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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
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Extraocular Muscles: three complimentary pair
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Measuring Eye Movements/Position
Scleral search coil
older methods: electro-oculogram (EOG), coil contacts, suction caps of Yarbus
Infrared Eye Tracking
Temporal resolution: analogSpatial resolution: <0.1 deg.
Temporal resolution: video frame rate, <500 HzSpatial resolution: <0.25 deg.
scleral coil
magnetic field(2 axes)
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Adapted from Yarbus (1967)
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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
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Combinations of eye movement types.
OptokineticNystagmus (OKN):Slow phase-optokineticQuick phase-saccadic
time
Saccades and pursuit:Pursuit pre- and post-saccadic
Withoutsaccade
Withsaccade
Left eye
VergenceAngle
Right eye
Saccades and vergence:Vergence with a saccade is much faster
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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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Sparks and Mays, 1980
Tuning of SC burst neuron to direction and amplitude of saccades
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‘Movement field’ of Superior Colliculus neuron
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Map of Stimulation Evoked Saccades
amplitude
elevation
Rostral
Caudal
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Enhancement of Superior Colliculus Visual Responses and the Need to Dissociate Behavioral Components
Passive fixation
Saccade toRF target
Saccade toControl target
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Superficial Layers
Intermediate andDeep Layers
Retina
Major Connections of the Superior Colliculus
Striate cortex (V1) Extrastriate cortex (e.g. V4, MT)
Parietal cortex (e.g. LIP)
Frontal Eye Field
Inferior PulvinarBrainstem Saccade generator
Dorsal lateral geniculate nucleus (dLGN)
Medio-dorsal thalamus
SC
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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
Superficial Layers:
Intermediate:
Deep Layers
SC
Visual Receptive Fields,Some enhanced Visual Responses, butno Presaccadic (motor) bursts; ‘visual’cells
Visual Receptive Fields and PresaccadicBursts 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
(FEF)
(SEF)
Lateral Intraparietal Area (LIP)
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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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Arcuate
ant. post.
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
(FEF)
(SEF)
Lateral Intraparietal Area (LIP)
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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