1. Grab Bag! (Palatography, Fricatives + Perception, part 2)
April 10, 2012

2. Almost There… Categorical Perception homeworks are due!
(Stay on target…)
Two oral presentations on Thursday: Christine + Jonathan
Then we’ll wrap up auditory perception + maybe do some synthetic speech
(I can’t hold him! He’s coming in too fast!)
If people are interested, we can do a review session on Monday.
(WHAHWHAHAWBOOOSH!)

3. Electro-palatography

4. Therapeutic Applications

5. Glamour Shots!
thaw saw shop

6. More Photographic Flattery
Important things to keep in mind:
Don’t forget your camera!
Keep a record of everything that your consultant produces.
top law

7. Finally, Fricatives
The last type of sound we need to consider in speech acoustics is an aperiodic, continuous noise.
Ideally:
Q: What would the spectrum of this waveform look like?

8. White Noise Spectrum Technical term: White noise
has an unlimited range of frequency components
Analogy: white light is what you get when you combine all visible frequencies of the electromagnetic spectrum

9. Turbulence
We can create aperiodic noise in speech by taking advantage of the phenomenon of turbulence.
Some handy technical terms:
laminar flow: a fluid flowing in parallel layers, with no disruption between the layers.
turbulent flow: a fluid flowing with chaotic property changes, including rapid variation in pressure and velocity in both space and time
Whether or not airflow is turbulent depends on:
the volume velocity of the fluid
the area of the channel through which it flows

10. Turbulence Turbulence is more likely with: a higher volume velocity
less channel area
All fricatives therefore require:
a narrow constriction
high airflow

11. Fricative Specs Fricatives require great articulatory precision.
Some data for [s] (Subtelny et al., 1972):
alveolar constriction  1 mm
incisor constriction  2-3 mm
Larger constrictions result in -like sounds.
Generally, fricatives have a cross-sectional area between 6 and 12 mm2.
Cross-sectional areas greater than 20 mm2 result in laminar flow.
Airflow = 330 cm3/sec for voiceless fricatives
…and 240 cm3/sec for voiced fricatives

12. Turbulence Sources
For fricatives, turbulence is generated by forcing a stream of air at high velocity through either a narrow channel in the vocal tract or against an obstacle in the vocal tract.
Channel turbulence
produced when airflow escapes from a narrow channel and hits inert outside air
Obstacle turbulence
produced when airflow hits an obstacle in its path

13. Channel vs. Obstacle
Almost all fricatives involve an obstacle of some sort.
General rule of thumb: obstacle turbulence is much noisier than channel turbulence
[f] vs.
Also: obstacle turbulence is louder, the more perpendicular the obstacle is to the airflow
[s] vs. [x]
[x] is a “wall fricative”

14. Sibilants
Alveolar, dental and post-alveolar fricatives form a special class (the sibilants) because their obstacle is the back of the upper teeth.
This yields high intensity turbulence at high frequencies.

15. vs.
“shy” “thigh”

16. Fricative Noise Fricative noise has some inherent spectral shaping
…like “spectral tilt”
Note: this is a source characteristic
This resembles what is known as pink noise:
Compare with white noise:

17. Fricative Shaping
The turbulence spectrum may be filtered by the resonating tube in front of the fricative.
(Due to narrowness of constriction, back cavity resonances don’t really show up.)
As usual, resonance is determined by length of the tube in front of the constriction.
 The longer the tube, the lower the “cut-off” frequency.
A basic example:
[s] vs.

18. vs.
[s]
“sigh” “shy”

19. Sampling Rates Revisited
Remember: Digital representations of speech can only capture frequency components up to half the sampling rate
the Nyquist frequency
 Speech should be sampled at at least Hz
(although there is little frequency information in speech above 10,000 Hz)
[s] has higher acoustic energy from about Hz
Note: telephones sample at 8000 Hz
44100 Hz
8000 Hz

20. Further Back
In more anterior fricatives, turbulence noise is generally shaped like a vowel made at the same place of articulation.
[xoma]
palatal vs velar

21. Even Further Back
Examples from Hebrew:

22. At the Tail End [h] exhibits a lot of coarticulation
[h] is not really a “fricative”;
it’s more like a whispered or breathy voiced vowel.
“heed” “had”

23. Aspirated Fricatives Like stops, fricatives can be aspirated.
[h] follows the supraglottal frication in the vocal tract.
Examples from Chinese:
[tsa]
[tsha]

24. Back at the Ranch
There is not much of a resonating filter in front of labial fricatives…
so their spectrum is flat and diffuse
(like bilabial stop release bursts)
Note: labio-dentals are more intense than bilabial fricatives
(channel vs. obstacle turbulence)

25. Fricative Internal Cues
The articulatory precision required by fricatives means that they are less affected by context than stops.
It’s easy for listeners to distinguish between the various fricative places on the basis of the frication noise alone.
Result of both filter and source differences.
Examples:
There is, however, one exception to the rule…
sh, f, s

26. Huh?
The two most confusable consonants in the English language are [f] and .
(Interdentals also lack a resonating filter)

27. Helping Out
Transition cues may partially distinguish labio-dentals from interdentals.
Normally, transitions for fricatives are similar to transitions for stops at the same place of articulation.
Nonetheless, phonological confusions can emerge--
Some dialects of English substitute [f] for
Top--fie transition, then thigh transition
Middle -- die, sigh, shy
Videos -- check out E.1, E.5 and E.2
Visual cues may also play a role…

28. Acoustic Enhancement
Fricative distinctions can be enhanced through secondary articulations.
E.g.: is post-alveolar and [s] is alveolar
 more space in vocal tract in front of
including a “sub-lingual cavity”
This “filter” of resonates at lower frequencies
In English, this acoustic distinction is enhanced through lip rounding for
this extends the vocal tract
further lowers the resonant frequencies of
another form of “adaptive dispersion”

29. The Sub-lingual Cavity
Compare “shade” (H.6) and “soil”
Then look at “reach” (E.3) again
Let’s check the videotape...

30. Behind the Constriction
Look at “shake” vs. “save”.
Let’s check the ultrasound…

31. Secondary Articulations
What effect might lowering the center of the tongue have on formant values?
(think: perturbation theory)
Check it out in Praat.

32. And now for something completely different…
Q: What’s a category?
A classical answer:
A category is defined by properties.
All members of the category exhibit the same properties.
No non-members of the category exhibit all of those properties.
 The properties of any member of the category may be split into:
Definitive properties
Incidental properties

33. Classical Example
A rectangle (in Euclidean geometry) may be defined as having the following properties:
Four-sided, two-dimensional figure (quadrilateral)
Four right angles
This is a rectangle.

34. Classical Example
Adding a third property gives the figure a different category classification:
Four-sided, two-dimensional figure (quadrilateral)
Four right angles
3. Four equally long sides
This is a square.

35. Classical Example
Altering other properties does not change the category classification:
Four-sided, two-dimensional figure (quadrilateral)
Four right angles
definitive properties
3. Four equally long sides
This is still a square.
A. Is red.
incidental property

36. Classical Linguistic Categories
Formal phonology traditionally defined all possible speech sounds in terms of a limited number of properties, known as “distinctive features”. (Chomsky + Halle, 1968)
[d] = [CORONAL, +voice, -continuant, -nasal, etc.]
[n] = [CORONAL, +voice, -continuant, +nasal, etc.] …
Similar approaches have been applied in syntactic analysis. (Chomsky, 1974)
Adjectives = [+N, +V]
Prepositions = [-N, -V]

37. Prototypes
The psychological reality of classical categories was called into question by a series of studies conducted by Eleanor Rosch in the 1970s.
Rosch claimed that categories were organized around privileged category members, known as prototypes.
(instead of being defined by properties)
Evidence for this theory initially came from linguistic tasks:
Semantic verification (Rosch, 1975)
Is a robin a bird?
Is a penguin a bird?
Category member naming.

38. Prototype Category Example: “Bird”

39. Exemplar Categories
Cognitive psychologists in the late ‘70s (e.g., Medin & Schaffer, 1978) questioned the need for prototypes.
Phenomena explained by prototype theory could be explained without recourse to a category prototype.
The basic idea:
Categories are defined by extension.
 Neither prototypes nor properties are necessary.
Categorization works by comparing new tokens to all exemplars in memory.
Generalization happens on the fly.

40. A Category, Exemplar-style
“square”

41. Back to Perception
When people used to talk about categorical perception, they meant perception of classical categories.
A stop is either a [b] or a [g]
(no in between)
Remember: in classical categories, there are:
definitive properties
incidental properties
Q: What are the properties that define a stop category?
The definitive properties must be invariant.
(shared by all category members)
So…what are the invariant properties of stop categories?