Acknowledgements
This research is supported by National Natural Science Foundation of China (No. 61703357) and the Research Grants Council of the Hong Kong S.A.R., China (No. HKU 17607018 and No. HKU 17608621). Publication made possible in part by support from the HKU Libraries Open Access Author Fund sponsored by the HKU Libraries. We appreciate anonymous reviewers for detailed comments on an earlier manuscript. We also thank the contributions of participants to the user experiment.