Shape encoding may start in the retina

Sep 12, 2007

New evidence from the University of Southern California suggests that there may be dedicated cells in the retina that help compile small bits of information in order to recognize objects. The research was conducted by Ernest Greene, professor of psychology in the area of brain and cognitive sciences at USC. The study is published in the Public Library of Science journal, PLoS ONE.

It is well established that the images the observer sees are divided in half as they are sent to the two hemispheres of the brain. When a person looks at the center of an object, the image from the right half of the object will be sent to one hemisphere of the brain and the image of the left half is sent to the other. This is true whether a person uses one eye or two to look at the object. “Given that the primary visual areas in each hemisphere are seeing only half of the object, it has been assumed that communication between the hemispheres was needed to combine the information,” said Greene.

By using a high-speed LED array to display the images, Greene found evidence that the two sides of the retina interact to enhance the effectiveness of shape cues, which he describes as “linkage.” The cells in the retina appear to be coordinating their responses in a way that benefits shape recognition. Further, they do so with unexpected temporal precision.

The study was done by positioning dots around the outer boundaries of objects, forming stimuli similar to silhouettes. The dots were shown, in successive pairs, one pair after the other, and the observers were then asked to identify each shape. Recognition was best if time intervals that separated pairs and pair members were in the submillisecond range. This was true whether both members of the pair were displayed on the same side of the object or on opposite sides. “This finding suggests that the responses from the two sides of the retina are being linked in some manner, and the process of joining the two halves of an object is not done only in the brain,” says Greene.

“It is unlikely that the nerve signal being sent from the eye to the brain can be precise enough to preserve submillisecond timing differences,” says Greene. Also, for the brain to coordinate nerve signals being sent from opposite sides of the retina, communication between the two hemispheres would be needed. “It strains credulity that these additional processing steps could be accomplished while preserving submillisecond precision in the responses to pair members,” Greene says. He thinks it is more likely that cell structures in the retina link the responses prior to sending the information to the visual cortex. The retina itself may be assessing global relationships among boundary locations, these operations being required for recognition of the shape.

Source: Public Library of Science

Explore further: First vital step in fertilization between sperm and egg discovered

add to favorites email to friend print save as pdf

Related Stories

Terminator-style info-vision takes step towards reality

Nov 21, 2011

The streaming of real-time information across your field of vision is a step closer to reality with the development of a prototype contact lens that could potentially provide the wearer with hands-free information ...

'Bionic eye' implant offers hope to the blind

Apr 03, 2011

For a man whose view of the world has slowly faded to black over 30 years, a device that allows him to see flashes of light has enkindled his hope of one day gazing upon his grandson's face.

Artificial retina helps some blind people

Feb 14, 2011

For two decades, Eric Selby had been completely blind and dependent on a guide dog to get around. But after having an artificial retina put into his right eye, he can detect ordinary things like the curb and ...

Setting his sights on a cure

Jan 11, 2011

For poets and lovers, the eyes are windows to the soul. But for researchers like Dr. Henry Klassen, they provide unparalleled access to the central nervous system.

Brain's visual circuits do error correction on the fly

Dec 07, 2010

(PhysOrg.com) -- The brain's visual neurons continually develop predictions of what they will perceive and then correct erroneous assumptions as they take in additional external information, according to new ...

Recommended for you

Researchers transplant regenerated oesophagus

Apr 15, 2014

Tissue engineering has been used to construct natural oesophagi, which in combination with bone marrow stem cells have been safely and effectively transplanted in rats. The study, published in Nature Communications, shows ...

User comments : 0

More news stories

HIV+ women respond well to HPV vaccine

HIV-positive women respond well to a vaccine against the human papillomavirus (HPV), even when their immune system is struggling, according to newly published results of an international clinical trial. The study's findings ...

Revealing camouflaged bacteria

A research team at the Biozentrum of the University of Basel has discovered an protein family that plays a central role in the fight against the bacterial pathogen Salmonella within the cells. The so cal ...