1. Quantifying Sensitivity

2. 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)

3. 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

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

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

6. 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)

7. See Excel worksheet sensitivity.xls

8. Quantifying Differences

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

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

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

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

13. 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?

14. 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

15. Standard Error is the Standard Deviation of sample means.

16. 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?

18. Development of Speech Perception in Infancy

19. Voice Onset Time (VOT)
60 msec

20. Perceiving VOT
‘Categorical Perception’

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

22. 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

23. Three Classics

24. 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, Kindersprache, Aphasie und allgemeine Lautgesetze, 1941

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

26. #1 - Infant Categorical Perception
Eimas, Siqueland, Jusczyk & Vigorito, 1971

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

28. high amplitude sucking non-nutritive sucking

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

30. 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]

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

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

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

34. 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

35. #2 - Becoming a Native Listener
Werker & Tees, 1984

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

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

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

39. 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”

40. #3 - What, no minimal pairs?
Stager & Werker, 1997

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

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

45. PRETEST

46. HABITUATION
TEST
SAME
SWITCH

47. Word learning results
Exp 2 vs 4

48. 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
!!??

49. 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

50. 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,

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

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

54. 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

55. Questions about Development

56. 6-12 Months: What Changes?

57. Structure Changing
Patricia Kuhl U. of Washington

58. 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

59. 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, ]

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

61. 5 hours’ exposure to Mandarin
± human interaction
Alveo-palatal affricate vs. fricative contrast
[2003, Proceedings of the National Academy of Sciences]

63. Alveo-palatals
affricate
fricative

65. Jessica Maye, Northwestern U.

68. 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?

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

75. 1.0 .5
.25 .1

77. Invariance
(Jusczyk 1997)

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

79. 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

80. 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