The system uses substrate guided optics to project the forward field of view
image through the HUD via an optical waveguide.
Although the head-up presentation of data on the HMD provided faster detection for cued targets, the clutter produced by the symbology in the forward field of view proved to be costly in the detection of low-salience targets, particularly when they were uncued.
The data in Figure 7 revealed that superimposing imagery onto the forward field of view imposed a time cost for target detection of approximately 3 s relative to the head-down display, F(1, 7) = 7.42, p < .05.
Although the imagery used in the current study was semitransparent, its presentation directly in the forward field of view and the high level of detail used to present the topographical data probably reduced the visibility of far-domain information that appeared behind the imagery to a greater degree than that of any HUD symbology or of the very simplified imagery employed by Yeh et al.
However, these benefits must be weighed against the potential costs of using a see-through HMD: (a) The optics required for such a system are heavy and may impose a substantial amount of weight on the user's head; (b) the visibility of the far domain is reduced because of reduced light transmittance or a reduced field of view; (c) there is increased clutter in the forward field of view, such that in a worst-case scenario, the additional symbology in the near domain (i.e., the display) may obscure information in the real world (or far domain); and (d) there is a potential for cognitive tunneling in which one domain captures attention so that events in the second domain are missed or ignored.
As in Experiment 1, the lock-on reticle was not used to signal the presence of any uncued targets that might appear in the participant's forward field of view.
However, in light of the apparent virtues of HUDs in minimizing reaccommodation times and sustaining attention within the forward field of view, they are being considered for application in the automotive domain (Dellis, 1988; Sojourner and Antin, 1990).
The main findings of this study indicate that the nature of the background scene on which a HUD is superposed, as well as the placement within the forward field of view, has significant consequences for the legibility of HUD-presented images.