5. Vision for Action copy.docx

CRITICAL READING: CORNELL NOTES Vision for Action Name: Date: 8 August 2023 Section: Lecture 5 Period: Questions/Main Ideas/Vocabulary Notes/Answers/Definitions/Examples/Sentences Why do we Move Our Eyes? The distribution of spatial resolution across the retina isn’t uniform. Two C...

CRITICAL READING: CORNELL NOTES Vision for Action Name: Date: 8 August 2023 Section: Lecture 5 Period: Questions/Main Ideas/Vocabulary Notes/Answers/Definitions/Examples/Sentences Why do we Move Our Eyes? The distribution of spatial resolution across the retina isn’t uniform. Two Common Eye Movements Saccades: Made 3-5 times a second. ~150-200ms for initiation. Rapid acceleration to new location (20 – 20ms). Some visual processing is suppressed during the execution of the saccade movement. Allow us to foveate (fixate) points of interest (~100-150ms). Smooth pursuit eye movements: Allow us to track an item of interest (often seen with a saccade). Constant velocity once at same speed as target. Yarbus (1967) Scene shown to participants (the visitor). Free viewing. Estimate economic level of the people. Judge their ages. Guess what they had been doing before the visitor’s arrival. Remember the clothes worn by the people. Eye movements (saccades) aren’t random: Top-down influence on saccades. Eye movement strategies differed depending on the question. Reasons to Move the Eyes Limited spatial resolution in the periphery. Shifting the eyes shifts the fovea: a way to gather higher resolution information about the environment. Avoid adaptation effects. Gather information about a scene. Preparing us for action. Goal-Directed Movements Made to interact with our environment. Goal often visually defined. Outcome often important. Using Vision for Action Visual information (target location, speed) is used to plan and guide hand movements. The planning phase. The guidance phase. Visual information (target location, speed) is also used to plan and guide eye movements. To Make a Goal-Directed Hand Movement Localise a target in space. Formulate a plan to move the hand. Execute the hand movement. The Planning Phase Reaches are planned in eye-centred coordinates. Visual information about a target is received by the eye. But reaching out towards a target requires a motor movement of the arm. Evidence that eye and hand movements are planned with respect to a common framework. The Guidance Phase Observers are comparing their visible hand trajectory to an invisible planned trajectory. Corollary discharge: proprioceptive feedback from our muscles. Factors Limiting Performance Biomechanical costs: Fatigue, energy expenditure. Visual error: Low light, compromised stereo. Motor error: Fitts’s law. Fitts’s Law Simple, repetitive tasks. Speed accuracy trade off: The faster the movement, the less accurate the response will be. Hols across different testing contexts, tasks and situations. With some limitations like old age. Precision is Limited by Visual & Motor Error Motor error was once thought to dominate the precision of rapid pointing movements, but the quality of the visual information also contributes significantly. Goal-Directed Movements Rapid: Initial visual information significant in determining pointing performance. Little time for online correction. Slow, guided movements: A lot of time for online correction. Online Control of Movement Our movements aren’t ballistic. Online control is the alteration of the motor plan on the basis of a discrepancy between predicted and real feedback (guidance phase). ~110 – 150ms needed to update a slow, reaching movement online. Correcting rapid pointing takes ~150ms. Posterior Parietal Cortex Plays a Role in Online Correction TMS applied over the PPC reduces our ability to make online correction to reaching movements. “Look Ahead” Saccades Used to Plan a Sequence of Slow, Guided Movements Eye and hand movements are usually spatially correlated. Eye and hand movements are also usually temporally correlated but depends on task demands. During rapid pointing: Eye typically leads the hand. Distance between first saccade and hand ~1.5°. Eye & Hand Movements Often yoked but not always. It’s possible to complete tasks without looking. Direction of gaze can have a significant impact on pointing performance. Speaks to the shared framework used to plan and execute eye and hand movements. How do we Select a New Target? Superior colliculus is part of circuits for visual processing and deployments of saccades. Decreased ability to select a target of the superior colliculus is inactivated. Some shared mechanisms for deploying attention and making an eye movement. How Might it Fit All Together?