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Wilkie R.M. & Wann J.P. (In Press) Journal of Experimental Psychology: Human Perception and
Performance
During locomotion retinal
flow, gaze-angle direction and vestibular information can all contribute
to our perception of self-motion. The relative roles of these sources were
investigated by manipulating each one in turn: retinal flow and gaze angle
were biased subtly by altering the visual information projected during
computer-simulated locomotion and vestibular information was controlled
through use of a motorised chair that rotated the participant around their
vertical (yaw) axis. Chair rotation could be made appropriate to the
steering control of the participant, or inappropriate by rotating a
proportion of the veridical amount. Large steering errors resulted from
selective manipulation of the visual information, retinal flow and gaze
angle, and the pattern of errors provided strong evidence for an additive
model of combination. Vestibular information, however, had little or no
effect upon steering performance in our task, suggesting that vestibular
signals are not always integrated with retinal flow and gaze angle during
control of locomotion. Because veridical vestibular information did not
improve steering performance when gaze angle information was biased, we
also propose that gaze angle estimation is not reliant upon a vestibular
input.
Wann J. P. & Wilkie R. M. (2004)
In L. M. Vaina & S. A. Beardsley & S. K. Rushton (Eds.), Optic
Flow and Beyond. Dordrecht: Kluwer Academic Publishers.
We routinely travel at high speed, in a car or on a
bicycle, and also steer complex paths with relatively little conscious
processing or explicit procedures as to how we 'judge a bend'. The consequences
of an error, however, could be considerable. Within this chapter we tackle the
issue of how optic flow and other sources of information can enable locomotor
animals to steer effectively. Although there has been a strong body of research
into how we might judge locomotor heading we will argue that this does not
equate to active locomotor control and that there is relatively little research
into effective steering, despite the latter being the ecological skill that all
locomotor animals need to achieve. We have written this chapter in a tutorial
style to try and make a difficult field accessible to undergraduate and
postgraduate students. In this respect we do not attempt to cite every
contribution on the use of optic flow or other information sources, but provide
some basic background and then concentrate on the components that we believe can
be linked into a coherent account of high speed steering. A glossary of terms is
also provided in an appendix.
Kluwer
Academic Publishers, Dordrecht
Hardbound, ISBN 1-4020-2091-0
April 2004, 528 pp.
eBook
, ISBN 1-4020-2092-9
Wilkie R.M. & Wann J.P. (2003)
Journal of Vision, 3 (11), 677-684
Eye-movements
have long been considered a problem when trying to understand the visual control
of locomotion. They transform the retinal image from a simple expanding pattern
of moving texture elements (pure optic flow), into a complex combination of
translation and rotation components (retinal flow). In this article we
investigate whether there are measurable advantages to having an active free
gaze, over a static gaze or tracking gaze, when steering along a winding path.
We also examine patterns of free gaze behavior to determine preferred gaze
strategies during active locomotion.
Participants
were asked to steer along a computer-simulated textured roadway with free gaze,
fixed gaze, or gaze tracking the center of the roadway. Deviation of position
from the center of the road was recorded along with their point of gaze. It was
found that visually tracking the middle of the road produced smaller steering
errors that for fixed gaze. Participants performed best at the steering task
when allowed to sample naturally from the road ahead with free gaze. There was
some variation in the gaze strategies used, but sampling was predominantly of
areas proximal to the center of the road. These results diverge from traditional
models of flow analysis.
Wilkie R.M. & Wann J.P. (2003)
Journal of Experimental Psychology: Human Perception and Performance, Vol. 29,
No. 2, 363-378
The contribution of retinal flow (RF), extra
retinal (ER), and egocentric visual direction (VD) information in locomotor
control was explored. First, the recovery of heading from RF was examined when
ER information was manipulated; results confirmed that ER signals affect heading
judgments. Then the task was translated to steering curved paths and the
availability and veracity of VD was manipulated with either degraded or
systematically biased RF. Large steering errors resulted from selective
manipulation of RF and VD, providing strong evidence for the combination of RF,
ER, and VD. The relative weighting applied to RF and VD was estimated. A
point-attractor model is proposed that combines redundant sources of information
for robust locomotor control with flexible trajectory planning through active
gaze.
Wilkie R.M. & Wann J.P. (2002)
Current Biology, 12 (23), 2014-2017
We have the ability to locomote at high speeds, and
we usually negotiate bends safely, even when visual information is degraded, for
example, when driving at night. There are three sources of visual information
that could support successful steering. An observer fixating a steering target
that is eccentric to the current heading must rotate their gaze. The gaze
rotation may be detected by using head and eye movement signals (extra-retinal
direction: ERD) or their retinal counter-part, visual direction (VD). The gaze
rotation also transforms the global retinal flow (RF) field, which may enable
direct steering judgments. In this study, we manipulate VD and RF to determine
their contribution toward steering a curved path in the presence of ERD. The
results suggest a model that uses a weighted combination of all three
information sources, but results also suggest that this weighting may change in
reduced visibility, such as in low-light conditions.
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