Psychological Aspects of Motor Control

updated September 26, 2011

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.

What will be covered

The problem of sequential movement
Reaction time
The problem of skill acquisition
The information processing view (if there is time)

Sequential action

Examples of serial movement

cyclic rhythms

breathing
walking

coordination of breathing with gait

chewing

more complex

tapping a rhythm

talking
writing
reach-grasp-manipulate

more complex

eat breakfast
go to class
solve a physics problem
go to college

groups

the wave at football game

Why study it?

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".

The Problem of Serial Order in Behavior in Cerebral Mechanisms in Behavior 1951

consider language

predetermined sequence of actions/symbols that are unique for each language

but the same action/symbol can have many meanings

For example

Hawaiian - "humuhumunukunukuapuaa

which is a fish

Cree Indian word "kekawewechetushekamikowanowow"

literal translation: "you will I wish together remain he-you it-man you"
free translation: "may it remain with you"

English - supercalifradgilisticexpialidoscious

contrast English in which verb is early in sentence with German in which verb is at end of sentence

Response chaining

next movement in sequence triggered by feedback from previous movement
many problems

timing

e.g., arpeggio can be done faster than afferent latency

why does one movement necessarily follow another?

e.g., "tire" and "rite" involve same motor elements acting in opposite order
some organizing principle must impose the order based on desired meaning

but the process of actual production of movement is somewhat independent of the organizing principle

errors of production

e.g., typing 'wrapid writing'

prior to production of sentence certain words can be primed

Speech errors

Spoonerisms - "The queer old dean" instead of "The dear old queen"
Errors are not arbitrary

consonants exchange with one another and vowels exchange with one another. nouns exchange with nouns, and verbs, with verbs
thus there is some organization even in the error. These regularities indicate existence of levels of representation in planning and production of speech

speech comprehension too emphasizes fact that understanding meaning requires maintaining 'activation' for a period after the stimulus has occured

sensory feedback is not needed for sequential action

deafferented human or animal can still produce serial movements even if not executed correctly

anticipatory movement effects

coarticulation

"tulip" - note rounding of lips for 'u' before 't' pronounced
examples from typing

Motor program concept: Hierarchy

superordinate element controls lower order element

'rite' instead of 'tire' because of higher order plan

The key measures used to test concept of motor program are

errors
response time

Reaction time

History

H.L.F. von Helmholtz

1850, measured rate of nerve conduction
obtained estimate of sensory nerve conduction by measuring manual reaction times to stimulation at different parts of limbs
"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

F.C. Donders

1868, conceived of using reaction times to measure speed of mental operations using subtraction method

S. Exner

1874 - christened 'reaction time' experiments

"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.

W. Wundt

'father of experimental psychology'; first used term 'Physiological Psychology' 1880s, detailed analysis of reaction times, mental chronometry

Simple reaction time

one signal and one response
unpredictable

distribution of RTs is skewed toward longer tail

analysis of RTs provides opportunity for mathematical model of processes

Accumulator models

shorter RTs if younger, alert, practiced, can predict when the signal will occur, if the signal is brighter or louder

Choice reaction time

multiple signals associated with multiple responses
slower unless probability of one stimulus and response is higher
Faster RTs for more likely stimuli may be due to stimulus processing, response preparation or both

Experiment - map more than one stimulus to a response [S1, S2 --> R1 & S3, S4 --> R2]
If response preparation, choice RTs reduced by repeated testing of response regardless of stimulus
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
Results - both response preparation and stimulus processing play a role.

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.

Choice RT increases with the number of choices, i.e., S-R pairs

Hick-Hyman law, choice RT increases linearly with log2 [S-R pairs]

Decision making characterized by bits needed to uniquely define particular response
Slope of line indicates rate at which decisions are made
Interpretation in terms of information theory (Shannon)
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'

Stimulus-response compatibility

If the response to a stimulus is easily mapped onto the stimulus, then RT is faster and less perturbed.
Experiment - finger on vibrator, press it when it vibrated.

When more vibrators & fingers used, there was no increase in RT with increasing choices when stimulus and response were compatible.
When an arbitrary finger was used in response to a given vibration, then the typical increasing RT with number of choices was seen.

Response-response compatibility

Interactions between responses so that the choice RT for a given response varies according to the other responses that are tested
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.
Results - choice RT from right index was shorter when left index finger was other response
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

Countermanding paradigm

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.
Performance is unpredictable. Sometimes you stop and sometimes you go.

The "inhibition function" plots the percent of trials on which movements are produced in spite of the stop signal as a function of time.

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).
The race model allows the investigator to estimate the time needed to cancel the partially prepared movement -- the "stop signal reaction time".

Skill acquisition

Stages of learning a new skill (Fitts, 1964)

3 stages of skill acquisition

cognitive

learning basic procedures and requirements
involves talking to oneself

associative

stop verbalizing, becoming more automatic
feedback is important

automatic

skilled movements
performance not disrupted by other conscious tasks
performer shifts from continual to intermittent reliance on feedback

Role of feedback, Knowledge of results (KR)

Thorndike (1927)

blindfolded Ss learned to draw a line of specific length if given feedback but not otherwise

Adams (1971) Closed-loop theory

motor learning proceeds through refinement of perceptual-motor feedback loops. Movements are repeated and refined to correct perceived errors.
potential problems

closed-loop theory can be reduced to response-chaining, but many movements can be performed well without feedback
may apply to simple movements like reaching, but it is unclear how it would apply to something like speech
predicts that the more KR, the better the performance. A number of experiments have not found this, e.g., fig 3.2 (p 88)

Generalized programs

learners form schemas or generalized programs when acquiring new skills
schema is knowledge structure that can be instantiated in different ways depending on the values of its underlying variables or parameters
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.
Evidence for parameter setting in a learned motor program

sequential finger-tapping experiment

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

both supporting and contradicting evidence
example of supporting evidence: bean bag tossing

Hierarchical learning

as skill is acquired, exercise of low-level units promote formation of higher-level units
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.
performance speed decreases with practice in systematic manner. Data can be fit with equation of the form0

T = a / P^b

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

Language production benefits from knowledge of meaning

MacKay experiment

Mental practice

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.
generally, imagined practice is better than no practice but not as good as real practice

MacKay speeded recitation task
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

Physical changes

muscle growth
muscle efficiency

shorter bursts of high tension

improved patterns of interlimb coordination

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

neural changes

implicit and explicit learning of sequence
learning and consolidation of movement in variable force field
motor cortex plasticity during skill learning

larger cortical representation of hand in string instrument players

brain activation during motor imagery