RESEARCH NOTE Scaling of Flash Rate for a Deceleration Signal

This study is concerned with determining the number of different flash rates that could be used in an automobile braking signal to inform a following driver of the degree of deceleration. Two methods, magnitude estimation and just noticeable differences (iND) scaling, were employed to relate perceived flash rate to the physical frequency at which an automobile stop signal lamp was flashing. Differences between red and yellow lamps were examined, but no effects were found due to the lamp color. A category scaling procedure showed that only three flash rates between 1 and 7 Hz could be discriminated by absolute judgments. The iND and magnitude estimation experiments yielded similar flash rates (e.g., 1.0, 2.6, and 6.8 Hz) for the presentation of the deceleration information.