Psychological Aspects of Motor Control

updated October 3, 2005

Temporally integrated actions do occur even among insects, but they do not reach any degree of complexity until the appearance of the cerebral cortex. They are especially characteristic of human behavior, and they contribute as much as does any single factor to the superiority of man's intelligence. - Karl Lashley (1951) The problem of serial order in behavior  In: Cerebral Mechanisms in Behavior, L.A. Jeffress (Ed.), New York: Wiley, pp. 112-146.

  1. What will be covered
    1. The problem of sequential movement
    2. Reaction time
    3. The problem of skill acquisition
    4. The information processing view (if there is time)
  2. Sequential action
    1. Examples of serial movement
      1. cyclic rhythms
        1. breathing
        2. walking
          1. coordination of breathing with gait
        3. chewing
      2. more complex
        1. tapping a rhythm

          2. what is difference between 123-123... and 1234-1234...? Why can both not be produced at same time (except by talented musicians)?

        2. talking
        3. writing
        4. reach-grasp-manipulate
      3. more complex
        1. eat breakfast
        2. go to class
        3. solve a physics problem
        4. go to college
      4. groups
        1. the wave at football game
    2. Why study it?
      1. Lashley - Because it is "the most complex type of behavior that I know; the logical and orderly arrangement of thought and action" because it requires "explicit consideration of what is already going on within the system".
      2. consider language
        1. predetermined sequence of actions/symbols that are unique for each language
          1. but the same action/symbol can have many meanings
        2. For example
          1. Hawaiian - "humuhumunukunukuapuaa
            1. which is a fish
          2. Cree Indian word "kekawewechetushekamikowanowow"
            1. literal translation: "you will I wish together remain he-you it-man you"
            2. free translation: "may it remain with you"
          3. English - supercalifradgilisticexpialidoscious
        3. contrast English in which verb is early in sentence with German in which verb is at end of sentence
    3. Response chaining
      1. next movement in sequence triggered by feedback from previous movement
      2. many problems
        1. timing
          1. e.g., arpeggio can be done faster than afferent latency
        2. why does one movement necessarily follow another?
          1. e.g., "tire" and "rite" involve same motor elements acting in opposite order
          2. some organizing principle must impose the order based on desired meaning
            1. but the process of actual production of movement is somewhat independent of the organizing principle
              1. errors of production
                1. e.g., typing 'wrapid writing'
          3. prior to production of sentence certain words can be primed
            1. Speech errors
              1. Spoonerisms - "The queer old dean" instead of "The dear old queen"
              2. Errors are not arbitrary
                1. consonants exchange with one another and vowels exchange with one another. nouns exchange with nouns, and verbs, with verbs
                2. thus there is some organization even in the error. These regularities indicate existence of levels of representation in planning and production of speech
            2. speech comprehension too emphasizes fact that understanding meaning requires maintaining 'activation' for a period after the stimulus has occured

              3. e.g., "Rapid righting with his uninjured hand saved from loss the contents of the capsized canoe."
        3. sensory feedback is not needed for sequential action
          1. deafferented human or animal can still produce serial movements even if not executed correctly
        4. anticipatory movement effects
          1. coarticulation
            1. "tulip" - note rounding of lips for 'u' before 't' pronounced
            2. examples from typing
    4. Motor program concept: Hierarchy
      1. superordinate element controls lower order element
        1. 'rite' instead of 'tire' because of higher order plan
      2. The key measures used to test concept of motor program are
        1. errors
        2. response time
  3. Reaction time
    1. History
      1. H.L.F. von Helmholtz
        1. 1850, measured rate of nerve conduction
        2. obtained estimate of sensory nerve conduction by measuring manual reaction times to stimulation at different parts of limbs
        3. "One of the lines of experimental investigation most diligently followed of late years is that of the ascertainment of the time occupied by nervous events. Helmholtz led off by discovering the rapidity of the current in the sciatic nerve of the frog. But the methods he used were soon applied to the sensory nerves and the centres, and the results caused much popular scientific admiration when described as measurements of the 'velocity of thought'. The phrase 'quick as thought' had from time immemorial signified all that was wonderful and elusive of determination in the line of speed; and the way in which Science laid her doomful hand upon this mystery reminded people of the day when Franklin first eripuit coelo fulmen [stole the lightning from the sky], foreshadowing the reign of a newer and colder race of gods." - William James (1891) The Principles of Psychology
      1. F.C. Donders
        1. 1868, conceived of using reaction times to measure speed of mental operations using subtraction method
      2. S. Exner
        1. 1874 - christened 'reaction time' experiments

          2. "Everyone who makes reaction-time experiments for the first time is surprised to find how little he is master of his own movements, so soon as it becomes a question of executing them with a maximum of speed. Not only does their energy lie, as it were, outside the field of choice, but even the time in which the movement occurs depends only partly upon ourselves. We jerk our arm, and we can afterwards tell with astonishing precision whether we have jerked it quicker or slower than another time, although we have no power to jerk it exactly at the wished-for moment." in Pflüger's Archive 8:526.

      3. W. Wundt
        1. 'father of experimental psychology'; first used term 'Physiological Psychology' 1880s, detailed analysis of reaction times, mental chronometry
    1. Simple reaction time
      1. one signal and one response
      2. unpredictable
        1. distribution of RTs is skewed toward longer tail
      3. analysis of RTs provides opportunity for mathematical model of processes
        1. Accumulator models
      4. shorter RTs if younger, alert, practiced, can predict when the signal will occur, if the signal is brighter or louder
    2. Choice reaction time
      1. multiple signals associated with multiple responses
      2. slower unless probability of one stimulus and response is higher
      3. Faster RTs for more likely stimuli may be due to stimulus processing, response preparation or both
        1. Experiment - map more than one stimulus to a response [S1, S2 --> R1 & S3, S4 --> R2]
        2. If response preparation, choice RTs reduced by repeated testing of response regardless of stimulus
        3. If stimulus processing, choice RTs reduced by repeated testing with particular stimulus.  Switching to another stimulus should yield long RTs whether the same or a different response is used
        4. Results - both response preparation and stimulus processing play a role.
          1. When S1 repeatedly, R1 RT decreases.  Then when S1 replaced with S2, R1 RT increased some but not as much as when S1 replaced with S3 or S4.
        5. Choice RT increases with the number of choices, i.e., S-R pairs
          1. Hick-Hyman law, choice RT increases linearly with log2 [S-R pairs]
            1. Decision making characterized by bits needed to uniquely define particular response
            2. Slope of line indicates rate at which decisions are made
            3. Interpretation in terms of information theory (Shannon)
            4. This hypothesis was abandoned when it was shown that the amount of information held in short-term memory  was related to how many meaningful chunks it included rather than just 'bits'
    3. Stimulus-response compatibility
      1. If the response to a stimulus is easily mapped onto the stimulus, then RT is faster and less perturbed.
      2. Experiment - finger on vibrator, press it when it vibrated.
        1. When more vibrators & fingers used, there was no increase in RT with increasing choices when stimulus and response were compatible.
        2. When an arbitrary finger was used in response to a given vibration, then the typical increasing RT with number of choices was seen.
    4. Response-response compatibility
      1. Interactions between responses so that the choice RT for a given response varies according to the other responses that are tested
      2. Experiment - choice RT with 2 finger presses.  In one condition the 2 fingers were right index and right middle.  In the other condition the 2  fingers were right index and left index.
      3. Results - choice RT from right index was shorter when left index finger was other response
      4. Explained by independence of left & right index fingers and linkage of  right index and right middle fingers  movements of middle fingers accompanied by index finger movements
    5. Countermanding paradigm
      1. The countermanding paradigm probes a subject's ability to control the initiation of movements by infrequently presenting an imperative stop signal in a reaction time task.  The subjects' task is to cancel a planned speeded movement if the stop signal is presented.
      2. Performance is unpredictable.  Sometimes you stop and sometimes you go.
        1. The "inhibition function" plots the percent of trials on which movements are produced in spite of the stop signal as a function of time.
      3. Performance can be explained in terms of a race between two processes that have random finish times -- if a GO process finishes first, the movement is produced, but if a STOP process finishes first, then the movement is canceled.  (see Logan, G.D. & Cowan, W.B., 1984, On the ability to inhibit thought and action: A theory of an act of control. Psychological Review, 91:295-327).
      4. The race model allows the investigator to estimate the time needed to cancel the partially prepared movement -- the "stop signal reaction time".
        5.  
  1. Behavioral evidence for hierarchical representation of motor sequences
    1. Restle & Burnside (1972)
    2. Povel & Collard (1982)
    3. Sternberg (e.g., Monsell & Sternberg (1981))
    4. MacKay (1982; ...)
    5. Motor program concept: Modules
      1. Two inherent ideas
        1. separate subsystems that perform specialized computations
        2. different modules interfaced
      2. e.g., reaching grasping manipulating
      3. e.g, writing with different hands, different motions
        1. evidence that representation of sequences of action can be interfaced to different effector mechanisms
      4. analysis of modularity of sequencing in a key-press task
  2. Skill acquisition

    3. First, let us forget about the term skill which has been so blunted by colloquial usage and research practice that it lacks scientific value. - J.A. Adams (1971) Journal of Motor Behavior 3:111-150

    1. Stages of learning a new skill (Fitts, 1964)
      1. 3 stages of skill acquisition
        1. cognitive
          1. learning basic procedures and requirements
          2. involves talking to oneself
        2. associative
          1. stop verbalizing, becoming more automatic
          2. feedback is important
        3. automatic
          1. skilled movements
          2. performance not disrupted by other conscious tasks
          3. performer shifts from continual to intermittent reliance on feedback
    2. Role of feedback, Knowledge of results (KR)
      1. Thorndike (1927)
        1. blindfolded Ss learned to draw a line of specific length if given feedback but not otherwise
      2. Adams (1971) Closed-loop theory
        1. motor learning proceeds through refinement of perceptual-motor feedback loops. Movements are repeated and refined to correct perceived errors.
        2. potential problems
          1. closed-loop theory can be reduced to response-chaining, but many movements can be performed well without feedback
          2. may apply to simple movements like reaching, but it is unclear how it would apply to something like speech
          3. predicts that the more KR, the better the performance. A number of experiments have not found this, e.g., fig 3.2 (p 88)
    3. Generalized programs
      1. learners form schemas or generalized programs when acquiring new skills
      2. schema is knowledge structure that can be instantiated in different ways depending on the values of its underlying variables or parameters
      3. this notion provides some accounting for the variability and novelty but individual consistency of movement. Thus, handwriting reflects same schema whether done with hand, mouth or foot.
      4. Evidence for parameter setting in a learned motor program
        1. sequential finger-tapping experiment
      5. Generalized program theory predicts that practicing a task under different conditions will result in better performance on related tasks than practicing a task under limited set of or single conditions
        1. both supporting and contradicting evidence
        2. example of supporting evidence: bean bag tossing
    4. Hierarchical learning
      1. as skill is acquired exercise of low-level units promote formation of higher-level units
      2. e.g., Bryan & Harter, 1897 in learning Morse code, operators first learn dot/dash, then letter combinations are heard automatically and then words are heard automatically.
      3. performance speed decreases with practice in systematic manner (fig 3.4). Data can be fit with equation 

        4. T = a / Pb

        where T = performance time, P = practice trials, a,b are constants

        this is the power law of learning because practice trials is raised to bth power

      4. Language production benefits from knowledge of meaning
        1. Review MacKay experiment
          2.  
    5. Mental practice
      1. if low level performance is improved by shaping up high level representations, then just dealing with the high level units through imagination should improve performance.
      2. generally, imagined practice is better than no practice but not as good as real practice
        1. MacKay speeded recitation task
        2. Minas (1978) study of task throwing balls of different weights into sequence of bins. Mental rehearsal improved sequencing but not force modulation; balls were thrown to correct bin, but with incorrect force
    6. Physical changes
      1. muscle growth
      2. muscle efficiency
        1. shorter bursts of high tension
      3. improved patterns of interlimb coordination
        1. during early learning joints stiffened to reduce degrees of freedom. with experience the joints are relaxed and limb acquires ability to compensate to produce more accuracy
      4. neural changes
        1. implicit and explicit learning of sequence
        2. learning and consolidation of movement in variable force field
        3. motor cortex plasticity during skill learning
          1. larger cortical representation of hand in string instrument players