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

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)

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.

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

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

Sparks and Mays, 1980

Tuning of SC burst neuron to direction and amplitude of saccades

‘Movement field’ of Superior Colliculus neuron

Map of Stimulation Evoked Saccades

amplitude

elevation

Rostral

Caudal

Enhancement of Superior Colliculus Visual Responses and the Need to Dissociate Behavioral Components

Passive fixation

Saccade toRF target

Saccade toControl target

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

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

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

Major Pathways for Saccadic Eye Movements in the Monkey

(FEF)

(SEF)

Lateral Intraparietal Area (LIP)

Continuum of Visual and Motor Responses in the FEF

Microstimulation of the Frontal Eye Field

Arcuate

ant. post.

Functional Organization of Macaque FEF

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

(FEF)

(SEF)

Lateral Intraparietal Area (LIP)

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