Greg Francis 5/27/081Phrase treesIIE 269: Cognitive PsychologyGreg FrancisLecture 26Dr. Francis says something new!Language Conveys information Allows us to know about things we havenever experienced moon flights mating habits of tigers,… How do we do it? Two key aspectsSymbols and grammar Symbols words are arbitrary the sound “dog” has nothing to do with dogs compare driving on parkway to parking ondriveway, blueberries and cranberries,hamburger… Grammar the order of words matters Dog bites man. vs. Man bites dog.Grammar Discrete combinatorial system combinations of words How many combinations? if interrupted anywhere in the middle of asentence, there are about 10 words one couldselect before finishing it up if sentences average around 20 words, thatmeans there are 10^20 sentencesGrammar But in fact, there are infinitely manydifferent sentences there is no limit to how long a sentence canbe For any sentence I give you, you canalways make it longer by addingsomething like Professor Francis said that, “….”Vastness It is amazing how powerful language is You have probably never heard thefollowing sentence moreover, it is probably its first utterance inhuman history, but you understand it anyhowI am going to have to find a new demo to replace the gorilla video because too many students have already seen it.Greg Francis 5/27/082Grammar You not only understand language, you sensewhen a sentence is ungrammatical Please try your Nice Chinese Food with Chopsticks: thetraditional and typical of Chinese glorious history andcultual. Is raining. The child seems sleeping. Sally poured the glass with water. It’s a flying finches, they are. Rarely is the question asked: Is our children learning?Sometimes youstill understandwhat was meant!Grammar You can also have sentences withoutmeaning that are perceived as grammatical Colorless green ideas sleep furiously. It’s a fact the whole world knows, that Pobbles arehappier without their toes. ‘Twas brillig, and the slithy tovesDid gyre and gimble in the wabe:All mimsy were the borogoves,And the mome raths outgrabe.Grammar These properties of language suggest that yourknowledge about language grammar is a basiccomponent of language systems It is distinct from both meaning and understanding Much of linguistics explores the rules of language we are interested in how people perceive grammar this is different from the grammar rules you may havelearned in school!» Which often focus on forming sentences that are easyto understandModern linguistics Noam Chomsky used the properties ofgrammar to demonstrate that language isquite different from other types of learningthat might occur it’s not like learning to play a piano or learning about statistical regularities in theenvironment (stimulus-response)Nonsense sentences Think about the sentence Colorless green ideas sleep furiously. What is the probability that in normal life youwould hear the word “green” follow the word“colorless”? it must be close to zero But we recognize it as a grammaticallycorrect sentence!Statistics If you just learned the statisticalcombinations of words, you might thinksomething like this was a grammaticalsentenceHouse to ask for is to earn our living byworking towards a goal for his team in old New York was a wonderful place wasn’t iteven pleasant to talk about and laugh hardwhen he tells lies he should not tell me the reason why you are is evidentGreg Francis 5/27/083Statistics The previous paragraph creates coherentgroups of 4 words at a time (generator madesure 4 words were with high probability) Maybe by including a larger number of wordsgrouped together you can insure that everysentence is appropriate Actually you cannot Because sentences have no maximum lengthLong-term dependencies Language has rules that determine what types ofwords can be used and when A word choice early in a sentence can have an effectat the end of a sentenceHow Ann Salisbury can claim that Pam Dawber’s angerat not receiving her fair share of acclaim for Mork and Mindy’s success derives from a fragile ego escapes me.1) “at not receiving ” --> noun “acclaim”2) “anger” --> “derives” (singular)3) “How” --> “escapes” (number)Long-term dependencies Chomsky demonstrated that long termdependencies can be very long Consider “If…then…” and “Either…or…” sentencesIf the girl eats ice cream, then the boy eats hot dogs.Either the girl eats ice cream, or the boy eats hot dogs.Recursion In fact, any sentence can go inside the“if…then” part of a sentence embed a sentence in a sentence Thus the following is a (ugly) validsentence recursion cannot be learned by statistics, ithas to be based on rulesEither if the girl eats ice cream, then the boy eats ice cream, or if the girl eats ice cream then the boy eats candy.Phrases Every sentence is built out of phrasesThe happy boy eats candy.The first three words form a unit calleda noun phrase (NP)The happy boyWhat identifies a noun phrase?This is not the same analysis you didin grammar school!Phrases All noun phrases obey certain rules rewrite rules NP -- noun phrase det -- determinant: “the”, “a”, “an” A -- adjective N -- noun ( ) -- optional * -- as many as you wantNP-->(det)A*Nthe happy boythe boyJohnthe tall slender womanGreg Francis 5/27/084Phrase tree It helps to describe rules as phrase trees Specifies both what can be used in thephrase and where it must be usedNPdet A Nthe happy boyPhrases Similarly, there are rules for all sorts ofphrases in a language There may be many ways to rewrite aphrase!S-->NP VPVP-->V NPS -- sentenceNP -- noun phraseVP -- verb phraseLexicon We also need a mental dictionary(lexicon) that specifies parts of speech N --> boy, girl, candy, hot dogs, ice cream,… V --> eats, likes, bites,… det --> a, the one,… A --> lucky, tall,...Phrase tree With rewrite rules and a mental dictionary,you can create a sentence by linking therules togetherNPdet A Nthe happyboySVPVNPNice creameatsSockets In a phrase tree, a phrase is like a componentthat snaps into the right place any appropriate phrase works! (even nonsensephrases)NPA A Ncolorlessgreen ideaSVPVNPNice creameatsdettheUsefulness It is important to appreciate how