What determines the maximum displacement limit for spatially broadband kinematograms?

Two experiments are described that are designed to investigate what determines the maximum spatial displacement detectable (d(max)) for spatially broadband patterns exposed in a two-frame motion sequence. In experiment 1, d(max) was found to be 1.63 times greater for a two-dimensional (2-D) broadband random pattern with a 1/f Fourier amplitude spectrum (equal contrast in each octave) than for a 2-D binary-valued random-dot pattern with a flat spectrum (higher contrast in higher-frequency octaves). In experiment 2, d(max) was shown to vary in inverse proportion to the lowest stimulus frequency for random patterns with a one-octave bandwidth and normalized contrast. Furthermore, when these five one-octave patterns were summed together, d(max) for this new five-octave pattern was found to be only 1.46 times lower than d(max) for the lowest-frequency one-octave pattern presented alone. A model is described in which direction discrimination is based on the nearest-neighbor matching of zero crossings in the output of a single-spatial-filter bandpass in both spatial frequency and orientation. Data from the model show that the difference between d(max) for the five-octave and the lowest one-octave patterns can be accounted for by the same filter passing some of the additional higher frequencies in the former pattern. Furthermore, it is argued that all the data can be accounted for by assuming that d(max) is determined by the coarsest spatial filter activated by each stimulus. Modeling the results of both experiments suggests that the bandwidth of this filter is similar to 2.6 octaves and reaches peak sensitivity at similar to 0.47 c/deg. The model is shown to be capable of accounting for a wide range of other two-frame d(max) data. (C) 1996 Optical Society of America