The relationship between temporal integration and persistence.

We measured the persistence for gratings of three different spatial frequencies after they had been equated for visibility by manipulating: (1) the contrast of the stimulus, (2) the duration of the stimulus, or (3) both contrast and duration. When we presented gratings of equal apparent contrast and equal duration, persistence increased with increasing spatial frequency. This effect occurred when apparent contrast was equated in terms of extended-duration or brief duration contrast sensitivity. However, when we examined persistence using gratings equated for temporal integration (i.e. equal apparent contrast but unequal durations), no differences in persistence as a function of spatial frequency were observed. Thus, the increase in persistence which is typically found with higher spatial frequencies can be accounted for by knowledge of the spatio-temporal characteristics of the visual system. Our findings are discussed in terms of the notion of different filter time-constants for different spatial channels.