Quantifying Sensitivity

Quantifying Sensitivity Response bias Two measures of discrimination Accuracy: how often is the judge correct? Sensitivity: how well does the judge distinguish the categories? Quantifying sensitivity Hits Misses False Alarms Correct Rejections Compare p(H) against p(FA)

Quantifying Sensitivity Is one of these more impressive? p(H) = 0.75, p(FA) = 0.25 p(H) = 0.99, p(FA) = 0.49 A measure that amplifies small percentage differences at extremes z-scores

√( ) Normal Distribution Dispersion around mean Standard Deviation A measure of dispersion around the mean. Mean (µ) √( ) ∑(x - µ)2 n

The Empirical Rule 1 s.d. from mean: 68% of data

Quantifying Sensitivity A z-score is a reexpression of a data point in units of standard deviations. (Sometimes also known as standard score) In z-score data, µ = 0,  = 1 Sensitivity score d’ = z(H) - z(FA)

See Excel worksheet sensitivity.xls

Quantifying Differences

(Näätänen et al. 1997) (Aoshima et al. 2004) (Maye et al. 2002)

√( ) Normal Distribution Dispersion around mean Standard Deviation A measure of dispersion around the mean. Mean (µ) √( ) ∑(x - µ)2 n

The Empirical Rule 1 s.d. from mean: 68% of data

Normal Distribution Standard deviation Heights of American  = 2.5 inches Heights of American Females, aged 18-24 Mean (µ) 65.5 inches

If we observe 1 individual, how likely is it that his score is at least 2 s.d. from the mean? Put differently, if we observe somebody whose score is 2 s.d. or more from the population mean, how likely is it that the person is drawn from that population?

If we observe 2 people, how likely is it that they both fall 2 s. d If we observe 2 people, how likely is it that they both fall 2 s.d. or more from the mean? …and if we observe 10 people, how likely is it that their mean score is 2 s.d. from the group mean? If we do find such a group, they’re probably from a different population

Standard Error is the Standard Deviation of sample means.

If we observe a group whose mean differs from the population mean by 2 s.e., how likely is it that this group was drawn from the same population?

Development of Speech Perception in Infancy

Voice Onset Time (VOT) 60 msec

Perceiving VOT ‘Categorical Perception’

Discrimination A More Systematic Test D D D T T T Same/Different 0ms 60ms 0ms 20ms D 20ms 40ms T Same/Different 0ms 10ms T T 40ms 60ms Same/Different Within-Category Discrimination is Hard 40ms 40ms

Abstraction Representations Behaviors Sound encodings - clearly non-symbolic, but otherwise unclear Phonetic categories Memorized symbols: /k/ /æ/ /t/ Behaviors Successful discrimination Unsuccessful discrimination ‘Step-like’ identification functions Grouping different sounds

Three Classics

Development of Speech Perception Unusually well described in past 30 years Learning theories exist, and can be tested… Jakobson’s suggestion: children add feature contrasts to their phonological inventory during development Roman Jakobson, 1896-1982 Kindersprache, Aphasie und allgemeine Lautgesetze, 1941

Developmental Differentiation Universal Phonetics Native Lg. Phonetics Native Lg. Phonology 0 months 6 months 12 months 18 months

#1 - Infant Categorical Perception Eimas, Siqueland, Jusczyk & Vigorito, 1971

Discrimination A More Systematic Test D D D T T T Same/Different 0ms 60ms 0ms 20ms D 20ms 40ms T Same/Different 0ms 10ms T T 40ms 60ms Same/Different Within-Category Discrimination is Hard 40ms 40ms

high amplitude sucking non-nutritive sucking

English VOT Perception To Test 2-month olds High Amplitude Sucking Eimas et al. 1971

General Infant Abilities Infants’ show Categorical Perception of speech sounds - at 2 months and earlier Discriminate a wide range of speech contrasts (voicing, place, manner, etc.) Discriminate Non-Native speech contrasts e.g., Japanese babies discriminate r-l e.g., Canadian babies discriminate d-D [these findings based mostly on looking/headturn studies w/ 6 month olds]

Universal Listeners Infants may be able to discriminate all speech contrasts from the languages of the world!

How can they do this? Innate speech-processing capacity? General properties of auditory system?

What About Non-Humans? Chinchillas show categorical perception of voicing contrasts! PK Kuhl & JD Miller, Science, 190, 69-72 (1975)

Suitability of Animal Models More recent findings… Auditory perceptual abilities in macaque monkeys and humans differ in various ways Discrimination sensitivity for b-p continua is more fine-grained in (adult) humans (Sinnott & Adams, JASA, 1987) Sensitivity to cues to r-l distinctions is different, although trading relations are observed in humans and macaques alike (Sinnott & Brown, JASA, 1997) Some differences in vowel sensitivity… Joan Sinnott, U. of S. Alabama

#2 - Becoming a Native Listener Werker & Tees, 1984

When does Change Occur? About 10 months Janet Werker U. of British Columbia Conditioned Headturn Procedure

When does Change Occur? Hindi and Salish contrasts tested on English kids Janet Werker U. of British Columbia Conditioned Headturn Procedure

What do Werker’s results show? Is this the beginning of efficient memory representations (phonological categories)? Are the infants learning words? Or something else?

Korean has [l] & [r] [rupi] “ruby” [kiri] “road” [saram] “person” [irumi] “name” [ratio] “radio” [mul] “water” [pal] “big” [s\ul] “Seoul” [ilkop] “seven” [ipalsa] “barber”

#3 - What, no minimal pairs? Stager & Werker, 1997

A Learning Theory… How do we find out the contrastive phonemes of a language? Minimal Pairs

Word Learning Stager & Werker 1997 ‘bih’ vs. ‘dih’ and ‘lif’ vs. ‘neem’

PRETEST

HABITUATION TEST SAME SWITCH

Word learning results Exp 2 vs 4

Why Yearlings Fail on Minimal Pairs They fail specifically when the task requires word-learning They do know the sounds But they fail to use the detail needed for minimal pairs to store words in memory !!??

One-Year Olds Again One-year olds know the surface sound patterns of the language One-year olds do not yet know which sounds are used contrastively in the language… …and which sounds simply reflect allophonic variation One-year olds need to learn contrasts

Maybe not so bad after all... Children learn the feature contrasts of their language Children may learn gradually, adding features over the course of development Phonetic knowledge does not entail phonological knowledge Roman Jakobson, 1896-1982

Werker et al. 2002 14 months 17 months 20 months 14 17 20 60 300 600

Swingley & Aslin, 2002 14-month olds did recognize mispronunciations of familiar words Dan Swingley, UPenn

Alternatives to Reviving Jakobson Word-learning is very hard for younger children, so detail is initially missed when they first learn words Many exposures are needed to learn detailed word forms at early stages of word-learning Success on the Werker/Stager task seems to be related to the vocabulary spurt, rapid growth in vocabulary after ~50 words

Questions about Development

6-12 Months: What Changes?

Structure Changing Patricia Kuhl U. of Washington

Structure Adding Evidence for Structure Adding (i) Some discrimination retained when sounds presented close together (e.g. Hindi d-D contrast) (ii) Discrimination abilities better when people hear sounds as non-speech (iii) Adults do better than 1-year olds on some sound contrasts Evidence for Structure Changing (i) No evidence of preserved non-native category boundaries in vowel perception

Sources of Evidence Structure-changing: mostly from vowels Structure-adding: mostly from consonants Conjecture: structure-adding is correct in domains where there are natural articulatory (or acoustic) boundaries [cf. Phillips 2001, Cogn. Sci., 25, 711-731]

So how do infants learn…? Surface phonetic patterns Tests of experimentally induced changes…

5 hours’ exposure to Mandarin ± human interaction Alveo-palatal affricate vs. fricative contrast [2003, Proceedings of the National Academy of Sciences]

Alveo-palatals affricate fricative

Jessica Maye, Northwestern U.

Infants at age 6-8 months are still ‘universal listeners’, cf Infants at age 6-8 months are still ‘universal listeners’, cf. Pegg & Werker (1997) Infants trained on bi-modal distribution show ‘novelty preference’ for test sequence with fully alternating sequence How could the proposal scale up?

p(a) = p(b) p(a) = 2 x p(b)

1.0 .5 .25 .1

Invariance (Jusczyk 1997)

Training on [g-k] or [d-t], generalization across place of articulation. (Dis-)habituation paradigm. [Maye & Weiss, 2003]

So how do infants learn…? Phoneme categories and alternations Perhaps more like a phonologist than like a LING101 student - look directly for systematic relations among phones Gradual articulation of contrastive information encoded in lexical entries Much remains to be understood

Abstraction in Infant Speech Encoding From a very early age infants show great sensitivity to speech sounds, possibly already with some ‘category-like’ structure Although native-like sensitivity develops early (< 1 year), this should be distinguished from adult-like knowledge of the sound system of the language Children still need to learn how to efficiently encode words (phoneme inventory) Children presumably still need to learn how to map stored word forms onto pronunciations (phonological system of the language) Popular distributional approaches to learning the sound system address rather non-abstract encodings of sounds, at best