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Abstract

The stabilization of gaze may involve multiple sensory systems. In blowflies, the reflex depends on input from the compound eyes, ocelli, halteres and campaniform sensilla located on the wings to provide input for the reflex. Individually, the corresponding pathways involved cover different dynamic input ranges, incur different processing delays, and suffer from different levels of sensor and processing noise. Information from multiple sensory pathways must be integrated in order to effect appropriate movements of the head to stabilize gaze, however it is not entirely clear how this happens. We investigated the combination of information from the two visual pathways contributing to gaze stabilization: the motion vision pathway provided by the compound eyes, and the ocellar pathway, measuring light intensity changes in the dorsal visual hemisphere due to attitude changes. Using high speed videography we measured compensatory rotations of the head in response to a simulated roll rotation of a false-horizon around the fly, oscillating at up to 10 Hz. We applied a linear systems analysis to obtain the individual frequency responses for the two pathways. We found that the ocellar input reduces the response delay by an average of 5 ms but does not significantly affect the response gain or bandwidth. Our result suggests a non-linear integration of compound eye and ocellar information. We are now performing intracellular recordings from elements along the visuo-motor pathway likely to be involved in the integration of motion vision and ocellar signals, in response to the same visual stimulus used to evoke head movements in our behavioural experiments. This will allow us to study how signals induced by a common visual input, and affected by different processing delays along the two visual pathways, are combined to ultimately reduce the delay in the behavioural output.