Researchers are creating a single mathematical
model that unites years of biological experiments and explains how the brain
produces elaborate visual reproductions of the world based on scant visual
information. They have been building their model by incorporating one basic
element of vision at a time. They’ve explained how neurons in the visual cortex
interact to detect the edges of objects and changes in contrast, and now
they’re working on explaining how the brain perceives the direction in which
objects are moving. In lab experiments, researchers present primates with
simple visual stimuli — black-and-white patterns that vary in terms of contrast
or the direction in which they enter the primates’ visual fields. Using
electrodes hooked to the primates’ visual cortices, the researchers track the
nerve pulses produced in response to the stimuli. A good model should replicate
the same kinds of pulses when presented with the same stimuli.
Currently they are working on adding
directional sensitivity into their model — which would explain how the visual
cortex reconstructs the direction in which objects are moving across your
visual field. After that, they’ll start trying to explain how the visual cortex
recognizes temporal patterns in visual stimuli. They hope to decipher, for
example, why we can perceive the flashes in a blinking traffic light, but we
don’t see the frame-by-frame action in a movie. At that point, they’ll have a
simple model for activity in just one of the six layers in the visual cortex —
the layer where the brain roughs out the basic outlines of visual impression.
Their work doesn’t address the remaining five layers, where more sophisticated
visual processing goes on. It also doesn’t say anything about how the visual
cortex distinguishes colors, which occurs through an entirely different and
more difficult neural pathway. While their model is far from uncovering the
full mystery of vision, it is a step in the right direction.
More information: