. Author manuscript; available in PMC: 2022 Feb 24.
Published in final edited form as: Proc ACM Symp User Interface Softw Tech. 2021 Oct 12;2021:1122–1143. doi: 10.1145/3472749.3474811
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Figure 8:
(a): a straight tunnel. (b): a narrowing tunnel. (c): a circular tunnel.