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Describe your results in the ball-catching lab. Describe the relation between the first and second labs. The second lab demonstrated (a) that the feedback delay can be 200 msec or more and (b) when intercepting a rapidly moving object, this delay is too
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Describe your results in the ball-catching lab. Describe the relation between the first and second labs. The second lab demonstrated (a) that the feedback delay can be 200 msec or more and (b) when intercepting a rapidly moving object, this delay is too great for accurate targeting. Therefore the subject must learn to predict where the target will be. That is, the subject must switch from a feedback mode to a feedforward mode. In the first lab, we see evidence of prediction (feedforward) when the eye saccades to the bounce point ahead of the ball. If the eye had followed the ball (using feedback) it would take too long to relocate it after the bounce.
How does the speed of a movement (e.g. reaching) affect its accuracy? Explain why. Role of Visual Feedback Question: why does error increase with speed? Note: 50 cm/sec = 5cm/100msec
Describe the effect on reaching movements of large-fiber sensory neuropathy (degeneration of the afferent fibers from the muscles and skin) when visual feedback is eliminated? Sketch the movements to illustrate your answer.
Consequences of loss of feedback on reaching Large fibre sensory neuropathy leads to loss of proprioceptive feedback from muscles Loss of vision leads to moderate errors. Errors in direction,distance Normal: proprioception only No vision or proprioception Vision compensates for lack of proprioception Loss of proprioception and vision causes large errors. Vision of hand at start can reduce the size of the errors. Vision alone can almost completely compensate for loss of proprioception.
How can examples from robotics help us understand the human visuo-motor system? Give examples from videos. Robotics helps understand what theoretical problems need to be solved, and the consequences of particular solutions to those problems. Eg flipping an egg: Grasping: need location information. How is it found? How is grasp formed? Passive compliance helps solves the problem. Seems likely humans solve it that way too. Move to pan. Need to know where pan is. How is this found? Note that telling the program the location is not a good general solution because someone might move the pan. Etc Could solve this problem using visual feedback, but feedback is slow, as shown when Pook guided the robot arm with her own arm. Feedback delays made it very inefficient.
What is measured by the standard deviation and the standard error of the mean. How are they related? The standard deviation is a measure of the spread or variability in a population or set of measurements. The standard error of the mean is a measure of the variability of the mean of a set of measurements. The standard error of the mean is equal to the standard deviation divided by the square root of N, where N is the number of measurements in the sample.
Describe the visual capabilities of Mike May after his sight was restored. What are the implications of this?
Describe the visual capabilities of Mike May after his sight was restored. What are the implications of this? Lost vision at age 3 - scarred corneas. Restored at age 40; Poor acuity. Answer to Molyneux’s question: Mike May couldn’t tell difference between sphere and cube. Improved, but does it logically rather than perceptually. (cf other cases) Color and motion sensitivity good. Cannot recognize faces. (eyes, movement of mouth distracting) Can’t perceive distance very well. Can’t recognize perspective. No size constancy or lightness constancy/ segmentation of scene into objects, shadows difficult. Vision most useful for catching balls (inconsistent with Held & Hein??) and finding things if he drops them. Note: fMRI shows no activity in Infero-temporal cortex (corresponding to pattern recognition) but there is activity in MT, MST (motion areas) and V4 (color). Other parts of brain take over when a cortical area is inactive.
MT/MST (motion) V4 (color) Infero-temporal cortex
Implications? Basic object perception (recognition and segmentation) requires experience. (Experience prior to 3 yrs not enough.) Geometric cues about scene structure (perspective, distance) also require experience. Color and motion more robust - either present at birth, or acquired before 3yrs, and preserved without continued experience.
Describe sequence of eye movements in an everyday task. Give reasons. Making breakfast: Upon entering the kitchen: saccade to the cupboard on the basis of memory, as I know cereal is located there. Approach cupboard and saccade to door handle to guide hand to open door. Search for cereal with several saccades, maybe landing on boxes of similar size and appearance. When saccade lands on the correct box, stay fixating to guide the grasp of the box. Rotate body and head to exit the cupboard and make a big saccade to the cupboard containing the bowls. Fixate the cupboard while I walk there and make a fixation to the handle to guide opening….
Goal of Lab 3: Can we demonstrate adaptation to new sensory-motor relationships? How fast is the adaptation? Are some relationships easier to learn than others?
Method Virtual environment: head mounted display with virtual racquetball. PhaseSpace monitors hand and head position. Auditory cue when S hits ball. Environment obeys normal dynamics. (ie laws of physics/ bounces etc) Visual scene translated by 0.5 m or compressed (90 deg field compressed into 50 deg) Task: Procedure: 20 baseline, 40 trials in altered environment, 20 recovery trials. Data recorded: XYZ position of hand and ball every 17 msec. Also whether S hit the ball or not.
Results How do we measure adaptation? Successful versus unsuccessful hit Trajectories: X vs Y relative to ball. Plot performance as proportion correct every 5 trials. Plot baseline, adaptation, and recovery. How complete is the adaptation? (compare last adaptation trial with baseline) Is there any after effect? (compare recovery trials with baseline) How does trajectory change with practice? Do trajectories get closer to baseline? Is there a difference between translation and compression? Why?
Discussion Review findings. Evaluate extent of adaptation. Was plasticity demonstrated? Are subjects really learning a new set of relationships of just learning to ignore the visual feedback? How could we distinguish these possibilities?
Neural basis of adaptation? Possible sites: Posterior parietal cortex (AIP, MIP), supplementary motor area, pre-motor, motor cortex, cerebellum, basal ganglia …
Why do we need to retain plasticity for new visuo-motor relationships? 1. Need to adjust to changes in body size during development. 2. Need to adjust to damage/aging. 3. Need to adjust to environmental changes eg ice, loads etc. 4. Need to learn arbitrary mappings for tool use etc. 5. Need to acquire new motor skills. 6. Visuo-motor coordination is a computationally difficult problem for the brain. Need flexibility to correct errors.
Role of Experience in Development of Visuo-motor coordination Held & Hein 1 2 Both kittens get visual experience and motor experience Visual experience correlated with motor commands/proprioceptive feedback/vision of limbs Gets both, but uncorrelated. Kitten 2 -abnormal visuo-motor coordination.
Adaptation to different relation between vision and movement. • George Stratton • Wore inverting lens for 8 days If he saw an object on the right he would reach with his right hand and discover he should have reached with his left. He could not feed himself very well, could not tie his shoelaces, and found himself severely disoriented. His image of his own body became severely distorted. At times he felt his head had sunk down between his shoulders,and when he moved his eyes and head the world slid dizzyingly around. As time went by Stratton achieved more effective control of his body. If he saw an object on the right he would reach with his left hand. He could accomplish normal tasks like eating and dressing himself. His body image became almost normal and when he moved his eyes and head the world did not move around so much. He began to feel as though his left hand was on the right, and his right hand on the left. If this new location of his body was vivid, the world appeared right side up, but sometimes he felt his body was upside down in a visually right-side-up world. After removing the prisms, he initially made incorrect reaching movements. However, he soon regained normal control of his body.
Adaptation to different relation between vision and movement. George Stratton • Wore inverting lens for 8 days • Believed that we learn visual directions by associating visual experiences with other forms of sensory feedback (e.g. proprioceptive). • Alternatively… Adaptation results from learning correlation betweeen vision and actively generated motor commands (Held, 1965).
Function of Different Areas monitor/plan movements target selection saccade decision saccade command inhibits SC signals to muscles
Schematic Representation of Feedback and Feed-forward Systems Eg: pursuit, reaching, grasping Eye velocity=image velocity Motor command sensory retinal velocity delay Eg: saccade, throwing Load/fatigue/current position wind ballistic Learnt motor command guided
Flipping an Egg Autonomous control: robot is pre-programmed - no human input Problems to be solved: 1. Grasp spatula locate handle (vision) some mechanism to translate location into arm movement some mechanism for controlling fingers - “passive compliance” 2. Move to pan locate pan (vision) translate location into arm movement 3. Lower spatula to pan vision or proprioception: lower until force > 0 4. Flatten proprioception: rotate until forces on fingers are equal 5. Locate egg vision or proprioception: move forwards until horizontal force > 0
Describe 2 functions of eye movements and give an example of each. Types of Eye Movement Information GatheringStabilizing Voluntary (attention) Reflexive Saccades vestibular ocular reflex (vor) new location, high velocity, ballistic body movements Smooth pursuit optokinetic nystagmus (okn) object moves, velocity, slow whole field image motion Vergence change point of fixation in depth slow, disjunctive (eyes rotate in opposite directions) (all others are conjunctive) Fixation: period when eye is relatively stationary between saccades.
Draw a sketch of the brain showing the structures involved in the generation of a saccadic eye movement. Specify the function of these structures (to the extent that this is possible)
Flipping an Egg (ctd) Problems to be solved: 6. Lift need to keep spatula level: vision or proprioception (keep tension constant) 7. Flip need to learn how much to rotate hand: rotate until forces = 0 Limitations of autonomous control: inflexible - can’t adapt to changed circumstances requires high precision
Mike May - world speed record for downhill skiing by a blind person. Lost vision at age 3 - scarred corneas. Optically 20/20 - functionally 20/500 (cf amblyopia) Answer to Molyneux’s question: Mike May couldn’t tell difference between sphere and cube. Improved, but does it logically rather than perceptually. (cf other cases) Color: an orange thing on a basket ball court must be a ball. Motion: can detect moving objects, distinguish different speeds. Note: fMRI shows no activity in Infero-temporal cortex (corresponding to pattern recognition) but there is activity in MT, MST (motion areas) and V4 (color). Other parts of brain take over when a cortical area is inactive. Cannot recognize faces. (eyes, movement of mouth distracting) Can’t perceive distance very well. Can’t recognize perspective. No size constancy or lightness constancy/ segmentation of scene into objects, shadows difficult. Vision most useful for catching balls (inconsistent with Held & Hein??) and finding things if he drops them.