Dr. Markus Lappe
Computational and Cognitive Neuroscience,
Dept. Zoology & Neurobiology,
Ruhr-University Bochum, Germany
will speak on
Perception of Travel Distance from Optic Flow
Abstract:
Effective navigation through an environment requires knowledge about the
direction of motion and the distance traveled. Humans can use optic flow
do estimate the direction of self-motion. But on its own, i.e., without
additional cues about the 3D structure of the environment, optic flow is
ambiguous with regard to travel distance. In my talk I will pursue the
question under which conditions humans can perceive travel distance from
optic flow. First, I show that humans are able to discriminate and
reproduce distances of two visually simulated self motions when they are
performed in the same simulated environment. In this case, two visually
simulated motions can be discriminated under the assumption that the depth
structure of the environment is not changed between the motions. Subjects
are asked to discriminate distances of two visual simulated self motions
of different velocity and duration in four different environments. These
environments varied in the depth cues given to the subjects. We found that
discrimination was possible in all environments. This suggests that motion
parallax, which was the only depth cue available in all environments, is
sufficient. In a second set of experiments, we modified the visual information about
the structure of the environment between the two motions, thereby altering
the speed distribution in the flow without altering the travel distance.
This included variations of the height above ground and variations of the
visibility range. When the height of the observer above the ground was
changed without the subject noticing the change, errors occured that could
be predicted by the change in flow speed due to the modification of
height. When the height was altered visibly and the subject watched the
height change, thw errors were strongly reduced. The results of the second
set of experiments suggest that humans can transfer distance estimates
from visual flow across changes in the visible structure of the
environment. In a third experiment, we asked subjects to actively
reproduce the depth of a given movement by driving the simulator with a
joystick. Subjects were well able to do the task. Their behavior suggested
that they remembered and reproduced the velocity profile of the seen
movement.
The lecture will take place in the Lecture Hall, Room 203, 44 Cummington
St.
on Wednesday, August 8, 2001
at 4:00 pm
Hosted by the
Brain and Vision Research Laboratory