Brightness Perception of Automobile Head-Up Displays

Influence of the Observer's Age and Subsidiary Tasks

Abstract

Indoor evaluation experiments have been carried out on the perception of the brightness of car speed indications projected by an automobile head-up display (HUD).
We did two types of experiment. One was to examine the influence of the observer's age on the evaluation data. The observers were to determine the appropriate brightness of the HUD as it changed from dark to bright (ascending order) and from bright to dark (descending order). The observers were categorized by age levels (in their 20s, 40s, or 60s).
The other experiment had observers evaluate the brightness while we interfered with their observational concentration by having them do subsidiary tasks during the evaluation. As well as the subjective evaluation results, we also examined electrocardiograms from the subjects to calculate the RRV (R-R Variance), which expresses the extent of a mental load.
The main results are:
(1) The range of HUD brightness judged as appropriate is narrower for older people than for younger people.
(2) Subjective judgments of HUD brightness perception changed when the observers also had to do a subsidiary task. In other words, evaluations range from too bright or too dark to neither too bright or too dark.
(3) The RRV values revealed that the extent of the mental load differs according to the nature of the subsidiary task. When there was a heavy mental load, an observer's subjective judgments changed considerably.