Infant Speech Perception LSCP Infant Lab
Outline • Introduction to Phonology • Problem of Speech Perception • Testing two theories of speech perception – Infant Categorical Perception – Cross-species categorical perception – The use of visual cues
Universal Structural Design _____________________________
English Consonants
1. Introduction to Phonology 15
Phonemes Vowels: unimpeded sound through vibrating vocal cords Vary by: • Placement of tongue – ee is high front – ah is low back • Rounding of lips
Phonemes Consonants: Sound is impeded in some way Vary by: 1. Place of articulation m, p, b n, t, d ng, k, g
Phonemes Consonants vary by 2. Kind of articulation: • stop: p, b, d • nasal: n,m • fricative: ch, th, f 3. Voicing , Nasality, Creaky Voice, Clicks • voiced: b, d, z.... • voiceless: p, t, s...
Phonemes are bundles of features • P: bilabial, voiceless, stop • B: bilabial, voiced, stop • S: dental, voiceless, fricative
Phonemes are bundles of features p: bilabial, voiceless, stop s: dental, voiceless, fricative
Evidence • Phonological features participate in speech errors • Phonological rules typically refer to features: – plural marker assimilates the voicing of the consonant before it – cup/s/, beet/s/, back/s/ – cub/z/, bead/z/, bag/z/
? Phonemes Phonemes
2. A Brief Tour of Speech Perception 10:25 15
The String Fallacy • Speech sounds seem separable and sequential: like beads on a string • Reality: – Speech sounds overlap (co-articulation) – Each speech sound is affected by the elements around it
Two problems of speech perception • Segmentation – how do we discover where one phoneme ends and the next begins • Invariance: – How can we identify a phoneme when it’s sound changes depending on context? We won’t be answering these questions today
One Hint: some complex features of a speech sound may stay constant
Speech sounds vary along a continuum
Yet we perceive them as discrete categories B D G
Categorical Perception: Identification % identification
Categorical Perception: Discrimination
3. Where does this ability come from? 10:40 12
Two theories • The Motor Theory: – perception is informed by our innate knowledge of articulation • The Auditory Theory: – speech perception is based solely on auditory properties of speech
Motor Theory We have innate knowledge of how articulation changes depending on context
Motor Theory Innate knowledge of Used to predict changes in articulation sound wave and recover phonemes
Auditory Theory Auditory system breaks speech into phonemes •innate property of sensory system or •perceptual learning
Contrasting the two theories The Motor Theory The Auditory Theory 1. Perception is based on 1. Perception by generic production auditory mechanisms • Process: • Process – Determine what – Auditory system articulatory gestures a transforms sound wave speaker made so phonemes available – Then identify phoneme
Contrasting the two theories The Motor Theory The Auditory Theory 2. Perception is species 2. Not species specific specific – Production system evolved to make use of – Speech production and existing auditory speech perception capacities evolved together – No special adaptations – Only humans speak, so to speech only humans have SP system
Contrasting the two theories The Motor Theory The Auditory Theory 3. SP is innate 3. SP may be innate – Tacit knowledge of – Innate properties of the articulation given by auditory system may evolution be adequate to isolate phonemes – Or Perceptual Learning may be required
4. Is Speech Perception Innate? 10:52 18
Do newborns perceive phonemes categorically? Predictions: • If categorical perception requires knowledge of contrastive phonemes: NO • If it requires exposure to language: NO • If it is an innate ability: YES But how can you test immobile infants?
High Amplitude Sucking Procedure • Infant given a pacifier • Contains sensor to monitor sucking rates • Each time the infant sucks the paci, a stimulus is played LSCP Infant Lab
High Amplitude Sucking Procedure • Initially sucking rate increases (novelty) • Then it decreases • This decline in response is habituation LSCP Infant Lab
High Amplitude Sucking Procedure • When sucking rate declines to set point ( habituation criterion ) • The computer switches the auditory stimulus LSCP Infant Lab
High Amplitude Sucking Procedure • If sucking rate increases • Then we know the infant has detected the change • The renewed response is dishabituation LSCP Infant Lab
Stimuli for the Eimas Study Voice Onset Time: time btw consonant release and vocal cord vibration S1 S2 S3 0 20 40 60 80 VOT in milliseconds
Stimuli for the Eimas Study Phoneme Category Boundary at 25ms BA PA 1 PA 2 0 20 40 60 80 VOT in milliseconds
Predictions Within Category Between Category Innate remain dishabituate Categorical habituated Perception Untuned dishabituate dishabituate Sensitivity Insensitive remain remain habituated habituated
Stimuli from different phonological categories are distinguished SPM “PA 1 ” “BA” sucks per minute Time Eimas, et al., 1971
But stimuli from the same phonological category are not “PA 2 ” “PA 1 ” SPM sucks per minute Time Eimas, et al., 1971
Speech Perception is Innate Predicted by Motor Consistent with Auditory Theory Theory • Speech Perception • Speech perception due driven by innate to innate structure of knowledge of auditory system articulation
5. Is Speech Perception Species Specific? 11:10 10
Do other animals perceive phonemes categorically? • Kuhl & Miller, 1978: test chinchillas and humans with identical stimuli • Human Task: identification (b or p) • Chinchillas: avoidance conditioning
Avoidance Conditioning Procedure Shock paired with speech sound at one end of continuum (A) PA 0 80 VOT in milliseconds
Avoidance Conditioning Procedure Sound at other end (B) paired with safety 0 80 BA VOT in milliseconds
Avoidance Conditioning Procedure Animal learns to run to other side of cage when it hears sound A but stay after B What will they do for sounds in between? stay ? ? ? run
Predictions 100 Categorical Perception 90 Graded Perception 80 Percent labelled [b] 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 Voice Onset Time (ms)
Kuhl & Miller, 1978 100 90 English Speakers 80 Percent labelled [b] 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 Voice Onset Time (ms)
Kuhl & Miller, 1978 100 English Speakers 90 Chinchillas 80 Percent labelled [b] 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 Voice Onset Time (ms)
Not all aspects of speech perception are species specific Consistent with Auditory Contrary to Motor Theory Theory • General auditory • Claim: only humans abilities adequate for have knowledge (some aspects of) (innate or learned) of speech perception articulation
6. Is Speech Perception Affected by Knowledge of Articulation? 11:20 10
McGurk Effect • Vary visual information about place of articulation – palatal: GA – dental: DA – bilabial: BA • Vary auditory stimulus (BA → DA → GA) • Task: phoneme identification
McGurk Effect • Finding: phoneme category boundary affected by visual information – sound BA + visual GA = percept DA • Adult speech perception affected by visual cues • Did they learn it?
Do infants know visual cues to articulation? • No evidence of visual cues influencing categorization • But can infants match sound with the correct mouth shape?
Preferential Looking (Kuhl & Meltzoff, 1982 [a]-face [i]-face
a...a....a...a..a [a]-face [i]-face
Speech Perception is influenced by information about articulation Inconsistent with Predicted by Motor Auditory Theory Theory • Though a visual- • Innate connection btw auditory theory might production and explain this perception • Would require perceptual learning
Provisional Conclusions • Speech Perception makes use of auditory mechanisms which evolved prior to language – These abilities are innate • Speech Perception also makes use of our knowledge of articulation – This ability MAY be innate
McGurk Effect Revisited McGurk_large.mov
Development of Phonological Representations
Working toward a model…. Syntactic Syntactic Constructed Lexical Lexical Phonological Phonological Auditory Phonetic Articulatory Auditory Phonetic Articulatory Innate?
What’s innate? • Auditory abilities • Articulatory rudiments – Not developed – Desire to coo and babble even in deaf infants Auditory Auditory Articulatory Auditory Auditory Articulatory Innate Innate
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