L5 - Active Vision Flashcards
What proportion of the cortex is devoted to visual processing?
Approximately one third
What is the dominant sensory modality in humans?
Vision
How are goals ‘visually defined’?
We have a goal, and we use cues from vision to determine if we are accomplishing the goal
(e.g. I want to type something and I see visually if I have typed the correct thing)
What are the 3 steps we do to make a ‘goal-directed hand movement’?
- Localize a target in space
- Formulate a plan to move the hand
- Execute the hand movement=
The control of hand movements can be broken down conceptually into two components.
What are those components?
- The planning phase
- The guidance phase
What does the planning phase involve?
Thinking about what you intend to do.
What does the guidance phase involve?
Observing your visible movements to your invisible planned trajectory.
What are the features of rapid goal-directed movements?
Initial visual information significant in determining pointing performance
Little time for online correction
What are the features of slow, guided goal-directed movements?
What is an example of this?
A lot of time for online correction
Precise movements
e.g. surgery, knitting
What is corollary discharge?
What is this helpful for?
A copy of a motor command that is sent to the muscles to produce movement.
This is directed to other regions of the brain to inform them of impending movement.
Helpful for depth perception, signals from muscles where the location of your eye is
Explain this model of the guidance phase of goal-directed movement.
The top is what you would like to do.
The bottom is your actual movement - predicted then with real time sensory feedback - then gives you your error - then with a correction so that you can obtain the goal.
It is a loop as you go through this
What are the 4 limiting factors for performance?
Biomechanical costs
Risk - outcomes and losses
Visual error
Motor error (e.g. Fitts’ Law)
What does ‘biomechanical cost’ refer to?
Energy expenditure and also bodily damage (e.g. cutting yourself)
(e.g. eye movement very little energy to move, however, moving body has high energy expenditure)
What does risk - outcomes and losses refer to as a limiting factor for performance?
The utility function of movements, the modelling of our expected performance used in movement control and decision making.
Hand movements are responsive to the risk function of tasks, meaning we take into the account the risk factor (biomechanical cost) before engaging in movement.
What does visual error refer to as a limiting factor for performance?
How good the visual information is about where the target is.
What is Fitts’ Law?
There is a speed-accuracy tradeoff in human performance
The faster the movement, the less accurate the response will be
What was Fitts’ pin transfer task?
Used repetitive simple tasks (moving pins from one place to another)
Varied amplitude and information content of the tasks
Measured time to complete and error
What was Fitts’ pin transfer task trying to determine?
If information content had any part to play in performance
If there was 1 piece of information or 10 pieces to choose from, would this impact the time needed
What were the results of the Fitts’ pin transfer task?
He found a lawful relationship existed between how much information is available and how fast we are able to complete the task
Fitts’ law can be used to estimate….
Motor Error
What is motor error?
How accurately and quickly you can perform a task involving movement.
Hand precision and visual precision must be nearly identical in tasks where movements are…
slowly and continuously guided
e.g. surgery, painting, embroidery etc.
Noise can limit precision.
What types of ‘noise’ limits precision?
Biological noise
Processing noise
Motor error comes about because of what two factors?
The precision of rapid pointing movements (motor error)
Quality of the visual information
What is the ideal way to minimise visual error?
Try to keep targets stationary and large in your vision
to increase the quality of visual information
What is meant by the online control of movement?
Online control is the alteration of the motor plan on the basis of a discrepancy between predicted and real feedback.
If there is a discrepancy between where you think your target will be and where it appears you will need to update your plan.
How long does it take to update a slow, reaching movements (over 1.5seconds) online?
110-150ms
How long does it take to update a rapid pointing movements (300-400ms) online?
roughly 150ms
What is meant by ballistic?
When you don’t bother with feedback and just deploy the information.
Are movements ballistic?
No, we use visual information throughout the movement to update performance
What are Saccades?
Rapid eye movements you make with your eyes to fixate different locations
Are Saccades ballistic?
No, evidence suggests you can update your trajectory for them.
What is this model?
Simplified hybrid circuit using a forward model of arm dynamics.
In which pathways do you make the correction in movements?
Dorsal Action Stream
and
Ventral Perception Stream
What evidence shows that the two visual streams of processing (dorsal and ventral) play a role in online correction?
Applying TMS (Transcranial Magnetic Stimulation) to the posterior parietal cortex interferes with these regions and people can’t make a correction.
Therefore correction is in part in the posterior parietal lobes
What can understanding perception and online correction help with in the world?
Creating virtual reality displays for prosthetics and for fun (VR/AR)
Helping kids with developmental coordination disorder (DCD)
Helping understand people with parietal damage and how to help them
What does developmental coordination disorder entail?
Why might this be happening?
Children being clumsy, deficits in visual to motor mapping may contribute.
Parietal cortex might be compromised.
How does parietal damage usually happen?
Stroke
What symptoms can occur following parietal damage?
Visual neglect
Where they ignore half of space, making it hard to do functional activities
