Uas, uav, multiple resource theory, response times, multimodal


Operator responsiveness to critical alarm/alert display systems must rely on faster and safer behavioral responses in order to ensure mission success in complex environments such as the operator station of an Unmanned Aerial System (UAS). An important design consideration for effective UAS interfaces is how to map these critical alarm/alert display systems to an appropriate sensory modality (e.g., visual or auditory) (Sarter, 2006). For example, if an alarm is presented during a mission in a modality already highly taxed or overloaded, this can result in increased response time (RT), thereby decreasing operator performance (Wickens, 1976). To overcome this problem, system designers may allow the switching of the alarm display from a highly-taxed to a less-taxed modality (Stanney et al., 2004). However, this modality switch may produce a deleterious effect known as the Modality Shifting Effect (MSE) that erodes the expected performance gain (Spence & Driver, 1997). The goal of this research was to empirically examine a technique called bridging which allows the transitioning of a cautionary alarm display from one modality to another while simultaneously counteracting the Modality Shifting Effect. Sixty-four participants were required to complete either a challenging visual or auditory task using a computer-based UAS simulation environment while responding to both visual and auditory alarms. An approach was selected which utilized two 1 (task modality) x 2 (switching technique) ANCOVAs and one 2 (modality) x 2 (technique) ANCOVA, using baseline auditory and visual RT as covariates, to examine differences in alarm response times when the alert modality was changed abruptly or with the bridging technique from a highly loaded sensory channel to an underloaded sensory channel. It was hypothesized that the bridging technique condition would show faster response times for a new unexpected modality versus the abrupt switching condition. The results indicated only a marginal decrease in response times for the auditory alerts and a larger yet not statistically significant effect for the visual alerts; results were also not statistically significant for the analysis collapsed across modality. Findings suggest that there may be some benefit of the bridging technique on performance of alarm responsiveness, but further research is still needed before suggesting generalizable design guidelines for switching modalities which can apply in a variety of complex human-machine systems.


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Graduation Date





Mouloua, Mustapha


Doctor of Philosophy (Ph.D.)


College of Sciences



Degree Program

Psychology; Human Factors Psychology








Release Date

May 2015

Length of Campus-only Access


Access Status

Doctoral Dissertation (Open Access)

Included in

Psychology Commons