Transitions + Perception
April 1, 2014
Palatography Preparations!• We will do the palatography demo on Tuesday of next week.
• We’ve already gotten a volunteer for a speaker!
• We also need someone to volunteer for:
• Photography
• Transcription
• I’ll bring the goodies!
• Now: let’s do a perception experiment!
Laterals• Laterals are produced by constricting the sides of the tongue towards the center of the mouth.
• Air may pass through the mouth on either both sides of the tongue…
• or on just one side of the tongue.
Lateral Palatography
Lateral Acoustics• The central constriction traps the flow of air in a “side branch” of the vocal tract.
• This side branch makes the acoustics of laterals similar to the acoustics of nasals.
• In particular: acoustic energy trapped in the side branch sets up “anti-formants”
• Also: some damping
• …but not as much as in nasals.
• Primary resonances of lateral approximants are the same as those of for vocal tract length of 17.5 cm
• 500 Hz, 1500 Hz, 2500 Hz...
• However, F1 is consistently low (300 - 400 Hz)
4 cm
17.5 cm
• Anti-formant arises from a side tube of length 4cm
• AF1 = 2125 Hz
Laterals in Reality• Check out the Mid-Waghi and Zulu laterals in Praat
Mid-Waghi: [alala]
Velarization of [l]• [l] often has low F2 in English because it is velarized
• = produced with the back of the tongue raised
• = “dark” [l]
• symbolized
• Perturbation Theory flashback:
• There is an anti-node for F2 in the velar region
• constrictions there lower F2
Dark vs. Clear /l/
[alala]
•/l/ often has low F2 in English because it is velarized.
[l] vs. [n]• Laterals are usually more intense than nasals
• less volume, less surface area = less damping
• break between vowels and laterals is less clear
[ ] [ n ]
[l] vs.• [l] and are primarily distinguished by F3
• much lower in
• Also: [l] usually has lower F2 in English
[ ] [ ]
Glides
• Each glide corresponds to a different high vowel.
Vowel Glide Place
[i] [j] palatal (front, unrounded)
[u] [w] labio-velar (back, rounded)
[y] labial-palatal (front, rounded)
velar (back, unrounded)
• Glides are vowel-like sonorants which are produced…
• with slightly more constriction than a vowel at the same place of articulation.
• Each glide’s acoustics will be similar to those of the vowel they correspond to.
Glide Acoustics• Glides look like high vowels, but…
• are shorter than vowels
• They also tend to lack “steady states”
• and exhibit rapid transitions into (or from) vowels
• hence: “glides”
• Also: lower in intensity
• especially in the higher formants
[j] vs. [i]
[w] vs. [u]
Vowel-Glide-Vowel
[iji] [uwu]
More Glides
[wi:] [ju:]
Transitions• When stops are released, they go through a
transition phase in between the stop and the vowel.
• From stop to vowel:
1. Stop closure
2. Release burst
3. (glide-like) transition
4. “steady-state” vowel
• Vowel-to-stop works the same way, in reverse, except:
• Release burst (if any) comes after the stop closure.
Stop Components
• From Armenian: [bag]
closure voicing
vowel
formant transitions
another closure
stop release burst
Confusions• When the spectrogram was first invented…
• phoneticians figured out quite quickly how to identify vowels from their spectral characteristics…
• but they had a much harder time learning how to identify stops by their place of articulation.
• Eventually they realized:
• the formant transitions between vowels and stops provided a reliable cue to place of articulation.
• Why?
Formant Transitions• A: the resonant frequencies of the vocal tract change as stop gestures enter or exit the closure phase.
• Simplest case: formant frequencies usually decrease near bilabial stops
Stops vs. Glides
• Note: formant transitions are more rapid for stops than they are for glides.
“baby”
“wave”
Formant Transitions: alveolars• For other places of articulation, the formant transition that appears is more complex.
• From front vowels into alveolars, F2 tends to slope downwards.
• From back vowels into alveolars, F2 tends to slope upwards.
• In Perturbation Theory terms:
• alveolars constrict somewhat closer to an F2 node (the palate) than to an F2 anti-node (the lips)
[hid]
[hæd]
Formant Locus• Whether in a front vowel or back vowel context...
• The formant transitions for alveolars tend to point to the same frequency value. ( 1650-1700 Hz)
• This (apparent) frequency value is known as the locus of the formant transition.
• In the ‘50s, researchers theorized:
• the locus frequency can be used by listeners to reliably identify place of articulation.
• However, velars posed a problem…
Velar Transitions• Velar formant transitions do not always have a reliable locus frequency for F2.
• Velars exhibit a lot of coarticulation with neighboring vowels.
• Fronter (more palatal) next to front vowels
• Locus is high: 1950-2000 Hz
• Backer (more velar) next to back vowels
• Locus is lower: < 1500 Hz
• F2 and F3 often come together in velar transitions
• “Velar Pinch”
The Velar Pinch
[bag] [bak]
“Velar” Co-articulations
• The earliest experiments on place perception were conducted in the 1950s, using a speech synthesizer known as the pattern playback.
Testing the Theory
Pattern Playback Picture
Haskins Formant Transitions• Testing the perception of two-formant stimuli, with varying F2 transitions, led to a phenomenon known as categorical perception.
Categorical Perception• Categorical perception =
• continuous physical distinctions are perceived in discrete categories.
• In the in-class experiment:
• There were 11 different syllable stimuli
• They only differed in the locus of their F2 transition
• F2 Locus range = 726 - 2217 Hz
Source: http://www.ling.gu.se/~anders/KatPer/Applet/index.eng.html
Stimulus #1 Stimulus #6
Stimulus #11
Example stimuli from the in-class experiment.
Identification• In Categorical Perception:
• All stimuli within a category boundary should be labeled the same.
Discrimination• Original task: ABX discrimination
• Stimuli across category boundaries should be 100% discriminable.
• Stimuli within category boundaries should not be discriminable at all.
In practice, categorical perception means: the discrimination function can be determined from the
identification function.
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