ABSTRACT
Three modes of attention - selective attention, divided attention, and focussed attention - are relevant to the processing of information in head-up displays (HUDs), and therefore serve to link theoretical experimental psychology, with an applied human factors concern via engineering psychology. Furthermore, space-based theories of visual attention invoke processing mechanisms to explain the effects of scanning and clutter on divided, selective and focussed attention, while object-based theories invoke mechanisms of parallel processing to explain divided attention effects. In addition, selective attention is modulated by top-down goals of allocation policy. All of these mechanisms are relevant to the comparison of head-down displays with HUDs, as the latter superimpose instrument information over the pilot’s view of the world beyond the aircraft.
We describe three sets of experiments that have compared HUDs with head-down displays, using equivalent tasks and symbology. The collective results identify the contributing role of all four mechanisms (scanning, clutter effects, object processing, and allocation policy). They suggest that scanning effects are probably dominant, and therefore that HUDs generally are more beneficial (because of reduced scanning) than harmful (because of increased clutter). The benefits may be enhanced with conformal imagery that fuses near and far domain imagery into a single object. The benefits may be reduced and actually reversed for the detection of very unexpected events, because of the adverse effects of clutter.
