Direction-specific losses in sensitivity were found for a test grating which was superimposed on a stationary contrast pedestal and which moved either in the same or opposite direction as a prior biasing stimulus. Three types of biasing stimuli were employed: a grating swept through 270 degrees in 45 degrees steps, a single 90 degrees step of a grating, and a single 90 degrees step of a grating which contained a blank IFI and whose perceived direction was reversed. For the biasing sweep and the single 90 degrees step, the response of directionally selective mechanisms (directional motion energy) is greatest for the direction which corresponds to the actual physical displacement of the stimulus. For the biasing step with an IFI, the response is maximum for the opposite direction. For all three types of biasing stimuli, directional sensitivity for a test stimulus was reduced most when it moved in the biasing direction, i.e. the direction which produced the strongest signal in directionally selective mechanisms. Unlike the effects of the same types of biasing stimuli on the perceived direction of a suprathreshold 180 degrees step of a grating [Pinkus, A., & Pantle, A. (1997). Probing motion signals with a priming paradigm. Vision Research, 37, 541-52; Pantle, A., Gallogly, D.P., & Piehler, O.C. (2000). Direction biasing by brief apparent motion stimuli. Vision Research, 40, 1979-91], all the direction-specific losses of sensitivity can be explained by changes in the response characteristics of directionally selective mechanisms.
Contrast Sensitivity Humans