Receptive Field
In this simulation, the horizontal
cell simply averages all the photoreceptor outputs. It establishes spatial
context to which the bipolar
cells can use to compare the outputs of the photoreceptors.
In
addition, the horizontal cell does a low-pass termporal filtering. You
can see this if you suddenly apply a wide field stimulus
to the entire photoreceptor array. You will
see that the horizontal cell takes some time to respond.
Real horizontal
cells form a lateral mesh of cells underlying the photoreceptors. These
horizontal cells are laterally coupled by ohmic junctions, so the horizontal
cells form a true resistive, or spreading, network.
We only modeled a
single horizontal cell because the computation of a true spreading network is
expensive, and would not buy us much for such a small spatial
extent.