Attentional effects with superimposed symbology: Implications for head-up displays

Previous research has shown that the presence of head-up display (HUD) symbology containing altitude information improves altitude performance at the cost of terrain path performance, implying that these information sources may not be available for concurrent cognitive processing. In two flight simulation experiments, the influence of attentive field size on this concurrent processing limitation was evaluated. In Experiment 1, a superimposed digital altitude (i.e., HUD) indicator was presented at three distances from a flight-relevant ground track. A control condition eliminated the digital altitude indicator. Altitude symbology improved performance on the altitude maintenance task, but impaired performance on the ground track task only when directly superimposed. Experiment 2 tested a visual masking explanation of the performance tradeoff. Irrelevant HUD information yielded identical results to the HUD absent condition, ruling out effects of visual masking. An explanation in which visual/spatial attention cannot be directed to both HUD information and terrain information simultaneously is proposed. The absence of a performance tradeoff when the HUD and the terrain information are not directly superimposed is attributed to a breaking of attentional tunneling on the HUD, possibly due to eye movements