Wolffsohn, J.S., Edgar, G.K., & McBrien, N.A. (1998). The effect of viewing a car head up display on ocular accommodation and response times. In A.G. Gale, I.D. Brown, C.M. Haselgrave, & S.P. Taylor, Vision in Vehicles – VI (pp.143-151)
This paper was at a Vision in Vehicles VI Proceedings and it’s from 1998. It reminded me of this one in the sense that both present two overlayed stimuli to attend.
The authors manipulated the distance at which they collimated the HUD in order to verify differences in accommodation and in reaction time to detect changes in the environment. They were constantly measuring the accomodation of the eyes whereas the drivers were attenting the environment only or the HUD+ environment.
The question under this research is: Is there an optimal distance at which an HUD should be focused? A driver, unlike a pilot, focuses on stimuli at very different distances, varying from 1m to infinity.
Results showed that although there was a trend to higher accommodative levels when the HUD was focused closer to the subject, there was not a significant difference in accommodative level over the range of distances at which the virtual HUD image was focused.
The response times of subjects for detecting changes in the external environment (traffic lights) was consistently faster than for detecting changes in the HUD indicators under all conditions.
However, subject response times to detecting changes in the traffic lights and HUD indicators did not significantly vary with the distance at which the virtual HUD image was focused.
When performing the HUD assisted driving task, there was a significant increase in the percentage of traffic light changes missed and HUD indicator changes missed over all distances tested.
So these results are very important, as they suggest that, with a HUD, vital danger signs, such as warning boards, are more likely to be missed.