FRYE, M.A.*; DICKINSON, M.H.: Fusion of visual and olfactory signals for flight control in flies

Fruit flies exhibit remarkable capacity for locating desirable odor sources within variable and complex visual environments. Using a combination of real-time 3-D video tracking during free flight, and a visual ‘virtual reality’ flight simulator modified to deliver odor during tethered flight, we studied how visual processing is affected by sensory signals from the olfactory system. In these experiments, responses to an attractive odor were compared for different visual conditions. During free flight, flies presented with either a textured background or individual visual features demonstrate greatly enhanced ability to localize an invisible odor source compared to flies presented with a uniform white background. This suggests that flies rely on visual cues to track the position of an odor source. During tethered flight in visual ‘closed-loop’ conditions (i.e. the fly controls the rotational velocity of a visual pattern in a panoramic arena), total wingstroke amplitude and frequency increase during odor stimuli – kinematic responses which were similar for all visual conditions. The variance in rotational image velocity decreases in odor when flies are controlling their view of a textured background, however this visual stabilizing response is absent when flies control a single vertical stripe. In free flight flies approach closer to arena walls near an odor source, suggesting that collision avoidance is suppressed in odor. However, responses to collision stimuli in closed-loop tethered flight are not affected by odor. Our results suggest that olfactory signals are selectively fused with optomotor signals used to stabilize gaze during flight, thereby enhancing the discrimination of stationary visual objects – potential odor sources – while preserving motion dependent feature tracking and collision avoidance behaviors.