Academic journal article Human Factors

Target Cuing in Visual Search: The Effects of Conformality and Display Location on the Allocation of Visual Attention

Academic journal article Human Factors

Target Cuing in Visual Search: The Effects of Conformality and Display Location on the Allocation of Visual Attention

Article excerpt

Two experiments were performed to examine how frame of reference (world-referenced vs. screen-referenced) and target expectancy can modulate the effects of target cuing in directing attention for see-through helmet-mounted displays (HMDs). In the first experiment, the degree of world referencing was varied by the spatial accuracy of the cue; in the second, the degree of world referencing was varied more radically between a world-referenced HMD and a hand-held display. Participants were asked to detect, identify, and give azimuth information for targets hidden in terrain presented in the far domain (i.e., the world) while performing a monitoring task in the near domain (i.e., the display). The results of both experiments revealed a cost-benefit trade-off for cuing such that the presence of cuing aided the target detection task for expected targets but drew attention away from the presence of unexpected targets in the environment. Analyses support the observation that this effect can be mediated by the display: The world-referenced display reduced the cost of cognitive tunneling relative to the screen-referenced display in Experiment 1; this cost was further reduced in Experiment 2 when participants were using a hand-held display. Potential applications of this research include important design guidelines and specifications for automated target recognition systems as well as any terrain-and-targeting display system in which superimposed symbology is included, specifically in assessing the costs and benefits of attentional cuing and the means by which this information is displayed.

INTRODUCTION

See-through helmet-mounted displays (HMDs) allow a user to perform real-world tasks with a head-mounted guide - that is, information is presented in a way that overlays the user's forward field of view. For example, in the field of medical imaging, see-through HMDs allow doctors to view patient data in real time and superimpose data onto the patient (Azuma, 1997). Such displays have at least four apparent benefits: (a) the ability to operate in hostile or hazardous environments remotely (Drascic & Milgram, 1996); (b) hands-free operation for a mobile operator performing tasks requiring high information content (e.g., as an aid to maintenance engineers; Ockerman & Pritchett, 1998); (c) the ability to reduce scanning and, in particular, head movement while accessing information that would otherwise be presented in a head-down format; and (d) possibly using head tracking to capitalize on world-referenced imaging -- that is, information that has direct spatially defined referents in the world beyond. Such imager y has sometimes been characterized as creating an augmented reality, in the sense that the far-domain imagery (reality) that is directly viewed is augmented by computer imagery that indicates or highlights particular locations, objects, or dimensions within that reality (Drascic & Milgram, 1996). For example, the user might see a pointer on the display designating the location of the target in the far domain.

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. Such tunneling may be induced not only by superimposing information at the same location (Fadden, Ververs, & Wickens, 1998; McCann, Foyle, & Johnston, 1992; National Research Council, 1997; Wickens & Long, 1995) but also by the use of world-referenced imagery because of its higher degree of apparent realism (Ververs & Wic kens, 1998a). …

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