Drosophila integrates visual evidence and counterevidence in self motion estimation.

In selecting a behavior, animals should weigh sensory evidence both for and against their beliefs about the world. For instance, animals use optic flow to estimate and control their own rotation. However, existing models of flow detection can confuse the movement of external objects with genuine self motion. Here, we show that stationary patterns on the retina, which constitute negative evidence against self rotation, are used by the fruit fly Drosophila to suppress inappropriate stabilizing rotational behavior. In parallel in silico experiments, we show that artificial neural networks trained to distinguish self and world motion incorporate similar negative evidence. We used neural measurements and genetic manipulations to identify components of the circuitry for stationary pattern detection, which is parallel to the fly’s motion- and optic flow-detectors. Our results exemplify how the compact brain of the fly incorporates negative evidence to improve heading stability, exploiting geometrical constraints of the visual world.