Featured Research

from universities, journals, and other organizations

The world is full of darkness, reflected in the physiology of the human retina

Date:
October 5, 2010
Source:
University of Pennsylvania
Summary:
Physicists and neuroscientists have linked the cell structure of the retina to the light and dark contrasts of the natural world, demonstrating the likelihood that the neural pathways humans use for seeing are adapted to best capture the world around us.

Dandelions rectified into bright/dark contrasts. More intense pixels correspond to stronger contrasts.
Credit: Univ. of Pennsylvania

Physicists and neuroscientists from the University of Pennsylvania have linked the cell structure of the retina to the light and dark contrasts of the natural world, demonstrating the likelihood that the neural pathways humans use for seeing are adapted to best capture the world around us.

Researchers found that retinal ganglion cells that see darkness are more numerous and cluster closer together than those that see light, corresponding to the fact that the natural world contains more dark spots than light. Now physicists, and not just pessimists, see the world for the dark place it is.

The results suggest that the brain's separation of retinal circuitry into off and on mosaics that separately process dark and bright spots allows for structural adaptation to the natural scenes humans must see.

The team took the study a step further by constructing artificial images that matched the characteristics of the natural world and by testing what sorts of off and on mosaics best represented information from these images. According to the authors, the total flow of information peaked for mosaics with more densely clustered off cells, as in the human retina, suggesting that human vision has evolved to efficiently represent visual information in the natural world.

Researchers looked at the physiology of the retinal ganglion cells whose job it is to respond to a dark spot on a brighter background, simply called off cells, wondering why the brain would have clusters of off cells and not an even distribution across the retina. In addition to being more numerous and branching together in dense, bushy clusters, they also have smaller dendritic fields than the cells responsible for seeing light spots. By branching together more densely in clusters, they collect more synapses per visual angle. Thus, researchers concluded that the retina devotes more resources to processing dark contrasts, a natural capability reflected in the fact that there is more dark information in the world around us.

Researchers tested the hypothesis by measuring the spatial contrasts in natural images and quantifying the distribution of lightness and darkness. At all scales, the authors found that natural images contain relatively more dark contrasts than light.

"Photoreceptors respond to light," Vijay Balasubramanian, professor of physics and the study's lead author, said. "But a couple of layers deeper down in the retina, cells are responding to changes and differences in the amount of light across the image. The eye is not a digital camera, recording little pixels. The eye doesn't do that. The eye tells the brain that there are differences in light between neighboring points. The brain learns about contrast. And in this case, there is about twice as much brain activity responding to darker spots."

The team confirmed this across a range of spatial scales and traced the origin of this phenomenon to the statistical structure of natural scenes. Researchers showed that the optimal mosaics for encoding natural images are also asymmetric, with off elements smaller and more numerous, thus matching retinal structure. Finally, the concentration of synapses within a dendritic field matches the information content, suggesting a simple principle to connect a concrete fact of neuroanatomy with the abstract concept of "information": equal synapses for equal bits.

Researchers were interested in how the visual system is adapted to the physical structure of the world, an assumption that makes sense from an evolutionary standpoint. The physics of the natural world should correspond to the processing capabilities of the brain and there are many observable incidences of this phenomenon in the human and animal world. For example, frogs eat flies. That fact predicted that frog's eye contains "fly detectors." Flies, in turn, track potential mates in mid-air, predicting specialized neural fly circuits that detect other flies.

This study demonstrates the opposite case. Here, a particular feature of the human neural circuitry predicted a surprising property of the visual environment.

The study was conducted by Balasubramanian of the Department of Physics and Astronomy at Penn and the Department of Neuroscience at the University of Pennsylvania School of Medicine, Charles Ratliff of the Department of Physics and Astronomy at Penn and Bart Borghuis, YenHong Kao and Peter Sterling of the Department of Neuroscience at Penn Med.

The study, published in the Proceedings of the National Academy of Sciences, was supported by the National Institutes of Health and the National Science Foundation.


Story Source:

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


Cite This Page:

University of Pennsylvania. "The world is full of darkness, reflected in the physiology of the human retina." ScienceDaily. ScienceDaily, 5 October 2010. <www.sciencedaily.com/releases/2010/10/101005121818.htm>.
University of Pennsylvania. (2010, October 5). The world is full of darkness, reflected in the physiology of the human retina. ScienceDaily. Retrieved October 2, 2014 from www.sciencedaily.com/releases/2010/10/101005121818.htm
University of Pennsylvania. "The world is full of darkness, reflected in the physiology of the human retina." ScienceDaily. www.sciencedaily.com/releases/2010/10/101005121818.htm (accessed October 2, 2014).

Share This



More Matter & Energy News

Thursday, October 2, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Japan Looks To Faster Future As Bullet Train Turns 50

Japan Looks To Faster Future As Bullet Train Turns 50

Newsy (Oct. 1, 2014) Japan's bullet train turns 50 Wednesday. Here's a look at how it's changed over half a century — and the changes it's inspired globally. Video provided by Newsy
Powered by NewsLook.com
US Police Put Body Cameras to the Test

US Police Put Body Cameras to the Test

AFP (Oct. 1, 2014) Police body cameras are gradually being rolled out across the US, with interest surging after the fatal police shooting in August of an unarmed black teenager. Duration: 02:18 Video provided by AFP
Powered by NewsLook.com
Raw: Japan Celebrates 'bullet Train' Anniversary

Raw: Japan Celebrates 'bullet Train' Anniversary

AP (Oct. 1, 2014) A ceremony marking 50 years since Japan launched its Shinkansen bullet train was held on Wednesday in Tokyo. The latest model can travel from Tokyo to Osaka, a distance of 319 miles, in two hours and 25 minutes. (Oct. 1) Video provided by AP
Powered by NewsLook.com
Robotic Hair Restoration

Robotic Hair Restoration

Ivanhoe (Oct. 1, 2014) A new robotic procedure is changing the way we transplant hair. The ARTAS robot leaves no linear scarring and provides more natural results. Video provided by Ivanhoe
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


Space & Time

Matter & Energy

Computers & Math

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