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207 > ch 7- sensorimotor control models > Flashcards

ch 7- sensorimotor control models Flashcards

1
Q

Motor program theory

A

motor program= NOT a sequence of commands
–> if it were a sequence it would require a search through the “database” of possible sequences to match it to the task

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2
Q

motor command

A

specific info about timing and force sent from the brain to muscles

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3
Q

Motor program

A

a procedure/formula for generating motor commands that produce related movements: “class of actions”
-ex. throwing can be done underhand, overhand, sidearm etc. (all have the same goal)

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4
Q

A generalized motor program (GMP) controls

A

a CLASS of actions rather than specific movements/sequences

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5
Q

Components of the GMP

A
  1. Invariant features= features of the command that remain almost the same each time
  2. Parameters= ways that the command can be varied
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6
Q

Invariant features

A

-features remain almost the same.
-all motor skills within a class of action will have similar features
-ex. saccades: direction, amplitude may vary but kinematic profiles remain the same

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7
Q

Parameters

A

-variants
-can be added to invariant features to meet specific movement demands of a situation

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8
Q

Motor schema response concept

A

provides rules that decide the performance of a skill in a given situation/context
-selects parameters for motor program
-ex. you have an idea of what walking entails (moving your legs)

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9
Q

schema

A

a rule/set of rules that provide the basis for a decision
-identifies the class of action
-ex. you have seen many dogs, they range in appearance, you have developed a schema/set of rules for identifying a dog

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10
Q

Motor equivalence

A

varying parameters produce the same output

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11
Q

motor equivalence:
writing name w different body parts example

A

parameter= using different body parts
invariant features= aspects of the written text (the shape of letters, the general shape of words)

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12
Q

does the nervous system store sequences of commands to be sent out to spinal circuitry?

A

NO!!! there are wayyy too many sequences to store.
A motor program (rules for generating motor commands) can be stored.

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13
Q

motor programs are planned before the movement. can they be adjusted if the task requires it?

A

YES! sensory feedback can be used
-sensory feedback: stretch receptors
-visual feedback:

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14
Q

Limitations of sensory feedback

A

-Delays of sensory feedback: processing and integrating
-Noise: the info is not always accurate
-Encoding issue: needs common encoding (sensorimotor integration problem)
-Distinguishing between reafference and exafference

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15
Q

Delays
(sensory feedback)

A

the longer the path of travel, the longer the sensory info is delayed

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16
Q

Noise
(sensory feedback)

A
  1. Sensor noise= inaccurate/noisy sensory receptors
  2. Motor noise= noise in motor commands, results in variable movements
  3. Sensorimotor noise= noise from combining sensory feedback signals and transforming info to motor system
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17
Q

Potential causes of sensory noise

A

-Ion channel properties (random opening and closing)
-Spontaneous action potentials generated by receptors/neurons
-Muscle fatigue

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18
Q

Reafference

A

self generated motor behaviour

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19
Q

Exafference

A

external events of stimuli

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20
Q

How is your vision not blurry when you move your eyes to look at something (saccade)

A

nervous system uses predictive signalling (from efference copy signals)

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21
Q

Internal Models

A

-understand how the body works
-processes occur in the brain
-different brain regions responsible for different aspects
-argued to exist in the spinal cord
-develop over time (through experience)

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22
Q

3 types of internal models

A
  1. Cognitive model
  2. Inverse model
  3. Forward model
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23
Q

cognitive internal model

A

-how external objects work based on prior experience with the object/similar object (we know a ball bounces)
-you act differently depending on what the object is
-you choose a goal depending on the object or hazard in environment

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24
Q

inverse internal model

A

calculates motor commands needed from desired trajectory information

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25
Q

Inverse model subcomponents

A
  1. Inverse kinematic transformation/model= calculation of set joint angles than can reach an endpoint
  2. Inverse dynamic transformation/model= calculation of torques at each joint needed to achieve the motion
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26
Q

Describe how an inverse model (dynamic and kinematic) works when reaching for a cup

A

-locate your hand and the cup
-form a motor plan
-the plan is sent to the inverse kinematic model (determines joint angles needed)
-the inverse dynamic model takes the joint angle info and determined joint torques needed

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27
Q

What is the output of this inverse internal model example?

A

the motor command that is sent to the arm muscles to reach the cup

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28
Q

The motor plan to move is based on

A
  1. The goal (to reach the cup): can be influences by the cognitive model, we want to reach the cup because we are thirsty
  2. State of the limb: state estimate, position/velocity of limb
  3. Target (the cup): distance between limb and the target= difference vector
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29
Q

Forward internal model

A

-models the relationship between actions and consequences
-2 components= forward dynamic model and forward sensory model
-PREDICTS state estimation and sensory consequences from a copy of the motor command

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30
Q

What is a copy of the motor command called?

A

Efference copy

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31
Q

State estimation

A

Combining predicted sensory feedback with actual feedback to form a belief about the state of our body/world/environment

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32
Q

Describe how the forward model and state estimation works: goal= move finger to face

A

-A previous state estimate (where is the finger approximately?) is the basis for a new state estimate
-A motor command is generated using the state estimate. command to move the arm to face.
-An efference copy is sent to the forward dynamic model which predicts the current state of the finger
-The forward sensory model predicts the sensory feedback
-Sensory prediction error is used to correct the estimate of the current finger position
-The final estimate of the finger position has less error and become the new estimate for other movements
-Cycle repeats

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33
Q

can you form a motor command without info about the state of your limb?

A

NO!!

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33
Q

If the model is really good…

A

the nervous system can use the predicted state to plan to reach for a cup (for example) without waiting for sensory feedback

34
Q

Predicted feedback is determined by

A

the forward sensory model

35
Q

the forward sensory model uses

A

the predicted state from the forward dynamic model

36
Q

how do internal models develop over time?

A

change with experience, growth, injury etc..

37
Q

Why are movements sometimes not very accurate?

A

-accuracy of motor command is only as good as the internal model and its inputs
-noise

38
Q

How does the nervous system know the state of the limb if sensory information is delayed????

A

the FORWARD internal model and STATE ESTIMATION

39
Q

Difference vector

A

The state estimate of the hand is compared to the estimated cup location
(distance between the two)

40
Q

Movement:
1. reach and grasp cup
2. bring cup to mouth
Describe how nervous system would compare sensory info (two quick sequential movements)

A

Incoming sensory feedback is compared to the predicted sensory feedback (from forward sensory model) and used to correct the sate estimate

41
Q

When you grasp the cup with your hand, you have reduced the difference vector to

A

zero

42
Q

Sensory-to-motor transformation
–> which model?

A

Inverse model
-converts sensory-based info related to a motor plan to a motor command

43
Q

Motor-to-sensory transformation

A

Forward model
-converts motor based info about movement to a sensory-based prediction

44
Q

What does it mean when there is a sensory prediction error?

A

predicted and actual sensory feedback don’t match

45
Q

What does the nervous system do when there is a temporary sensory prediction error?

A

adjust the weighting between predicted vs. actual sensory feedback

46
Q

What should the nervous system to if there is a constant sensory prediction error?

A

update its internal models
(could be caused by growth, injury etc.)

47
Q

Credit Assignment problem

A

nervous system needs to assign a cause of the error
-is it body/limb based or world based?
-internal or external factors?

48
Q

Examples of internal sources of error

A

factors within the body; altered sensorimotor mapping, injury, fatigue etc.

49
Q

Examples of external sources of error

A

environmental factors; wind, object bumping into you, object that you are manipulating

50
Q

Credit assignment problem is the opposite of the — problem

A

DOF

51
Q

How are the credit assignment and DOF problems opposite?

A

credit assignment= determine which or the many neurons, muscles, limbs was the problem
DOF problem= choose and control different neurons, muscles, limbs for a particular movement

52
Q

Two common paradigms to study motor learning

A
  1. Force-field perturbations
  2. Prism glasses or visuomotor rotation
53
Q

Force field perturbations cause

A

dynamic adaptation over repeated trials

54
Q

Prism glasses or visuomotor rotation cause

A

kinematic adaptation over repeated trials

55
Q

task error in visuomotor rotation

A

difference between the end cursor position and the target position

56
Q

sensory prediction error in visuomotor rotation

A

difference between predicted and actual sensory feedback (cursor doesn’t move in expected way)

57
Q

Dynamic adaptation

A

a force field pushes a person’s arm off course so that initial trajectories start in the WRONG direction and curve to correct the error

58
Q

Dynamic adaptation: what happens with practice?

A

-the person learns to adapt to the force field and produce a straight reaching movement
-learns a new relationship between the motor command and the motion of the limb

59
Q

Kinematic adaptation

A

person learns a new relationship between between coordinate systems (such as arm joint angle/observed hand position relationship)

60
Q

Wearing prism goggles cause…
(kinematic adaptation)

A

cause a visual shift so that the hand and target positions are perceived at different locations
-with practice, reaching movements change from being curved to being straight

61
Q

aftereffect

A

removing a perturbation (such as prism goggles) the person inappropriately compensates with a reaching error in the opposite direction

62
Q

The presence of the aftereffect is an indication of

A

updating of the person’s internal models

63
Q

Visuomotor rotation paradigm usually involves

A

-moving a cursor on a screen
-person sees the start position, target location and a cursor on a screen
-can’t see their hand
-goal= move cursor to target as accurately as possible

64
Q

The brain becomes — sensitive to errors with greater uncertainty

A

less

65
Q

explanation for slower adaptation in the noise conditions?

A

the only way the brain knows there is a foot placement error is through visual feedback.
NOISE –> brain trusts forward model predictions more than vision
-uses visual feedback less to adjust the state estimate= slowed rate of adaptation

66
Q

How can sensory prediction error drive a corrective response?
Example of modifying grip and load force to lift an object

A

-object is too heavy for your grip/slipping from fingers
-sensory prediction error drives corrective response (increase/decrease grip)

67
Q

If cutaneous receptors discharge earlier or later than normal (or predicted based on previous experience)…

A

the object you are holding is too heavy for your grip and is slipping from your finger
–> the mismatch in timing is a sensory prediction error

68
Q

Experiment: object is heavier than expected, cutaneous receptor activity measured.
Real life example= ?

A

Open fridge to get a carton of milk and expect it to be empty, but someone replaced it with a full carton so it is much heavier than expected

69
Q

Heavier object than expected; how is the corrective response triggered?

A

-Nervous system is expecting the cutaneous afferent to discharge at a specific time
-BUT heavier object= longer to develop good grip and load force to lift object up
-this means that the cutaneous afferent discharge occurs later
-absence of expected cutaneous receptor event signalling at the predicted time triggers a corrective response

70
Q

Forward models distinguish between — and — generated movement

A

internally and externally

71
Q

Muscle stretch: internally generated and externally generated examples

A

-muscle stretch is detected by changes in muscle spindle length
-internally generated= voluntary= you move your own muscles
-externally generated= involuntary= someone or something moves your muscle

72
Q

Forward model allows the nervous system to determine if a — error is present

A

sensory predicition

73
Q

If a sensory prediction error is present, this suggests — generated movement

A

externally

74
Q

If mismatch is not constant, should model be updated?

A

NO!!! no need to update bc it could be a one-time external event such as someone bumping into you or a gust of wind etc.

75
Q

voluntary movement: how does a muscle contraction occur?

A

the corticospinal tract sends a motor command to alpha motor neurons in the spinal cord, which leads to a muscle contraction (and change in muscle length)

76
Q

How is the resulting sensory feedback of the movement predicted?

A

An efference copy is sent to the forward model which predicts the resulting sensory feedback

77
Q

Sensory feedback is compared to actual muscle spindle feedback which enters the — from the —

A

cerebellum from the dorsal spinocerebellar tract

78
Q

muscle spindle feedback is also sent to the primary somatosensory cortex through

A

primary somatosensory cortex through the dorsal column medial lemniscus tract to inform the person of the movement

79
Q

If there is a match between actual muscle spindle feedback and sensory feedback…

A

a signal from the cerebellum is sent to reduce the signal that reaches other parts of the brain

80
Q

Why suppress activity in the cortex?

A

you don’t need to be consciously aware that you moved in a certain way if it was done as INTENDED

81
Q

If there is a mismatch between actual muscle spindle feedback and sensory feedback…

A

the inhibitory influence is reduces/absent

82
Q

when would a mismatch between actual and sensory feedback occur?

A

if someone or something caused a change in muscle length

83
Q

You get a — activity in the cortex when the movement was — generated

A

larger
externally generated

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