Lecture 11 - Reflexes Flashcards
Dewhurst proposed that _____
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
Dewhurst Responses/reflexes (M3’s)
M1: the monosynaptic reflex (30ms)
M2: the long loop latency reflex (80-120ms)
- > aka the triggered reaction
M3: the voluntary response (150-200ms)
Characteristics of reflexes
- > 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
relate movement duration to type of reflex
for actions of short duration, M1 and M2 will contribute more to the programmed (voluntary) action
open loop motor control
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
motor program
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
slater-hammel (evidence of motor program)
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
controlled (stoppable) vs ballistic (unstoppable) processes
- > point of no return of action, once you reach a certain point of the motion, you can’t stop or modify it
afferent vs efferent info
Afferent
- > to/input
Efferent
- > from output
when does motor program use efferent and afferent info
Open loop
- > efferent info only
Closed loop
- > afferent and efferent info
deafferentation
in deafferentation experiments, the afferent info to the spinal cord is prevented (severed or blocked)
Wadman et al
- > 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
Lee concluded that
(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
motor control hierarchy
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)
what are errors (relate to motor programs)
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
variables of Fitts Index of difficulty
Independent variables
- > amplitude and width
Dependent variables
- > movement time (average)
describe Fitts law
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
when two hands aim for targets of different indexes of difficulty, when will the target be reach by both hands
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
coordinative structures (synergies) are usually ____
the temporary and flexible high level organization of low level elements
the coordinative structures ______ the degrees of freedom problem
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
dynamic systems/self organizing systems
- > 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
