1. And a big thanks to Julie Markant
Categorical perception of speech: Task variations in infants and adults
Bob McMurray
Jessica Maye
Andrea Lathrop
and
Richard N. Aslin
And a big thanks to Julie Markant

2. Categorical Perception & Task Variations
Overview
Previous work
Categorical perception and gradient sensitivity to subphonemic detail.
Categorical perception in infants
Reassessing this with HTPP & AEM
Infants show gradient sensitivity
A new methodology
Adult analogues

3. Categorical Perception
Is subphonemic detail retained [and used] during speech perception?
For a long time…
NO!
Subphonemic variation is discarded in
favor of a discrete label.
Categorical perception & gradiency

4. Non-categorical Perception
A number of psychophysical-type results showed listeners’ sensitivity to within-category detail.
4AIX Task
Pisoni & Lazarus (1974)
Speeded Response
Carney, Widen & Viemeister (1977)
Training
Samuel (1977)
Pisoni, Aslin, Henessey & Perey (1982)
Rating Task
Miller (1997)
Massaro & Cohen (1983)

5. Word Recognition These results did not reveal:
Whether on-line word recognition is sensitive to such detail.
Whether such sensitivity is useful during recognition.

6. Word Recognition Mounting evidence that word-recognition is sensitive:
Lahiri & Marslen-Wilson (1991): vowel nasalization
Andruski, Blumstein & Burton (1994): VOT
Gow & Gordon (1995): word segmentation
Salverda, Dahan & McQueen (in press): embedded words and vowel length.
Dahan, Magnuson, Tanenhaus & Hogan (2001): coarticulatory cues in vowel.

7. Gradient Sensitivity McMurray, Tanenhaus & Aslin (2002)
Eye-movements to objects after hearing items from 9-step VOT continuum.
McMurray, Tanenhaus & Aslin (2002)
Systematic relationship between VOT and looks to the competitor. 5 10 15 20 25 30 35 40
0.02
0.03
0.04
0.05
0.06
0.07
0.08
VOT (ms)
Category
Boundary
Response=
Looks to
Competitor Fixations
Bear

8. Gradient Sensitivity ….BUT
This systematic, gradient relationship between lexical activation and acoustic detail would allow the system take advantage of fine-grained regularities in the signal.
Gow, McMurray & Tanenhaus (Sat., 6:00 poster session)
Anticipate upcoming material.
Resolve Ambiguity
If fine-grained detail is useful we might expect infants and children to
Show gradient sensitivity to variation
Tune their sensitivity to learning environment
….BUT

9. Infant categorical perception
Early findings of categorical perception for infants (e.g. Eimas, Siqueland, Jusczyk & Vigorito) have never been refuted.
Most studies use:
Habituation (many repetitions)
Synthetic Speech
Single continuum
Perhaps a different method would be more sensitive?
Categorical perception in infants

10. Head-Turn Preference Procedure
Jusczyk & Aslin (1995)
Infants exposed to a chunk of language:
Words in running speech.
Stream of continuous speech (ala stat. learning)
Word list
After exposure, memory for exposed items (or abstractions) is assessed by comparing listening time to consistent items with inconsistent items.

11. How do we measure listening time?
After exposure…
Center Light blinks.
Brings infant’s attention to center.

12. How do we measure listening time?
When infant looks at center…
One of the side-lights blinks.

13. How do we measure listening time?
Beach… Beach… Beach…
When infant looks at side-light…
she hears a word.

14. How do we measure listening time?
When infant looks at side-light…
she hears a word.
…as long as she keeps looking…

15. Experiment 1: Gradiency in Infants
7.5 month old infants exposed to either 4 b-, or 4 p-words Bomb Bear Bail Beach
Palm Pear Pail Peach
80 repetitions total
Form a category of the exposed class of words.
Infants show gradient sensitivity
Measure listening time on
Bear Pear (Original word)
Pear Bear (opposite)
Bear* Pear* (VOT closer to boundary).

16. Experiment 1: Stimuli
Stimuli constructed by cross-splicing natural, recorded tokens of each end point.
B: M= 3.6 ms VOT
P: M= 40.7 ms VOT
B*: M=11.9 ms VOT
P*: M=30.2 ms VOT
Both were judged /b/ or /p/ at least 90% consistently by adult listeners.
B: 98.5% B*: 97%
P: 99% P*: 96%

17. Measuring gradient sensitivity
Looking time is an indication of interest.
After hearing all of those B-words
P sounds pretty interesting.
So: infants should look longer for pear than bear.
What about in between?
Listening Time
Bear
Pear
Gradient
Bear*
Categorical

18. Individual Differences
Novelty/Familiarity preference varies across infants and experiments.
We’re only interested in the middle stimuli (b*, p*).
Infants categorized as novelty or familiarity preferring by performance on the endpoints.
Novelty
Familiarity B 27 11 P 19 10
Within each group will we see evidence for gradiency?

19. Novelty Results Novelty infants, Trained on B
VOT: p=.001** Linear Trend: p=.001**
4000
5000
6000
7000
8000
9000
10000 B B* P
Listening Time (ms)
.14
.004**

20. Novelty Results Novelty infants, Trained on P
VOT: p=.001** Linear Trend: p=.001**
4000
5000
6000
7000
8000
9000
10000 P P* B
Listening Time (ms) .1
.001**

21. Familiarity Results Familiarity infants showed similar effects.
B exposure
Trend: p=.001
B vs B*: p=.19
B* vs P: p=.21
P exposure
Trend: p=.009
P vs P*: p=.057
P* vs. B: p=.096
Trained on B
Trained on P

22. Experiment 1: Conclusions
7.5 month old infants show gradient sensitivity to subphonemic detail.
Individual differences in familiarity/novelty preferences. Why?
Length of exposure?
Individual factors?
Limitations of paradigm may hinder further study:
More repeated measures
Better understanding of “task”
Wider age-range.

23. Anticipatory Eye-Movements
An ideal methodology would
Yield an arbitrary, identification response.
Yield a response to a single stimuli
Yield many repeated measures
Much like a forced-choice identification
A new methodology
Anticipatory Eye-Movements (AEM):
Train Infants to look left or right in response to a single auditory stimulus

24. Anticipatory Eye-Movements
Visual stimulus moves under occluder.
Reemergence serves as “reinforcer”
Concurrent auditory stimulus predicts endpoint of occluded trajectory.
Subjects make anticipatory eye-movements to the expected location—before the stimulus appears.
Teak
Lamb

25. Anticipatory Eye-Movements
After training on original stimuli, infants are tested on a mixture of
original, trained stimuli (reinforced)
Maintain interest in experiment.
Provide objective criterion for inclusion
new, generalization stimuli (unreinforced)
Examine category structure/similarity relative to trained stimuli.

26. Experiment 2: Pitch and Duration
Goals:
Use AEM to assess auditory categorization.
Assess infants’ abilities to “normalize” for variations in pitch and duration…
or…
Are infants’ sensitive to acoustic-detail during a lexical identification task...

27. Experiment 2: Pitch and Duration
Training:
“Teak” -> rightward trajectory.
“Lamb” -> leftward trajectory.
“teak!”
“lamb!”
Test:
Lamb & Teak with changes in:
Duration: 33% and 66% longer.
Pitch: 20% and 40% higher
If infants ignore irrelevant variation in pitch or duration, performance should be good for generalization stimuli.
If infants’ lexical representations are sensitive to this variation, performance will degrade.

28. The Stimuli
Training stimulus

29. The Stimuli
Testing stimulus

30. Results Each trials is scored as
correct: longer looking time to the correct side.
incorrect: longer looking time to incorrect side.
Binary DV—similar to 2AFC.
On trained stimuli:
11 of 29 infants performed better than chance–this is a tough tasks for infants. Perhaps more training.

31. Results On generalization stimuli: Pitch p>.1 Duration p=.002
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Pitch
p>.1
Duration
p=.002
Proportion Correct Trials
Duration
Pitch
Training
Stimuli
D1 / P1
D2 / P2
Stimulus

32. Experiment 2: Conclusions
Infants’ developing lexical categories show graded sensitive to variation in duration.
Possibly not to pitch
Might be an effect of “task relevance”
AEM yields
more repeated measurements
better understood task: 2AFC
Could it yield a picture of the entire developmental time course? Is AEM applicable to a wider age range?

33. Treating undergraduates like babies
Extreme case: Adult perception.
Adults generally won’t
Look at blinking lights…
Suck on pacifiers…
Kick their feet at mobiles…
Result: few infant methodologies allow direct analogues to adults.
They do make eye-movements…
…could AEM be adapted?

34. Treating undergraduates like babies
Pilot study.
5 adults exposed to AEM stimuli.
Training:
“Ba” left
“Pa” right
Test
Ba – Pa (0-40 ms) VOT continuum.

35. Results Second group of subjects run in an explicit 2AFC.
Same category boundary.
Steeper slope: less sensitivity to VOT. 1
0.9
0.8
0.7
0.6
% /p/
2AFC
0.5
0.4
AEM
0.3
0.2
0.1 5 10 15 20 25 30 35 40
VOT (ms)

36. Adult AEM: Conclusions
AEM paradigm can be used unchanged for adults.
Should work with older children as well.
Results show same category boundary as traditional 2AFC tasks, perhaps more sensitivity to fine-grained acoustic detail.
Potentially useful for speech categorization when categories are not:
nameable
pictureable
immediately obvious

37. Conclusions
Like adults,7.5-month-old infants show gradient sensitivity to subphonemic detail.
VOT
Duration
Perhaps not pitch (w.r.t. lexical categories)

38. Conclusions Task makes the difference:
Moving to HTPP from habituation revealed subphonemic sensitivity.
Taking into account individual differences crucial.
Moving to AEM yields
Better ability to examine tuning over time.
Ability to assess perception across lifespan with a single paradigm.

39. And a big thanks to Julie Markant
Categorical perception of speech: Task variations in infants and adults
Bob McMurray
Jessica Maye
Andrea Lathrop
and
Richard N. Aslin
And a big thanks to Julie Markant

40. Natural Stimuli Infants may show more sensitivity to natural speech
Stimuli constructed from natural tokens of
actual words with progressive cross-splicing.
Palm
Bomb

41. Experiment 1: Reprise
Difficult to examine how sensitivity might be tuned to environmental factors in head-turn-preference procedure.
High variance/individual differences—can’t predict novelty/familiarity.
Only a single point to look at.
Between-subject comparison.
Difficult interaction to obtain
Listening Time
6 m/o
10 m/o
8 m/o
Bear
Bear*
Pear

42. Experiment 1: Reprise AEM presents a potential solution:
1) Looking at whole continuum would yield more power.
6 m/o
8 m/o
10 m/o
Bear
Pear
2) Is AEM applicable to a wider age range?

43. The Stimuli
Training stimulus

44. Data analysis
Data coded by naive coders from video containing pupil & scene monitors.

45. Data analysis
Left
Right -
out
Start In
Center
Off
Left-out
Right-out
Left-In
Right-In
Left-out, Right-out, center & start treated as “neither”.
Left-in, Left treated as anticipation to left.
Right-in, Right treated as anticipation to right.
Eye-movements coded from
maximal size of stimulus to first appearance (or end of trial).