The H1 neuron is a directionally sensitive motion-detector neuron with a large field that is fed by many high-resolution motion detectors in the fly optic lobe. As a stimulus pattern for it we used a random pattern of 50% bright and 50% dark squares on an oscilloscope screen. When this pattern is jumped by a small increment the H1 neuron gives a directional response. When the jump is greater than one pixel on the screen the response falls and becomes non-directional because jump direction can no longer be inferred. When the contrast is reversed at the jump, the response is the same for both directions, and is the same as when the contrast is reversed without motion. For the motion receptors this represents a non-directional `on' or `off' response. The result is discussed with reference to theories of motion perception.