Week 4 Flashcards
when is there the greatest chance at predicting anticipation?
1 stimulus and 1 response
sensation
activation of sensory receptors
- specialized sensory organs are activated by a stimulus
- organs decode sensory information transforming it into neural signals
perception
interpretation of those sensory signals
- involves the combination and integration of sensory (afferent) information from multiple sources
what processes are required for us to understand the world?
sensation and perception
5 senses
- vision
- touch
- smell
- taste
- hearing (audition)
other important senses
- sense of balance (equilibrioception) - argued as part of proprioception
- sense of body position (proprioception)
- sense of temperature (thermoreceptor)
- pain sense (nociception)
wetness perception
hygroreception
- based on touch and temperature
what is proprioception often paired with?
tactile (touch senses)
sensory information
used for both movement planning (feedforward) and movement control (feedback)
use of sensory feedback to modify motor commands
closed-loop control
closed loop control
- system receives instructions (input)
- goal is defined (reference mechanism)
- executive level relays instructions to achieve the goal
- effector level enacts the instructions that are relayed (produced output)
- sensors in environment produce feedback
- feedback is compared to the goal
example of feedback control
- thermostat
- cruise control
- electric kettle
where does visual sensation begin?
at the eye
visual sensation in the eye
light from an object in the visual field is refracted and focused onto the retina
photoreceptors
light sensitive cells line the back of the retina
two main types of photoreceptors
rods and cones
rods and cones
- different structures and response profiles
- different types of visual information
rods
motion/detection
- mainly in periphery
- shadows and motion
cones
fine detail
functions of rods
when rods are exposed to light they fire, then slowly reduce firing
- binary response to light
functions of cones
graded response to light
what is the blind spot caused by?
the optic nerve
visual information
travels through the optic nerve and various subcortical structures to the lateral geniculate nucleus (LGN)
where is visual information relayed to the primary visual cortex (V1)
from the LGN in the thalamus
primary visual cortex
where visual features such as stimulus direction, stimulus speed and object orientation
2 visual streams visual information can travel two from the V1?
- dorsal stream
- ventral stream
dorsal stream
where visual information travels to the parietal areas
- inputs from the full visual field
what is the dorsal stream known as?
vision to perform action stream
ventral stream
where visual information travels to the temporal lobe
- inputs from the LGN mainly from central vision
what is the ventral stream known as?
the vision for perception stream
where does evidence for the 2 streams come from?
the perception-action dissociation experiments
optic ataxia
stroke affecting parietal area (less temporal area)
- participant can tell orientation, but cant touch it (perception is fine, action is affected)
evidence for the dorsal and ventral streams
- muller-lyer illusion
- ebbinghaus-tichner illusion
trickier illusion
tables are the exact same shape
illusions
perception scales to illusions, however grip aperture (action) does not
grip aperture
measure of the distance between index and thumb when performing reaching movements
- unaffected by illusion
muller-lyer illusion
no relationship between constant error and tail-orientation
- perception affected
- grip aperture unaffected
peak acceleration in the trajectory of planning events
process occurring during movement planning
gunslinger effect
person who reacts is not the person who initiated the movement
influences on different parts of the trajectory (roberts et. al, 2017)
action was affected due to the illusion
- travelled a further distance due to the illusion (looks longer)
roberts et. al, 2017 results
- replicated the gunslinger effect in the movement trajectory
- suggest that the ventral (action) stream may be used for more limb target control and the dorsal stream (perception) may be used more for planning
vision
visual system indicates where your head and eyes are in space (tells orientation)
- has an effect on balance
optic flow
when we move out head, the angle the light rays hit the cells on retina changes
- the environment flows past us as our head and body move
what does optic flow do?
gives us crucial information about out position and the position of objects (relative position of us compared to environment)
optic flow effect on children
moving room experiments have found that children lose balance if the walls of the room shift
moving room
lose balance due to the illusion
- lee and aronson, 1974
what did moving room experiments show?
we are highly dependent on vision for our position
what is losing balance due to?
optic flow
what does the rate of change of the size of an object in the retina indicate?
whether the object is coming toward you or going away from you
- retinal image (A) increases as ball comes closer
what can we estimate from the rate of change of the size of an object on the retina?
time to contact (Tau)
what is the time to contact directly proportional to?
size of the image (A) divided by the rate of change of the image A dot) multiplied by a constant (K)
- true regardless of distance, size or velocity
Tua
k x A/A dot
proprioception
sensory information about the position of the body in space
- also known as kinesthesis or kinesthesia
what does proprioception include?
information from:
1. vestibular system
2. sensory organs in the muscles and joints
3. cutaneous receptors in skin
where is the vestibular system located?
in the inner ear
otolith organs
provide information about the orientation of the head with respect to gravity
utricle and saccule
sense linear accelerations
semicircular canals
three fluid-filled half-circles that give orientation on how you’re aligned
- in a position sense directions (aligned to the horizontal, sagittal and frontal planes)
- can sense rotations
thick fluids in semi-circular canals
displace hair cells (mechanoreceptors)
what is the vestibular system important for?
balance and orientation
how is the vestibular system disrupted?
by stimulating the mastoid process
vestibular-ocular reflexes
when we move our heads - our eyes stay stable
- when our head moves in one direction - out eyes slowly move in the other direction
what happens when we go too far and our eyes reach a limit?
eyes remained fixated and moved in opposite direction as head was moving
nystagmus
alternating slow and fast movements
- stop if the head keeps rotating and quickly return to straight position
spinning challenge - what helps overcoming dizzy feeling?
use of spotting
- focus on a stable visual stimulus (keeping head still)
spinning challenge - what may reduce the time the head is spinning?
turning the head after the body has undergone motion
what might training with spotting do?
shift sensory feedback use to more visual sources
- may not improve dance performances in novices
- may get people trained to deal with the feeling of being dizzy faster (just helper people tolerate the feeling)
muscle spindles
provides information about muscle stretch
where are muscle spindles located?
- in the fleshy part of the muscle body (contractile unit)
- oriented in line with the muscle fibre (when muscle is stretched, the spindle is stretched)
what are muscle spindles comprised of?
intrafusal muscles fibres
what are intrafusal muscles fibres innervated by?
a la afferent fiber
- firing rate is related to length and rate in change in length
what do muscle spindles connect to?
alpha motor neurons of the muscles through simple reflex circuit
- basis of the stretch reflex
when is there more firing?
more firing with more stretch
motor neurons
causes contraction of muscle spindles
golgi tendon organs (GTOs)
located at the muscle tendon junction
- highly sensitive to active muscle tension
- can respond to forces caused by less than 0.1g
GTO attachment
each GTO is attached in series to small groups of muscle fibres (<25)
- only a few motor units represented by the innervated muscle fibres
hypothesis of GTOs
hypothesized to contribute less to overall position sense than muscle spindles
joint receptors
embedded in the joint capsule
where are joint receptors located?
primarily located in the areas of the capsule that are stretched the most (joint capsule in elbow, shoulder, knees)
research into the joint receptors
neural signals are the strongest at the end ranges of the joint movement
- less involved in position sense than muscle spindles
where is proprioception processed?
in the primary somatosensory cortex
how does information get into the cortex?
via dorsal root
role of proprioception
plays a role in rapid-feedback based responses
- stretch reflex based responses to perturbations
- critical to both optimal movement control
proprioception role (bagestiero, 2006)
proprioception is used to plan distances and vision to plan direction
proprioception role and cisek et. al, 1998)
proprioceptions may be the key feedback based mechanism
- both the speed of processing and reflex circuitry make it possible
dorsal stream processes mainly what?
action-related visual information
ventral stream processes for mainly what?
perception-related visual information
golgi tendon organs sense muscle what?
muscle tension
muscle spindles sense muscle what?
muscle stretch
issues with motor programming theory?
- storage problem
- degrees of freedom problem
- novelty problem
storage problem
brains have limited capacity = not enough room to store separate motor programs for each movement
degrees of freedom problem
system has too many independent states to control at the same time
novelty problem
how do we learn new actions if each new action requires a pre-determined program
auditory information
more reliable for temporal features of movements
- telling where something is can also be done with auditory feedback (if someone calls tour name, you turn in the right direction)
what is open-loop control?
no feedback
- don’t have senses that measure feedback from the environment
open loop control
there is an executive level and an effector level
executive level of open loop control
sends the motor program to the effectors
effector level of open loop control
carries out instructions without modification based on feedback
open
= dont reset
when is a response open loop?
when the response unfolds without feedback
example of open loop response
pointing without vision
- bad example because you still have other sources of sensory information
when is a system open loop?
if the system doesn’t take feedback into account
example of a open loop system
living with a sensory neuropathy
- lack of sensation = no sensory feedback
examples of open loop control
- intersection: traffic lights on and off - even when collision the traffic lights keep going, they don’t get modified
- different sets of instructions - but when you choose setting it doesn’t make corrections during cooking
do open loop systems make feedback-based corrections?
no
feedforward control
involves a signal that
1. readies the system for the motor command
2. readies the system for som input
- use sensory information to plan action
where did the concept of feedforward control emerge from?
the study of eye movements (saccades)
what happens when our eyes move?
light hits the retina at different angles
- the same occurs if the world moves
von holst and mittlestadt (1950)
- discovered concept of ‘reafference’ or corollary discharge
- a copy of the motor command that was sent to muscles is delivered to sensory regions in the brain
- the individual therefore perceives the world as moving
efference copy
the copy of the motor command
- sends information
subcortical sauron
feedback control in eye movements
kiernan et. al, 2016
- saccade end points adjusts to target jumps
- even if jumps were unconscious (subcortical mechanism) - provides some evidence than eye movements could be affected by feedback
what does the efference copy allow?
the prediction of the action outcome and the sensory consequences of the action
what does the efference copy tell the sensory system?
what was “ordered” by the motor system
- prepares the motor system for outcomes about to be experienced
what does the sensory system use to compute an error?
the predicted and actual sensory feedback
how can we test for the existence of feedforward control in limb movements?
use active vs. passive task
active vs. passive tasks
participants are generally better at error estimate when they have efferent information
- proprioception may play more of a role than previously thought
- can predict the outcome of their actions when there is efferent information
result of efferent copy?
helped with predicting error of the movement
why we cannot tickle ourselves (forward models)
because you are predicting what it’s expecting to feel like (efference copy)
- preparing your own action
blackmore et. al, 1998, 1999, 2000 results
- as the robot hand movement offset increased, trials were more ticklish
- authors concluded the sensory predictions were less accurate with greater hand-robot offsets
- ability to predict sensory consequences of our actions affects perception
forward models
used to establish predictions about the desired state
- produce predictions about the movements intended outcome and desired feedback
(tells sensory system what it’s supposed to feel like)
what does a forward model establish?
a reference of correctness for which to compare to based on sensory information
- they are used continuously throughout the movement to update the reference of correctness
computational solution of motor programming problems
- motor problems must be generalized (schmidt, 1985)
- motor programs must resemble a function
what is a function
X = mean (4,8,2)
X= answer
mean= set of processes to be performed
(4,8,2)= input
function
what the function does, does not change
- function is invariant
- input can change though
invariant or algorithmic features of the GMP?
- relative timing
- relative force
- sequence of events
- these components are in the function - not changed by the user
relative timing
the timing of muscle activations relative to others (don’t change)
relative force
the force of muscle activations relative to others (don’t change)
sequence of events
the sequence of events (don’t change)
motor equivalence
writing your name with left and right hand
parameters (inputs) into the GMP
- overall duration of the movement
- overall force
- effector (limb) used
overall force
- don’t get a change in pattern of acceleration
- produce bigger word in same amount of time - don’t change patterns, change accerlation
effector (limb) used
right and left hand produce the same acceleration
what serves as a solution to theoretical problems with regard to motor programming ?
generalized motor programs
