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
