Navigation Links
Rutgers-Camden researcher examines how the brain perceives shades of gray

CAMDEN How the brain perceives color is one of its more impressive tricks. It is able to keep a stable perception of an object's color as lighting conditions change.

Sarah Allred, an assistant professor of psychology at RutgersCamden, has teamed up with psychologists from the University of Pennsylvania on groundbreaking research that provides new insight into how this works.

Allred conducted the research with Alan L. Gilchrist, a professor of psychology at RutgersNewark, and professor David H. Brainard and post-doctoral fellow Ana Radonjic, both of the University of Pennsylvania. Their research will be published in the journal Current Biology.

"Although we recognize easily the colors of objects in many different environments, this is a difficult problem for the brain," Allred says. "For example, consider just the gray scale that goes from black to white. A white piece of paper in bright sunlight reflects thousands of times more light to the eye than a white piece of paper indoors, but both pieces of paper look white. How does the brain do this?"

The process of seeing an object begins when light reflected off that object hits the light-sensitive structures in the eye. The perception of an object's lightness (in terms of color shade) depends on the object's reflectance. Objects that appear lighter reflect a larger percentage of light than those that appear darker.

Allred says the brain processes perceptual differences between black and white objects even when illumination of the object changes. If the brain did not do this, it would fail to distinguish color shade in different light.

In general, white objects reflect about 90 percent of the light that hits them, and black objects reflect about three percent, a ratio of 30-to-1, she explains.

"However, if you look at the intensities of light that enter the eye from a typical scene, like a field of lilies, that ratio is much higher, usually somewhere between 10,000-to-1 and a million-to-1," Allred says.

This happens because in addition to having objects with different reflectance, real "scenes" also have different levels of illumination. One example might be a shadowed area under a tree. Allred and her research colleagues wanted to determine how the brain maps a large range of light intensity onto a much smaller reflectance range.

One long-time hypothesis is that the brain segments scenes into different regions of illumination and then uses ratio coding to decide what looks white.

To test if this hypothesis was true, the researchers conducted an experiment where participants viewed images that had a very large range of light intensities. Participants were asked to look at a 5x5 checkerboard composed of grayscale squares with random intensities spanning the 10,000-to-1 range. They were asked to report what shades of gray a target square looked like by selecting a match from a standardized gray scale.

If the visual system relied only on ratios to determine surface lightness, then the ratio of checkerboard intensities the participants reported should have had the same ratio as that of the black and white samples on the reflectance scale, about 100-to-1.

Instead, the researchers found that this ratio could be as much as 50 times higher, more than 5,000-to-1.

"This research is important because we have falsified the ratio hypothesis, which is currently the most widely invoked explanation of how we perceive lightness," Allred says. "We also were able to reject several similar models of lightness. We were able to do this because we measured lightness in such high-range and relatively complex images."

She continues, "In addition, even though we used behavioral rather than physiological measures, our results provide insight into the neural mechanisms that must underlie the behavioral results."

A Philadelphia resident, Allred received her undergraduate degree from Brigham Young University and her graduate degree from the University of Washington. She is also conducting research on color memory and perception through a five-year grant from the National Science Foundation.


Contact: Ed Moorhouse
Rutgers University

Related biology news :

1. Rutgers-Camden professor engineers E. coli to produce biodiesel
2. NSF grant supports Rutgers-Camden program for science majors
3. Rutgers-Camden developing enzyme function database
4. Evolution and climate change research advances at Rutgers-Camden
5. USC researchers discover key aspect of process that activates breast cancer genes
6. Researchers confirm new cancer-causing virus
7. Researchers get $7.5M grant to combat nerve agents
8. Researchers uncover why the body cant defend against tuberculosis
9. Results triple researchers projections with use of adult stem cells for heart failure
10. Researchers develop more effective way to discover and test potential cancer drugs
11. Researchers closer to the super bug puzzle
Post Your Comments:
(Date:10/29/2015)... RESTON, Va. , Oct. 29, 2015 ... announced today that it has released a new version ... Daon customers in North America ... gains. IdentityX v4.0 also includes a FIDO UAF ... customers are already preparing to activate FIDO features. These ...
(Date:10/29/2015)... 29, 2015 Today, LifeBEAM , ... with 2XU, a global leader in technical performance ... hat with advanced bio-sensing technology. The hat will ... monitor key biometrics to improve overall training performance. ... two companies will bring together the most advanced technology, ...
(Date:10/26/2015)... , October 26, 2015 /PRNewswire/ ... --> adds Biometrics ... to 2021 as well as Emerging ... research reports to its collection of ... . --> ...
Breaking Biology News(10 mins):
(Date:11/24/2015)... ... ... The Academy of Model Aeronautics (AMA), led by its Executive Council, has ... Prix, to represent the First–Person View (FPV) racing community. , FPV racing has exploded ... of racing and several new model aviation pilots have joined the community because of ...
(Date:11/24/2015)... , November 24, 2015 ... market research report released by Transparency Market Research, the ... at a CAGR of 17.5% during the period between ... Market - Global Industry Analysis, Size, Volume, Share, Growth, ... non-invasive prenatal testing market to reach a valuation of ...
(Date:11/24/2015)... CITY , Nov. 24, 2015 /PRNewswire/ - ... "Company") announced today that the remaining 11,000 post-share ... Share Purchase Warrants (the "Series B Warrants") subject ... were exercised on November 23, 2015, which will ... Shares.  After giving effect to the issuance of ...
(Date:11/24/2015)... Urdorf, Switzerland (PRWEB) , ... November 24, 2015 ... ... the plant and the environment are paramount. Insertion points for in-line sensors can ... TOLEDO has developed the InTrac 781/784 series of retractable sensor housings , ...
Breaking Biology Technology: