Competing Goals for Visual System Design Maximize spatial resolution Maximize field of view Minimize neural resources

1. Competing Goals for Visual System Design Maximize spatial resolution Maximize field of view Minimize neural resources

2. Solution High resolution foveal vision Low resolution peripheral vision Eye movement system

4. Why study eye movements • Where we look determines what we see • Tightly linked to perception and cognition • Relatively simple and well characterized • Amenable to precise, quantitative study • One of the best understood systems in terms of anatomy, physiology and computations • Sensory-motor integration

5. Types of Eye Movements • •Saccadic Movements: • –Scanning movements where the gaze is abruptly shifted from one point to the next: conjugate, ballistic, no visual feedback • •Vergence Movements: • –Cooperative movements that keep both eyes fixed on the target; converge or diverge • •Pursuit movements: • –Smooth tracking movements that keep an object’s image fixed in place on the retina • •Vestibulo-Ocular Reflex (VOR) • –Stabilize image during head and body movements • •Micro movements • –Tremor, drift, microsaccades

6. Properties of saccades • •Average 3-4 saccades/sec (>100,000/day) • •Average 5-7 deg • •Max ~40 deg (from center) • •Stereotyped (ballistic) • •Peak velocity Up to 900 deg/sec • •Variable reaction time

7. Saccade control