eye movements

oculomotor musculature

six muscles that are attached to each eye, arranged in three pairs

superior and inferior rectus

control vertical orientation of the eye

lateral and medial rectus

control horizontal orientation of he eye

superior and inferior obliques

control torsion of the eye

lateral intraparietal aera (lip)

in the parietal cortex

frontal eye fields (fef)

in the frontal cortex

superior colliculus (sc)

in the midbrain

involuntary eye movements

fixational eye movements, optokinetic nystagmus (okn), vestibulo-ocular reflex (vor)

voluntary eye movements

vergence, smooth pursuit, saccades

fixational eye movements

tremor, drift, microsaccades

tremor

noisy oscillating movement with frequency of about 90 Hz an amplitude about the diameter of a cone

drift

slow motions of the eye that occur between microsaccades; seem to be important for reducing information redundancy in retinal image

microsaccades

fast, jerky eye movements tat carry the retinal image over a range of many (dozens to hundreds of) photoreceptor widths; critical for forestalling troxler fading

optokinetic nystagmus

movement triggered by tracking of a moving field (i.e., as opposed to tracking a single target)

nystagmus

a jerky-looking oscillatory movement of the eyes

vestibulo-ocular reflex

maintain vergence and line of sight when head is moved during fixation or smooth pursuit; works as a reflex that depends, in part, on input from the vestibular system, necessary for stabilizing vision during body movements s

vergence

eye movements meant to bring a common point into fixation (‘focus’) in both eyes

convergent

eye movements turn the eyes inward

divergent

eye movements turn the eyes outward

smooth pursuit

movements are voluntary eye movement in which the eyes move smoothy to follow a moving object; useful for tracking objects and for discriminating or identifying physical details of moving objects

saccades

type of eye movement that can be made voluntarily or elicited involuntarily, in which the eyes rapidly change fixation from one object or location to another

efference copy

or corollary discharge signal; when an eye movement is issued, the motor command is copied and sent to other areas of the sensory cortices

afferent

signals sent from peripheral nervous system (pns) and/or sensory receptors to central nervous system (cns)

efferent

signals sent from cns (usually but not always, to pns)

comparator

an area of the visual system that receives one copy of the order issued by the motor system when the eyes move (the other copy goes to the eye muscles) can compensate for the image changes caused by the eye movement

saccadic suppression

the reduction of visual sensitivity that occurs when we make saccadic eye movements; eliminates smear from retinal image motion during eye movement

dynamic remapping of receptive fields

a saccade is planned but not yet executed, some neurons in lip remap their receptive fields relative to the upcoming fixation location- saccade is executed, receptive fields are already processing info from new location before eye lands there