Lecture 11 - Reflexes

Question 1

Dewhurst proposed that _____

Answer 1

if the CNS processes info through the stages of info processing identified perviously, then any corrections should not be observed until 150-200ms after movement onset

Question 2

Dewhurst Responses/reflexes (M3’s)

Answer 2

M1: the monosynaptic reflex (30ms)

M2: the long loop latency reflex (80-120ms)

• > aka the triggered reaction

M3: the voluntary response (150-200ms)

Question 3

Characteristics of reflexes

Answer 3

• > involuntary response to a stimulus
• > do not require attention
• > used in closed loop mechanisms
• > short latencies (less than a reaction time)
• > fast and stereotypical
• > mechanisms that control reflexes are found in the spinal cord and brain stem

Question 4

relate movement duration to type of reflex

Answer 4

for actions of short duration, M1 and M2 will contribute more to the programmed (voluntary) action

Question 5

open loop motor control

Answer 5

instructions for motor control are programmed in advance to the action in open loop control processes

• > there is no (voluntary) detection and correction of errors because of time constraints

Question 6

motor program

Answer 6

a set of muscle commands that are structured before a sequence begins, and that allows the sequence to be carried out uninfluenced by peripheral feedback (open loop only)

• > a motor program is an abstract (blueprint) representation for movement

Question 7

slater-hammel (evidence of motor program)

Answer 7

the task was for the subjects to lift the finger once a clock reached a certain time

• > on some trials the actions could be stopped and on others the action could not be stopped
• > the likelihood of stopping decreases as the time to the target decreases

Question 8

controlled (stoppable) vs ballistic (unstoppable) processes

Answer 8

• > point of no return of action, once you reach a certain point of the motion, you can’t stop or modify it

Question 9

afferent vs efferent info

Answer 9

Afferent

• > to/input

Efferent

• > from output

Question 10

when does motor program use efferent and afferent info

Answer 10

Open loop

• > efferent info only

Closed loop

• > afferent and efferent info

Question 11

deafferentation

Answer 11

in deafferentation experiments, the afferent info to the spinal cord is prevented (severed or blocked)

Question 12

Wadman et al

Answer 12

• > experiment about the preservation of sequencing and timing in the EMG when no movement occurs indicates a motor program
• > theses changes apply for the first 100ms or so, after which time peripheral info affects the central commands of the motor program

- > showed evidence for a long loop latency reflex

Question 13

Lee concluded that

Answer 13

(cont’d of Wadman et al)

• > there was indication of postural preparations in support of a pending movement

movement was detected before any EMG in the muscles were produced

Question 14

motor control hierarchy

Answer 14

Hard wired control

• > reflexes: involuntary and dependant on mechanisms of control (stimulus-response)
• > central pattern generators: independent control mechanisms (NOT reflex)

Soft wired control

• > motor program: the flexible control of neural pathways produces different outputs (“software” determines the input-output relationship)

Question 15

what are errors (relate to motor programs)

Answer 15

Program selection

• > incorrect program is selected

Programming

• > errors in the movement planning resulting in incorrect spacial-temporal characteristics

Program Execution

• > unexpected disruptions (perturbations) to the movement being produced
• > requires “on-line” corrections to the movement being produced

Question 16

variables of Fitts Index of difficulty

Answer 16

Independent variables

• > amplitude and width

Dependent variables

• > movement time (average)

Question 17

describe Fitts law

Answer 17

SPEED ACCURACY TRADE-OFF

increasing width, decreases movement time

increasing amplitude increases movement time

under certain conditions, long movement’s to wide targets take the same movement as short movements to narrow targets

Question 18

when two hands aim for targets of different indexes of difficulty, when will the target be reach by both hands

Answer 18

both targets are reached at the same time

• > this shows evidence of coordinating structures: the two hands are controlled together as a single functional entity

Question 19

coordinative structures (synergies) are usually ____

Answer 19

the temporary and flexible high level organization of low level elements

Question 20

the coordinative structures ______ the degrees of freedom problem

Answer 20

REDUCE

i.e. if your have 2 hands (n=2) and your brain coordinates them, you only have 1 degree of freedom (n=1), thus simplifying the control problem

Question 21

dynamic systems/self organizing systems

Answer 21

• > examines change n a system over time
• > specifically the transition in a system between different stable states (equilibrium)
• > these transitions occur spontaneously as a result of self organizing properties