In the next phase the fly turns around its abdominal tip and finally it increases its forward velocity. The angular velocity during the latter two phases remains about constant until the fly is headed in the desired direction. During several consecutive steps of a final phase all the legs already recover in the desired direction. A representation of this direction is likely to exist. Of special interest is the role of the central complex in turning.
Flies walk freely on a glass surface covered with a thin layer of red laser light.
For the present analysis we added a third camera that images the fly from above. Orientation and position of the longitudinal body axis is extracted on-line and automatically combined with the spatial and temporal reconstruction of the leg actions. A concentric cylinder of 4 x 180 LED's around the detector allows for the display of rotating visual stimuli.