Presentation on theme: "Chapter 13 Artificial Intelligence. 2 Thinking Machines A computer can do some things better --and certainly faster--than a human can: Adding a thousand."— Presentation transcript:
Chapter 13 Artificial Intelligence
2 Thinking Machines A computer can do some things better --and certainly faster--than a human can: Adding a thousand four-digit numbers Counting the distribution of letters in a book Searching a list of 1,000,000 numbers for duplicates Matching finger prints
3 Thinking Machines BUT 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 13.1 A computer might have trouble identifying the cat in this picture.
4 Thinking Machines Artificial: humanly contrived often on a natural model Intelligence: the ability to apply knowledge to manipulate one's environment or to think abstractly as measured by objective criteria Clearly, intelligence is an internal characteristic. How can it be identified?
5 In the beginning… In 1950 Alan Turing wrote a paper titled Computing Machinery And Intelligence, in which he proposed to consider the questionCan machines think? Computing Machinery And Intelligence But the question is loaded so he proposed to replace it with what has since become known as the Turing Test.
6 The Turing Test The important question for Turing wasnt 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.
7 The 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.
8 The Imitation Game The 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.
9 The 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?
10 The Turing Test Figure 13.2 In a Turing test, the interrogator must determine which respondent is the computer and which is the human
11 The Turing Test There 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.
12 The Turing Test Weak 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.
13 The Turing Test The Turing Test, they argue, can demonstrate weak equivalence, but not strong. So even if a computer passes the test we wont 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.
14 The Turing Test The other objection is that a computer might seem to be behaving in an intelligent manner, while its 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 wouldnt a computer be considered intelligent (at least to some small degree) for imitating other human bevaviour?
15 Turings View I believe that in about fifty years time it will be possible to programme computers with a storage capacity of about 10 9 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.
16 Can Machines Think? No machine has passed the Turing Test, yet. Loebner Prize established in 1990 Loebner Prize $100,000 and a gold medal will be awarded to the first computer whose responses are indistinguishable from a human's Lets look at one of the more difficult tasks for AI…
17 Aspects of AI Knowledge Representation Semantic Networks Search Trees Expert Systems Neural Networks Natural Language Processing Robotics
18 Knowledge 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 doesnt lend itself to efficient processing.
19 Semantic Networks Semantic network: A knowledge representation technique that focuses on the relationships between objects. A directed graph is used to represent a semantic network (net).
20 Semantic Networks Figure 13.3 A semantic network
21 Semantic Networks The 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
22 Search Trees Search 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.
23 Search Trees Figure 13.4 A search tree for a simplified version of Nim
24 Search Trees Search 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.
25 Search 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.
26 Search Trees Figure 13.5 Depth-first and breadth-first searches
27 Search Trees Even 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
28 Expert Systems Knowledge-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.
29 Expert Systems Example: What type of treatment should I put on my lawn? NONEapply no treatment at this time TURFapply a turf-building treatment WEEDapply a weed-killing treatment BUGapply a bug-killing treatment FEEDapply a basic fertilizer treatment WEEDFEEDapply a weed-killing and fertilizer combination treatment
30 Expert Systems Boolean variables BAREthe lawn has large, bare areas SPARSEthe lawn is generally thin WEEDSthe lawn contains many weeds BUGSthe lawn shows evidence of bugs
31 Expert Systems Some rules if (CURRENT – LAST < 30) then NONE if (SEASON = winter) then not BUGS if (BARE) then TURF if (SPARSE and not WEEDS) then FEED if (BUGS and not SPARSE) then BUG if (WEEDS and not SPARSE) then WEED if (WEEDS and SPARSE) then WEEDFEED
32 Expert Systems An execution of our inference engine System: Does the lawn have large, bare areas? User: No System: Does the lawn show evidence of bugs? User: No System: Is the lawn generally thin? User: Yes System: Does the lawn contain significant weeds? User: Yes System: You should apply a weed-killing and fertilizer combination treatment. eos
33 Artificial Neural Networks Attempt to mimic the actions of the neural networks of the human body. Lets 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.
34 Artificial 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.
35 Artificial Neural Networks Figure 13.6 A biological neuron
36 Artificial 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.
37 Artificial 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.
38 Sample Neuron Artificial neurons can be represented as elements. Inputs are labelled v1, v2 Weights are labelled w1, w2 The threshold value is represented by T O is the output
39 Artificial 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*w2 If 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.
40 Artificial 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.
41 Sample Neuron If the input Weights and the Threshold are set to the above values, how does the neuron act? Try a Truth Table…
42 Sample Neuron v1v2v1*w1v2*w2O w1=.5, w2=.5, T=1 With the weights set to.5 this neuron behaves like an AND gate.
43 Sample Neuron How about now?
44 Sample Neuron v1v2v1*w1v2*w2O w1=1, w2=1, T=1 With the weights set to 1 this neuron behaves like an OR gate. eos
45 Natural Language Processing There are three basic types of processing going on during human/computer voice interaction: Voice recognition recognizing human words Natural language comprehension interpreting human communication Voice synthesis recreating human speech Common 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.
46 Voice Synthesis There are two basic approaches to the solution: Dynamic voice generation Recorded speech Dynamic 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.
47 Voice Synthesis Figure 13.7 Phonemes for American English
48 Voice Synthesis Recorded 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.
49 Voice Synthesis Each 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
50 Voice Recognition The 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.
51 Voice Recognition Furthermore, humans speak in a continuous, flowing manner. Words are strung together into sentences. Sometimes its 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
52 Natural 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.
53 Natural 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.
54 Natural 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.
55 Natural 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.
56 Natural Language Comprehension (syntax) The table below summarises the various possibilities. The a priori total number of syntactical interpretations is: 3 * 2 * 5 * 1 * 2 = 60 adjectiveadverbarticlenounprepositionverb time flies like an arrow
57 Natural 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. adjectiveadverbarticlenounprepositionverb time flies like an arrow
58 Natural 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: Adjective Noun Verb (intr)
59 Natural Language Comprehension (syntax) An adjective is the part of speech that modifies a noun so whentime 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. adjectiveadverbarticlenounprepositionverb time flies like an arrow skip
60 Natural Language Comprehension (syntax) adjectiveadverbarticlenounprepositionverb time flies like an arrow When time is a noun there appear to be 10 possibilities, but there can only be one verb so there are only 5. adjectiveadverbarticlenounprepositionverb time flies like an arrow
61 Natural 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. adjectiveadverbarticlenounprepositionverb time flies like an arrow The syntactical analysis reveals a total of 10 possible ways these words can form a sentence.
62 Natural Language Comprehension (semantics) A syntactical analysis provides a structure, a semantic analysis adds meaning. Consider the first case in the syntactical analysis. adjectiveadverbarticlenounprepositionverb time flies like an arrow What would the words mean under this syntactical interpretation?
63 Natural 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) enjoy an arrow (watching it, chasing it, eating it)
64 Natural 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) enjoy an arrow (watching it, chasing it, eating it)
65 Natural 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) enjoy an arrow (watching it, chasing it, eating it)
66 Natural 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) enjoy an arrow (watching it, chasing it, eating it)
67 Natural 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) enjoy an arrow (watching it, chasing it, eating it?)
68 Natural Language Comprehension (semantics) This interpretation sounds absurd to us, but as our analysis showed, its 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
69 Natural Language Comprehension (semantics) Consider the cases in which time is a verb. The Free DictionaryThe 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.
70 Natural 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. Lets 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. Weve seen one meaning, heres another of the 12 listed in The Free Dictionary : The Free Dictionary 5. Baseball A fly ball.
71 Natural 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 isnt 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.
72 Natural 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: The Free Dictionary 1. 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?
73 Natural Language Comprehension (semantics) The Free DictionaryThe Free Dictionary lists only one definition: Third person singular present tense of fly.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? Its easy to see why NLC is difficult for computers. eos
74 Natural 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?
75 Natural 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
76 Robotics Mobile 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 13.8 The sense-plan-act (SPA) paradigm
77 Subsumption 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 behaviour Figure 13.9 The new control paradigm
78 Subsumption Architecture Figure Asimovs laws of robotics are ordered. eof