Random attention can explain apparent object choice behavior in free-walking blowflies

Flies are often observed to approach dark objects. To a naïve observer they seem to pay selective attention to one out of several objects although previous research identified a reflex-like fixation behavior integrating responses to all objects as possible underlying mechanism. In a combination of behavioral experiments and computational modelling, we investigate the choice behavior of flies freely walking towards an arrangement of two objects placed at a variable distance from each other. The walking trajectories are oriented towards one of the objects much earlier than predicted by a simple reactive model. We show that object choice can be explained by a continuous control scheme in combination with a mechanism randomly responding to the position of each object according to a stochastic process. Although this may be viewed as a special form of an attention-like mechanism, the model does not require an explicit decision mechanism or a memory for the drawn decision. Summary Statement Walking blowflies apparently choose one of two objects to approach. In model simulations, a fixation scheme combined with random attention replicates this behavior without an explicit decision mechanism.