Are the inverse-duration and inverse-proximity effects in temporal integration subserved by independent mechanisms?

Displays shorter than about 100 ms are normally seen as lasting longer than their physical duration. This visible persistence can bridge a temporal gap between two sequential stimuli causing them to be temporally integrated into a single percept. We investigated two findings in the temporal-integration literature: the inverse duration effect (temporal integration is progressively impaired as the duration of the first stimulus is increased) and the inverse proximity effect (temporal integration is progressively impaired as the spatial proximity between the stimuli is increased). In two experiments we asked whether the two effects are separable (i.e., whether they are subserved by independent mechanisms) or interact with one another. To estimate the duration of visible persistence we used the missing element paradigm in Experiment 1 and directional stroboscopic motion between two lines in Experiment 2. In both experiments we manipulated the duration of the leading stimulus and the spatial gap between the elements of the two sequential displays. Additive-factors logic was employed to examine the separability of the effects of duration and proximity. Independence (separability) of the two factors would be evidenced in a graph in which the functions of duration over proximity are parallel. The results pointed uniformly to separability. A plausible mechanism for the inverse duration effect is the burst of processing activity time-locked to stimulus onset. A plausible mechanism for the inverse proximity effect is lateral inhibition that acts to reduce the visible persistence of the leading stimulus.