Road sign conspicuity against natural background of varying complexity

Abstract

A scale of visual complexity of photographs of road scenes was established by subjective measures. Targets (road signs) were superimposed on these road scenes of varying complexity and two laboratory experiments were conducted where conspicuity was measured by reaction time (RT). The independent variables were scene complexity, target shape, background brightness, and target brightness. The design of the two experiments were identical except for the stimulus exposure duration, which was 250 msec for Experiment 1 and 10,000 msec for Experiment 2. Significant main effects and interactions were found to be common in both experiments with the exceptions of the main effect of target shape, the two-way interaction between scene complexity and target shape, and the three-way interaction between target shape, background brightness, and target brightness, which were significant in Experiment 2, but not in Experiment 1. The different stimulus exposure durations explained these differences. Scene complexity gave a reasonable prediction of target conspicuity. It was found that brightness contrast between the target and its background was an important determinant of conspicuity. It was concluded that a more comprehensive definition of complexity was needed when scaling it by subjective means.