Coordinative structures: The basic units of speech motor control1. The motor system is organized in task-specific hierarchical control programs2. This is revealed by trading relations at several levels of description3. Coordinative structures are feed-forward control programs 4. Motor programs are the size of metrical feet5. Children acquire coordinative structures gradually1. The motor system is organized in task-specific hierarchical control programsConsider the mucles involved in moving the lower lip up and down.Lower lip Down: Depressor Labii Inferior, Incisivus InferiorUp: Obicularis Oris Inferior, MentalisAdd also the muscles that must cooperate to move the jawDown: Geniohyoid, Mylohyoid, DigastricusUp: Masseter, TemporalisDepressor Labii InferiorIncisivus InferiorObicularis Oris InferiorMentalisGeniohyoidMylohyoidDigastricusMasseterTemporalisRaise thelower lipA flat control structure: Each muscle gets a target length independently of the othersThere is a “degrees of freedom” problem with this arrangement - many independent parameters to control - not much constraint on possible motor plans - brittle arrangement (not robust against error)Depressor Labii InferiorIncisivus InferiorObicularis Oris InferiorMentalisGeniohyoidMylohyoidDigastricusMasseterTemporalisRaise thelower lipLLJawA hierarchical control scheme solves the degrees of freedomproblem - intermediate targets specified for functional groups of muscles.2. The hierarchical organization of speech motor control is revealed by trading relations at several levels of descriptionWhen the upper lip doesn’t come down so far, the lower lip compensates. Upper lip and lower lip are coordinated for [p].2. The hierarchical organization of speech motor control is revealed by trading relations at several levels of descriptionPosition of the lower lip (LL)Position of the jawRelative position of the lowerlip on the jaw (LL - jaw)apaapaapaWhen the jaw doesn’t move as much, the lower lip compensates. The jaw and LL are coordinated for [p].Lower lip positionOO inferiorDepressor Anguli OrisObicularis Oris SuperiorObicularis Oris InferiorDepressor Labii InferiorMentalisMentalis5 mm200 msec2. The hierarchical organization of speech motor control is revealed by trading relations at several levels of descriptionWhen the OOI doesn’t fire as strongly, the mentalis compensates. The OOI and mentalis are coordinated for [p].Lower lipUpper liplower lipjawOOIMentalisLip closureA (partial) coordinative structure for [p]3. Coordinative structures are feed-forward control programs Feedback system - take information from sensation into central nervous system, say cortex, and adjusted motor commands are sent to the muscles.Feed-forward system - the motor program includes coordination/compensation mechanisms that can be invoked without cortical involvement. The hierarchical organization of coordinative structures is compatible with feed-forward, modular, organization.Lip paddle impedes lower lip during [b] in [aba].Response from both upper and lower lip muscles results in successful [b].Upper lip response to perturbation is large in[aba], but nonexistant in [afa].This response to proprioceptive information indicates that the [aba] response is not a reflex - i.e. that it is a task-specific response.Why the response to lower lip perturbation is nota feedback response: It happens too fast.Nerve fiber transmission speed is slow (10 cm/msec at the fastest)so it is likely that these fast response latencies indicate that the response is precompiled as a part of the coordinative structure commands sent to the spinal cord.4. Motor programs are the size of metrical feet320300280260240 10008006004002000AB Mean Latency (ms) Mean Utterance Duration (ms) Number of words in UtteranceTime to begin speaking is a function of the number of stressed syllables in the utterance to be spoken, not of the number of syllables, number of unique words, memory load.Sternberg, Monsell, Knoll & Wright (1978) The latency and duration of rapid movement sequences: Comparisons of speech and typewriting. In G.E. Stelmach (ed.) Information Processing in Motor Control and Learning. NY: Press.Recent evidence that coordinative structures for speech are not innately prespecified. Children gradually get their gestures tuned up.Green, J.R., Moore, C.A. and Reilly, K.J. (2002) The sequential development of jaw and lip control for speech. Journal of Speech, Language, and Hearing Research 45, 66-79.5. Children acquire coordinative structures graduallyHow well do children’s articulations correlate with a typical adult?jawlower lipupper