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.