Cognition – 2/e Dr. Daniel B. Willingham Chapter 8: Motor Control PowerPoint by Glenn E. Meyer, Trinity University

How Do We Select a Movement? Efficiency Theories Synergy Theories The Mass Spring Model Which Model is Right? ©2004 Prentice Hall

Efficiency Theories Important Terms: Degrees of Freedom Problem The problem of how the mind selects which way to execute a movement, given that there are many ways to make any given movement Trajectory: The path of a movement Effector: Part of the body that you use to have an effect on the environment (e.g., the hand, the foot). Efficiency Theory: A solution to the degrees of freedom problem in motor control, which claims that movements are evaluated for their efficiency and the most efficient movement, is selected. Problem: What is best measure of efficiency? Joint space: In motor control, a representation for planning movements that uses joint angles Cartesian Space Minimum Joint Torque Minimizing Jerk: Rate of acceleration. Used as a measure of efficiency in one theory addressing the degrees of freedom problem ©2004 Prentice Hall

Synergy Theories Synergy Biases for joints or muscle groups to work together in a particular way Evidence for: Santello, et al (1998) as seen in Fig. 8.2, argue for two basic postures and synergies that explain a grasping situation Anticipatory Postural Adjustment Muscle contractions that counteract changes in the center of gravity that occur due to other movements (e.g., reaching movements) – seen in reaching behavior, counteracting what makes you unstable ©2004 Prentice Hall

The Mass Spring Model Which Model is Right? A model addressing the degrees of freedom problem that capitalizes on a biomechanical property of the way our muscles and limbs are designed. It proposes that endpoints are selected for movements, but trajectories are not planned – as seen in Fig 8.3 Evidence: Polit and Bizzi (1978) as seen in Fig. 8.4 , use and non-use of proprioceptive information by monkey Proprioception A sense of the body’s location generated by any of a number of special receptors in the joints, skin, and muscles Graziano, et al. (2002) – electrical simulation of motor cortices in monkey – stimulated predicted endpoints Which Model is Right? Correct model needs to incorporate many of the models Rosenbaum, et al. (1993, 1995, 2001) combines many factors: Endpoints selected Trajectory develops naturally as joint angles go to target posture Movement selected by criteria: accuracy and energy ©2004 Prentice Hall

How are the Movements Sequenced? Response Chaining Motor Program Theories Hierarchical Control in Motor Programs ©2004 Prentice Hall

Response Chaining Response chaining A theory of how sequences are organized in motor control. A movement Glossary triggers a proprioceptive feeling of having completed the movement, which triggers the next movement, and so on. Suggested by James – based on proprioceptive feedback as seen in Fig. 8.6 Lashley (1951) – argued against as speed of skilled movements argues against use of proprioception Experiments severing dorsal roots of spinal cord don’t support the theory ©2004 Prentice Hall

Motor Program Theories Motor program Theory (Keele, 1981) A representation supporting movement that has three key features: it contains a set of commands for movement peripheral feedback is not needed the commands can be applied to different effectors Supporting evidence – Henry and Dodd (1960) – time it takes to initiate a series of commands depends on the number of movements in the series Taub shows monkeys can produce actions without propioception You can write your name with the nondominate hand or a foot – as seen in Fig. 8.7 ©2004 Prentice Hall

Hierarchical Control in Motor Programs Motor sequences are organized hierarchically as seen in Fig. 8.8. Hierarchical schemes contain: Movement nodes: In a hierarchical sequencing representation, the movement nodes control muscles Control nodes: In a hierarchical sequencing representation, the control nodes tell the movement nodes what to do. Supporting Evidence: Rosenbaum, et al. (1983) as seen in Fig. 8.9. Time between key presses depends on number of nodes traversed MacKay and Bowman (1969) as seen in Table 8.1 – argues for two levels of speech production Control of articulators Abstract Control of words to be said ©2004 Prentice Hall

How Is Perceptual Information Integrated into Ongoing Moments? Vision Propioception ©2004 Prentice Hall

Vision Questions: What is the relation of the visual system’s “How” system to motor control Is visual feedback needed for motor control, as in reaching? Zelaznik et al. (1983), as in Fig. 8-10, found for fastest movements vision did not contribute but when movements took > 150 ms, feedback made them more accurate Constant visual feedback not needed, periodic feedback can be substituted as seen in Fig. 8-11 (Elliot, et al., 1994) ©2004 Prentice Hall

Propioception Proprioception : A sense of the body’s location generated by any of a number of special receptors in the joints, skin, and muscles: Muscle receptors: Muscle Spindles: Receptors in the fleshy part of muscles that detect muscle stretch. They are important for proprioception Golgi Tendon Organs: Receptors located where the muscles and tendons join that are active when muscles stretch. They are important for proprioception Cutaneous receptors: Receptors in and under the skin. Some of these respond when the skin is displaced by pressure. This is important in detecting the pressure exerted by muscle contraction, as when you grip a glass Joint Receptors: located in joints and fire for extreme joint angles Loss of propioception is devastating and vision cannot substitute in some tasks (Cole, 1995) but can in others (Sanes et al., 1985 as seen in Fig, 8-12) Propioception contributes egocentric spatial representation: A spatial representation in which objects are located relative to part of the body as seen in Fig. 8-13 Evidence suggest egocentric spatial representation is used to support movement as seen in Fig. 8-15 (Blouin, et al., 1993) ©2004 Prentice Hall

How Are Motor Skills Learned? Three Obvious Properties of Motor Skill Learning Two Approaches to Motor Skill Learning ©2004 Prentice Hall

Three Obvious Properties of Motor Skill Learning Motor skill learning Increasing accuracy (either spatial or temporal accuracy) of motor acts that occur as a result of practice Three Properties Generalization Transfer depends not just on overall similarity but on representation of the skill (Willingham, 1997,1998) Long-Term Retention As seen in Fig 8.18 (Fleishman and Parker, 1962) Automaticity: When motor skills are practiced to sufficient degree, the attentional demand for the action is reduced as is the felt need for conscious direction of the action. Consistent feature of well trained skills (Wulf and Prinz, 2001) ©2004 Prentice Hall

Two Approaches to Motor Skill Learning Generalized Motor Programs: A motor program that can produce not just a specific movement, but a whole class of movements Motor skill learning is matter of acquiring generalized motor programs – Schmidt’s (1975) schema theory Can be thought of as a function that relates some input parameters to a pattern of movements that will produce a desired outcome as seen in Fig 8.18 Ability to generalize will be better if you have trained in a broader set of circumstances There is ongoing debate about the predictions of the theory ©2004 Prentice Hall

Two Approaches - Continued Multiple Processes - Willingham Many brain areas involved, suggesting several systems Motor skill learning is the adjustment of motor control processes to work more effectively in particular environments Suggested Processes to Support Motor-Skill Learning (as seen in Table 8.2) Strategic: Selects goal of movement in environment coordinates. Perceptual-motor integration: Selects spatial targets for movement that will fulfill environmental goal; represented in egocentric space. Sequencing: Orders spatial targets in the correct sequences Dynamic: Translates egocentric spatial targets and a pattern of muscle firing Processes can operate in conscious or unconscious mode, rely on different neural structures ©2004 Prentice Hall