DS_Pre_Fac   Complex direction selective (DS) cells are created within a spiking network model from pair-wise interactions of spiking inputs from non-DS, orientation-tuned simple cells. The DS interaction involves (i) cell pairs with spatial RFs that are phase-offset by about 90 deg, (ii) a temporal delay that is implemented pre-synaptically (relative to the synapse at the transformation from non-DS to DS), and (iii) a facilitatory interaction. This is a hierarchical model containing four distinct populations of spiking units: LGN (ON and OFF center), V1 simple inhibitory, simple excitatory, and complex DS. The spiking cells are conductance-driven integrate and fire units modeled on those of Troyer et al. (1998).