Speech Science IX How is articulation organized?

Topics Same sound, different gestures? How do we control our articulation? At what level do we control our articulation? - individual muscles? - gestures for individual sounds? - sequences of gestures for syllables? - …. for words? Reading: BHR, Chap. 5, pp ff. (Variation, Feedback, Prod.-Models) P.-M.1.4,8. pp (Steuerung)

Sound Variants A fundamental problem in speech is the “many-to-one” relationship between speech events and their causes. One acoustic event (speech sound) can result from different articulatory configurations (= “articulatory compensation”) One articulatory configuration can result from different patterns of muscular activity (= “neuromuscular compensation”)

Sound Variants (example) articulatory compensation “Standard” vs. Saarland

Sound Variants (other example) Another well-known example of articulatory compensation is the „American /r/“ ( [  ] ) The tongue may be a) turned back (retroflex) b) bunched Lip-rounded vowels (like [ y ]) can be produced with strongly rounded, protruded lips, or with retracted tongue and neutral (or even spread) lips (with or without a lowered larynx).

Free variation vs conditioned variants Articulatory differences (requiring different commands to muscles) are not only the result of having acquired a particular variant. Sounds occur in context, and the gestures are different with every different preceding sound! This makes the relationship between one speech sound (in linguistic terms “a phoneme”) and the commands to produce it complicated.

Context variation: Coarticulation Lip- rounding Tongue tip Example: Tüte [ t u  t  ] When a property of one sound affects the way in which a neighbouring sound is produced, we call the effect “coarticulation”. Here lip-rounding in the initial /t/ of „Tooter“.

Different movements in context Contextual differences in gestures affect every part of the articulatory patterns. Here, chin and tongue-tip interaction.

What does this say about speech production? The motor activity involved in producing speech sounds is much more complex than the (relatively simple) phonetic/phonological categorisation of speech sounds We have to decide whether there is (can be) any link between linguistic description and production models …. It would be unfortunate if we had to say that the two had nothing to do with each other!

But the observations also tell us …. The acoustic (  perceptual) identity of sounds seems more important than the motor equivalence When we learn to articulate, we match our own production to what we hear. The acoustic patterns from other speakers are our only models … Nobody shows us how to move our lips, tongue, velum or larynx …….

… although … There seems to be an innate ability to imitate peoples‘ facial expressions This has been systematically observed in very young babies, who mimic their mother‘s expressions. So there may be some visual input as well as the predominant acoustic input to the speech learning process. But only a small fraction of the articulatory activity is visible/observable.

Must our normal production processes be related to processes used in learning? Theories of speech production do not always model articulation from a perceptual standpoint. Linguistic (phonological) models of sound systems are concerned with the patterns of sound produced, not with the processes that are required to produce them (BHR p. 152 f.) The IPA system is articulatorily orientated. Distinctive Feature theory (more abstract) can be articulatory or acoustic.

Speech Science X Production models

How can we model the production process? We need to explain how we control the complex articulatory activity in terms of the different sounds that we can hear. = How do we move the articulators to where they have to be? = How do we know when they have reached the correct position so that we can move on to the next sound? Whether or not the orientation is perception, the change from one sound to another has to be explained.

How do we move the articulators to where they have to be? How is the movement defined? - as a target position of the (main) articulator? - as a spatial configuration? - as (a position related to) an auditory percept? - as a specific gesture? - as a gesture of a specific duration? The target concepts are closely related to one another … All the ideas take the sound segment (phoneme) as the unit which is being controlled.

How do we know whether the articulators have reached their target? There are a number of “feedback” channels - “proprioceptive” feedback? (yes) - auditory feedback? (too late) - tactile feedback? (yes, but not enough Tactile and proprioceptive feedback provide information about the momentary position. So we know whether an articulatory action “feels right” or not. - kinaesthetic feedback? (yes) - visual feedback? (no use in speech)

Types of feedback? Closed loop reports on a preceding action and this triggers the next command:

Types of feedback 2 Open loop allows a sequence of commands to be carried out:

Do we use closed loop feedback at all? Open-loop feedback allows rapid sequences of commands to be carried out (we don‘t think about each syllable, but we still have to monitor events) Closed-loop feedback is useful (and necessary) for units that take long enough for us to observe them …. …and for units that require some conscious decisions or planning. E.g. at phrase level (phonologically, the intonation phrase)

Evidence for open loop at syllable level Khozhevnikov & Chistovich (K&C) from Leningrad provided the first evidence in den 60s and 70s, showing different degrees of variance in different size units. In sentence repetitions of: "Tonya topila banyu", they found that syllable-duration variance was greater than phrase duration variance. …and they found that neighbouring syllables correlated negatively with one another (i.e., if one was shorter the next was longer)

But what is the basic production unit? K&C looked at syllables in the phrase, but they didn‘t take for granted that the syllable is THE basic unit of articulatory planning. They deduced it from the patterns of effects with changes of speech rate. They found: - Rate changes occur between phrases, - Rate changes do not affect the relationship between syllables and words, - But rate changes do affect the relationship between consonants and vowels.

Syllable units but C+V together) K&C’s results and our lip-rounding observations indicate that C and V commands seem to be issued at the same time.

Control of gestures towards targets We have still not explained how the very fast and muscularly complex gestures are controlled. Different muscle tension, and even different muscles are important for one sound in different contexts. An automatically feedback-controlled servo-system would be the engineering solution.

Muscle spindles as a servo system 1

Muscle spindles as a servo system 2

Muscle spindles as a servo system - summary The muscle spindle is set to the required target tension. Fast afferent (feedback) nerve fibres report on the discrepancy between momentary muscle tension and target tension. Fast commands direct to the muscle correct the discrepancy between momentary muscle tension and target tension. = target reached, independent of the position of the articulator prior to movement.

Mass spring model of speech production 1 The picture painted so far is simple because we have only considered one muscle. As we have discussed before, any one gesture requires the coordination of many muscles….. and any one sound requires the coordination of a number of gestures (tongue, lips, etc.) The target position for any given sound is the product of all the target tensions of all participating agonist and antagonist muscles.

Mass spring model of speech production 2 If all the target tensions are set, the servo- system moves the articulators “automatically” towards the target position. This is compared to a mass moving under the influence of a (damped) spring. The movement stops when the point of equilibrium is reached. Advantage of model: It explains „undershoot“ (a frequently observed reduction of a sound). How? Another target is defined before the previous one is reached,

Coordinative structures Disadvantage of the “mass spring model“ as originally conceived: It is therefore assumed (no real proof) that the “mass“ is made up of sub-structures which work together and compensate for each other. A well-documented coordinative structure of this kind is the jaw + lips; but also the jaw + tongue. It cannot explain the compensation for articu- latory disturbances that are observed!

Coarticulation vs. Co-production “Coarticulation” assumes that features from one phonemes spread into a neighbouring one. - There is no explanation for the different durations of sound segments (as a function of stress & tempo). Different durations are the result of differing degrees of overlap. - There is no explanation for how certain features spread. In short, no real link to production models. “Co-production” assumes a fixed (but unknown) duration for each speech sound. Phonemes are not abstract, but concrete articulatory things.

Advantage of a co-production view Stronger (stressed) syllables have less overlap among their segments. Unstressed syllables have more overlap. But the different phonetic realisation is not the result of a different articulatory plan for the sound. - More overlap implies that the command for the following segment comes before the target of the preceding segment is reached. - This results in a “reduced“ realisation (shorter and often spectrally less well defined).

Summary We have shown that a target-orientated model can be explained physiologically We have seen that feedback is vital and can be used in an automatic servo-system. We have seen that complex articulatory patterns a) depend on mutually compensating muscle synergies, b) can fit into „packets“ of lower-order commands („macros“) which allow more complex units to be produced automatically.