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On the relationship between human search strategies, conspicuity and search performance

Author: Hogervorst, M.A. · Toet, A. · Bijl, P.
Institution: TNO Defensie en Veiligheid
Source:Holst, G.C., Infrared Imaging Systems: Design, Analysis, Modeling, and Testing XVI, 240 - 251
Proceedings of SPIE - The International Society for Optical Engineering
Identifier: 15994
Keywords: Vision Informatics · Visual search · Field of view · Target detection · Conspicuity · Detection probability · Detection time · Field of Regard · Field of View · Modelling · Scan path · Search performance · Search strategy · Zooming · Computer simulation · Computer vision · Demodulation · Image sensors · Mathematical models · Target drones · Tracking (position) · Conspicuity · Detection probability · Detection time · Field of regard · Field of views · Scan path · Search performance · Search strategy · Zooming · Imaging systems


We determined the relationship between search performance with a limited field of view (FOV) and several scanning- and scene parameters in human observer experiments. The observers (38 trained army scouts) searched through a large search sector for a target (a camouflaged person) on a heath. From trial to trial the target appeared at a different location. With a joystick the observers scanned through a panoramic image (displayed on a PC-monitor) while the scan path was registered. Four conditions were run differing in sensor type (visual or thermal infrared) and window size (large or small). In conditions with a small window size the zoom option could be used. Detection performance was highly dependent on zoom factor and deteriorated when scan speed increased beyond a threshold value. Moreover, the distribution of scan speeds scales with the threshold speed. This indicates that the observers are aware of their limitations and choose a (near) optimal search strategy. We found no correlation between the fraction of detected targets and overall search time for the individual observers, indicating that both are independent measures of individual search performance. Search performance (fraction detected, total search time, time in view for detection) was found to be strongly related to target conspicuity. Moreover, we found the same relationship between search performance and conspicuity for visual and thermal targets. This indicates that search performance can be predicted directly by conspicuity regardless of the sensor type. Keywords: Search performance, Field of Regard, Field of View, Modelling, Conspicuity, Scan path, Zooming, Detection time, Detection probability, Search strategy