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Abstract

In blowflies, two visual systems input to the gaze stabilization system: the motion vision pathway provided by the compound eyes, and the ocelli, which signal light intensity changes in the dorsal visual hemisphere. Individually, these pathways cover different dynamic input ranges and incur different processing delays. The signals provided by these two pathways are integrated and used to effect appropriate movements of the head to stabilize gaze, but the underlying mechanisms have not yet been studied quantitatively. In behavioural experiments we simulated body roll and measured compensatory head rotations in response to oscillations of a false-horizon at up to 10 Hz. We found that the ocellar input reduces the response delay by an average of 5 ms but does not significantly affect the response gain, suggesting a non-linear integration of compound eye and ocellar signals. We are now performing intracellular recordings from descending neurons receiving input from the motion vision pathway and the ocelli in response to the same visual stimulus used in our behavioural experiments. This will allow us to study how the signals are combined to give the behavioural output observed.