Coordinative structures The basic units of speech motor control 1 The motor system is organized in task specific hierarchical control programs 2 This is revealed by trading relations at several levels of description 3 Coordinative structures are feed forward control programs 4 Motor programs are the size of metrical feet 5 Children acquire coordinative structures gradually 1 The motor system is organized in task specific hierarchical control programs Consider the mucles involved in moving the lower lip up and down Lower lip Down Depressor Labii Inferior Incisivus Inferior Up Obicularis Oris Inferior Mentalis Add also the muscles that must cooperate to move the jaw Down Geniohyoid Mylohyoid Digastricus Up Masseter Temporalis A flat control structure Each muscle gets a target length independently of the others Depressor Labii Inferior Incisivus Inferior Obicularis Oris Inferior Raise the lower lip Mentalis Geniohyoid Mylohyoid Digastricus Masseter Temporalis There 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 A hierarchical control scheme solves the degrees of freedom problem intermediate targets specified for functional groups of muscles Depressor Labii Inferior LL Raise the lower lip Jaw Incisivus Inferior Obicularis Oris Inferior Mentalis Geniohyoid Mylohyoid Digastricus Masseter Temporalis 2 The hierarchical organization of speech motor control is revealed by trading relations at several levels of description When 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 description apa apa apa Position of the lower lip LL Position of the jaw Relative position of the lower lip on the jaw LL jaw When the jaw doesn t move as much the lower lip compensates The jaw and LL are coordinated for p 2 The hierarchical organization of speech motor control is revealed by trading relations at several levels of description Depressor Anguli Oris Obicularis Oris Superior Lower lip position 5 mm OO inferior Obicularis Oris Inferior Mentalis Depressor Labii Inferior When the OOI doesn t fire as strongly the mentalis compensates The OOI and mentalis are coordinated for p Mentalis 200 msec A partial coordinative structure for p Lip closure Lower lip lower lip OOI Mentalis Upper lip jaw 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 not a 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 feet 300 280 260 A 1000 Mean Utterance Duration ms Mean Latency ms 320 B 800 600 400 200 240 0 Number of words in Utterance Time 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 5 Children acquire coordinative structures gradually 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 How well do children s articulations correlate with a typical adult jaw lower lip upper lip