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, and will be available online from
September
12 at plosone/doi/pone.0000871.
The new research made use of well-established facts about how images that
the observer sees are sent to the two hemispheres of the brain.
Specifically, it is known that if a person looks at the center of an
object, the image from the right half of the object will be sent to the
left
hemisphere of the brain and the image of the left half is sent to the
right hemisphere. 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 has 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 may be combining information to aid in 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 that were
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.
Citation: Greene E (2007) Retinal Encoding of Ultrabrief Shape Recognition
Cues. PLoS ONE 2(9): e871. doi:10.1371/journal.pone.0000871
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