Articulation and Coarticulation

1. Articulation and Coarticulation March 16, 2010

2. Update • The hard drive on the computer in the booth failed. • It will hopefully be fixed soon. • The lab assignment will have to be postponed until (at least) Tuesday the 23rd… • I will give you more info as it comes to me.

3. Recap • There are lots and lots of muscles involved in the articulation of speech sounds. • (Check out Praat’s articulatory synthesis!) • Their motions are generally organized in a hierarchical fashion: • coordinative structures, speech motor equivalence, acoustic goals • “We speak in order to be heard in order to be understood.” • Specific gestures can vary according to context, • and can adapt quite rapidly to physical perturbations. • The role of feedback remains unclear…

4. Delayed Auditory Feedback • In the 1950s, engineers accidentally discovered the delayed auditory feedback (DAF) effect. • = Talkers speak into a microphone, and listen to themselves over headphones • …but they don’t hear what they say until 100-200 ms after they’ve said it. • Q: What do you think happens? • A: Fluent speakers sound, well, drunk… • they speak with pauses, delays, interruptions, etc. • However, stutterers can often become fluent with delayed auditory feedback!

5. Closed Feedback Loops • The DAF effect inspired “closed feedback loop” models of speech production. • In this model, articulatory commands are supposed to operate like a servomechanism. • = an automatic device that uses error-sensing feedback to correct the performance of a mechanism • Hypothesis: motor commands keeps firing until an articulatory goal is met. • Only then do the commands for the next sound (or gesture) begin. (like your thermostat)

6. Outstanding Issues • The closed feedback loop model had some problems… • Motor commands couldn’t refer to other articulators • (and therefore couldn’t account for on-the-fly adjustments made with respect to other articulators) • Also: feedback doesn’t always seem to be important to speakers. • Attempts were made to deprive speakers of auditory and tactile feedback: • They mainly resulted in poorer accuracy for sounds like [s] (and other fricatives) • Though note: “Lombard effect”

7. Open Feedback Loops • The alternative model is an “open feedback loop”. (Kozhevnikov and Chistovich, 1966) • In this model, commands to produce syllables are issued without regard to feedback. • Each syllable command is automatically generated with respect to an internal “rhythm generator”. • Rhythm and phrase timing remains relatively constant; • Individual syllable timing can vary.

8. Aufhebung • Browman & Goldstein’s Articulatory Phonology model is an attempt to combine what is known about: • Higher-level (task) organization in speech production • With the dynamic adaptation of speech gestures to changing contexts and conditions. • This model assumes a hierarchy of articulatory representations, ranging from high-to-low dimensionality:

9. Nuts and Bolts • vocal tract variables reflect configurations of articulators in the vocal tract vocal tract variables

10. Nuts and Bolts • Gestures are goal-directed manipulations of the vocal tract variables • primarily change aperture • implemented dynamically gestures vocal tract variables

11. Dynamics • Note: kinematics is the study of motion without regard to forces that cause it • dynamics is the study of motions that result from forces. •  The trajectory of dynamic motions can be shaped by different forces over time. • In articulatory phonology, the basic gestural model has a sinusoidal pattern of activation: • = the articulator behaves like a mass on a spring

12. Dynamics • But the motion of the articulator can be damped in proportion to its proximity to an “equilibrium” point • = the closer the articulator gets to its goal, the slower it moves • Critical damping  the mass on the spring doesn’t keep bouncing around the equilibrium point. • Simplifying assumption: the articulator reaches its goal at the 240 degree point of the wave cycle.

13. Gestural Scores • Different gestures may exhibit a phase relationship with each other. • A gestural score organizes a series of gestures in time. • Mutliple gestures may be happening on different articulatory tiers at the same time. • Gestural scores roughly resemble an autosegmental representation of phonological structure.

14. Autosegmental Phonology • The “Feature Geometry” of autosegmental phonology organized features into sub-groupings of related features. • The relationships were primarily articulatory in nature. Example feature tree from Halle et al. (2000)

15. Feature Spreading • Feature Geometry made useful predictions about what kinds of features were likely to function together in phonological processes. • A typical example: the Place features. 

16. Assumptions • There are some important differences between the Feature Geometry and Articulatory Phonology models. • Feature Geometry generally assumed some sort of unifying “root” node, representing a segment; • Articulatory Phonology did not. • (There are no phonemes!) • Processes in Feature Geometry were discrete; • In Articulatory Phonology, they can be gradient. • Representations in Feature Geometry are static; • In Articulatory Phonology, they are dynamic.

17. Advantages • The “translation” between phonology and phonetics is directly encoded into the model in Articulatory Phonology. • I.e., the gestures may be discrete, but they represent instructions for moving articulators over time. • Also: Articulatory Phonology can account for gradient phenomena that discrete/symbolic phonology cannot. • Two possible levels of phonological action: • Discrete • ( = elimination/addition/alteration of units in the gestural score) • Gradient • (= changes in the magnitude/duration/phasing of gestures)

18. For Instance • Farnetani (1986) investigated the coarticulation of /n/ with palatals and post-alveolars in Italian. • …using electropalatography (EPG)

19. EPG: Therapeutic Applications

20. EPG: Scientific Applications • The contact pattern of electrodes has to be interpreted with respect to phonological categories of interest. • (Better for more anterior places of articulation.) • The contact pattern also changes quite rapidly over time. (from Barry 1992)

21. Gradient vs. Discrete • Results of Farnetani (1986): • “Gestural overlap” between /n/ and post-alveolars is complete  discrete assimilation • Timing overlap between /n/ and palatal articulation is partial  gradient assimilation

22. B + G (1990): Predictions • “We propose that most of the phonetic units (gestures) that characterize a word in careful pronunciation will turn out to be observable in connected speech, although they may be altered in magnitude and in their temporal relation to other gestures. In faster, casual speech, we expect gestures to show decreased magnitudes (in both space and time) and to show increasing temporal overlap.” • Test cases (Brown, 1977): • Are these “connected speech processes” best described as discrete or gradient phenomena?

23. Theoretically Gestural score for hyperspeech Gestural score for hypospeech • In this model, the /t/ in “must be” is not deleted--it’s just hidden behind the /b/, due to temporal reorganization.

24. X-Ray Microbeam Data! • Browman & Goldstein fine-tuned their model on the basis of data collected from an X-ray microbeam study of connected speech. • This data also verified some of their suspicions about the presence of “hidden” gestures in connected speech.

25. Perfect Memories Hyperspeech production: Hypospeech production:

26. “Place Assimilation” “Hyperspeech” = not completely assimilated Hypospeech = assimilated production • Important: there is no reassignment of feature values between segments; • There is just a reorganization of the timing and magnitude of gestures.

27. This is the End? • Moral of the story: • Articulatory Phonology can capture the gradient, highly variable nature of gestures in context. • Timing reorganizations may also lead to insertions: • Or eltse? • Another gradience: Magnitude reduction

28. Place Assimilation: the EPG view • There is evidence from EPG studies that the magnitude of coronal gestures may be reduced in an “assimilatory” context. • Data from Kerswill & Wright (1989): • note: time scale is the same in all productions • (10 ms/frame)

29. Place Assimilation: the EPG view • There is evidence from EPG studies that the magnitude of coronal gestures may be reduced in an “assimilatory” context. • Data from Kerswill & Wright (1989): • note: time scale is the same in all productions • (10 ms/frame)

30. Assimilation Perception • Kerswill & Wright (1989) presented these four types of tokens to trained phoneticians in a combined transcription + identification task. • Transcription results: • Note: heavy bias towards /d/ responses. • (Why?)

31. Assimilation Perception • The phoneticians also classified all of the items transcribed as /d/ as one of the three types: Place perception, like place production, seems to be gradient.

32. Stress = Hyperspeech? • DeJong et al. (1993) collected X-ray microbeam data on the effects of stress on coarticulation across syllables. • Note: stress involves a complex set of acoustic correlates. • Stressed syllables are higher in pitch than unstressed syllables (usually) • Stressed syllables are longer in duration than unstressed syllables (usually) • Stressed syllables are higher in intensity than unstressed syllables (usually) • DeJong et al. found: stressed syllables exhibit less gestural overlap than unstressed syllables.

33. Prompting Hyperspeech, version 47 • DeJong et al. (1993) sat speakers in front of the X-ray microbeam and had them read sentences in the following frames: • Prompt: Did you say, “throw the toads on the table?” Target: I said “PUT the toads on the table.” • Prompt: Did you say, “put the frogs on the table?” Target: I said “put the TOADS on the table.” • Question: how much coarticulation is there between “put” and “the” in the two conditions?

34. X-ray microbeam data Focus on TOAST Focus on PUT Focus on PUT Focus on TOAST

35. X-ray microbeam thoughts • “Stress locally shifts articulations toward the hyperarticulate end of the continuum. Speakers do whatever is necessary to enhance the realization of segmentally contrasting features. A primary mechanism for enhancing distinctions is to decrease coarticulatory overlap so that gestures for segments in stressed syllables blend less with each other or with segments in neighboring syllables.” • Counter-thought: coarticulation between segments can often be a useful perceptual cue. • Especially in the case of stop consonants…