Brain Mechanisms of Vision

Hubel DH, Wiesel TN. Brain Mechanisms of Vision. Scientific American. 1979 Sep; 241(3):150-62

Summary:

The brain's primary visual cortex processes images in a modular, distorted way. The rods and cones in the eyes send messages from the retina to the geniculate cells in the brain, which then relay the message to the visual cortex. These geniculate cells are in a layer called Layer IV, are unsophisticated, and receive the bulk of the visual input.

Cells outside of layer IV have "orientation specificity", where a bar of light falling in a certain orientation will activate some cells and have no affect on others. The response for each cell appears to be around 10-20 degrees, at which point the response is lessened or abolished.

At the time (1979), there was no evidence to support that the orientation specific cells had anything to do with visual perception.

As electric signals moved into more complex layers of the visual cortex, some patterns emerged. Cells close to one another often have the same optimal stimulus orientation. Changes in orientation happen in small increments, such as 25-50 micrometers between cell groups mapping to a change of 10 degrees with varying direction reversals.


Discussion:

Really interesting information on how the structure and hierarchy of the primary visual cortex. Although the orientation information did not prove that the brain recognizes shapes using features such as line orientations, other papers citing this one might. I'll have to find some...