Meeting Abstract
As they navigate their environments, insects must parse the moving visual scene and respond to different features appropriately. In particular, they must distinguish between visual motion arising from their own movements relative to the environment (ego-motion) and those arising externally. Ego-motion creates optic flow across the entire visual field, called wide-field motion. In contrast, an external agent moving in the visual field (e.g. a wavering flower or an approaching predator) stimulates only a small patch that travels coherently across the retina, hence called small-field motion. To fixate a moving scene, the hawkmoth, Manduca sexta, can either reorient its entire body or change the angle of its head to redirect gaze. For pitch stabilization, moths respond predominately to wide-field motion, modulating both body posture and head orientation to follow expansive visual stimuli. Our recent experiments also show that for some visual scenes, moths exhibit head movements strongly correlated to the small-field visual motion, suggesting that head motion and body posture reorientation are separable strategies for visual fixation. To identify these parallel strategies, we investigate which aspects of the visual scene elicit head motion by changing the relative salience of the wide- and small-field stimuli. Moths are tethered at the center of a cylindrical visual arena and presented an image of a flower against mottled backgrounds of varying contrast and spatial frequency. The flower and background oscillate vertically at different temporal frequencies. A Fourier analysis reveals the extent to which the moth nods its head in response to each stimulus. Our data suggests that moths use the head-motion strategy to follow the small-field target provided the background has sufficiently low spatial frequency (blurry and lacking prominent edges).
