Physiology and Psychophysics of Eye Movements

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Physiology and Psychophysics of Eye Movements

• 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

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Extraocular Muscles three complimentary pair
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Measuring Eye Movements/Position
Scleral search coil
Infrared Eye Tracking
magnetic field (2 axes)
scleral coil
Temporal resolution analog Spatial resolution
lt0.1 deg.
Temporal resolution video frame rate, lt500
Hz Spatial resolution lt0.25 deg.
older methods electro-oculogram (EOG), coil
contacts, suction caps of Yarbus
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Adapted from Yarbus (1967)
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Classes of Eye Movements

• Vestibulo-Ocular (VOR)
• Hold images of the seen world steady on the
  retina during brief head
• movements (angular or translational).
• -very short latency (lt15 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.

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Combinations of eye movement types.
Optokinetic Nystagmus (OKN) Slow
phase-optokinetic Quick phase-saccadic
Saccades and pursuit Pursuit pre- and
post- saccadic
Left eye
Saccades and vergence Vergence with a saccade is
much faster
Right eye
Vergence Angle
Without saccade
With saccade
time
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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
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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)
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abducens, trochlear, om nucleus
cerebellum, brainstem
pprf, mrf
dorsal raphe
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Major Pathways for Saccadic Eye Movements in the
Monkey
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Tuning of SC burst neuron to direction and
amplitude of saccades
Sparks and Mays, 1980
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Movement field of Superior Colliculus neuron
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Map of Stimulation Evoked Saccades
Rostral Caudal
amplitude
elevation
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Enhancement of Superior Colliculus Visual
Responses and the Need to Dissociate Behavioral
Components
Passive fixation
Saccade to RF target
Saccade to Control target
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Major Connections of the Superior Colliculus
SC
Retina
Superficial Layers
Intermediate and Deep Layers
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Tasks used to characterize saccade-related
activity
1. step task (simultaneous, overlap, gap)
fixation point
saccade target
eye position (h)
time
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Tasks used to characterize saccade-related
activity
2. visually-guided, delayed saccade task
fixation point
saccade target
eye position (h)
time
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Tasks used to characterize saccade-related
activity
3. memory-guided, delayed saccade task
fixation point
saccade target
eye position (h)
time
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Tasks used to characterize saccade-related
activity
4. anti-saccade task
fixation point
saccade target
eye position (h)
time
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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 Deep Layers
Visual Receptive Fields and Presaccadic Bursts
before saccades to movement field visuomotor
cells, visually-triggered motor cells
No visual RFs, just movement fields, Presaccadic
burst gets earlier as you go deeper
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Major Pathways for Saccadic Eye Movements in the
Monkey
(SEF)
Lateral Intraparietal Area (LIP)
(FEF)
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Continuum of Visual and Motor Responses in the FEF
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Microstimulation of the Frontal Eye Field
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Functional Organization of Macaque FEF
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Stimulation-Evoked Smooth Pursuit Movements
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Stimulation-Evoked Vergence Movements
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Cortical Connections of the FEF organized and
reciprocal connections with dorsal and
ventral visual pathways
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Major Pathways for Saccadic Eye Movements in the
Monkey
(SEF)
Lateral Intraparietal Area (LIP)
(FEF)
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Lateral Intraparietal Area (LIP) visual,
saccade-related and mnemonic responses
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Incidence of light-sensitive,
saccade-coincident and memory activity in LIP
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Microstimulation of Parietal Cortex fixed and
modified vector saccades