Upon observing a fly in the flight simulator, it is striking that the
fly neither keeps the cylinder immobilized nor rotates it continuously:
phases of fairly straight flight are interrupted by sudden turns at high
angular velocity. Monitoring the fly's yaw torque, the turns are due to
short pulses of torque (torque spikes, Fig. 4). The fly generates these
torque spikes by reducing the wing beat amplitude by about 12° on the
side to which it intends to turn (wing hitch; Götz et al. 1979; Götz,
1983). These sudden turns ("body saccades") can be observed in
free flying Drosophila as well. Based on previous work from Heisenberg
and Wolf (1979), Heisenberg and Wolf (1984), Mayer et al. (1988) and Heisenberg
and Wolf (1993), the present study assumes that the spikes are the primary
behavior by which the fly adjusts its orientation in the panorama; further
evidence in accordance with this assumption is discussed below (3.3).
Fig.
4: Illustration of typical flight orientation behavior in the flight simulator.
The pattern, in this case a single vertical black stripe, is assumed to
be at infinite distance from the fly, i.e. the angular position of the
stripe does not change during straight flight. a. Flight trace, consisting
of torque and position trace, used to calculate the flight trajectory depicted
in b. Forward flight velocity was assumed to be constant. It can be seen
that the torque spikes in (a) correspond with the stepwise turning of the
panorama. (Redrawn from Heisenberg and Wolf, 1984)
Fig.
4: Illustration of typical flight orientation behavior in the flight simulator.
The pattern, in this case a single vertical black stripe, is assumed to
be at infinite distance from the fly, i.e. the angular position of the
stripe does not change during straight flight. a. Flight trace, consisting
of torque and position trace, used to calculate the flight trajectory depicted
in b. Forward flight velocity was assumed to be constant. It can be seen
that the torque spikes in (a) correspond with the stepwise turning of the
panorama. (Redrawn from Heisenberg and Wolf, 1984)