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The landing response of tethered flying housefliesMusca domestica elicited by motion of periodic gratings is analysed. The field of view of the compound eyes of a fly can be subdivided into a region of binocular overlap and a monocular region. In the monocular region the landing response is elicited by motion from front to back and suppressed by motion from back to front. The sensitivity to front to back motion in monocular flies (one eye covered with black paint) has a maximum at an angle 60°–80° laterally from the direction of flight in the equatorial plane. The maximum of the landing response to front to back motion as a function of the contrast frequencyw/λ is observed at around 8 Hz. In the region of binocular overlap of monocular flies the landing response can be elicited by back to front motion around the equatorial plane if a laterally positioned pattern is simulataneously moved from front to back. 40° above the equatorial plane in the binocular region the landing response in binocular flies is elicited by upward motion, 40° below the equatorial plane in the binocular region it is elicited by downward motion. The results are interpreted as an adaptation of the visual system of the fly to the perception of a flow field having its pole in the direction of flight.

The optomotor yaw torque response of fixed flying female houseflies, Musca domestica to three different types of visual stimuli is analyzed. In contrast to most previous investigations, the stimuli were displayed for short time intervals only in order to approximate transiently occuring visual stimuli, which mainly govern the torque generation during free flight. Monocular stimulation with a periodic pattern moving in different positions in the equatorial plane of the compound eyes reveals that (1) flight torque responses are mainly induced by progressive (front to back) motion; regressively moving stimuli are significantly less effective. (2) the strength of the response to motion in the horizontal direction depends on the position of the stimulus and (3) vertical motions do not elicit flight torque responses. Correspondingly the response to a single vertical black stripe moving clockwise in a cylindrical panorama centered around the fly is small if the stripe is in the visual field of the left eye but becomes large and strongly depending on position if the stripe enters the visual field of the right eye. The response to counterclockwise motion of the stripe is small if the stripe is in the visual field of the right eye but becomes large and strongly depending on position if the stripe enters the visual field of the left eye. Torque responses to two adjacent stripes whose intensities are modulated in time with a rectangular function can be elicited if apparent motion is generated by means of a phase difference between the intensity modulations of the two stripes. Apparent progressive motion elicits strong torque responses, apparent regressive motion is less effective. Synchronous flicker of both stripes does not elicit torque responses. The extraction of positional information from the incoming visual signals has been considered to play an important role in the orientation behaviour, and especially in the tracking behaviour of flies. The results of the experiments indicate, that under transient stimulation the evaluation of positional information is in general not mediated by formerly postulated flicker detectors but is bound to the computation of motion. These findings are implemented in a model, describing the free flight tracking behaviour of a female fly on the horizontal plane. It is shown that tracking can be achieved by a mechanism whose sensitivity to motion is parametrized in the stimulus position as outlined above. The results of the behavioural experiments are interpreted in view of electrophysiological and anatomical data on giant interneurons in the third optic ganglion of the fly.

The visually controlled height orientation of fixed flying flies (Musca domestica) was investigated. The flight lift force measured by a transducer drives the vertical motion of a panorama. The dynamical conditions of the free flight are electronically simulated for the fly with respect to this degree of freedom of motion. In most of the experimentally investigated cases the panorama consists of a horizontally oriented narrow dark stripe on a bright background. The fly orientates with respect to the stripe, transporting it into a stable fixation position just below the equatorial plane of its compound eyes. It is experimentally demonstrated that the formalism of the linearized theory of the pattern induced flight orientation -- Poggio and Reichardt (1973a) -- can be applied to describe the height orientation of the fly. The experimental evidence concerning the simultaneous perception of stripes moving in a well defined manner in front of each of the two compound eyes is consistent with the hypothesis that the two halves of the visual system are perceptually additive.

The flight trajectories of free flying female and male houseflies have been analyzed in 3 dimensions. Both female and male flies track other flies. The turning velocity agr (around the vertical axis) is linearly dependent upon the horizontal angle psgrF (that is the angle between the trajectory of the tracking fly and the target) for small values of psgrF in females and for the whole range of psgrF in males. The 3-dimensional velocity ugr xyz of the chasing fly is linearly dependent upon the distance between leading and chasing fly in males but not in females. Male chasing thus appears to be more efficient than female tracking. It is shown that earlier assumptions on visual control of flight in female flies derived from experiments on fixed flying flies are justified.

Color vision in humans is independent over a wide range of the spectral composition of the illuminating light (Young 1807; Hering 1879). The retinex theory accounts for this color constancy by assuming that for each of the three waveband channels determined by the retinal cones a global lightness record of the scene is first computed by the visual system. The three records then serve to generate color at every point (Land 1983). Where do these computations take place? In this report a scene consisting of fourteen colored fields was viewed while one band of wave-lengths enters one eye and a different band enters the other (dichotpic case) or while both bands enter both eyes (normal case) under otherwise identical conditions. The perceived color of every field is very similar in both cases although the physical stimulation of the eyes differs. It is also found that color constancy is maintained under dichoptic conditions. The results show that the cortex is crucial for the computation of color.

Flies were filmed simultaneously from above and from the side. Their flight tracks were analyzed frame by frame. Male and female flies were found to chase other flies. But female chases are brief and poorly controlled as compared to male chases. Female flies use the lower frontal part of their visual field for tracking other flies. Male flies use the upper frontal part of their visual field for that purpose. Male flies are capable of controlling their forward velocity roughly proportional to the distance to their target. Implications for the function of recently found sexdimorph visual interneurones are discussed.

The lift response of houseflies Musca domestica in fixed flight to periodic gratings movins in 12 different orientations has been measured. Two projectors were arranged symmetrically to the flies stimulating successively 18 circular patches of 50 degrees (25 degrees) diameter (9 for each eye) in their visual field. The shapes of the lift responses measured as a function of the orientation of the moving grating varied when different patches in the visual field were stimulated. A qualitative comparison of these response curves leads to the conclusion that the orientation of the movement detecting substrate acting on the flight lift response varies as a function of the stimulated area in the visual field. A straightforward correlation between the geometry of the ommatidial pattern and the orientation of the movement detecting substrate valid for all stimulated areas of the compound eyes does not seem very likely.

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.