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Speech Perception

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Basic Issues in Speech Perception

• Speaker Normalization

• Time Normalization

• Integration: Segmental &

Suprasegmental Information

• Defining Units of Speech Perception

• Cross-Modal Aspects of Speech

Perception

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Speaker Normalization• Normalization needed because of differences in

acoustic measures of speech• Women & men are biologically and acoustically

different– How do we perceive these differences?

– This perception is present in infants:• Can recognize the same phonetic element produced by a woman or

a man

– Word recognition performance is poorer for words from a mixed group of talkers than for words produced by a single talker

• Conclusion: Listeners make adjustments for different talkers

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Speech: 4 Types of Information

• Phonetic Quality– Linguistic content

• Affective Quality– Paralinguistic emotional quality that accomplishes the

linguistic message

• Personal Quality– Extralinguistic information about the talker but not the

message

• Transmittal Quality– Perspectaval information about the talkers location,

including distance between talker & listener, orientation is space & presence of background noise

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Time Normalization

• Different talkers speak at different rates & different rates at different times

• Speaking rates vary because segment durations are flexible

• Variable acceptance of different duration VOT

• Is speech intelligibility reduced for speakers who deviate from typical temporal patterns of normal adult speech? – Children & disordered speech

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Integrating Segmental & Suprasegmental Information

• Suprasegmental cues (intonation, rhythm, & pausing) help the listener segment the incoming message

• How is suprasegmental information used with segmental information?–Acoustic cues (f0, duration & intensity)

signal suprasegmental structure such as stress & rhythm

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What is the Basic Unit of Perception?

• When we listen to speech, do we analyze it in terms of features, phonemes, syllables or words?

– Listeners of different ages and linguistic competence prefer different size units• Young children operate with syllable-sized units• Adults extract phoneme level information

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Cross-Model Speech Perception

• Do listeners with normal hearing attend to visual cues in speech?–McGurk effect: This effect was produced by

studying different combinations of visual and auditory cues• ex. subjects would view a video tape of a

speaker saying the syllable [ba], but would hear the acoustic signal [da]– Subjects identified the sound as [g]: Phonetic decision

was based on a synthesis of auditory & visual cues

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Speech Perception: Infancy & Childhood

• We hear in the womb– Early auditory experiences biases the

neonate to the mother’s voice

– By the 1st year, infants can specialize sounds of the mother tongue• By this age they have lost discrimination for

foreign sounds• Auditory reorganization• Children continue to improve basic

discrimination of frequency, intensity & duration until age 7 years

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Speech Perception, Language, Learning & Education

• Children are less able to discriminate speech in noisy or reverberant environments

• Children are more prone to some diseases that disrupt speech perception–Otitis Media• ex. may not recognize VOT variation (history of

ear infections)

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Speech Perception, Language, Learning & Education

• Speech perception difficulties contribute to language disorders in children-

–Certain grammatical morphemes in English have low “phonetic substance”• ex. “s” in dogs or past tense marker in talked– These morphemes are harder to hear & are difficult

to perceive

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Speech Perception, Language, Learning & Education

• Speech perception and classroom learning-– Environment not ideal:• teacher’s speech about 6 dB more intense than

background noise• Teacher turning head away from listener• Typical classroom has a reverberation time of 0.45

seconds• Distance of teacher to student– ex. % of words heard by 5- to 7- year old children

with normal hearing with varied distance• 89% at 6 feet• 55% at 12 feet• 36% at 24 feet