A Simple Vision-Based Algorithm for Decision Making in Flying Drosophila
Animals must quickly recognize objects in their environment and act accordingly. Previous studies indicate that looming visual objects trigger avoidance reflexes in many species 1, 2, 3, 4, 5; however, such reflexes operate over a close range and might not detect a threatening stimulus at a safe distance. We analyzed how fruit flies (Drosophila melanogaster) respond to simple visual stimuli both in free flight and in a tethered-flight simulator. Whereas Drosophila, like many other insects, are attracted toward long vertical objects 6, 7, 8, 9, 10, we found that smaller visual stimuli elicit not weak attraction but rather strong repulsion. Because aversion to small spots depends on the vertical size of a moving object, and not on looming, it can function at a much greater distance than expansion-dependent reflexes. The opposing responses to long stripes and small spots reflect a simple but effective object classification system. Attraction toward long stripes would lead flies toward vegetative perches or feeding sites, whereas repulsion from small spots would help them avoid aerial predators or collisions with other insects. The motion of flying Drosophila depends on a balance of these two systems, providing a foundation for studying the neural basis of behavioral choice in a genetic model organism.
© 2008 Elsevier Ltd. Received 10 January 2008, Revised 20 February 2008, Accepted 21 February 2008, Available online 13 March 2008. We thank Michael Reiser for extensive help with the tethered-flight paradigm and helpful comments. Andrew Gartland and Tong-Wey Koh first developed the polar-plot method of analyzing the closed-loop tethered-flight data during experiments on this topic in Woods Hole, MA (2005). We would like to acknowledge Aza Raskin for the idea of a flux transit-probability histogram. We would like to thank David O'Carroll for useful comments. This work was supported by grants from the National Science Foundation (FIBR 0623527), Office of Naval Research (N00014-01-1-0676), and the Air Force Office of Scientific Research (FA9550-06-1-0079) (to M.H.D), as well as a Caltech Della Martin Fellowship (to G.M.).
Supplemental Material - 1-s2.0-S0960982208002418-mmc1.pdf