Figure 5.

Vehicles in motion driven by an odor gradient. The type A vehicle relies on instantaneous olfactory perception and utilizes an indirect orientation mechanism where turning rate and velocity are a function of the stimulus concentration (kinesis). The underlying simple orientation rule is: If the concentration is low, turn frequently. Conversely, if the concentration is high, suppress random turns and go straight. This rule results in an indirect trajectory toward the odor source. The type B vehicle is equipped with a moveable head (side-to-side) with two sensors. The underlying orientation rule is: When the head is engaged to the side, inhibit the ipsilateral motor at a level proportional to the sensory input. This rule results in a trajectory sequentially aligned with the vector field of the stimulus gradient (taxis). The type C vehicle has the capacity to simultaneously measure concentrations at different points in space via purely spatial comparisons (osmotropotaxis). The underlying orientation rule is: If the difference in concentration across the two sensors is zero, increase the activation both motors at a level proportional to the sensory input. Conversely, if a concentration difference is measured across the two sensors, activate more strongly the motor opposite the side of highest odor concentration. This rule results in a trajectory aligned with the vector field of the stimulus gradient. Behaviors following source acquisition are illustrated in the panels on the right.