Microsaccade
Encyclopedia
Microsaccades are a kind of fixational eye movement. They are small, jerk-like, involuntary eye movements, similar to miniature versions of voluntary saccade
s. They typically occur during prolonged visual fixation
(of at least several seconds), not only in humans, but also in animals with fovea
l vision (primates, cats, etc.). Microsaccade amplitudes vary from 2 to 120 arcminutes. The first empirical evidence for their existence was provided by Robert Darwin
, the father of Charles Darwin
.
has been a highly debated topic which is still largely unresolved. It has been proposed that microsaccades correct displacements in eye position produced by drifts, although non-corrective microsaccades also occur. Microsaccades were also believed to prevent the retina
l image from fading, but they do not occur often enough for that purpose, considering that perfectly stabilized images
can disappear from perception in a few seconds or less. The current consensus is that all fixational eye movements are important for the maintenance of visibility.
Experiments in neurophysiology
from different laboratories showed that fixational eye movements, particularly microsaccades, strongly modulate the activity of neurons in the visual areas of the macaque
brain. In the lateral geniculate nucleus
(LGN) and the primary visual cortex (V1), microsaccades can move a
stationary stimulus in and out of a neuron's receptive field
, thereby producing transient neural responses. Microsaccades might account for much of the response variability of neurons in visual area V1 of the awake monkey.
Current research in visual neuroscience
and psychophysics
is investigating how microsaccades relate to fixation correction, control of binocular fixation disparity
and attention
al shifts. Recent research has found a direct correlation between illusory motion
and microsaccades.
Saccade
A saccade is a fast movement of an eye, head or other part of an animal's body or device. It can also be a fast shift in frequency of an emitted signal or other quick change. Saccades are quick, simultaneous movements of both eyes in the same direction...
s. They typically occur during prolonged visual fixation
Fixation (visual)
Fixation or visual fixation is the maintaining of the visual gaze on a single location. Humans typically alternate saccades and visual fixations, the notable exception being in smooth pursuit, controlled by a different neural substrate that appear to have developed for hunting prey...
(of at least several seconds), not only in humans, but also in animals with fovea
Fovea
The fovea centralis, also generally known as the fovea , is a part of the eye, located in the center of the macula region of the retina....
l vision (primates, cats, etc.). Microsaccade amplitudes vary from 2 to 120 arcminutes. The first empirical evidence for their existence was provided by Robert Darwin
Robert Darwin
Dr Robert Waring Darwin, F.R.S. was an English medical doctor, who today is best known as the father of the naturalist Charles Darwin. He was a member of the influential Darwin-Wedgwood family.-Biography:...
, the father of Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
.
Function
The role of microsaccades in visual perceptionVisual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
has been a highly debated topic which is still largely unresolved. It has been proposed that microsaccades correct displacements in eye position produced by drifts, although non-corrective microsaccades also occur. Microsaccades were also believed to prevent the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
l image from fading, but they do not occur often enough for that purpose, considering that perfectly stabilized images
Stabilized images
Stabilized Images are images on the retina that are unaffected by microsaccade or ocular microtremor . Experiments by Riggs and Ratliff ) established the remarkable finding that stabilized images result in the fading and disappearance of the visual percept...
can disappear from perception in a few seconds or less. The current consensus is that all fixational eye movements are important for the maintenance of visibility.
Experiments in neurophysiology
Neurophysiology
Neurophysiology is a part of physiology. Neurophysiology is the study of nervous system function...
from different laboratories showed that fixational eye movements, particularly microsaccades, strongly modulate the activity of neurons in the visual areas of the macaque
Macaque
The macaques constitute a genus of Old World monkeys of the subfamily Cercopithecinae. - Description :Aside from humans , the macaques are the most widespread primate genus, ranging from Japan to Afghanistan and, in the case of the barbary macaque, to North Africa...
brain. In the lateral geniculate nucleus
Lateral geniculate nucleus
The lateral geniculate nucleus is the primary relay center for visual information received from the retina of the eye. The LGN is found inside the thalamus of the brain....
(LGN) and the primary visual cortex (V1), microsaccades can move a
stationary stimulus in and out of a neuron's receptive field
Receptive field
The receptive field of a sensory neuron is a region of space in which the presence of a stimulus will alter the firing of that neuron. Receptive fields have been identified for neurons of the auditory system, the somatosensory system, and the visual system....
, thereby producing transient neural responses. Microsaccades might account for much of the response variability of neurons in visual area V1 of the awake monkey.
Current research in visual neuroscience
Neuroscience
Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...
and psychophysics
Psychophysics
Psychophysics quantitatively investigates the relationship between physical stimuli and the sensations and perceptions they effect. Psychophysics has been described as "the scientific study of the relation between stimulus and sensation" or, more completely, as "the analysis of perceptual...
is investigating how microsaccades relate to fixation correction, control of binocular fixation disparity
Fixation disparity
Fixation disparity exists when there is a small misalignment of the eyes when viewing with binocular vision. The misaligment may be vertical, horizontal or both. The misalignment is much smaller than that of strabismus, which prevents binocular vision, although it may reduce a patient's level of...
and attention
Attention
Attention is the cognitive process of paying attention to one aspect of the environment while ignoring others. Attention is one of the most intensely studied topics within psychology and cognitive neuroscience....
al shifts. Recent research has found a direct correlation between illusory motion
Illusory motion
The term illusory motion, also known as motion illusion, is used to define the appearance of movement in a static image.This is an optical illusion in which a static image appears to be moving due to the cognitive effects of interacting color contrasts and shape position.Another type of motion...
and microsaccades.