Spatiotemporal interpolation and quality of apparent motion

We investigate the conditions under which stimuli in apparent (sampled) mot ion are indistinguishable from those in smooth motion and compare this disc rimination with the precision achieved by the visual system in interpolatin g apparent motion. In an initial experiment, observers were required to dis criminate smooth from apparent motion, at variable step sizes, contrasts, v elocities, and stimulus types (broadband line or bar stimuli and grating pa tches of different spatial frequency). Thresholds for discriminating smooth from sampled motion were similar to 40 arc min under optimal conditions, c orresponding to the diameter of foveal photoreceptors. The tolerated step s ize between stations increased with velocity, more so for low- than for hig h-spatial-frequency stimuli. Tolerated step size decreased with presentatio n duration and with stimulus contrast, A separate experiment examined preci sion of interpolation. Vernier offsets were produced through temporal delay s along the trajectory of an apparent motion, and thresholds for the discri mination of direction of offset were measured as a function of speed of mot ion and of distance between stations of apparent motion. Perfect interpolat ion was achieved for distances between stations of similar to2 arc min. A m odel based on spatiotemporal filtering at an early stage of processing acco unts well for the results of both types of experiments. (C) 2001 Optical So ciety of America.