Transcript Document

CS 551/651:
Structure of Spoken Language
Lecture 6: Phonological Processes
John-Paul Hosom
Fall 2010
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Phonological Processes
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Phonemes undergo systematic variation depending on their
context
•
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 phonemes
that are a result of cultural and/or physiological processes, but
do not distinguish meaning of utterance
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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/
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/s
p ih
th
s
t ih
kh
s
k ih n/
Phonological Processes
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Other types of phonetic processes:
Assimilation, Deletion, Reduction, Insertion, Substitution,
Me'tathesis (switching order of two phonemes)
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Assimilation
“A feature of one segment is shared by a neighboring segment”
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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
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Assimilation may be due to coarticulation, or it may be
language-specific, “arbitrary”:
“word-final alveolar obstruent may take on place
of articulation of following word-initial segment
if 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
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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
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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/
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Metathesis:
changing order of two phonemes within a word
(dialect variation)
pretty
/p er dx iy/
ask
/ae k s/
For the history of ask/aks, Google “axe ask england”:
http://www.randomhouse.com/wotd/index.pperl?date=19991216
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Phonological Processes
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Deletion:
Barbara
Memory
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Reduction:
unstressed vowels become /ax/
conduct (verb) /k ax n d ah k t/
conduct (noun) /k aa n d ax k t/
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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 nasal
nine
/n ay n ax/
dictionary pronunciation=
/b aa r b ax r ah/  /b aa r b r ah/
/m eh m ax r iy/  /m eh m r iy/
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Phonological Processes
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Deletion:
/m
eh
m
r
iy/
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Phonological Processes
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Insertion:
/f ae n
t s
iy
ch aa m p s
k iy/
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Phonological Processes: Ladefoged Rules
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[–voiced, +stop]  [+aspirated] when syllable initial
pit vs. spit
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[ax]  [–voiced] after syllable-initial [–voiced, +stop] and
before [–voiced, +stop]
potato
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[+consonantal]  longer at end of phrase
bib, did, don, nod
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[–voiced, +stop]  [–aspirated] after syllable-initial /s/
spew, stew, skew
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[+vowel]  shorter before unvoiced phonemes in same syllable
cap vs. cab, back vs. bag
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Phonological Processes: Ladefoged Rules
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Devoicing, End-of-Phrase Length:
/ph ax tcl
th
ey
dx
ow/
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/d
aa
n
n
aa
dcl d/
Phonological Processes: Ladefoged Rules
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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
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[–voiced]  longer when at end of syllable
sass, shook vs. push
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[+stop]  unreleased before [+stop]
apt, act (often see some mark in spectrogram)
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[–voiced, +alveolar, +stop]  [+glottal stop] when
before an alveolar nasal in same word
beaten  /b iy q en/
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[+nasal]  [+syllabic] at word end when following [+obstruent]
chasm  /k ae z em/
NOT film (obstruent = complete closure of airway; /l/ is not)
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[+liquid]  [+syllabic] at word end and following [+consonant]
paddle, whistle, kennel, razor, hammer, tailor
NOT snarl; change to “following [+obstruent]”? 14
Phonological Processes: Ladefoged Rules
/ae
pcl tcl th
/bcl
b
iy
ae
q tcl
kcl tcl
en
th/
ax_h/
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Phonological Processes: Ladefoged Rules
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[+alveolar, +stop]  [+voiced, +flap] when between
two vowels, second of which is unstressed
This rule has speaker-dependent variations
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[+alveolar, +stop]  omitted between two consonants
most people, sandpaper, grand master
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[+consonant]  shortened before identical [+consonant]
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  [–voice, +stop] between [+nasal] and [–voice, +fricative]
when following vowel absent or unstressed
prince vs. prints
(e'penthesis)
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  [&] following word-final [+nasal, +consonantal]
nine come sang
(e'penthesis)
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Phonological Processes: Ladefoged Rules
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“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 pc17ph er/
Phonological Processes: Ladefoged Rules
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“nine come sang”
/n
ay
n ax kcl kh ah
m ax
s
ae
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ng ax/
Phonological Processes: Ladefoged Rules
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[+vowel]  longer in open syllables
sea vs. seed vs. seat
sigh vs. side vs. sight
(equalize length of syllables with differing numbers of segments)
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[+vowel]  longer in stressed syllable
below vs. billow
(stressed syllables are longer in duration than unstressed)
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[+vowel]  [+nasal] before [+nasal] consonant
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[+vowel, –stressed]  schwa (vowel reduction)
able vs. ability
Canada vs. Canadian
photograph vs. photography
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Phonological Processes: Ladefoged Rules
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“sigh side sight”
/s
ay
s
ay
dcl d
s
a tcl 20th/
Phonological Processes: Ladefoged Rules
•
“below billow”
/b ax l
ow
b ih l
ow/
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Phonological Processes
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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
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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
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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
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Difficulty is in providing comprehensive, accurate rules
that are not inappropriately “forced” on a system
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