Fatigue has become an increasing problem in our modern society. Using MATLAB as a generic modelling tool, a fatigue model was developed based on an existing one and compared with a commercial fatigue software for prediction of cognitive performance under total and partial sleep deprivation. The flexibility of our fatigue model allowed additions of new algorithms and mechanisms for non-sleep factors and countermeasures and thus improved model predictions and usability for both civilian and military applications. This was demonstrated by model simulations of various scenarios and comparison with experimental studies. Our future work will be focused on model validation and integration with other modelling tools. Practitioner Summary: Mental fatigue affects health, safety and quality of life in our modern society. In this paper, we reported a cognitive fatigue model based on existing models with newly incorporated components taking both the operator's state of alertness and task demand into account. The model provided the additional capability for prediction of cognitive performance in scenarios involving pharmaceutical countermeasures, different task demands and shift work.

Dynamic viewpoint tethering is an innovative display technique which has been proposed to support effective navigation in large-scale virtual environments, by integrating information from different frames of reference. The present study examines the effect of dynamic viewpoint tethering on performance, with respect to both local guidance and global awareness measures, in comparison with three conventional display formats: egocentric, exocentric and rigidly tethered displays. Participants were instructed to control an aircraft-shaped cursor navigating in a virtual tunnel and to answer questions about the environment. The results confirmed that global awareness performance decreased with increased egocentricity in the display frame of reference. The two tethered displays (dynamic and rigid) supported the best local guidance performance. No significant performance differences were found between the two tethered displays.

Dynamic viewpoint tethering is an innovative display technique which has been proposed to support effective navigation in large-scale virtual environments, by integrating information from different frames of reference. In this paper, we explain the modelling of a dynamic tether and report our latest research findings in investigating the optimal parametric values of tether configuration and their relations to human users' navigational performance. Tethered displays with different parametric configurations were compared. Participants were instructed to control an aircraft-shaped cursor flying in a virtual tunnel and to answer questions about the environment. The results revealed that critically damped tethers supported the best local guidance performance. No significant global awareness performance differences were observed under all display conditions.

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Guidelines generated from this study support future viewpoint design in interactive virtual reality applications.