DS_Simp   Simple direction selective (DS) cells inspired by linear models. Synapses from weakly orientation tuned, non-DS excitatory and inhibitory simple cells (themselves constructed from ON and OFF LGN cells), are integrated by the postsynaptic DS cells. This model has anti-phase inhibitory conductances in the DS cells that shares direction tuning with the input excitatory conductances, consistent with data from Priebe and Ferster (2005).