1 CS 551/651: Structure of Spoken Language Lecture 6: Phonological Processes John-Paul Hosom Fall...

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CS 551/651:Structure of Spoken Language

Lecture 6: Phonological Processes

John-Paul HosomFall 2010

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Phonological Processes

• Phonemes undergo systematic variation depending on theircontext

• For example, forming the past tense:cause /k aa z/ caused /k aa z d/talk /t aa k/ talked /t aa k t/

/d/ vs. /t/ is predictable based on voicing of word-final phoneme

• Allophones can be viewed as systematic variations of phonemesthat are a result of cultural and/or physiological processes, butdo not distinguish meaning of utterance

• For example, /p/ and /ph/ in English is predictable:word or syllable initial voiceless stops are aspirated

pit [ph ih t[h]] tip [th ih p[h]] kin [kh ih n]spit [s p ih t[h]] stick [s t ih k[h]] skin [s k ih n]

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Phonological Processes

/ph ih th th ih ph kh ih n/

/s p ih th s t ih kh s k ih n/

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Phonological Processes

• Other types of phonetic processes:Assimilation, Deletion, Reduction, Insertion, Substitution,Me'tathesis (switching order of two phonemes)

• Assimilation“A feature of one segment is shared by a neighboring segment”

• Examples of Assimilation Nasalization of vowels before nasal consonants in- (negative prefix) becomes im- in words beginning with bilabial consonant (imbalance, imperfect, indifferent, intolerance)

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Phonological Processes

• Assimilation may be due to coarticulation, or it may belanguage-specific, “arbitrary”:

“word-final alveolar obstruent may take on placeof articulation of following word-initial segmentif word-initial segment is palato-alveoar”

this /dh ih s/ shop /sh aa ph/ this shop /dh ih sh sh aa ph/this /dh ih s/ fish /f ih sh/ this fish /dh ih s f ih sh/this /dh ih s/ thing /th ih ng/ this thing /dh ih s th ih ng/

also, depending on dialect, not within-word: misshapen /m ih s sh ei p en/

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Phonological Processes

• Example of assimilation of /s/ with /sh/ but not /f/:

/dh ih sh sh aa pcl ph dh ih s f ih sh/

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Phonological Processes

• Substitution:common in foreign accents or speaking impairments:

welcome /v eh l k ah m/McDonald /m a k uw d ow n aa r uw d ow/Roger /w aa jh er/

• Metathesis:changing order of two phonemes within a word(dialect variation)

pretty /p er dx iy/ask /ae k s/

http://www.randomhouse.com/wotd/index.pperl?date=19991216

For the history of ask/aks, Google “axe ask england”:

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Phonological Processes

• Deletion:Barbara /b aa r b ax r ah/ /b aa r b r ah/Memory /m eh m ax r iy/ /m eh m r iy/

• Reduction:unstressed vowels become /ax/

conduct (verb) /k ax n d ah k t/conduct (noun) /k aa n d ax k t/

• Insertion:voiceless stop inserted between nasal and voiceless consonant; voiceless stop always has same place of articulation as nasal

fancy /f ae n t s iy/Chomsky /ch aa m p s k iy/

schwa inserted after word-final nasalnine /n ay n ax/

dictionary pronunciation=

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Phonological Processes

• Deletion:

/m eh m r iy/

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Phonological Processes

• Insertion:

/f ae n t s iy ch aa m p s k iy/

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Phonological Processes: Ladefoged Rules

• [–voiced, +stop] [+aspirated] when syllable initialpit vs. spit

• [ax] [–voiced] after syllable-initial [–voiced, +stop] and before [–voiced, +stop]

potato

• [+consonantal] longer at end of phrasebib, did, don, nod

• [–voiced, +stop] [–aspirated] after syllable-initial /s/spew, stew, skew

• [+vowel] shorter before unvoiced phonemes in same syllablecap vs. cab, back vs. bag

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Phonological Processes: Ladefoged Rules

• Devoicing, End-of-Phrase Length:

/ph ax tcl th ey dx ow/

/d aa n n aa dcl d/

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Phonological Processes: Ladefoged Rules

• Length before Voiceless:

/khae pc ph kh ae bc b b ae kc kh b ae gc g/

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Phonological Processes: Ladefoged Rules

• [–voiced] longer when at end of syllablesass, shook vs. push

• [+stop] unreleased before [+stop]apt, act (often see some mark in spectrogram)

• [–voiced, +alveolar, +stop] [+glottal stop] when before an alveolar nasal in same word

beaten /b iy q en/

• [+nasal] [+syllabic] at word end when following [+obstruent]chasm /k ae z em/NOT film (obstruent = complete closure of airway; /l/ is not)

• [+liquid] [+syllabic] at word end and following [+consonant]paddle, whistle, kennel, razor, hammer, tailorNOT snarl; change to “following [+obstruent]”?

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Phonological Processes: Ladefoged Rules

/ae pcl tcl th ae kcl tcl th/

/bcl b iy q tcl en ax_h/

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Phonological Processes: Ladefoged Rules

• [+alveolar, +stop] [+voiced, +flap] when betweentwo vowels, second of which is unstressed This rule has speaker-dependent variations

• [+alveolar, +stop] omitted between two consonantsmost people, sandpaper, grand master

• [+consonant] shortened before identical [+consonant]

[–voice, +stop] between [+nasal] and [–voice, +fricative]when following vowel absent or unstressedprince vs. prints (e'penthesis)

[&] following word-final [+nasal, +consonantal]nine come sang (e'penthesis)

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Phonological Processes: Ladefoged Rules

• “most people and grand masters use sandpaper”

/m ow s pc ph iy pc ph el n gc g r ae n m ae s tc th er z yu z s ae n pc ph ey pc ph er/

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Phonological Processes: Ladefoged Rules

• “nine come sang”

/n ay n ax kcl kh ah m ax s ae ng ax/

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Phonological Processes: Ladefoged Rules

• [+vowel] longer in open syllablessea vs. seed vs. seatsigh vs. side vs. sight

(equalize length of syllables with differing numbers of segments)

• [+vowel] longer in stressed syllablebelow vs. billow

(stressed syllables are longer in duration than unstressed)

• [+vowel] [+nasal] before [+nasal] consonant

• [+vowel, –stressed] schwa (vowel reduction)able vs. abilityCanada vs. Canadianphotograph vs. photography

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Phonological Processes: Ladefoged Rules

• “sigh side sight”

/s ay s ay dcl d s a tcl th/

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Phonological Processes: Ladefoged Rules

• “below billow”

/b ax l ow b ih l ow/

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Phonological Processes

• Why is this useful? (a) Providing models of known phenomenon is better

than having classifier learn the phenomenon from data(b) Provides humans with appropriate cues for understanding,

naturalness(c) Accurate phonetic modeling improves ability of

classifier to discriminate between classes

• Example for Text-to-Speech (case (b)): Create a TTS system Don’t shorten vowels before voiceless plosives Creates, by default, acoustic cue for voiced plosives Decrease intelligibility or at least naturalness of system

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Phonological Processes

• Example for Automatic Speech Recognition (case (c)): Train a speech recognizer using “dictionary” pronunciation Then, in all cases where

[–voice, +stop] between [+nasal] and [–voice, +fricative]such as “fancy” (in CMU dictionary as /f ae n s iy/), acoustics show alveolar stop, but trained as either nasal /n/ or fricative /s/.

Decreases ability of model to discriminate classes Decreases performance of system

• Difficulty is in providing comprehensive, accurate rulesthat are not inappropriately “forced” on a system