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Physiology and Psychophysics of Eye Movements
1. Muscles and (cranial) nerves
2. Classes of eye movements/oculomotor behaviors
3. Saccadic Eye Movements, metrics and factoids
4. Brainstem control of saccadic eye movements
5. Superior Colliculus and cortical control of saccades
6. Saccades and Visual Perception
Extraocular Muscles: three complimentary pair
Measuring Eye Movements/Position
Scleral search coil
Infrared Eye Tracking
magnetic field
(2 axes)
scleral
coil
Temporal resolution: analog
Spatial resolution: <0.1 deg.
Temporal resolution: video frame rate, <500 Hz
Spatial resolution: <0.25 deg.
older methods: electro-oculogram (EOG), coil contacts, suction caps of Yarbus
Adapted from Yarbus (1967)
Classes of Eye Movements
1.
Vestibulo-Ocular (VOR):
Hold images of the seen world steady on the retina during brief head
movements (angular or translational).
-very short latency (<15 ms) because signal is from inner ear.
2. Visual Fixation:
Holds image of a stationary image on the fovea
3. Optokinetic:
Hold images of the seen world steady on the retina during prolonged head
movements.
4. Smooth pursuit:
Holds the image of a small (moving) target on the fovea.
-cannot move gaze smoothly without stimulus
5. Vergence:
Moves the eyes in opposite directions so that images of a single object are
placed or held simultaneously on both foveas.
-2 signals: disparity, accommodative
6. Saccadic Eye Movements:
Bring objects of interest onto fovea
Combinations of eye movement types.
Optokinetic
Nystagmus (OKN):
Slow phase-optokinetic
Quick phase-saccadic
Saccades and pursuit:
Pursuit pre- and postsaccadic
Saccades and vergence:
Vergence with a saccade is
much faster
Left eye
Right eye
Vergence
Angle
Without
saccade
time
With
saccade
Saccadic Eye Movements
(‘saccades’)
Subtypes often referred to:
1. Volitional (‘purposive’)
-predictive, anticipatory
-memory-guided
-antisaccades
2. Reflexive
3. Express saccades
4. Spontaneous
5. Quick phase of nystagmus
Velocity, Duration and the ‘Main Sequence’
Visually Guided Saccades
Deviations from main sequence:
-saccades in complete darkness
-saccades to auditory stimuli
-saccades to remembered targets
-saccades made in the opposite
direction (antisaccades)
[abducens, trochlear, om nucleus]
[cerebellum, brainstem]
[pprf, mrf]
[dorsal raphe]
Major Pathways for Saccadic Eye Movements in the Monkey
Tuning of SC burst neuron to direction and amplitude of saccades
Sparks and Mays, 1980
‘Movement field’ of Superior Colliculus neuron
Map of Stimulation Evoked Saccades
Rostral
Caudal
amplitude
elevation
Enhancement of Superior Colliculus Visual Responses
and the Need to Dissociate Behavioral Components
Passive
fixation
Saccade to
RF target
Saccade to
Control target
Major Connections of the Superior Colliculus
Striate cortex (V1)
Extrastriate cortex
(e.g. V4, MT)
Parietal cortex (e.g. LIP)
SC
Retina
Superficial Layers
Intermediate and
Deep Layers
Frontal Eye Field
Dorsal lateral geniculate
nucleus (dLGN)
Inferior Pulvinar
Brainstem Saccade
generator
Medio-dorsal thalamus
Tasks used to characterize saccade-related activity
1. step task (simultaneous, overlap, gap)
fixation point
saccade target
eye position (h)
time
Tasks used to characterize saccade-related activity
2. visually-guided, delayed saccade task
fixation point
saccade target
eye position (h)
time
Tasks used to characterize saccade-related activity
3. memory-guided, delayed saccade task
fixation point
saccade target
eye position (h)
time
Tasks used to characterize saccade-related activity
4. anti-saccade task
fixation point
saccade target
eye position (h)
time
Visual and Motor Related Properties of Cells in
the Superior Colliculus
SC
Superficial Layers:
Visual Receptive Fields,
Some enhanced Visual Responses, but
no Presaccadic (motor) bursts; ‘visual’
cells
Intermediate:
Visual Receptive Fields and Presaccadic
Bursts before saccades to ‘movement field’;
‘visuomotor cells’, ‘visually-triggered motor
cells’
Deep Layers
No visual RFs, just movement fields,
Presaccadic burst gets earlier as you go
deeper
Major Pathways for Saccadic Eye Movements in the Monkey
(SEF)
Lateral Intraparietal
Area (LIP)
(FEF)
Continuum of Visual and Motor Responses in the FEF
Microstimulation of the Frontal Eye Field
Functional Organization of Macaque FEF
Arcuate
ant.
post.
Stimulation-Evoked Smooth Pursuit Movements
Stimulation-Evoked Vergence Movements
Cortical Connections of the FEF: organized and reciprocal connections
with ‘dorsal’ and ‘ventral’ visual pathways
Major Pathways for Saccadic Eye Movements in the Monkey
(SEF)
Lateral Intraparietal
Area (LIP)
(FEF)
Lateral Intraparietal Area (LIP): visual, saccade-related
and mnemonic responses
Incidence of ‘light-sensitive’, ‘saccade-coincident’
and ‘memory’ activity in LIP
Microstimulation of Parietal Cortex: fixed and ‘modified’
vector saccades