Revision of Speech Perception

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Revision of Speech Perception

• Mark C. Flynn, PhD
• Dept of Speech Language Therapy

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Note

• At first glance these notes should look like
  revision.
• The emphasis of this lecture is on how hearing
  loss affects perception.

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Contents

• Supra-segmentals.
• Vowels.
• Consonants.
• Processing of the speech signal.
• Perception of speech by people with a hearing
  loss.

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Acoustic Phonetics

• Phoneme - smallest distinctive group or class of
  speech sounds.
• Phonemes are often classified into groups based
  on distinctive features.

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Spectrograms

• Time and frequency variations of the sounds.
• Darkness on a spectrogram indicates intensity.

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Example Spectrogram
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Supra-segmentals

• Lowest peak in the frequency spectrum is the
  fundamental frequency (F0), higher frequency
  peaks are the harmonics.
• Suprasegmental information is expressed by the
  intonation (F0), loudness (amplitude) and timing
  and rhythm (duration).

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Supra-segmentals

• Spread over more than one phoneme and provides
  information about stress and meaning.
• Pitch changes across a sentence whether it is a
  sentence or a question.

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Vowels

• Produced with the vocal tract relatively open.
• Formants broad peaks in the spectral envelope.
• Duration
• long vs short
• First formant.
• Second formant.

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Duration

• Long vs Short
• Short /I, U, E, V, Q, //
• Long /i, u, a, , _at_/
• Even with the smallest amount of low frequency
  hearing you can discriminate based on duration.

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First Formant (F1)

• Length of the pharynx.
• As the tongue is raised the length of the pharynx
  is increased and thus the F1 frequency decreases.

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Second Formant (F2)

• Length of the oral cavity.
• As the tongue moves forward the front cavity is
  shortened and the second formant wavelength is
  decreased, and the F2 frequency is increased.

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Vowel Examples
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Differences

• Gender (size of oral and pharyngeal cavities).
• Cultural background (nationality, social class,
  education).
• Speech and hearing handicaps.
• Also differences within the same person due to
  context, health, emotional well-being and word
  and sentence stress.

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Diphthongs

• A type of vowel where there is change of quality
  within the syllable.
• I.e. the tongue moves continuously from one vowel
  position to another producing a corresponding
  movement of F1 and F2.
• E.g. bay, boy, buy

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Diphthongs
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Consonants

• Produced by a constriction at some point in the
  vocal tract.
• Softer and shorter in duration than vowels.
• Properties/Features
• Voicing
• Manner
• Place

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Voicing

• Whether the vocal folds are vibrating
• Cues
• voice bar
• voice onset time
• preceding vowels are longer before stop consonants

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Manner and Place Cues

• Manner
• Plosives/stops
• Fricatives
• Affricates
• Nasals
• Semivowels/glides
• Liquids/laterals
• Place of production

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Consonants of English
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Plosives

• /p, b/, /t, d/ /k, g/
• Air stream is completely blocked and then
  released so that an explosion of sound is
  perceived.
• For voiced plosives the formant transition
  (particularly F2) provide the most important
  information for perception of place.

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Formant Transitions (F2)
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• For unvoiced plosives the plosive burst last
  longer and voicing may not begin until the
  transition is over. Here the frequency of the
  noise burst is the greatest cue to perception.
• For voicing information look at the VOT and the
  presence or absence of a voicing bar.

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Fricatives

• Air-stream is not completely blocked and a
  sustained airflow through a narrow constriction
  produces turbulence and a noisy sound.
• Voice bar determines whether voiced or unvoiced.
• Frequency of air burst determines place of
  production.

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Fricatives

• Formant transitions give clues to place as
  aspiration may be inaudible (esp. f, v, D).

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Affricates

• /J,_/
• Combination of the silent period and burst of a
  plosive with the frication noise.

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Nasals

• /m, n, N/
• Mouth opening is closed, velum is opened so sound
  goes through the nose.
• All voiced.
• Vowel-like formant structure.
• White area corresponding to the nasal zero
  (absence of sound) assists with perception of
  place.

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Semiglides, vowels and liquids

• /l, r, w, j/
• Vowel-like
• formant structure.
• voiced.
• Consonant features
• softer.
• rapid changes.
• occur between vowels.

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Loudness

• 30dB range in loudness
• Affected by
• distance.
• background noise.
• gender.

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Aided audiogram
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Effect of hearing loss
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125Hz

• F0 of most adult male voices

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250Hz

• Voicing cues
• F0 of most female and child voices
• Low harmonics of adult male voices
• Nasal murmur
• F1 of high back and high front vowels

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500Hz

• Cues for manner of production for most consonants
• Harmonics of most voices
• F1 and T1 of most vowels
• Noise bursts of plosives in back vowel contexts
• T1 of semi-vowels
• F1 of the laterals /l/ and /r/

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1000Hz

• Additional cues on manner
• Harmonics of most voices
• T1 of the laterals /l/ and /r/
• F2 of nasal consonants
• F2 and T2 of back and central vowels
• Noise bursts of most plosives
• T2 of the semi-vowels

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2000Hz

• Primary cues on place of consonant production
• Additional cues on manner
• Harmonics of most voices
• F2 and T2 of front vowels
• Noise bursts of plosives and affricates
• Turbulant noise of fricatives /sh, f, th/
• T2 and T3 of /l/ and /r/

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4000Hz

• Secondary cues of place of consonant production
• Upper range of harmonics, most voices
• F3 and T3 of most vowels
• Noise bursts of plosives and affricates
• Turbulent noise of voiced and unvoiced fricatives

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8000Hz

• Turbulent noise of all fricatives and affricates

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Aided Audiogram 2
V Left H Right
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SPL-o-gram
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Moderate Sloping Hearing LossNo Amplification
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Moderate Sloping Hearing Losswith Amplification
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Severe/Profound Sloping SNHLNo Amplification
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Severe/Profound Sloping SNHLwith Amplification