Microsaccade

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Microsaccades are a kind of fixational eye movement. They are small, jerk-like, involuntary eye movements, similar to miniature versions of voluntary saccades. They typically occur during prolonged visual fixation (of at least several seconds), not only in humans, but also in animals with foveal vision (primates, cats, dogs 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. [1] [2]

Contents

Function

The role of microsaccades in visual perception has been a highly debated topic that is still largely unresolved. It has been proposed[ by whom? ] that microsaccades correct displacements in eye position produced by drifts, although non-corrective microsaccades also occur. Some work has suggested that microsaccades are directly correlated with the perception of illusory motion. [3] [4] [5] Although microsaccades can enhance vision of fine spatial detail, [6] [7] they can also impair visual perception in that they are associated with saccadic suppression. [8] Microsaccades are also believed to be important for preventing the retinal image from fading. [9]

Microsaccades are tied to complex visual processing like reading. The specific timing pattern of microsaccades in humans changes during reading based on the structure of the word being read. [10] [11]

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. [12] [13] 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, memory, [14] control of binocular fixation disparity [15] and attentional shifts. [16]

Visual Impact of microsaccades

Microsaccades play a crucial role in the perception of objects. Researchers discovered that these motions improve our ability to catch minute details in a scene. Microsaccades help gain focus from Troxler fading. [17] Swiss philosopher Troxler had fixated images which tend to fade away during normal vision in 1804. Troxler effect is the fixating one's gaze in the visual field. A static field that would slowly fade into a blur. Microssacades are significant since it prevents image blur. [18] The brain activity stimulated by microsaccades across the visual system can aid in determining the neural coding of visibility because microsaccades are essential for preserving visibility during fixation. The neuronal reactions to alterations in visual inputs brought on by microsaccadic retinal displacements are known as visual responses to microsaccades.

Mechanisms

Microsaccades are generated through neural activity in the brain regions responsible for eye movement control. The superior colliculus plays an important role in initiating microsaccades. [19] Neural circuits within the superior colliculus integrate sensory inputs and motor commands, resulting in the precise, coordinated movements of microsaccades. [20]

This process involves excitatory and inhibitory interactions between neurons in different layers of the superior colliculus. Inputs from cortical areas such as the frontal eye fields and parietal cortex modulate these interactions, influencing microsaccade frequency and direction. [21] Experiments in primates have shown that electrically stimulating specific regions of the superior colliculus can evoke microsaccade-like movements, highlighting its role in their generation. [22]

In addition to the superior colliculus, subcortical structures like the basal ganglia may regulate the initiation or suppression of microsaccades. The basal ganglia's influence on fixation and spontaneous eye movements patterns suggest a contribution to attention shifts and stabilization during visual fixation. [23]

Microsaccades in disorders

Microsaccades in neurological disorders

Microsaccades are disrupted in various neurological disorders, including ADHD, schizophrenia, and Parkinson's disease, resulting in gaze instability during fixation. In ADHD, individuals show increased microsaccade rates and unstable gaze, which may improve with medication. In schizophrenia, microsaccades reveal similar total eye movement counts to healthy controls despite differences in large saccades. Parkinson's disease is associated with larger, more frequent, and slower microsaccades. [24]

Microsaccades in ophthalmologic disorders

Microsaccades are disrupted in several ophthalmologic disorders, including amblyopia, strabismus, myopia, and macular disease, reflecting the impact of visual impairment on eye movement control. In amblyopia, monocular fixation with the amblyopic eye leads to increased drift and frequent saccadic intrusions, especially in cases involving strabismus. Myopia is associated with larger microsaccades as uncorrected refractive error worsens, linking blurred vision to fixational instability. Along with this, macular disease results in increased drift and larger microsaccadic amplitudes, which correlate with visual acuity loss and serve as signs of fixation instability. [24]

See also

Related Research Articles

<span class="mw-page-title-main">Saccade</span> Eye movement

A saccade is a quick, simultaneous movement of both eyes between two or more phases of focal points in the same direction. In contrast, in smooth-pursuit movements, the eyes move smoothly instead of in jumps; it could be associated with a shift in frequency of an emitted signal or a movement of a body part or device. Controlled cortically by the frontal eye fields (FEF), or subcortically by the superior colliculus, saccades serve as a mechanism for focal points, rapid eye movement, and the fast phase of optokinetic nystagmus. The word appears to have been coined in the 1880s by French ophthalmologist Émile Javal, who used a mirror on one side of a page to observe eye movement in silent reading, and found that it involves a succession of discontinuous individual movements.

Saccadic masking, also known as (visual) saccadic suppression, is the phenomenon in visual perception where the brain selectively blocks visual processing during eye movements in such a way that neither the motion of the eye nor the gap in visual perception is noticeable to the viewer.

<span class="mw-page-title-main">Superior colliculus</span> Structure in the midbrain

In neuroanatomy, the superior colliculus is a structure lying on the roof of the mammalian midbrain. In non-mammalian vertebrates, the homologous structure is known as the optic tectum or optic lobe. The adjective form tectal is commonly used for both structures.

<span class="mw-page-title-main">Ocular tremor</span>

Ocular tremor is a constant, involuntary eye tremor of a low amplitude and high frequency. It is a type of fixational eye movement that occurs in all normal people, even when the eye appears still. The frequency of ocular microtremor has been found to range from 30 Hz to 103 Hz, and the amplitude is approximately four thousandths of a degree.

<span class="mw-page-title-main">Eye movement</span> Movement of the eyes

Eye movement includes the voluntary or involuntary movement of the eyes. Eye movements are used by a number of organisms to fixate, inspect and track visual objects of interests. A special type of eye movement, rapid eye movement, occurs during REM sleep.

The pars reticulata (SNpr) is a portion of the substantia nigra and is located lateral to the pars compacta. Most of the neurons that project out of the pars reticulata are inhibitory GABAergic neurons.

<span class="mw-page-title-main">Troxler's fading</span> Optical illusion affecting visual perception

Troxler's fading, also called Troxler fading or the Troxler effect, is an optical illusion affecting visual perception. When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and disappear. Research suggests that at least some portion of the perceptual phenomena associated with Troxler's fading occurs in the brain.

<span class="mw-page-title-main">Smooth pursuit</span> Type of eye movement used for closely following a moving object

In the scientific study of vision, smooth pursuit describes a type of eye movement in which the eyes remain fixated on a moving object. It is one of two ways that visual animals can voluntarily shift gaze, the other being saccadic eye movements. Pursuit differs from the vestibulo-ocular reflex, which only occurs during movements of the head and serves to stabilize gaze on a stationary object. Most people are unable to initiate pursuit without a moving visual signal. The pursuit of targets moving with velocities of greater than 30°/s tends to require catch-up saccades. Smooth pursuit is asymmetric: most humans and primates tend to be better at horizontal than vertical smooth pursuit, as defined by their ability to pursue smoothly without making catch-up saccades. Most humans are also better at downward than upward pursuit. Pursuit is modified by ongoing visual feedback.

<span class="mw-page-title-main">Frontal eye fields</span> Region of the frontal cortex of the brain

The frontal eye fields (FEF) are a region located in the frontal cortex, more specifically in Brodmann area 8 or BA8, of the primate brain. In humans, it can be more accurately said to lie in a region around the intersection of the middle frontal gyrus with the precentral gyrus, consisting of a frontal and parietal portion. The FEF is responsible for saccadic eye movements for the purpose of visual field perception and awareness, as well as for voluntary eye movement. The FEF communicates with extraocular muscles indirectly via the paramedian pontine reticular formation. Destruction of the FEF causes deviation of the eyes to the ipsilateral side.

<span class="mw-page-title-main">Supplementary eye field</span> Region of the frontal cortex of the brain

Supplementary eye field (SEF) is the name for the anatomical area of the dorsal medial frontal lobe of the primate cerebral cortex that is indirectly involved in the control of saccadic eye movements. Evidence for a supplementary eye field was first shown by Schlag, and Schlag-Rey. Current research strives to explore the SEF's contribution to visual search and its role in visual salience. The SEF constitutes together with the frontal eye fields (FEF), the intraparietal sulcus (IPS), and the superior colliculus (SC) one of the most important brain areas involved in the generation and control of eye movements, particularly in the direction contralateral to their location. Its precise function is not yet fully known. Neural recordings in the SEF show signals related to both vision and saccades somewhat like the frontal eye fields and superior colliculus, but currently most investigators think that the SEF has a special role in high level aspects of saccade control, like complex spatial transformations, learned transformations, and executive cognitive functions.

Alfred Lukyanovich Yarbus was a Soviet psychologist who studied eye movements in the 1950s and 1960s.

<span class="mw-page-title-main">Fixation (visual)</span> Maintaining ones gaze on a single location

Fixation or visual fixation is the maintaining of the gaze on a single location. An animal can exhibit visual fixation if it possess a fovea in the anatomy of their eye. The fovea is typically located at the center of the retina and is the point of clearest vision. The species in which fixational eye movement has been verified thus far include humans, primates, cats, rabbits, turtles, salamanders, and owls. Regular eye movement alternates between saccades and visual fixations, the notable exception being in smooth pursuit, controlled by a different neural substrate that appears to have developed for hunting prey. The term "fixation" can either be used to refer to the point in time and space of focus or the act of fixating. Fixation, in the act of fixating, is the point between any two saccades, during which the eyes are relatively stationary and virtually all visual input occurs. In the absence of retinal jitter, a laboratory condition known as retinal stabilization, perceptions tend to rapidly pass away. To maintain visibility, the nervous system carries out a procedure called fixational eye movement, which continuously stimulates neurons in the early visual areas of the brain responding to transient stimuli. There are three categories of fixational eye movement: microsaccades, ocular drifts, and ocular microtremor. At small amplitudes the boundaries between categories become unclear, particularly between drift and tremor.

Chronostasis is a type of temporal illusion in which the first impression following the introduction of a new event or task-demand to the brain can appear to be extended in time. For example, chronostasis temporarily occurs when fixating on a target stimulus, immediately following a saccade. This elicits an overestimation in the temporal duration for which that target stimulus was perceived. This effect can extend apparent durations by up to half a second and is consistent with the idea that the visual system models events prior to perception.

Transsaccadic memory is the neural process that allows humans to perceive their surroundings as a seamless, unified image despite rapid changes in fixation points. Transsaccadic memory is a relatively new topic of interest in the field of psychology. Conflicting views and theories have spurred several types of experiments intended to explain transsaccadic memory and the neural mechanisms involved.

Michele Rucci is an Italian born neuroscientist and biomedical engineer who studies visual perception. He is a Professor of Brain and Cognitive Sciences and member of the Center for Visual Science at the University of Rochester.

Binocular switch suppression (BSS) is a technique to suppress usually salient images from an individual's awareness, a type of experimental manipulation used in visual perception and cognitive neuroscience. In BSS, two images of differing signal strengths are repetitively switched between the left and right eye at a constant rate of 1 Hertz. During this process of switching, the image of lower contrast and signal strength is perceptually suppressed for a period of time.

<span class="mw-page-title-main">Doug Crawford</span> Canadian neuroscientist

John Douglas (Doug) Crawford is a Canadian neuroscientist and the Scientific Director of the Connected Minds program. He is a professor at York University where he holds the York Research Chair in Visuomotor Neuroscience and the title of Distinguished Research Professor in Neuroscience.

<span class="mw-page-title-main">Peter Schiller (neuroscientist)</span> German-born neuroscientist (born 1931)

Peter H. Schiller was a German-born neuroscientist. At the time of his death, he was a professor emeritus of Neuroscience in the Department of Brain and Cognitive Sciences at the Massachusetts Institute of Technology (MIT). Schiller is well known for his work on the behavioral, neurophysiological and pharmacological studies of the primate visual and oculomotor systems.

Michael E. Goldberg, also known as Mickey Goldberg, is an American neuroscientist and David Mahoney Professor at Columbia University. He is known for his work on the mechanisms of the mammalian eye in relation to brain activity. He served as president of the Society for Neuroscience from 2009 to 2010.

The corollary discharge theory (CD) of motion perception helps understand how the brain can detect motion through the visual system, even though the body is not moving. When a signal is sent from the motor cortex of the brain to the eye muscles, a copy of that signal is sent through the brain as well. The brain does this in order to distinguish real movements in the visual world from our own body and eye movement. The original signal and copy signal are then believed to be compared somewhere in the brain. Such a structure has not yet been identified, but it is believed to be the Medial Superior Temporal Area (MST). The original signal and copy need to be compared in order to determine if the change in vision was caused by eye movement or movement in the world. If the two signals cancel then no motion is perceived, but if they do not cancel then the residual signal is perceived as motion in the real world. Without a corollary discharge signal, the world would seem to spin around every time the eyes moved. It is important to note that corollary discharge and efference copy are sometimes used synonymously, they were originally coined for much different applications, with corollary discharge being used in a much broader sense.

References

Notes

  1. ↑ Darwin, R. W.; Darwin, E. (1786). "New Experiments on the Ocular Spectra of Light and Colours" (PDF). Philosophical Transactions of the Royal Society of London . 76: 313–348. doi: 10.1098/rstl.1786.0016 . JSTOR   106628.
  2. ↑ Rolfs, Martin (2009). "Microsaccades: Small steps on a long way". Vision Research . 49 (20): 2415–41. doi: 10.1016/j.visres.2009.08.010 . PMID   19683016.
  3. ↑ "Optical illusions: caused by eye or brain?"
  4. ↑ 200-year-old Scientific Debate Involving Visual Illusions
  5. ↑ The truth behind 'Where's Waldo?'
  6. ↑ Rucci, M., Iovin, R., Poletti, M., Santini, F. (2007). "Miniature Eye Movements Enhance Fine Spatial Detail." Nature,447(7146), 851-854.
  7. ↑ "Eye flickers key for fine detail". BBC News. June 2007.
  8. ↑ Beeler, G. W. (1967). "Visual threshold changes resulting from spontaneous saccadic eye movements". Vision Research. 7 (9): 769–75. doi:10.1016/0042-6989(67)90039-9. PMID   5608665.
  9. ↑ Alexander, R. G.; Martinez-Conde, S (2019). "Fixational eye movements". Eye Movement Research. Springer, Cham. pp. 73–115.
  10. ↑ Yablonski, M; Polat, U; Bonneh, YS; Ben-Shachar, M (21 June 2017). "Microsaccades are sensitive to word structure: A novel approach to study language processing". Scientific Reports. 7 (1): 3999. Bibcode:2017NatSR...7.3999Y. doi:10.1038/s41598-017-04391-4. PMC   5479819 . PMID   28638094.
  11. ↑ Krauzlis, Richard J. (2013). "Eye Movements". Fundamental Neuroscience (4 ed.). Academic Press. pp. 697–714. doi:10.1016/B978-0-12-385870-2.00032-9. ISBN   9780123858702.
  12. ↑ Rucci, Michele; Edelman, Gerald M.; Wray, Jonathan (2000). "Modeling LGN responses during free-viewing: A possible role of microscopic eye movements in the refinement of cortical orientation selectivity". Journal of Neuroscience. 20 (12): 4708–4720. doi: 10.1523/JNEUROSCI.20-12-04708.2000 . PMC   6772442 . PMID   10844040.
  13. ↑ Leopold, D. A.; Logothetis, N. K. (1998). "Microsaccades differentially modulate neural activity in the striate and extrastriate visual cortex". Experimental Brain Research. 123 (3): 341–5. doi:10.1007/s002210050577. PMID   9860273. S2CID   18751039.
  14. ↑ Martinez-Conde, S; Alexander, R (2019). "A gaze bias in the mind's eye". Nature Human Behaviour. 3 (5): 424–425. doi:10.1038/s41562-019-0546-1. PMID   31089295. S2CID   71148025.
  15. ↑ Valsecchi, Matteo; Gegenfurtner, Karl R. (2015). "Control of binocular gaze in a high-precision manual task". Vision Research. 110 (Pt B): 203–214. doi: 10.1016/j.visres.2014.09.005 . PMID   25250983.
  16. ↑ Laubrock; Engbert; Kliegl (2005). "Microsaccade dynamics during covert attention". Vision Research. 45 (6): 721–730. doi: 10.1016/j.visres.2004.09.029 . PMID   15639499.
  17. ↑ Martinez-Conde, Susana (January 2013). "The impact of microsaccades on vision: Towards a unified theory of saccadic function".
  18. ↑ Thomas, G (July 2017). "Troxler Effect".
  19. ↑ Gandhi, Neeraj J.; Katnani, Husam A. (2011-07-21). "Motor Functions of the Superior Colliculus". Annual Review of Neuroscience. 34 (1): 205–231. doi:10.1146/annurev-neuro-061010-113728. ISSN   0147-006X. PMC   3641825 .
  20. ↑ Yotsumoto, Yuko; Chang, Li-hung; Watanabe, Takeo; Sasaki, Yuka (2009). "Interference and feature specificity in visual perceptual learning". Vision Research. 49 (21): 2611–2623. doi:10.1016/j.visres.2009.08.001. PMC   2764795 . PMID   19665036.
  21. ↑ Krauzlis, Richard J.; Lovejoy, Lee P.; Zénon, Alexandre (2013-07-08). "Superior colliculus and visual spatial attention". Annual Review of Neuroscience. 36: 165–182. doi:10.1146/annurev-neuro-062012-170249. ISSN   1545-4126. PMC   3820016 . PMID   23682659.
  22. ↑ Hafed, Ziad M.; Goffart, Laurent; Krauzlis, Richard J. (2008-08-06). "Superior Colliculus Inactivation Causes Stable Offsets in Eye Position during Tracking". The Journal of Neuroscience. 28 (32): 8124–8137. doi:10.1523/JNEUROSCI.1317-08.2008. ISSN   0270-6474. PMC   2553276 . PMID   18685037.
  23. ↑ Beylergil, Sinem Balta; Murray, Jordan; Noecker, Angela M.; Gupta, Palak; Kilbane, Camilla; McIntyre, Cameron C.; Ghasia, Fatema F.; Shaikh, Aasef G. (2022). "Temporal Patterns of Spontaneous Fixational Eye Movements: The Influence of Basal Ganglia". Journal of Neuro-Ophthalmology. 42 (1): 45–55. doi:10.1097/WNO.0000000000001452. ISSN   1070-8022.
  24. 1 2 Alexander, Robert; Macknik, Stephen; Martinez-Conde, Susana (2018). "Microsaccade Characteristics in Neurological and Ophthalmic Disease". Frontiers in Neurology. 9 (144): 144. doi: 10.3389/fneur.2018.00144 . PMC   5859063 . PMID   29593642.

[1]

Bibliography

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