Since torque trace and position trace are measured simultaneously, the
torque trace can be used to calculate the effects of torque on arena position.

Angular Displacement Size. As another measure of spike dynamics
the angular displacement during each detected spike is calculated by the
distance between two position-data points in degrees, the corresponding
torque values of which denote the duration of the spike (Fig. 10).

Stepwise Arena Rotation. As a quantitative measure for the subjective
impression of sudden arena rotations accounted for by spikes, the sum of
angular displacements during spikes is compared to the sum of interspike
displacement for each 2 min. period in a rotation index: (r_{s}-r_{i})/(r_{s}+r_{i}),
where r_{s} denotes the sum of angular displacement during the
spikes and r_{i} the sum of arena displacements between two spikes.

Spike Detection Efficiency

A subjective test for spike detection efficiency was performed with
five members of the lab, only one of whom was familiar with Drosophila's
body saccades: they were presented with the task to count the number of
spikes in the torque traces of four deliberately chosen flies. The mean
number of detected spikes in the first three periods was compared to the
number the spike detector counted. Two of the flies were deemed to be 'regular'
flies producing spikes that were very easy to distinguish from the torque
baseline. The third fly was flying in the 'oscillating' mode and the fourth
fly in the 'quiet' mode.