Flight performance and visual control of flight of the free-flying housefly ( musca domestical L.) III. Interactions between angular movement induced by wide- and smallfield stimuli

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Abstract
The flights of free-flying houseflies are analysed in different behavioural and environmental situations. The angular movements about the vertical body axis are characterized by a cascade of steplike changes of long axis orientation (‘turns’). Most of these turns are separated by periods of little or no rotation. Turns about the vertical axis are short (under 120 ms). They are performed at angular velocities of up to about 4000 deg s -1 . These characteristics are found (i) when a single fly cruises in a stationary environment; (ii) if the visual input is eliminated; (iii) if a textured surround (optomotor stimulus) is moved around the fly; (iv) during visually guided pursuit of small targets in stationary as well as in moving environments. Optomotor stimulation increases the number of turns in the direction of pattern motion relative to those against it. This leads to a correlation between the average angular velocity of the fly and the stimulus velocity. However, optomotor stimulation does not interfere with chasing and tracking. A model is proposed that qualitatively accounts for the observed behaviour in free flight of houseflies.