We measured speed tuning of V1 cells in alert macaques to high and low contrast stimuli. Most V1 cells tested, both simple and complex, and directional as well as non-directional, shifted their speed tuning to slower speeds for lower contrast stimuli. We found that the space-time slant of the receptive field of directional simple cells differed for high and low contrast stimuli, with the space-time slant predicting higher optimum speeds for the higher contrast stimuli; i.e. there was a larger spatial shift of the receptive-field organization per unit time. Not only did the space-time maps of directional simple cells show different slants between high and low contrast stimuli, but they also showed a different organization, because for high-contrast stimuli the maps tended to show a complete inversion of the receptive-field spatial organization at long delays after stimulus onset, with initial excitation followed by suppression and initial suppression followed by excitation, but for low-contrast stimuli the receptive-field organization showed only a quadrature shift over time. We show that a simple modification of earlier models for the generation of direction-selective simple cells can account for these observations.