. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 198 J. SCHMITZ ET AL. This system with only eight or nine nonzero weights is able to generalize over a considerable range of untrained situations. Furthermore, the swing net is remarkably tolerant with respect to external disturbances (Fig. 3). The learned trajectories represent a kind of attractor to which the dis- turbed trajectory returns. This compensation for distur- bances is possible because the system does not compute explicit trajectories but—using actual sensor data—calcu- lates only the next movement increment. Th
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 198 J. SCHMITZ ET AL. This system with only eight or nine nonzero weights is able to generalize over a considerable range of untrained situations. Furthermore, the swing net is remarkably tolerant with respect to external disturbances (Fig. 3). The learned trajectories represent a kind of attractor to which the dis- turbed trajectory returns. This compensation for distur- bances is possible because the system does not compute explicit trajectories but—using actual sensor data—calcu- lates only the next movement increment. This ability to compensate for external disturbances permits simple exten- sions of the swing net in order to simulate avoidance be- haviors observed in insects (additional inputs "rl-r4" in Fig. Ib). Control of the Stance Movement To control the stance movement, it is not enough simply to specify a movement for each leg on its own: the mechan- ical coupling through the substrate means that efficient locomotion requires coordinated movement of all the joints of all the legs in contact with the substrate—that is, a total of 18 joints when all legs of an insect are on the ground. However, the number and combination of mechanically coupled joints varies from one moment to the next, depend- ing on which legs are lifted. A further complication occurs when the animal negotiates a curve, because then the dif- ferent legs move at different speeds. 10 , 5 E E TO n c « 1 8 N -5 -10. -15 -10 -5 10 15 20 25 x-coordinate [mm] Figure 3. Behavior of the swing net. The tine stippled line represents a trajectory (in the A-C plane, , in a side view) of the tibia endpoint of a middle leg of an undisturbed swing movement. The leg lifts off at the posterior extreme position (PEPI and swings forward to the anterior ex- treme position (AEP). The dashed line represents a swing trajectory of the middle leg in which the movement of the tibia was obstructed (arrow). The swing net insta
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
