Transcript lecture2-15b

Introduction to Eye Movements
Jan 27 2015
Date
Topic
Jan 20 Overview of the course: understanding human actions
Jan 22 Lecture: Eye movements: applications – review by Adam.
Jan 27 Lecture: Introduction to Eye Movements.
Lab: Calibration, and Measurement of basic types of eye movements.
Jan 29 Lab: Tracking the eyes while throwing and catching balls. Data
collection and analysis.
Feb 3 Lab: Data collection and analysis
Feb 5 Lab: Data collection and analysis
Lecture: Neural mechanisms underlying eye movements.
Feb 10 Class presentations Lab 1.
How to write a lab report.
Why do we move our eyes?
- Image stabilization
- Information acquisition
Muscles that move the eyes
Muscles innervated crania) nerves from the oculomotor nuclei in the brainstem.
Oculomotor neurons: 100-600Hz vs spinal motor neurons: 50-100Hz
The Eye and Retina
Photoreceptor density across the retina
Cone Photoreceptors are densely packed in the central fovea
Visual Acuity matches photoreceptor density
Relative visual acuity
Receptor density
Why do we move our eyes?
1. To bring objects of interest onto high acuity region in fovea.
Why eye movements are hard to measure.
A small eye rotation translates into a big change in visual angle
Visual Angle
x
18mm
a
d
tan(a/2) = x/d
a = 2 tan 1 x/d
1 diopter = 1/focal length in meters
0.3mm = 1 deg visual angle
55 diopters = 1/.018
Types of Eye Movement
Information Gathering
Voluntary (attention)
Stabilizing
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.
Different types of eye movement have different neural circuits.
https://www.youtube.com/watch?v=KSJksSA6Q-A
Acuity – babies
Rotational or translational
Acceleration
Velocity
Demonstration of VOR and its precision
It is almost impossible to hold the eyes still.
The vestibular labyrinth
Rotational (semi-circular canals) translational (otoliths)
Saccade latency approx 200 msec, pursuit approx 100 – smaller when there is a context that
allows prediction.
Primary Cortical Sub-divisions
Visual Projections
The mapping of objects in space onto the visual cortex
Brain Circuitry for Saccades
1. Neural activity
related to saccade
2. Microstimulation
generates saccade
3. Lesions impair
saccade
V1: striate cortex
Basal ganglia
Oculomotor nuclei
Function of Different Areas
monitor/plan
movements
target selection
saccade decision
inhibits SC
saccade command
signals to muscles
Posterior Parietal Cortex
reaching
Intra-Parietal Sulcus: area
of multi-sensory convergence
grasping
LIP: Lateral Intra-parietal Area
Target selection for saccades: cells fire before saccade to attended object
Brain Circuitry for Pursuit
& Supplementary
Smooth pursuit
Brain Circuitry for Pursuit
& Supplementary
Smooth pursuit
Velocity signal
Early motion analysis
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