We presented continuous sequences of compound gratings with multiple components that differed in direction, speed, and/or spatial frequency (hyperplaids). We used the resulting MT unit activity to estimate a simple model in which responses are given by linear combination of directionally-selective inputs preferring different directions and speeds, followed by half-rectification. For both CDS and PDS cells, this simple model predicted the responses to both grating, plaid, and hyperplaid stimuli with surprising accuracy, suggesting that CDS and PDS cells differ not in computational style but in parametric detail. Most cells had excitatory inputs near the preferred direction, balanced by a suppressive input from other directions, especially those near 180 deg from the preferred. This motion opponency was much stronger in PDS cells than in CDS cells, and the breadth of excitation in PDS cells was also usually greater than CDS cells. Taken together, these two factors account well for the distinction between the responses of PDS and CDS cells. Moreover, the continuous nature of their variation offers a natural explanation for the continuum of response patterns seen in MT.