* Categorical Perception
What is it?
Continuum- something that varies in a particular dimension, results in different perceptions of color The perception of a continuum in terms of categories
Another way to compensate for the lack of invariance in speech What is it good for?
Stable perception of a variable signal
Good discrimination between categories
Not hindered by variation within a category
We’ll investigate with experiments:
Is it learned? Innate?
Is it unique to speech?
Is it unique to humans?
Voicing and Voice Onset Time (VOT)
VOT (msec)- when a consonant ends and a vowel starts, when voicing starts of the following vowel, queue for voiced and unvoiced
1. pa (30 msec VOT)- mostly pa, some ba
2. ba (0 msec VOT)
3. pa (40 msec VOT)
4. ba (10 msec VOT)
5. pa (40 msec VOT)
6. pa (30 msec VOT)
7. pa (50 msec VOT)
8. ba (0 msec VOT)
9. pa (60 msec VOT)
10. pa (40 msec VOT)
25-30 msec VOT- “boundary” some will hear ba and some will hear pa 0-25: perceived unambiguously
After 30: perceived ambiguously
Assessing Categorical Perception
1. Forced choice identification
Subjects have to categorize sound as one thing or another (eg., [pa] or [ba]) 2. ABX discrimination
Subjects given two stimuli, A and B, which have different values along the continuum in question Subjects are then given X, which matches either A or B, and they have to indicate which it matches If subjects perceive A and B as different things, they are very good at matching X
Categorical Perception in Infants
Are we born perceiving speech categorically?
High Amplitude Sucking (HAS)
Every time infant sucks, it receives a speech stimulus
When infants get bored with what they’re doing
Same stimulus whenever infant sucks
Switch at predetermined threshold
Different stimulus from Habituation Phase
Either Dishabituation (increase sucking rate)
Or continued decrease in sucking rate
1 month old...