visional feedback Flashcards
intro of visual feedback
- skilled motor performance is series of accurate movements
- for slow movements
- visual feedback guides to make them more accurate
history
- attempts to determine processing time for visual feedback
- woodworth & Schlosberg (1954) found that visual choice reaction time is ¼ sec or longer
- therefore, processing visual error info is thought to be ¼ sec longer
- in repetitive movements at 100-180 strokes per minute, accuracy was no better with eyes open than with eyes closed
- study included time reversing direction which overestimates visual processing time
Keele and posner
- this study compared discrete movements with and without vision
- significance: estimate visual processing time not biased by the time to reverse movements ensuring consistent pre-movement strategy due to no knowledge about light on/off
apparatus
- 16x16 inch metal plate mounted on a table
- home position ¼ in diameter target contacts 6-inches away from the home position
- each side of the home position on the 45-225 degree axis
- white feedback light positioned 8 inches above back end of metal plate illuminated entire plate
- programmed to turn off immediately on leaving home position and the entire room remained dark until either the target or the metal plate was touched with the stylus
- a western union tape transmitter programmed order of target lights and whether feedback light stayed on or turned off
experiment
- movement times measured in hundredths of a second from the time a stylus left home position until touched target or metal plate
- if plate was touched before the target, a red light came on informing subject of a miss
- 8 subjects with no previous experience participants for two 1 hr sessions
- eight different sequences of 24 targets randomly constructed
- with restoration that each combination of the two targets with the feedback light on/off occurred equal number of times each sequence
procedure
-two practice sequences (self-determined movement speeds)
-followed by three sequences in each of four pacing conditions
-15, 25, 35, 45 seconds
-first of the three sequences in each condition was practice
-4 second pause between successive responses
day 2:
-same conditions but in a reverse order from the first day
-first of the three-sequences in each condition was for practice again
instructions
- movements as accurately as possible
- keep movement duration within + or – 10% of the intended time
- keep durations constant whether the feedback light stayed on/off
results
- small SD of movement times
- indicates consistent movement durations
- mean movement times slower than indicated on fastest pace but relatively close to intended on others
- reliable differences in feedback conditions at .25 and .35 movement but not at others
- fastest movement pace
- no difference in misses between lights on/off
- no visual feedback processing
hypothesis
1st hypothesis:
-speed-accuracy tradeoff in absence of visual feedback is that at slower speeds movement correction is made on kinesthetic spatial info. Found evidence kinesthetic reaction time as short as 11-13 sec
-if corrections made on bases of kinesthetic feedback, movements of too short duration for visual control could still be under kinesthetic control
2nd hypothesis:
-speed-accuracy tradeoff in light off conditions
-actual motor commands issued to muscles are compared to intended motor commands and adjustments are made
-researchers concluded that rapid movements in absence of vision are not under kinesthetic control
-evidence for motor programs in limited duration movements
what was the activity
- target shooting with gun (video game)
- different trials changing the target life span
open and closed loop
- open loop is the control system that has no feedback effects on the system
- closed loop is the control system that has feedback effects on the system
ex) throwing a dart
what is visual processing time
the time needed to identify and correct an error in terms of feedback
summary
- visual feedback processing occurs between 190msec and 260 msec
- so for fast movements creates evidence for motor programs
- open loop system
- visual feedback can affect the spatial accuracy of movements with durations less than 190mec
- with absence of direct visual input
- accurate representation of the environment is contained for 2 seconds after visual occlusion
application
ballistic movements:
boxing, tennis serves, throwing dart, reaching
-rehab for brain injury
-reaching/grasping tasks with injury is open loop
-after injury closed loop to relearn movements
other researchers found what
- motor program theory: feedback does not influence the execution and control of limited duration movements
- found that visual feedback can affect the spatial accuracy of movements with durations much less than 190 msec
- visual feedback can aid motor control via processes not associated with intermittent error corrections
- they support Keele &posners theory: when the movement time is fast enough, the visual feedback will not have an affect on the motor system
- found Keele and posner overestimated the visual feedback processing time
reason: - uncertainty & uncertainty of visual feedback for the subjects which increases reaction time
what did schenk and hesse find
- with absence of direct visual input
- accurate visual representation of the environment is contained for 2 seconds after visual occlusion
- it supports the point of Zelanznik’s. when the subjects are uncertain of the condition, the movement is less accurate
when movement is faster, you have less
proprioceptive info
what is more specific the slower the movement is
motor commands
change in keele and posner
Visual time in keele and posner was probably over estimated
-biggest change: they knew what was going to come: blocked: they knew random: they did not know
