why do we move our eyes? - image stabilization - information acquisition
TRANSCRIPT
Why do we move our eyes?
- Image stabilization
- Information acquisition
Visual Acuity matches photoreceptor density
Why do we move our eyes?
1. To bring objects of interest onto high acuity region in fovea.
Why do we move our eyes?
1. To bring objects of interest onto high acuity region in fovea.
2. Cortical magnification suggests enhanced processing of image in the central visual field.
Muscles that Move the Eye
Why eye movements are hard to measure.
18mm
0.3mm = 1 deg visual angle
x a
tan(a/2) = x/da = 2 tan
-1 x/d
Visual Angle
d
1 diopter = 1/focal length in meters
55 diopters = 1/.018
A small eye rotation translates into a big change in visual angle
Types of Eye Movement
Information Gathering StabilizingVoluntary (attention) Reflexive
Saccades vestibular ocular reflex (vor)new location, high velocity (700 deg/sec), body movements
ballistic(?)Smooth pursuit optokinetic nystagmus (okn)object moves, velocity, slow(ish) whole field image motion
Vergencechange point of fixation in depthslow, disjunctive (eyes rotate in opposite directions)(all others are conjunctive)
Fixation: period when eye is relatively stationary between saccades.
Demonstration of “miniature” eye movements
It is almost impossible to hold the eyes still.
DriftMicro-saccadesMicro-nystagmus
“main sequence”: duration = c Amplitude + bMin saccade duration approx 25 msec, max approx 200msec
What’s involved in making a saccadic eye movement?
Behavioral goal: make a sandwich
Sub-goal: get peanut butter
Visual search for pb: requires memory for eg color of pb or location
Visual search provides saccade goal - attend to target location
Plan saccade to location (sensory-motor transformation)
Coordinate with hands/head
Calculate velocity/position signal
Execute saccade/
Brain Circuitry for Saccades
Oculomotor nuclei
V1: striate cortex
Basal ganglia
1. Neural activity related to saccade
2. Microstimulation generates saccade
3. Lesions impair saccade
Dorso-lateral pre-frontal
target selection
signals to muscles(forces)
inhibits SC
saccade decision
saccade command(where to go)
monitor/plan movements
Function of Different Areas
H
V
LIP: Lateral Intra-parietal AreaTarget selection for saccades: cells fire before saccade to
attended object
Posterior Parietal Cortex
reaching
grasping
Intra-Parietal Sulcus: areaof multi-sensory convergence
Frontal eye fields
Voluntary controlof saccades.Selection from multiple targetsRelates to behavioral goals.
-Saccades/Smooth Pursuit
-Planning/ Error Checking
-relates to behavioral goals
Supplementary eye fields
Brain areas involved in making a saccadic eye movement
Behavioral goal: make a sandwich (learn how to make sandwiches) Frontal cortex.
Sub-goal: get peanut butter (secondary reward signal - dopamine - basal ganglia)
Visual search for pb: requires memory for eg color of pb or location (memory for visual properties - Inferotemporal cortex; activation of color - V1, V4)
Visual search provides saccade goal. LIP - target selection, also FEF
Plan saccade - FEF, SEF
Coordinate with hands/head
Execute saccade/ control time of execution: basal ganglia (substantia nigra pars reticulata, caudate)
Calculate velocity/position signal oculomotor nuclei
Cerebellum?
Superior colliculus
Smooth pursuit& Supplementary
Brain Circuitry for Pursuit
Velocity signal
Early motion analysis