parents we take all of these things to be signs of intelligence.If a parrot mimicking human sounds can be considered intelligent (at least to some small degree) then why wouldn’t a computer be considered intelligent (at least to some small degree) for imitating other human bevaviour?
15Turing’s View“I believe that in about fifty years time it will be possible to programme computers with a storage capacity of about 109 to make them play the imitation game so well that an average interrogator will not have more than 70 per cent chance of making the right identification after five minutes of questioning.”
16Can Machines Think? No machine has passed the Turing Test, yet. Loebner Prize established in 1990$100,000 and a gold medal will be awarded to the first computer whose responses are indistinguishable from a human'sLet’s look at one of the more difficult tasks for AI…
17Aspects of AI Knowledge Representation Expert Systems Neural Networks Semantic NetworksSearch TreesExpert SystemsNeural NetworksNatural Language ProcessingRobotics
18Knowledge Representation The knowledge needed to represent an object or event depends on the situation.There are many ways to represent knowledge. One is natural language.Even though natural language is very descriptive, it doesn’t lend itself to efficient processing.
19Semantic NetworksSemantic network: A knowledge representation technique that focuses on the relationships between objects.A directed graph is used to represent a semantic network (net).
21Semantic NetworksThe relationships that we represent are completely our choice, based on the information we need to answer the kinds of questions that we will face.The types of relationships represented determine which questions are easily answered, which are more difficult to answer, and which cannot be answered.eos
22Search TreesSearch tree: a structure that represents all possible moves in a game, for both you and your opponent.The paths down a search tree represent a series of decisions made by the players.
23Search TreesFigure A search tree for a simplified version of Nim
24Search TreesSearch tree analysis can be applied nicely to other, more complicated games such as chess.Because Chess trees are so large, only a fraction of the tree can be analyzed in a reasonable time limit, even with modern computing power.
25Search Trees Techniques for searching trees Depth-first: a technique that involves the analysis of selected paths all the way down the tree.Breadth-first: a technique that involves the analysis of all possible paths but only for a short distance down the tree.Breadth-first tends to yield the best results.
26Search TreesFigure Depth-first and breadth-first searches
27Search TreesEven tough the breadth-first approach tends to yield the best results, we can see that a depth-first search will get to the goal sooner – IF we choose the right branch.Heuristics are guidelines that suggest taking one path rather than another one.eos
28Expert SystemsKnowledge-based system: a software system that embodies and uses a specific set of information from which it extracts and processes particular pieces.Expert system: a software system based the knowledge of experts in a specialized field.An expert system uses a set of rules to guide its processing.The inference engine is the part of the software that determines how the rules are followed.
29Expert SystemsExample: What type of treatment should I put on my lawn?NONE—apply no treatment at this timeTURF—apply a turf-building treatmentWEED—apply a weed-killing treatmentBUG—apply a bug-killing treatmentFEED—apply a basic fertilizer treatmentWEEDFEED—apply a weed-killing and fertilizer combination treatment
30Expert Systems Boolean variables BARE—the lawn has large, bare areas SPARSE—the lawn is generally thinWEEDS—the lawn contains many weedsBUGS—the lawn shows evidence of bugs
31Expert Systems Some rules if (CURRENT – LAST < 30) then NONE if (SEASON = winter) then not BUGSif (BARE) then TURFif (SPARSE and not WEEDS) then FEEDif (BUGS and not SPARSE) then BUGif (WEEDS and not SPARSE) then WEEDif (WEEDS and SPARSE) then WEEDFEED
32Expert Systems An execution of our inference engine System: Does the lawn have large, bare areas?User: NoSystem: Does the lawn show evidence of bugs?System: Is the lawn generally thin?User: YesSystem: Does the lawn contain significant weeds?System: You should apply a weed-killing and fertilizer combination treatment.eos
33Artificial Neural Networks Attempt to mimic the actions of the neural networks of the human body.Let’s first look at how a biological neural network works:A neuron is a single cell that conducts a chemically-based electronic signal.At any point in time a neuron is in either an excited or inhibited state.
34Artificial Neural Networks A series of connected neurons forms a pathway.A series of excited neurons creates a strong pathway.A biological neuron has multiple input tentacles called dendrites and one primary output tentacle called an axon.The gap between an axon and a dendrite is called a synapse.
35Artificial Neural Networks Figure A biological neuron
36Artificial Neural Networks A neuron accepts multiple input signals and then controls the contribution of each signal based on the “importance” the corresponding synapse gives to it.The pathways along the neural nets are in a constant state of flux.As we learn new things, new strong neural pathways are formed.
37Artificial Neural Networks Each processing element in an artificial neural net is analogous to a biological neuron.An element accepts a certain number of input values and produces a single output value of either 0 or 1.Associated with each input value is a numeric weight.
38Sample “Neuron” Artificial “neurons” can be represented as elements. Inputs are labelled v1, v2Weights are labelled w1, w2The threshold value is represented by TO is the output
39Artificial Neural Networks The effective weight of the element is defined to be the sum of the weights multiplied by their respective input values:v1*w1 + v2*w2If the effective weight meets the threshold, the unit produces an output value of 1.If it does not meet the threshold, it produces an output value of 0.
40Artificial Neural Networks The process of adjusting the weights and threshold values in a neural net is called training.A neural net can be trained to produce whatever results are required.
41Sample “Neuron”If the input Weights and the Threshold are set to the above values, how does the neuron act?Try a Truth Table…
42With the weights set to .5 this neuron behaves like an AND gate. Sample “Neuron”v1v2v1*w1v2*w2∑O1.5w1=.5, w2=.5, T=1With the weights set to .5 this neuron behaves like an AND gate.
44With the weights set to 1 this neuron behaves like an OR gate. Sample “Neuron”v1v2v1*w1v2*w2∑O1w1=1, w2=1, T=1With the weights set to 1 this neuron behaves like an OR gate.eos
45Natural Language Processing There are three basic types of processing going on during human/computer voice interaction:Voice recognition — recognizing human wordsNatural language comprehension — interpreting human communicationVoice synthesis — recreating human speechCommon to all of these problems is the fact that we are using a natural language, which can be any language that humans use to communicate.
46Voice Synthesis There are two basic approaches to the solution: Dynamic voice generationRecorded speechDynamic voice generation: A computer examines the letters that make up a word and produces the sequence of sounds that correspond to those letters in an attempt to vocalize the word.Phonemes: The sound units into which human speech has been categorized.
47Voice SynthesisFigure Phonemes for American English
48Voice SynthesisRecorded speech: A large collection of words is recorded digitally and individual words are selected to make up a message.Telephone voice mail systems often use this approach:“Press 1 to leave a message for Nell Dale; press 2 to leave a message for John Lewis.”
49Voice SynthesisEach word or phrase needed must be recorded separately.Furthermore, since words are pronounced differently in different contexts, some words may have to be recorded multiple times.For example, a word at the end of a question rises in pitch compared to its use in the middle of a sentence.eos
50Voice RecognitionThe sounds that each person makes when speaking are unique.We each have a unique shape to our mouth, tongue, throat, and nasal cavities that affect the pitch and resonance of our spoken voice.Speech impediments, mumbling, volume, regional accents, and the health of the speaker further complicate this problem.
51Voice RecognitionFurthermore, humans speak in a continuous, flowing manner.Words are strung together into sentences.Sometimes it’s difficult to distinguish between phrases like “ice cream” and “I scream”.Also, homonyms such as “I” and “eye” or “see” and “sea”.Humans can often clarify these situations by the context of the sentence, but that processing requires another level of comprehension.Modern voice-recognition systems still do not do well with continuous, conversational speech.eos
52Natural Language Comprehension Even if a computer recognizes the words that are spoken, it is another task entirely to understand the meaning of those words.Natural language is inherently ambiguous, meaning that the same syntactic structure could have multiple valid interpretations.
53Natural Language Comprehension (syntax) Syntax is the study of the rules whereby words or other elements of sentence structure are combined to form grammatical sentences.So a syntactical analysis identifies the various parts of speech in which a word can serve, and which combinations of these can be assembled into sensible sentences.
54Natural Language Comprehension (syntax) A single word can represent multiple parts of speech.Consider an example:Time flies like an arrow.To determine what it means we first parse the sentence into its parts.
55Natural Language Comprehension (syntax) ‘time’ can be used as a noun, a verb, or an adjective.‘flies’ can be used as a noun, or a verb.‘like’ can be used as a noun, a verb, a preposition, an adjective, or an adverb.‘an’ can be used only as an indefinite article.‘arrow’ can be used as a noun, or a verb.
56Natural Language Comprehension (syntax) The table below summarises the various possibilities.The a priori total number of syntactical interpretations is:3 * 2 * 5 * 1 * 2 = 60adjectiveadverbarticlenounprepositionverbtimeflieslikeanarrow
57Natural Language Comprehension (syntax) This number can be reduced by applying syntactical rules. For example, articles are used to “indicate nouns and to specify their application” so ‘arrow’ must be a noun, not a verb. This cuts the number of possible sentences in half.adjectiveadverbarticlenounprepositionverbtimeflieslikeanarrow
58Natural Language Comprehension (syntax) Other grammar rules will reduce this number further, but how far?Rather than eliminate combinations, it may be easier to build a list of reasonable possibilities.Consider the ways in which ‘time’ can be used:AdjectiveNounVerb (intr)
59Natural Language Comprehension (syntax) An adjective is “the part of speech that modifies a noun” so when ‘time’ is an adjective, ‘flies’ must be a noun.A sentence needs a verb, so if ‘flies’ is a noun, ‘like’ must be the verb.If ‘time’ is an adjective there is only ONE possible meaning.adjectiveadverbarticlenounprepositionverbtimeflieslikeanarrowskip
60Natural Language Comprehension (syntax) When ‘time’ is a noun there appear to be 10 possibilities, but there can only be one verb so there are only 5.adjectiveadverbarticlenounprepositionverbtimeflieslikeanarrowadjectiveadverbarticlenounprepositionverbtimeflieslikeanarrow
61Natural Language Comprehension (syntax) A sentence can have only one verb, so when ‘time’ is a verb there are only 4 possible combinations of the other parts.adjectiveadverbarticlenounprepositionverbtimeflieslikeanarrowThe syntactical analysis reveals a total of 10 possible ways these words can form a sentence.
62Natural Language Comprehension (semantics) A syntactical analysis provides a structure, a semantic analysis adds meaning.Consider the first case in the syntactical analysis.adjectiveadverbarticlenounprepositionverbtimeflieslikeanarrowWhat would the words mean under this syntactical interpretation?
63Natural Language Comprehension (semantics) time flies (not house flies)enjoyan arrow (watching it, chasing it, eating it)‘time’ adjective “of, relating to, or measuring time”‘flies’ noun “two-winged insect”‘like’ verb “find pleasant or attractive”‘an’ article‘arrow’ noun “missile having a straight thin shaft with a pointed head at one end and often flight-stabilizing vanes at the other”
64Natural Language Comprehension (semantics) ‘time’ adjective “of, relating to, or measuring time”‘flies’ noun “two-winged insect”‘like’ verb “find pleasant or attractive”‘an’ article‘arrow’ noun “missile having a straight thin shaft with a pointed head at one end and often flight-stabilizing vanes at the other”time flies (not house flies)enjoyan arrow (watching it, chasing it, eating it)
65Natural Language Comprehension (semantics) time flies (not house flies)enjoyan arrow (watching it, chasing it, eating it)‘time’ adjective “of, relating to, or measuring time”‘flies’ noun “two-winged insect”‘like’ verb “find pleasant or attractive”‘an’ article‘arrow’ noun “missile having a straight thin shaft with a pointed head at one end and often flight-stabilizing vanes at the other”
66Natural Language Comprehension (semantics) time flies (not house flies)enjoyan arrow (watching it, chasing it, eating it)‘time’ adjective “of, relating to, or measuring time”‘flies’ noun “two-winged insect”‘like’ verb “find pleasant or attractive”‘an’ article‘arrow’ noun “missile having a straight thin shaft with a pointed head at one end and often flight-stabilizing vanes at the other”
67Natural Language Comprehension (semantics) time flies (not house flies)enjoyan arrow(watching it, chasing it, eating it?)‘time’ adjective “of, relating to, or measuring time”‘flies’ noun “two-winged insect”‘like’ verb “find pleasant or attractive”‘an’ article‘arrow’ noun “missile having a straight thin shaft with a pointed head at one end and often flight-stabilizing vanes at the other”
68Natural Language Comprehension (semantics) This interpretation sounds absurd to us, but as our analysis showed, it’s a perfectly logical interpretation of the words.This is problem is referred to as a lexical ambiguity.It arises because words have multiple syntactical and semantic associations.In this case there are many syntactically and semantically valid interpretations.skip
69Natural Language Comprehension (semantics) Consider the cases in which ‘time’ is a verb.The Free Dictionary lists 5 meanings:1. To set the time for (an event or occasion).2. To adjust to keep accurate time.3. To adjust so that a force is applied or an action occurs at the desired time: timed his swing so as to hit the ball squarely.4. To record the speed or duration of: time a runner.5. To set or maintain the tempo, speed, or duration of: time a manufacturing process.
70Natural Language Comprehension (semantics) Not only are there 4 syntactical interpretations of the sentence when ‘time’ is a verb, each of those must be analysed under 5 semantic interpretations.Let’s explore a few:4. To record the speed or duration of: time a runner.As a transitive verb, ‘time’ requires an object, so ‘flies’ is a noun. We’ve seen one meaning, here’s another of the 12 listed in The Free Dictionary :5. Baseball A fly ball.
71Natural Language Comprehension (semantics) So, when you measure the length of time it takes a fly ball to travel its route, use the same techniques that you use when you time an arrow.This interpretation isn’t as odd as it might seem.We know that the paths taken by fly balls and arrows are all parabolic arcs, so it makes sense to time them the same way.
72Natural Language Comprehension (semantics) Consider the interpretations in which ‘time’ is a noun and ‘flies’ is a verb. (These are the parts of speech we would usually map onto them in this context.)The Free Dictionary lists 29 distinct meanings for the noun ‘time’. Consider the first one:a. A nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future.This is a normal sense of what we mean by ‘time’ but which meaning of the verb ‘flies’ should be used?
73Natural Language Comprehension (semantics) The Free Dictionary lists only one definition:“Third person singular present tense of fly.”In this context, ‘fly’ can only be an intransitive verb, for which there are 14 different nuances. The most commonly used of these is “To engage in flight.”But can that be the meaning intended in our saying? How does a computer program decide?It’s easy to see why NLC is difficult for computers.eos
74Natural Language Comprehension A natural language sentence can also have a syntactic ambiguity because phrases can be put together in various ways.I saw the Grand Canyon flying to New York.Is it possible that the Grand Canyon flew to New York?
75Natural Language Comprehension Referential ambiguity can occur with the use of pronouns.The brick fell on the computer but it is not broken.Since ‘it’ is the subject of the second clause, its referent is the subject of the first clause – ‘the brick’!Are you happy knowing that no harm came to the brick?eos
76RoboticsMobile robotics: The study of robots that move relative to their environment, while exhibiting a degree of autonomy.In the sense-plan-act (SPA) paradigm the world of the robot is represented in a complex semantic net in which the sensors on the robot are used to capture the data to build up the net.Figure The sense-plan-act (SPA) paradigm
77Subsumption Architecture Rather than trying to model the entire world all the time, the robot is given a simple set of behaviours each associated with the part of the world necessary for that behaviourFigure The new control paradigm
78Subsumption Architecture Figure Asimov’s laws of robotics are ordered.eof