Featured Research

from universities, journals, and other organizations

Eye Movement: Involuntary Maybe, But Certainly Not Random

Date:
February 16, 2009
Source:
Salk Institute
Summary:
Our eyes are in constant motion. Even when we attempt to stare straight at a stationary target, our eyes jump and jiggle imperceptibly. Although these unconscious flicks, also known as microsaccades, had long been considered mere "motor noise," researchers found that they are instead actively controlled by the same brain region that instructs our eyes to scan the lines in a newspaper or follow a moving object.

Your eyes on the move: When you stare at the central black dot for about a minute and then look at the white dot next to it, you will notice a dark afterimage of the white grid, which -- as a result of your own fixational eye movements -- keeps moving around. The existence of such involuntary eye movements has been known for several decades, but how the brain generates them has remained a scientific mystery.
Credit: Reproduced, with permission, from: F. J. Verheijen, A simple after image method demonstrating the involuntary multidirectional eye movements during fixation, J. Modern Optics, 1961, Taylor & Francis Group. Image courtesy of Salk Institute

Our eyes are in constant motion. Even when we attempt to stare straight at a stationary target, our eyes jump and jiggle imperceptibly. Although these unconscious flicks, also known as microsaccades, had long been considered mere "motor noise," researchers at the Salk Institute for Biological Studies found that they are instead actively controlled by the same brain region that instructs our eyes to scan the lines in a newspaper or follow a moving object.

Related Articles


Their findings, published in the Feb. 13, 2009 issue of Science, provide new insights into the importance of these movements in generating normal vision.

"For several decades, scientists have debated the function, if any, of these fixational eye movements," says Richard Krauzlis, Ph.D., an associate professor in the Salk Institute's Systems Neurobiology Laboratory, who led the current study. "Our results show that the neural circuit for generating microsaccades is essentially the same as that for voluntary eye movements. This implies that they are caused by the minute fluctuations in how the brain represents where you want to look."

"There was a lot of past effort to figure out what fixational eye movements contribute to our vision," adds lead author Ziad Hafed, Ph.D., Sloan-Swartz Fellow in the Systems Neurobiology Laboratory, "but nobody had looked at the neural mechanism that generates these movements. Without such knowledge, one could only go so far in evaluating microsaccades' significance and why they actually exist."

Wondering whether the command center responsible for generating fixational eye movements resides within the same brain structure that is in charge of initiating and directing large voluntary eye movements, Hafed decided to measure neural activity in the superior colliculus before and during microsaccades.

He not only discovered that the superior colliculus is an integral part of the neural mechanism that controls microsaccades, but he also found that individual neurons in the superior colliculus are highly specific about which particular microsaccade directions and amplitudes they command—whether they be, say, rightward or downward or even oblique movements. "Data from the population of neurons we analyzed shows that the superior colliculus contains a remarkably precise representation of amplitude and direction down to the tiniest of eye movements," says Krauzlis.

The Salk researchers, in collaboration with Laurent Goffart, Ph.D., a professor at the Institut de Neurosciences Cognitives de la Mιditerranιe in Marseille, France, also temporarily inactivated a subset of superior colliculus neurons and analyzed the resulting changes in microsaccades. They discovered that a fully functional superior colliculus is required to generate normal microsaccades.

"Because images on the retina fade from view if they are perfectly stabilized, the active generation of fixational eye movements by the central nervous system allows these movements to constantly shift the scene ever so slightly, thus refreshing the images on our retina and preventing us from going 'blind,'" explains Hafed. "When images begin to fade, the uncertainty about where to look increases the fluctuations in superior colliculus activity, triggering a microsaccade," adds Krauzlis.

Microsaccades may, however, do more than prevent the world around us from fading when we stare at it for too long. Even when our gaze is fixed, our attention can shift to an object at the periphery that attracts our interest. In an earlier study, Hafed discovered that although we may avert our eyes from an attractive man or woman, microsaccades will reveal such objects of attraction because their direction is biased toward objects to which we are unconsciously attracted.

By showing in the current study that the superior colliculus is involved in generating microsaccades, Hafed and his colleagues could now explain why this happens. "The superior colliculus is a major determinant of what is behaviorally relevant in our visual environment, so paying attention to one location or the other alters superior colliculus activity and therefore alters these eye movements as well," says Hafed.


Story Source:

The above story is based on materials provided by Salk Institute. Note: Materials may be edited for content and length.


Cite This Page:

Salk Institute. "Eye Movement: Involuntary Maybe, But Certainly Not Random." ScienceDaily. ScienceDaily, 16 February 2009. <www.sciencedaily.com/releases/2009/02/090212141156.htm>.
Salk Institute. (2009, February 16). Eye Movement: Involuntary Maybe, But Certainly Not Random. ScienceDaily. Retrieved December 20, 2014 from www.sciencedaily.com/releases/2009/02/090212141156.htm
Salk Institute. "Eye Movement: Involuntary Maybe, But Certainly Not Random." ScienceDaily. www.sciencedaily.com/releases/2009/02/090212141156.htm (accessed December 20, 2014).

Share This


More From ScienceDaily



More Health & Medicine News

Saturday, December 20, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

The Best Tips to Curb Holiday Carbs

The Best Tips to Curb Holiday Carbs

Buzz60 (Dec. 19, 2014) — It's hard to resist those delicious but fattening carbs we all crave during the winter months, but there are some ways to stay satisfied without consuming the extra calories. Vanessa Freeman (@VanessaFreeTV) has the details. Video provided by Buzz60
Powered by NewsLook.com
Sierra Leone Bikers Spread the Message to Fight Ebola

Sierra Leone Bikers Spread the Message to Fight Ebola

AFP (Dec. 19, 2014) — More than 100 motorcyclists hit the road to spread awareness messages about Ebola. Nearly 7,000 people have now died from the virus, almost all of them in west Africa, according to the World Health Organization. Video provided by AFP
Powered by NewsLook.com
Researchers Test Colombian Village With High Alzheimer's Rates

Researchers Test Colombian Village With High Alzheimer's Rates

AFP (Dec. 19, 2014) — In Yarumal, a village in N. Colombia, Alzheimer's has ravaged a disproportionately large number of families. A genetic "curse" that may pave the way for research on how to treat the disease that claims a new victim every four seconds. Duration: 02:42 Video provided by AFP
Powered by NewsLook.com
Double-Amputee Becomes First To Move Two Prosthetic Arms With His Mind

Double-Amputee Becomes First To Move Two Prosthetic Arms With His Mind

Buzz60 (Dec. 19, 2014) — A double-amputee makes history by becoming the first person to wear and operate two prosthetic arms using only his mind. Jen Markham has the story. Video provided by Buzz60
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Health & Medicine

Mind & Brain

Living & Well

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins