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Abstract:
We conducted triangle completion experiments in virtual
environments to investigate the role of optic flow in human homing
performance. Ego-motion was visually simulated on an
half-cylindrical 180-degree-projection screen of 7m diameter using
the mouse buttons as input device. Subjects had to return to the
origin after moving outwards along two prescribed segments of the
triangle. To exclude scene-matching as a homing strategy, subjects
were "teleported" to a different, however similar environment for
the return path ("scene-swap condition"). Experiments were
performed in two simulated environments: A cloud-of-dot-like
environment and a photorealistic town. Only the latter contained
landmarks and explicit scaling information. We found systematic
errors in distances traveled, but not in turns performed. Homing
based on optic flow alone in the cloud-of-dot environment was
possible and led to similar performance as navigation in the town.
Omitting scene-swap in a control experiment led to almost perfect
homing performance in the town, suggesting that scene-matching
(whenever possible) plays the dominant role in homing accuracy. A
comparison with results from Loomis et al. (JEP, 1993), who studied
triangle completion based on path integration using proprioceptive
cues showed that optic flow information in our experiments led to
considerably smaller systematic errors. Using scene-swap and
virtual environments proved to be a successful paradigm to
disentangle the role of two major information sources in spatial
orientation: optic flow (path integration) versus landmarks
(piloting).
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