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1、Chapter3 SpeechPerception OverviewofQuestions Cancomputersperceivespeechaswellashumans Whydoesanunfamiliarforeignlanguageoftensoundlikeacontinuousstreamofsound withnobreaksbetweenwords Doeseachwordthatwehearhaveauniquepatternofairpressurechangesassociatedwithit Aretherespecificareasinthebrainthatare
2、responsibleforperceivingspeech Speechperceptionreferstotheprocessesbywhichhumansareabletointerpretandunderstandthesoundsusedinlanguage Thestudyofspeechperceptioniscloselylinkedtothefieldsofphoneticsandphonologyinlinguisticsandcognitivepsychologyandperceptioninpsychology Researchinspeechperceptionsee
3、kstounderstandhowhumanlistenersrecognizespeechsoundsandusethisinformationtounderstandspokenlanguage Speechresearchhasapplicationsinbuildingcomputersystemsthatcanrecognizespeech aswellasimprovingspeechrecognitionforhearing andlanguage impairedlisteners SpeechPerception Thefirststepincomprehendingspok
4、enlanguageistoidentifythewordsbeingspoken performedinmultiplestages 1 Phonemesaredetected b e t e r 2 Phonemesarecombinedintosyllables be ter 3 Syllablesarecombinedintowords better 4 Wordmeaningretrievedfrommemory Spectrogram Ioweyouayo yo Speechperception twoproblems Wordsarenotneatlysegmented e g
5、bypauses LackofphonemeinvarianceCoarticulation consecutivespeechsoundsblendintoeachotherduetomechanicalconstraintsonarticulatorsSpeakerdifferences pitchaffectedbyageandsex differentdialects talkingspeedsetc Thespeechinputconsistsof Frequencyrange 50 5600HzCriticalbandfilters 临界频带滤波器 Dynamicrange 50d
6、BTemporalresolution 瞬时清晰度 of 10msSmallestdetectablechangeinF0 2HzSmallestchangeinF1 40HzSmallestchangeinF2 100HzSmallestchangeinF3 150Hz TheSpeechStimulus Phoneme smallestunitofspeechthatchangesmeaninginawordInEnglishthereare47phonemes 23majorvowelsounds24majorconsonantsoundsNumberofphonemesinotherl
7、anguagesvaried 11inHawaiianand60insomeAfricandialects Table13 1MajorconsonantsandvowelsofEnglishandtheirphoneticsymbols TheAcousticSignal ProducedbyairthatispushedupfromthelungsthroughthevocalcordsandintothevocaltractVowelsareproducedbyvibrationofthevocalcordsandchangesintheshapeofthevocaltractThese
8、changesinshapecausechangesintheresonantfrequencyandproducepeaksinpressureatanumberoffrequenciescalledformants 共振峰 Figure13 1Thevocaltractincludesthenasalandoralcavitiesandthepharynx aswellascomponentsthatmove suchasthetongue lips andvocalcords TheAcousticSignal continued Thefirstformanthasthelowestf
9、requency thesecondhasthenexthighest etc SoundspectrogramsshowthechangesinfrequencyandintensityforspeechConsonantsareproducedbyaconstrictionofthevocaltractFormanttransitions rapidchangesinfrequencyprecedingorfollowingconsonants Figure13 3Spectrogramofthewordhadshowingthefirst F1 second F2 andthird F3
10、 formantsforthevowel ae SpectrogramcourtesyofKerryGreen Figure13 4Spectrogramofthesentence Royreadthewill showingtheformantssuchasF1 F2 andF3 andformanttransitionssuchasT2andT3 SpectrogramcourtesyofKerryGreen TheRelationshipbetweentheSpeechStimulusandSpeechPerception Thesegmentationproblem therearen
11、ophysicalbreaksinthecontinuousacousticsignalHowdowesegmenttheindividualwords Thevariabilityproblem thereisnosimplecorrespondencebetweentheacousticsignalandindividualphonemesVariabilityfromaphoneme scontextCoarticulation overlapbetweenarticulationofneighboringphonemes Figure13 5Spectrogramof Ioweyoua
12、yo yo Thisspectrogramdoesnotcontainpausesorbreaksthatcorrespondtothewordsthatwehear Theabsenceofbreaksintheacousticsignalcreatesthesegmentationproblem SpectrogramcourtesyofDavidPisoni Figure13 6Hand drawnspectrogramsfor di and du From PerceptionoftheSpeechCode byA M Liberman 1967 PsychologicalReview
13、 74 431 461 figure1 Copyright 1967bytheAmericanPsychologicalAssociation Reprintedbypermissionoftheauthor TheRelationshipbetweentheSpeechStimulusandSpeechPerception continued VariabilityfromdifferentspeakersSpeakersdifferinpitch accent speedinspeaking andpronunciationThisacousticsignalmustbetransform
14、edintofamiliarwordsPeopleperceivespeecheasilyinspiteofthesegmentationandvariabilityproblems Figure13 7 a Spectrogramof Whatareyoudoing pronouncedslowlyanddistinctly b Spectrogramof Whatareyoudoing aspronouncedinconversationalspeech SpectrogramcourtesyofDavidPisoni StimulusDimensionsofSpeechPerceptio
15、n Invariantacousticcues featuresofphonemesthatremainconstantShort termspectrogramsareusedtoinvestigateinvariantacousticcuesSequenceofshort termspectracanbecombinedtocreatearunningspectraldisplayFromthesedisplays therehavebeensomeinvariantcuesdiscovered Figure13 8Left ashort termspectrumoftheacoustic
16、energyinthefirst26msofthephoneme ga Right soundspectrogramofthesamephoneme Thesoundforthefirst26msisindicatedinred Thepeakintheshort termspectrum markeda correspondstothedarkbandofenergy markedainthespectrum Theminimumintheshort termspectrum markedb correspondstothelightarea markedbinthespectrogram Thespectrogramontherightshowstheenergyfortheentire500msdurationofthesound whereastheshort termspectrumonlyshowsthefirst26msatthebeginningofthissignal CourtesyofJamesSawusch Figure13 9Runningspectraldi
