Infant categorical perception

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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
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
Categorical perception & gradiency
Categorical Perception
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.
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)
Word Recognition
These results did not reveal:
Whether on-line word recognition is sensitive
to such detail.
Whether such sensitivity is useful during
recognition.
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.
Gradient Sensitivity
McMurray, Tanenhaus & Aslin (2002)
• Eye-movements to objects after hearing items from
9-step VOT continuum.
• Systematic relationship
between VOT and looks Bear
to the
competitor.
Response=
Response=
Competitor Fixations
0.08
0.07
Looks to
0.06
0.05
0.04
Looks to
Category
Boundary
0.03
0.020
5
10
15
20
VOT (ms)
25
30
35
40
Gradient Sensitivity
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
Categorical perception in infants
Infant categorical perception
c
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?
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.
How do we measure listening time?
After exposure…
Center Light blinks.
Brings infant’s attention to center.
How do we measure listening time?
When infant looks at center…
One of the side-lights blinks.
How do we measure listening time?
Beach…
Beach…
Beach…
When infant looks at side-light…
she hears a word.
How do we measure listening time?
When infant looks at side-light…
she hears a word.
…as long as she keeps looking…
Infants show gradient sensitivity
Experiment 1: Gradiency in Infants
c
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.
Measure listening time on
Bear
Pear
Pear
Bear
Bear*
Pear*
(Original word)
(opposite)
(VOT closer to boundary).
Experiment 1: Stimuli
Stimuli constructed by cross-splicing natural, recorded
tokens of each end point.
B:
P:
M= 3.6 ms VOT
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%
P: 99%
B*: 97%
P*: 96%
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.
Listening Time
What about in between?
Categorical
Gradient
Bear
Bear*
Pear
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?
Novelty Results
Novelty infants, Trained on B
VOT:
p=.001**
Linear Trend: p=.001**
.14
10000
.004**
Listening Time (ms)
9000
8000
7000
6000
5000
4000
B
B*
P
Novelty Results
Novelty infants, Trained on P
VOT:
p=.001**
Linear Trend: p=.001**
.001**
10000
.1
Listening Time (ms)
9000
8000
7000
6000
5000
4000
P
P*
B
Familiarity Results
Familiarity infants showed
similar effects.
P exposure
Trend: p=.009
P vs P*: p=.057
P* vs. B: p=.096
Listening Time (ms)
9000
8000
7000
6000
5000
4000
B
B*
P
Trained on P
10000
9000
Listening Time (ms)
B exposure
Trend: p=.001
B vs B*: p=.19
B* vs P: p=.21
Trained on B
10000
8000
7000
6000
5000
4000
P
P*
B
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.
Anticipatory Eye-Movements
A new methodology
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
Anticipatory Eye-Movements (AEM):
Train Infants to look left or right in response
to a single auditory stimulus
Anticipatory Eye-Movements
Visual stimulus moves under
occluder.
Reemergence serves as
“reinforcer”
Concurrent auditory stimulus
predicts endpoint of occluded
trajectory.
Subjects make anticipatory eyemovements to the expected
location—before the stimulus
appears.
Teak
Lamb
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.
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...
Experiment 2: Pitch and Duration
Training:
“Teak” -> rightward trajectory.
“Lamb” -> leftward trajectory.
“teak!”
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.
“lamb!”
If infants’ lexical representations are sensitive to this
variation, performance will degrade.
The Stimuli
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Training stimulus
The Stimuli
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Testing stimulus
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.
Results
Pitch
p>.1
Duration
p=.002
Proportion Correct Trials
On generalization stimuli:
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
Duration
Pitch
0.1
0
Training
Stimuli
D1 / P1
Stimulus
D2 / P2
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?
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?
Treating undergraduates like babies
Pilot study.
5 adults exposed to AEM stimuli.
Training:
“Ba”
“Pa”
left
right
Test
Ba – Pa (0-40 ms) VOT continuum.
% /p/
Results
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2AFC
AEM
0
5
10
15
20
25
30
35
40
VOT (ms)
Second group of subjects run in an explicit 2AFC.
Same category boundary.
Steeper slope: less sensitivity to VOT.
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
Conclusions
Like adults,7.5-month-old infants show gradient
sensitivity to subphonemic detail.
VOT
Duration
Perhaps not pitch (w.r.t. lexical categories)
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.
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
Natural Stimuli
Infants may show more sensitivity to natural speech
Stimuli constructed from natural tokens of
actual words with progressive cross-splicing.
Palm
Bomb
Experiment 1: Reprise
Difficult to examine how sensitivity might be tuned to
environmental factors in head-turn-preference procedure.
Listening Time
• High variance/individual differences—can’t predict
novelty/familiarity.
• Only a single point to look at.
• Between-subject comparison.
• Difficult interaction
to obtain
6 m/o
8 m/o
10 m/o
Bear
Bear*
Pear
Experiment 1: Reprise
AEM presents a potential solution:
1) Looking at whole continuum would yield more power.
10 m/o
8 m/o
6 m/o
Bear
Pear
2) Is AEM applicable to a wider age range?
The Stimuli
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Training stimulus
Data analysis
Data coded by naive
coders from video
containing pupil &
scene monitors.
Left
Left
Center
Data analysis
Left-In
Left-In
Left-out
Left-out
Right
Right
Right
Right-In
Start
Right-out
Right-out
Off
Eye-movements coded from
maximal size of stimulus to
first appearance (or end of
trial).
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.
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