The Effect of Background Context on the Size–Time Illusion

Abstract

Previous studies suggest that time perception may be altered by nontemporal stimulus properties, such as size and numerosity, where increases lead to a longer perception of time. These studies have led to the suggestion of a generalized magnitude system that processes abstract quantities. However, the majority of studies on this phenomenon have used simple stimuli, varying along one or two dimensions, and occurring in the same location. Here, we sought to explore the influence of the size–time illusion amongst complex visual scenes. Across five experiments, human participants judged the duration of two visual stimuli, of different sizes, appearing at different spatial locations for a range of sub-second durations. In half of the trials, these stimuli were overlaid on an image of a city street, with one stimulus presented farther away than the other. We found that larger stimuli were judged to be longer, but only when the larger stimulus was presented on the left side of space, and not when presented on the right or when the entire stimulus array was on the left. This effect extended to a marginal bias for left-sided stimuli to be judged as longer. However, we found that the size–time illusion for right-sided stimuli was reinstated when a background city context was presented, which may have been driven by an imposed effect of perceived distance. These results suggest that the size–time illusion is affected by the background context and location against which stimuli are presented, and provide important qualifications to theories of a common magnitude system.