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Abstract

Visually evoked torque and lift responses in fixed flying houseflies Musca domestica, were measured under open loop conditions. The visual stimuli were: a) Vertical stripes (60°×5°), moving horizontally in a range±30°. b) Horizontal stripes (60°×5°), moving vertically in a range±30°. c) Vertical stripes (30°×5°), moving horizontally in a range±55° in five different planes relative to the equatorial plane (θ=0) of the fly's eye. d) Horizontal stripes (30°×5°), moving vertically in a range±45° in seven different planes (ψ=-45°,-30°,-15°, 0°, 15°, 30°, 45°) relative to the symmetry line (ψ=0) between the two compound eyes. e) Periodic gratings displayed by two projectors at each side of the test animals (the middle part was situated at ψ=±50°). The stimulated area was roughly 52°×80° (∼2000 ommatidia). This stimulus was used only in lift experiments. The results are: 1) The preferred direction of the direction sensitive torque response corresponds with the z-direction (Braitenberg, 1971). 2) The direction sensitive torque response is elicited by stimulating above and below the equatorial plane. 3) The direction insensitive torque response is only elicited by stimulating close to and below the equatorial plane. 4) The preferred direction of the direction sensitive lift response has an angle tilted about 30° to the back relative to the vertical axis in the region described in e). 5) The magnitude of the direction sensitive lift response varies considerably over θ. 6) The w/γ dependence of the direction sensitive lift response corresponds qualitatively to the known w/γ dependence of the direction sensitive torque responses. 7) The direction insensitive lift response has its maximum at ψ=±15° and decreases with increasing ψ. 8) The findings reported in 3) and 8) indicate the existence of a two-dimensional potential from which the attraction towards a stripe in the two considered degrees of freedom can be derived. Implications for the visually induced orientation behaviour and connections with electrophysiological experiments are discussed.