Using a mouse-driven visual pointer, 10 participants made repeated open-loop egocentric localizations of memorized visual, auditory, and combined visual-auditory targets projected randomly across the two-dimensional frontal field (2D). The results are reported in terms of variable error, constant error and local distortion. The results confirmed that auditory and visual maps of the egocentric space differ in their precision (variable error) and accuracy (constant error), both from one another and as a function of eccentricity and direction within a given modality. These differences were used, in turn, to make predictions about the precision and accuracy within which spatially and temporally congruent bimodal visual-auditory targets are localized. Overall, the improvement in precision for bimodal relative to the best unimodal target revealed the presence of optimal integration well-predicted by the Maximum Likelihood Estimation (MLE) model. Conversely, the hypothesis that accuracy in localizing the bimodal visual-auditory targets would represent a compromise between auditory and visual performance in favor of the most precise modality was rejected. Instead, the bimodal accuracy was found to be equivalent to or to exceed that of the best unimodal condition. Finally, we described how the different types of errors could be used to identify properties of the internal representations and coordinate transformations within the central nervous system (CNS). The results provide some insight into the structure of the underlying sensorimotor processes employed by the brain and confirm the usefulness of capitalizing on naturally occurring differences between vision and audition to better understand their interaction and their contribution to multimodal perception.

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The goal of the U.S. Army’s Degraded Visual Environment Mitigation (DVE-M) Program was to develop technologies that enable Army rotorcraft to operate in low-visibility conditions. Technologies included low and highresolution terrain sensors, sensor fusion, pilot cueing, and advanced flight controls. This paper focuses on just one important aspect of the DVE-M system, the ability to sense and cue pilots of obstacles in the vicinity of the rotorcraft. This capability will provide pilots the situational awareness needed to navigate complex environments so that missions can be completed safely and successfully. Though visual displays are useful for conveying multiple viewpoints, an egocentric display is limited to obstacles within the field of view and an exocentric display requires a reference frame transformation relative to the observer. Spatial-auditory displays support an egocentric 360° immersive 3D space in which auditory cues can be placed in direction and distance, and rendered such that realistic motion cues in gain and/or frequency (Doppler) are provided. Though limited in spatial resolution, tactile displays can provide a needed alternative when the visual and auditory channels are overwhelmed or fixated. Leveraging the beneficial aspects of all three, a trimodal obstacle awareness and avoidance display was developed for the DVE-M Program. The display, in concert with a 360° azimuth, 24° elevation bumper radar, was flight tested in the Fort Eustis area by five experimental test pilots. A series of test points were developed that exercised the display for various obstacle types and phases of flight. Upon completion, each pilot was administered usability and workload questionnaires and participated in a cueing debrief session. This paper describes the display design and test points and reports the results of the pilot evaluations.