Ring Orientation Demo

Sweeping circular ring and cortical response Orientation map
a b c d e f
g h
Key:
  1. retinal image presented to map g.
  2. initial response of the cortex to that image
  3. orientation histogram of the initial response
  4. settled response of the cortex to that image
  5. orientation histogram of the settled response
  6. key showing color assigned to each angle
  7. self-organized RF-LISSOM orientation map
  8. orientation histogram of the orientation map
The sequence repeats after the image has been scrolled across the retina. A version of this page with smaller pictures is also available.

First check out the sweeping line orientation demo, because it is easier to understand one orientation at a time. These images show the response of the same network to a circular annulus. The entire retina is shown here (a); usually the retinal area outside the white outline is ignored because only neurons near the border process it.

Notice that as each part of the circle sweeps across the orientation map, it activates only those neurons with orientation preferences similar to the local orientation of that part. At the same time, the position and shape of the input is encoded in the position and shape of the cortical activity. After being processed by the eyes, natural images consist of many local orientations like those in the circle on the retina. Each oriented patch activates specific orientation-selective neurons like these in the cortex.

Note also that when less than half of the circle is visible, the orientation histograms are peaked around the colors representing vertical, because the visible portion consists primarily of vertical and near-vertical orientations. When the entire figure (or exactly half of it) is visible, the orientation histogram is essentially flat, because all orientations are represented equally in a circle or half-circle.