The Effect of Temporal Frequency and Hue on the Perceived Level of Caution While Driving

Background: The purpose of this study was to determine the effect of flicker frequency and hue on the perceived level of caution adopted by motorists when viewing emergency vehicle lights. Methods: Adult subjects (n=15) with normal acuity and color vision, rated their perceived level of caution of 2-degree equiluminant circular hue patches (Red, Green, Blue) flickered at 6 temporal frequencies (1, 2, 4, 8, 16, and 24Hz) using a magnitude estimation psychophysical technique. Stimuli were generated using Matlab and presented on a DELL LCD monitor. Six hue pairs (R, G, B, R/G, B/R, and B/G) were presented at each of six temporal frequencies which were interleaved randomly within a single experimental session. Subjects rated their perceived level of caution using a continuous 1-10 scale, with 10 being the most heightened sense of caution. Results: The perceived level of caution of subjects increased with increasing temporal frequency of flicker up to about 6.5 Hz, and declined progressively for higher temporal frequencies. The temporal frequency at which perceived caution was highest varied with the hue condition. The maximal rated caution also varied with hue condition and temporal frequency. Mean perceived caution rating for the R/B condition far exceeded the mean caution rating derived with R-only or B-only condition, suggesting a faciliatory interaction between these combined hues. The same trend was not evident with R/G and B/G hue pair. Conclusion: Higher rates of flicker increases perceived ratings of caution up to about 6.5 Hz. Red and blue hues are generally associated with higher perceived ratings of caution then green hue, especially when they are flickered consecutively as a pair. This latter finding may reflect the role of a societal conditioned bias.