This paper presents a novel three-dimensional (3-D) eye movement analysis algorithm for binocular eye tracking within virtual reality (VR). The user's gaze direction, head position, and orientation are tracked in order to allow recording of the user's fixations within the environment. Although the linear signal analysis approach is itself not new, its application to eye movement analysis in three dimensions advances traditional two-dimensional approaches, since it takes into account the six degrees of freedom of head movements and is resolution independent. Results indicate that the 3-D eye movement analysis algorithm can successfully be used for analysis of visual process measures in VR. Process measures not only can corroborate performance measures, but also can lead to discoveries of the reasons for performance improvements. In particular, analysis of users' eye movements in VR can potentially lead to further insights into the underlying cognitive processes of VR subjects.

This paper presents novel software techniques for binocular eye tracking within Virtual Reality and discusses their application to aircraft inspection training. The aesthetic appearance of the environment is driven by standard graphical techniques augmented by realistic texture maps of the physical environment. The user's gaze direction, as well as head position and orientation, are tracked to allow recording of the user's fixations within the environment. Methods are given for (1) integration of the eye tracker into a Virtual Reality framework, (2) stereo calculation of the user's 3D gaze vector, (3) a new 3D calibration technique developed to estimate the user's inter-pupillary distance post-facto, and (4) a new technique for eye movement analysis in 3-space. The 3D eye movement analysis technique is an improvement over traditional 2D approaches since it takes into account the 6 degrees of freedom of head movements and is resolution independent. Results indicate that although the current signal analysis approach is somewhat noisy and tends to underestimate the identified number of fixations, recorded eye movements provide valuable human factors process measures complementing performance statistics used to gauge training effectiveness.

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Research in aircraft inspection and maintenance has revealed the criticality of human inspection performance in improving aviation safety. If we are to provide the general public with a safe and reliable air transportation system, inspection must be performed effectively, efficiently and consistently. Even though it is difficult to eliminate errors completely, continuing emphasis must be placed on identifying interventions to reduce errors and improve consistency in performance. Training has been identified as the primary intervention strategy in improving the quality and reliability of aircraft inspection performance. If training is to be successful, it is clear that we need to provide aircraft inspectors with tools to help enhance their inspection skills and improve performance. In response to this need a Virtual Reality (VR) based simulator was developed for visual inspection task of an aft cargo bay. Presence and performance validation studies were conducted to evaluate the simulator and are described as part of this paper. INTRODUCTIONAircraft inspection and maintenance are an essential part of a safe, reliable air transportation system. Training has been identified as the primary intervention strategy in improving inspection performance (Gramopadhye, et. al, 1998). If training is to be successful, it is clear that inspectors need to be provided with training tools to help enhance their inspection skills. Existing training for inspectors in the aircraft maintenance environment tends to be mostly on-the-job. Nevertheless, this may not be the best method of instruction (Gramopadhye et al., 1995;Latorella et al., 1992). For example, in OJT feedback may be infrequent, unmethodical, and/or delayed. Moreover, in certain instances feedback is economically prohibitive or infeasible due to the nature of the task. Thus, because the benefits of feedback in training have been well documented (e.g., Weiner, 1975), and for other reasons as well, alternatives to OJT are sought. Furthermore, training for improving visual inspection skills of aircraft inspectors is generally lacking at aircraft repair centers and aircraft maintenance facilities (FAA, 1991; FAA 1993). However, the application of training knowledge to enhance visual inspection skills has been well documented in the manufacturing industry. Training has been shown to improve the performance of both novice and experienced inspectors (Gramopadhye et al., 1995;Drury et al., 1991;Weiner, 1975). Visual inspection skills can be taught effectively using representative photographic images showing a wide range of conditions with immediate feedback on the trainee's decision in a controlled environment (Blackmon, 1996). Using realistic photographic images as a training aid in controlled practice with feedback has also been shown to be superior to only onthe-job training (OJT) (Gramopadhye et al., 1995;Latorella et al., 1992).Thus, off-line training/retraining with feedback has a role to play in aircraft inspection training. One of the most viable approaches for delivering...