@article{vanacken2009multimodal,
title={Multimodal selection techniques for dense and occluded 3d virtual environments},
author={Vanacken, Lode and Grossman, Tovi and Coninx, Karin},
journal={International Journal of Human-Computer Studies},
volume={67},
number={3},
pages={237--255},
year={2009},
publisher={Elsevier}
}