Parametric Specification of Constriction Gestures

Transcription

1 Parametric Specification of Constriction Gestures Specify the parameter values for a dynamical control model that can generate appropriate patterns of kinematic and acoustic change over time. Model should account for as many details of the contrastive kinematic properties of gestures as possible (e.g., stops vs fricatives), from as few parameter differences as possible. Model should account for as many details of the variation in kinematic properties of gestures as function of speaking rate and style, from as few parameter differences as possible.

2 Elements of Toolkit for modeling constrictions Virtual Targets Relation of target to acoustic consequence Activation Interval Relation of activation interval to stiffness Release Gestures Coordinative Structures Articulator Weights

3 Lip Closures: Westbury & Hashi Less movement of Upper Lip than Lower Lip. Inflection in movement histories around the time of acoustic closure (t c ). Substantial movement during acoustic closure interval (t c - t min -t r ). LA greater at acoustic release than acoustic closure. No systematic differences among lip closures for/pbm/.

4 Speed movement maximum within 30 ms of acoustic closure. Release speed greater than closure speed (English).

5 Virtual goal of the lips for a stop gesture is to penetrate each other, thus forming an air-tight seal. Explains Changes in LA after acoustic closure Differences in LA at closure and release Trajectory inflections at closure (e.g. protrusion) Tight, short temporal coupling between deceleration and closure: deceleration of lips is actually caused by lip contact, rather than the dynamical control. Stops: Goal is Virtual Target (Löfqvist)

6 BUT: Another account of short temporal coupling Not necessary to appeal to mechanical forces, though they presumably are involved. Time from Vp to Ac ons AUDIO GLA LA LL will be a function of x o Why? Vp occurs at constant lag following Gest ons The larger the distance from x ons to x o, the earlier Ac ons will be achieved. ULy LLy vlly 5000 vll Vmax= 29 'LA' 'LA' JA=32,UH=5,LH= x o (LA)= -10 6

7 Activation Interval and Stiffness (k) Each gesture s parameters are active in the vocal tract for a specified interval of time (its Activation Interval). Each gesture also has a specified stiffness (k). For a critically-damped system (which does not oscillate), ω determines the time required to settle to the equilibrium position (xo) from any starting position. Distance from initial position to target does not effect time to target. That is determined only by ω. 7

8 Gestures:Task-Dynamic Specification Point Attractor dynamical systems for one or more tract variables (e.g. TTCD, TTCD) constriction and release (in some cases) b x k(x x ) = m x 0 Dynamical parameters (for each system): x 0 ω Equilibrium position (TV target) frequency = (sqrt(k/m)) Damping ratio = b/(2*ω) 8

9 Critical Damping Damping ratio = b/(2*ω) When ratio =1, damping is critical No oscillation: system approaches xo Effective settling time is 3/4 of the cycle duration, given ω. 9

10 Critical Damping b=2, ω=1 x o Undamped x o b=0, ω=1 10

11 Relation of Activation Interval and ω TaDA sets the activation duration of consonant gestures so they get close to their targets (about 3/4 of a period of ω). If activation duration is shortened (e.g. by speaking rate, then target undershoot will occur) 11

12 Target and Time to closure For a given activation interval and ω, as the target (xo ) specification for a constriction becomes more and more extreme (more compression), the time to acoustic closure gets earlier and earlier, as acoustic closure gets to be a smaller and smaller proportion of the way to the target (x o ) 12

13 Movement during Coronal stops (Gracco & Löfqvist, 2002) Despite the hard palate, coronal stop show considerable tongue movement during closure. even of the tongue tip.

14 Specification of Fricatives vs. Stops Are fricatives produced with a virtual goal (beyond the position observed during a constriction)? what is constriction degree? 14

15 Kinematic regularities in Stops vs. Fricatives Virtual target for fricatives? What is goal for fricatives? Observed effects: stops vs. fricatives voiced vs. voiceless fricatives coronals vs. labials Model

16 Stops vs. Fricatives Fricatives have longer lag from Vp to closure Time from Vp to clo/fric Voiced fricatives have longer lag than voiceless. Fricatives have lower Vp. ms Vp Clo lag Assume dynamical systems with the same value of freq, d. Assume different CD targets for stops, fricatives System will produce differences in Vp and closure lag. CM/sec p b m f v t d n s z Closing Velocity p b m f v t d n s z Peak At Clo/Fric

17 Velocity effects fall out of x o differences AUDIO LL AUDIO GLA LA GLA ULy LA LLy ULy vlly 5000 vll Vmax= 29 LLy vlly vll Vmax= 'LA' 'LA' JA=32,UH=5,LH= STOP 'LA' JA=32,UH=5,LH= x o (LA)= -10 FRICATIVE x o (LA)= 1

18 Voiced vs. voiceless fricatives Lag: Generation of turbulence is a function of both constriction size and airflow. Same gesture for voiced, voiceless will generate turbulence later for voiced, because a more narrow constriction is required to generate turbulence when the airflow is less constriction degree at closure and release p b m f v t d n s z pellet distance, closure (mm) pellet distance, release (mm) Predictions: narrower constriction at turb onset for v, z it will take time to narrow that much more longer acoustic duration for /s/

19 Voiced vs. voiceless fricative models /asa/ AUDIO /aza/ AUDIO GTBCD GTBCD GTTCD TTCD=4 GTTCD TTCD=1.8 TTCD TTCD TTy TTy vtty vtty Vp to turb ons = 35ms Vp to turb ons = 70ms X o (TTCD) = 1 X o (TTCD) = 1

20 Coronal vs. labial effects Vp effect can be due to initial conditions, assume same targeted constriction degree for coronals and labials. x init -x 0 for coronals > labials

21 Models of /t,d/ vs. /p,b/ /apa/ AUDIO /ata/ AUDIO GLA LA LA=14.2 GTBCD GTTCD TTCD=20 ULy TTCD LLy vlly V p (LLy)= TTy vtty V p (TTy)= X o (LA) = -2 X o (TTCD) = -2

22 Additional Tests How much of close temporal coupling of Vp and closure in stops due to the relation of the virtual target to closure; how much is due to the passive forces? deceleration peak coincides with closure If due to learning of (particular) virtual target we should see similar patterns for closure and release. How much change in goal variables during constriction intervals in stops vs. fricatives? 22

23 Different control for stops and fricatives? (Fuchs et al) Fricatives show lower magnitude deceleration peaks than stops (Hoole, 1996) Passive forces decelerate stops? Deceleration coincides with onset of oral closure Fricatives involve more precise positioning acquired later cause problems in speech impairements lateral positioning must be controlled to produce grooving in /s/ 23

24 Experiment: German Hypothesis: control of fricatives differs of that from stops Predictions: less overall movement in fricatives lower lower deceleration magnitudes longer durations less movement during constriction interval Ich habe gecvce nicht gecvc erwähnt. C = /t, z/, V = /a, u/ 24

25 Example Token AUDIO TTy TTv (tangential) TTa (tangential) 25

26 Movement amplitude Movement amplitude t > z 26

27 Closing gesture duration Gesture duration z > t, only for /a/ 27

28 Acceleration and Deceleration dec (ons) >> dec (rel) for /t/, but much less so for /z/ evidence for mechanical forces 28

29 Horizontal movement during closure/frication movement during clo/fric t > z 29

30 Conclusion Fuchs et al. conclude there is a different type of control for stops than for fricatives stops: target planned beyond contact location fricatives: target planned at lateral margins to produce mid-sagittal channel Just this difference in target seems sufficient to account for all observed kinematic differences, given a gestural dynamical model in the presence of mechanical effects of collision. 30

31 Fricative action goals Hypothesis: Goal is to generate turbulence. Consequences: TTCD goal value is crit, that degree of constriction that will produce turbulence. Does the actual degree of constriction vary with contextual conditions to ensure turbulence? Goal will not be a virtual one like stops, but the actual constriction size necessary But is the goal specifiable in mm, or is it functionally specific to generate turbulence?

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33 Wake vs. channel turbulence Wake Sibilants (/s/, /ʃ/) are produced by nozzling airsteam against the teeth (including the lower teeth) (Ladfoged & Maddieson, Catford). Channel For non-sibilant fricatives (θ,ç, x), turbulence is generated as air passes through narrow channel. Possible controlled variables to distinguish them: TTLT (distance from tongue tip to lower teeth), or LTH (lower teeth height).

34 /s/ - /S/ Contrast

35 /s/ - /S/ Contrast (Ladefoged & Maddieson, 1996)

36 /s/ - /ʃ/ Contrast Groove (Naraynan, 1995) /s/ /S/ 36

37 /s/ - /S/ Contrast Blue = asha; red = asa. Images courtesy of Michael Proctor.

38 Area Functions (Narayanan et al, 1995) /s/ /ʃ/ / /z/ /Z/ 38

39 Possible goal variables /s/ - /ʃ/ (Narayanan et al, 1995) TTCL alveolar vs. postalveolar TTCD does not appear to differ systematically apical-laminal /s/ more likely apical, but speakers differ. GROOVE /s/ has concavity behind constriction Wake Location between teeth for /s/, upper teeth for /ʃ/. TB Constriction Palatal for /ʃ/, possible velar for /s/ for some speakers

40 TTCD TTCL 40

41 Testing Goal Variables Goal variables will tend to be achieved despite perturbations Use context variability as a kind of natural perturbation Variables that exhibit relative invariance across contexts are plausible goals. 41

42 Gestures for stops and fricatives Goal: Characterize the gestural control for the tongue in English /t,s,ʃ/ Limited to mid-sagittal plane (TADA, EMMA) Expectations: TT controlled for each (TTCD? TTCL? TTLT?) More TB control for fricatives than stops (TB for s and ʃ should differ from one another; /t/?) Context-dependence (vowels) More for stops than fricatives For stops, only TT is controlled, so TB is completely controlled by the co-produced V. Can context-dependence in fricatives be modeled with invariant TB gesture that blends with TB gesture with vowel?

43 Data EMMA (Jaw, TT, TB1, TB2, TD) Control utterances from speech error experiment: Two-word phrases read to a metronome (about 15 reps) Two words identical: sip-sip sip-sip sop-sop sop-sop Vowels: /i/, /a/ Consonants: /t/, /s/, /ʃ/ Accent: Iambic and trochaic Rate: Fast and Slow Four Subjects

44 Results: Differences among coronals Horizontal position (all sensors): s > t > ʃ (s is most anterior) Vertical position (all sensors): ʃ > t > s TB: Large difference between and ʃ and t,s Others: small differences

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46 Results: Context Effects (i-a) Horizontal: /s/ most invariant All effects are small Vertical TB2 (TD): Large effects for s, t, but ʃ is pretty invariant Others: smaller effects Context effects always smallest for ʃ.

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48 Results: TT variables TTCD TTLT ship shop sip sop tip top 20 ship shop sip sop tip top 20 TTCL ship shop sip sop tip top

49 Implications for gestural control Small differences in TTx, TBx could result from differences in targets for TTCL, TTCD s - t differ in TTCD s - S differ in TTCL, TTLT Large differences in TBy Could result from TB gesture for S. Blending wt of this TB gesture is stronger than for Vs, preventing blending.

50 TADA modeling t s S TTCD TTCL 56 o 56 o 56 o TBCD 10 6 TBCL 125 o 65 o alpha 5 10

51 TADA results t s S a i

52 Aerodynamic or acoustic goals? Aerodynamic Compensation for velic leakage? Acoustic Lip-rounding for /ʃ/ Acoustic feedback for altered palate conditions 52

53 Perkell 53