Biomedical Engineering Reference
In-Depth Information
Eye Right
Eye Straight
Head:
←
Eye Left
Head:
↑
Head:
→
−6
−4
−2
0
2
4
6
Veering (
o
)
Fig. 6.6
The effect of head and eye orientation on veering. Thirteen participants walked in a large,
fully tracked lab with different combinations of eye and head orientations. Each combination was
tested 5 times for a total of 3 (Head:
Left
,
Straight
,
Right
)
×
×
5
(repetitions) = 45 randomized trials. The head orientation was blocked and randomized across
participants and within each block of head orientation, eye position was pseudo-randomized. For
each trial the participant viewed the target straight ahead of them until they had a good mental
image of its position and then walked to the target under the specified conditions of eye and head
orientation. Except for when looking at the target, the participant was always blindfolded when
walking. For safety an experimenter was always in the room with the participant and provided
specific instructions prior to each trial. The participant's position was recorded using a Vicon
tracking system. To specify eye position, a pair of safety goggles were customized with three red
LEDs that were positioned on the outer surface such that looking at them would create an angular
position of the eyes of approximately 45
◦
to the
left
or to the
right
,or
straight
ahead, relative to the
head. To control head orientation, on the other hand, no explicit reference was provided, but rather
participants were instructed to turn their heads as far as possible (to the
left
or
right
) without causing
any discomfort, and to hold their head there for the duration of a trial. Compliance was checked by
the experimenter. To prevent any view of the environment, an
opaque black
veil was donned after
orienting the eyes and head. However, the head's angle relative to the trunk was somewhat variable
across trials and participants. The participant wore a wireless headset playing noise to mask any
auditory feedback
3(Eyes,
Left
,
Straight
,
Right
)
also an apparent interaction between the head and eye orientation such that the bias
tended to diminish when the eyes were turned away from straight ahead and was
stronger when the head and the eyes were oriented in opposite directions. Statistical
analyses, however, showed marginally significant effects of head orientation and its
interaction with eye position. Whereas these results are qualitatively consistent with
those of Cutting et al. [
28
] and Readinger et al. [
82
], they are opposed to those of Jahn
et al. [
59
]. In fact, when we compare the average values, our and Jahn et al.'s results,
are highly negatively correlated (r
84). We can speculate that spontaneous
head turns would have contributed to the effect of veering from a straight trajectory
observed by [
93
], especially in the desert and forest experiments where participants
were free to look around as they pleased.
=−
0
.
