Figure 2.

On-center off-surround network. Some units in the upper layer are activated by bottom-up weighted connections. Excitation signals are sent via these units to the relevant units through direct top-down weights and inhibition signals are sent to all units. This amplifies the activities of cells within the matched (on-center) portion while suppressing the activities of irrelevant cells in the non-matched (surround) portion. Therefore, this network is named the on-center, off-surround network. The units in the first layer receive both excitation and inhibition in which additional excitations may overcome the inhibitions. In contrast, when the cells receive only top-down inhibition (off-surround), then one inhibition may counteract one excitation from the input.