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

Flies are often observed to approach dark objects. To a naive observer they seem to pay selective attention to one out of several objects although previous research identified as a possible underlying mechanism a reflex-like fixation behavior integrating responses to all objects. In a combination of behavioral experiments and computational modelling, we investigated the choice behavior of flies freely walking towards an arrangement of two objects placed at a variable distance from each other. The walking trajectories were 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. This may be viewed as a special form of an implicit attention-like mechanism, for which the model does not require an explicit decision mechanism or a memory for the drawn decision.