Visual steering under closed-loop conditions by flying locusts: flexibility of optomotor response and mechanisms of correctional steering

Abstract

1. Tethered locusts,Locusta migratoria, flying in a laminar air flow react to motion of the visual world with compensatory steering. 2. Vertical gratings surrounding the animal and rotating around the yaw axis elicit an optomotor yaw response. At the low light level used, gratings of spatial periods (λ) below 10° or of contrast frequency (CF) above 15 Hz are less effective. 3. In a flight simulator which converts torque into angular velocity of the vertical grating, the locust can control the motion of its visual surroundings. When the negative feedback loop is closed, locusts stabilize a vertical grating by modulation of their yaw torque. This indicates that the correctional steering behaviour described under open loop conditions is functionally relevant. 4. Under the same conditions, the optomotor reactions lead to the stabilization of a single vertical stripe in the frontal visual area (fixation). 5. With positive feedback (i.e. the pattern turns in the same direction as the torque), no corresponding inversion of steering is observed, and stabilization around the yaw axis fails. 6. Under similar negative feedback conditions, locusts stabilize the position of the visual horizon around the roll axis by modulating their roll torque. Positive feedback leads, however, to the stabilization of the horizon in the inverted position (reverse albedo). 7. The results suggest the existence of two steering strategies, one based on the parameters of visual movement and the other on position in the visual field and relative luminance. The use of these strategies is discussed.