Kg Götz

Flight control in Drosophila by visual perception of motion.

SummaryApparent motion was simulated in the visual system of the tethered fruitfly Drosophila melanogaster by projecting moving stripe patterns onto stationary screens positioned in front of the lateral eye regions. The reactions of the animal were recorded under conditions of stationary flight in still air. It was found that visual stimulation modifies, independently, torque and thrust of the flight system. The responses appear suitable to counteract involuntary changes of direction and altitude in free flight.Concerning the sensory system for visual flight control, the following was established:1.Both eyes are functionally equal, and sensitive to pattern motion in any direction.2.The motion detecting subunits possess a certain orientation on the eye surface, and discriminate between pattern motions that are progressive or regressive relative to this orientation.3.Progressive and regressive stimuli elicit opposite responses in the flight system.4.The subunit orientations are expected to group in at least two different directions that share a common line of symmetry with the internal eye structure.5.A minimum of two contralateral and two ipsilateral nerve connections between the visual system and the motor system is required for the various torque and thrust responses. Concerning the effect of pattern motion on the flight system, the following was found:1.The motion detectors control only the magnitude of the force of flight. With the tethered animal in still air, the inclination of the force vector remains constant.2.Consequently, the stroke plane and the wing pitch should be invariant to visual stimulation.3.Possible influences of pattern motion on the wing-beat frequency were ruled out by frequency measurements.4.The only major variables in wing articulation that respond to pattern motion are the wing-beat amplitudes on either side of the insect. In-flight photographs show that the difference and the sum of these amplitudes are, in fact, representative for the torque and the thrust of the flight system. The responses of the body posture may become important to flight performance at increased airspeed. Comparative experiments with the housefly Musca domestica indicate that the principle of independent torque and thrust control by vision is adopted in at least two different species.

Visual control of locomotion in the walking fruitflyDrosophila

SummaryTo investigate the optomotor leg responses ofDrosophila melanogaster the free walking fly is kept in stationary orientation and position on top of a ball. The stimulus consists of continuous pattern movement in the equatorial zone of the visual field. The rotatory and translatory responses are derived from the signals of a servo-system which maintains the stationary state of the walking fly by appropriate rotations of the ball.Course control, or the tendency to follow rotatory displacements of the visual surroundings, is established in the wild type and in a behavioural mutant with the eye colour markerwa.The movement detecting systems in the complex eyes on either side respond to the horizontal component of the stimulus and control, predominantly, the thrust of the ipsilateral legs in the wild type, and the thrust of the contralateral legs in the mutant. As a result, front-to-back movement is decreasing the walking speed of the wild type and increasing the walking speed of the mutant, andvice versa.The course control responses of flying and walking fruitflies depend on the signals of movement detecting systems which are equivalent with respect to the horizontal orientation, the dynamic range, and the resolving power. Leg responses show that the orientation of the movement detecting systems is independent of their position in the eye, and is invariant to the direction and velocity of the stimulus.The lift control response to the vertical component of the movement stimulus is a quality of the flight system. The response has no counterpart in the optomotor behaviour of the stationarily walking fruitfly.Functional specialization of the different pairs of legs is not detectable in the present experiments. The rotatory response as well as the translatory propulsion are almost equally accomplished by the fore legs, the middle legs and the hind legs of partially amputated fruitflies.The optomotor reactions of the fruitfly are accompanied by at least two side-effects of the visual stimulus: The flicker effect acts on the walking speed. The effect is elicited by the temporal sequence of bright and dark stripes in the receptive fields of the visual elements. It is independent of the direction of the pattern movement, and can be produced by a stationarely flickering light source. An after-effect of the pattern movement appears at the end of the visual stimulation. The effect depends on experimental parameters. An initial magnitude of -1/16 of the preceding course control response and a decay time of about 7 min were observed in the present experiments.

Die optischen Übertragungseigenschaften der Komplexaugen von Drosophila

SummaryThe transfer properties of the optical system in the arthropod compound eye are determined by the interommatidial angle Δ ϕ, influencing the resolving power, and by the width of the visual fields of single ommatidia Δ ϱ, influencing the response at high spatial frequencies of brightness distributions in the object space. The energy transfer/ receptor is proportional to (Δϕ Δ ϱ)2 and decreases with in-inreasing approximation of the perfect-imaging condition: gDϕ → 0; Δϱ → 0. However, a value Δϕ Δϱ > 0 has to be maintained in order to overcome the threshold of nervous excitation at a certain minimum-brightness level. Theoretical treatment yields Δϱ/Δϕ=0.62 to 0.88 as the corresponding optimum-imaging relation. The actual ratio can be derived from measurements of the optomotor reactions to the movement of periodic brightness patterns. The approximate value 0.76 is obtained from the fruitfly Drosophila with normal and mutant eye pigmentation. As a result, the parameters of this imaging system are found to be established in a way that enables optimum performance at sufficient illumination. An dieser Stelle möchte ich Dr. W. Reichardt für sein eingehendes Interesse und manche anregende Diskussion über die Sehvorgänge im Komplexauge meinen Dank sagen. Dr. K. Kirschfeld verdanke ich ebenfalls wertvolle Hinweise. Herrn E. Freiberg bin ich für die Anfertigung der Abbildungen sehr verbunden.

Optomotor control of wing beat and body posture in drosophila

Continuous movement of striped patterns was presented on either side of a tethered fruitfly, Drosophila melanogaster, in order to simulate the displacement of stationary landmarks within the visual field of the freely moving fly. The horizontal components of the stimulus elicit, predominantly, yaw-torque responses during flight, or turning responses on the ground, which counteract involuntary deviations from a streight course in the corresponding mode of locomotion. The vertical components elicit, predominantly, covariant responses of lift and thrust which enable the fly to maintain a given level of flight. Monocular stimulation is sufficient to produce antagonistic responses, if the direction of the stimulus is reversed. The following constituents of the responses were derived mainly from properties of wing beat and body posture on photographs of fixed flight under visual stimulation. Wing stroke modulation (W. S. M.): The difference, and the sum, of the stroke amplitudes on either side are independently controlled by horizontal and vertical movement components, respectively. The maximum range of modulation per wing (12.3°) is equivalent to a 63% change in thrust on the corresponding side. Leg stroke modulation (L.S.M.): In the walking fly each pair of legs is under control of visual stimulation. The details of leg articulation are still unknown. Abdominal deflection (A.D.): An actively induced posture effect. Facilitates steering during free flight at increased air speed. Hind leg deflection (H.L.D.): Same as before. On most of the photographs the hind legs were deflected simultaneously and in the same direction as the abdomen. Hitch inhibition (H.I.): The term “hitch” denotes a transient reduction of stroke amplitude which seems to occur spontaneously and independently on either side of the fly. The hitch angle (12.2±3.8° S.D.) is most probably invariant to visual stimulation. Hitches are comparatively frequent in the absence of pattern movement. Their inhibition under visual stimulation is equivalent to an increase of the average thrust of the corresponding wing. The different constituents contribute to the optomotor responses according to the following tentative scheme (Fig. 7). The torque response is essentially due to the effects of W.S.M., A.D., H.L.D. and H.I., and the turning response to L.S.M. and possibly H.L.D., if the landmarks drift from anterior to posterior. So far, H.I. seems to be the only source of the torque response, and L.S.M. the only source of the turning response, if the landmarks drift in the opposite direction. The lift/thrust response results essentially from the effects of W.S.M. and H.I., no matter whether the landmarks drift from inferior to superior or in the opposite direction. The results obtained so far suggest that the optomotor control of course and altitude in Drosophila requires at least eight independent input channels or equivalent means for the separation of the descending signals from the visual centres. Further extension and refinement of the “wiring scheme” is required in order to improve the identification of the sensory inputs of the motor system and the classification of optomotor defective mutants.

The optomotor equilibrium of theDrosophila navigation system

SummaryIn his discussion of the optomotor behaviour Kalmus claimed in 1964 that the visual systems of insects continuously resolve horizontal displacements relative to the surroundings into rotatory and translatory components, each associated with optomotor feedback of particular quality and sign. The feedback is supposed to achieve, simultaneously, minimization of the rotatory movements and maximization of the translatory movements, a behaviour repeatedly observed with actively moving insects such as the fruitflyDrosophila melanogaster.The present approach takes into account that the output of movement detectors in the visual system of insects is necessarily equivocal with respect to the speed of the stimulus (e.g. zero output at both zero and infinite speed). Decomposition of the stimulus is not feasible under these conditions. It is obviously the composite stimulus to which the insects respond. Moreover, there is experimental evidence that optomotor feedback on the translatory movement is not necessarily a response-determining factor in insects. The optomotor behaviour of the walking fruitfly is sufficiently described by the sum of itsrotatory responses to the composite stimuli on either side.A diagram representing the expected rotatory response of the walking fruitfly as a function of both the rotatory and the translatory stimulus component is used to derive the prevailing traits of the behaviour in resting, rotating and floating environments, respectively. Most conspicuous is the inversion of the course-control response in about one half of the possible states of stimulation. This effect gives rise to at least some of the apparently spontaneous turns of actively moving insects which have been ascribed by v. Holst and Mittelstaedt to efferent commands from higher centres of the brain, according to their principle of reafference. The present results merely disprove the necessity of these commands. Inversion of the response is also an inherent property of the course-control systems of the optomotorically active insects. The expected increase of these inversions with closer proximity of the visual environment is found by observation of walking fruitflies.The relation between the rotatory and translatory movements of the freely walking fly and its state of stimulation in a given environment is used to describe the expected behaviour in terms of the most probable transition of state. The approach is based on estimates of the power required by the fly in order to maintain a given state against the torque that is produced by its course-control system in response to the optomotor stimulation. The most probable transition of state is apparently determined by the tendency of the fly to decrease the power requirement by appropriate adaptation of its rotatory movement. The transition may come to an end in one of the states of minimum power requirement where the speed of the rotating fly is held in a stable optomotor equilibrium.

The use of mutations for the partial degradation of vision in Drosophila melanogaster

SummaryPartially blind mutants can be used to investigate the processing of visual information in the fruit flyDrosophila. This approach requires (1) procedures for the selection of a variety of partially blind mutants, and (2) a strategy for the identification and coordination of visual malfunctions by comparison of interrelated traits of behaviour.The two selection techniques so far employed to recover partially blind mutants use either the fast phototaxis or the optomotor response as selection determining behaviour. The second method is described here and is applied specifically to select mutants in which one of the two autonomous subsystems of vision designated asHigh Sensitivity System andHigh Acuity System is defective. (The mutants obtained are apparently normal with respect to their HAS whereas the HSS is blocked.)Two sets of experiments have been developed in order to test interrelated traits of behaviour in a comparatively large number of flies. One set of experiments measuresslow phototaxis as a function of light intensity. The other is to determine the optomotor response to moving patterns of different spatial periods as functions of both the average brightness and the speed of the movement. Further techniques such as electroretinography and optical inspection of the eyes are used to complement the behavioural approach.By combination of the different tests a first step has been made in the characterization and classification of partially blind mutants with neuronal disorders obtained by different selection procedures and in different laboratories.

Visual Guidance in Drosophila

One of the last enquiries inspired by Theodosius Dobzhansky is entitled, “How far do flies fly?”.1 The paper refers to several field studies where a labelled strain of Drosophila was released and its dispersal measured by recapture of labelled flies on subsequent days. If the dispersal is simply due to random movements of the flies, then it should be analogous to the dispersal of small particles performing Brownian movements. Expected, in this case, is a normal distribution of the flies such that the increase of their mean distance from the release point is proportional to the square root of the time elapsed since the release. The expected time dependence of the dispersal seems to hold, more or less, for colonies of D. pseudoobscura, and the diffusion model may be considered as a reasonable first approximation of the locomotor behavior. However, the expected profile of the distribution has not been verified. Conspicuously more flies were recaptured both near the release point and at the outer periphery of the field. This discrepancy was explained by the tendency of Drosophila either to remain in a favorable habitat, or to cover great distances in search of such a habitat. The observation suggests that the control of locomotion can be adapted by the fly to different situations and requirements. The locomotor behavior of D. melanogaster has been extensively studied in laboratory experiments. Most of the results obtained so far refer to optomotor responses which enable the fly to maintain a given course and altitude over extended periods of time.

Optomotor control of the force of flight in Drosophila and Musca

Drift of the retinal images of the surroundings elicits optomotor responses of flight control in the fruitfly, Drosophila melanogaster, and in the housefly, Musca domestica. The present investigation deals with the responses of tethered flies in still air. The responses were elicited by continuous movement of striped patterns in front of the eyes, and characterized by the magnitude and elevation of the resulting force of flight which is the average of the forces produced during a wingbeat cycle. The force of flight is resolved into the upward directed lift and the forward directed thrust.In either species, pattern movement acts upon the magnitude, but not upon the elevation of the force of flight. The elevation relative to the longitudinal body axis is almost invariably 24° in Drosophila, and 29° in Musca. The lift/thrust ratio in still air is fixed accordingly, and can be changed only by variation of the body angle. Keeping an angle of minimum body drag does not contribute significantly to the efficiency of insect flight at very low Reynolds numbers (Re). Control of the lift/thrust ratio by variation of the body angle is, therefore, less surprising in Drosophila where Re is in the order of 102, than in Musca, where Re is in the order of 103. Control of this ratio without variation of the body angle is actually established in insects flying at even higher Re.Covariance of lift and thrust in the investigated flies is achieved by control of wingbeat amplitude or wingbeat frequency, but not by control of wing pitch or stroke plane. A change in the latter parameters would have deflected the force of flight and is, therefore, inconsistent with the constant elevation found in the present experiments. The results obtained, so far, do not exclude active deflections of the force vector during occasional bouts of aerobatics, or passive deflections of this vector during flight at non-zero airspeed.

Der Einfluß des Schirmpigmentgehalts auf die Helligkeits- und Kontrastwahrnehmung bei Drosophila-Augenmutanten

SummaryThe function of the facet-separating pigments in the compound eyes of the fruitfly Drosophila melanogaster with hypernormal (se), normal (+), subnormal (wa), and missing (w) pigmentation was studied by investigation of: (1) the in-flight optomotor responses to movement of striped patterns with a mean brightness of 300 cd/m2, and (2) the retinal action potentials evoked by flashes in a program of .0003 cd/m2 average brightness. The pigment deficient mutants (wa, w) are less sensitive to the pattern contrast in the bright adapted state, and more sensitive to the flash intensity in the dark adapted state than either the wild-type (+) or the overpigmented mutant(se). These differences are complementary and can be explained by the increased translucency of the pigment cells. Thus the photoreceptors in the equally illuminated eyes of the normal and mutant animals +, se, wa, and w are expected to receive light in a ratio of about 1∶1∶7∶19. However the sensitivity of the receptors as well as the half-peak widths and the density of their visual fields are apparently independent of the eye pigmentation and seem to be equal at common levels of adaptation. The effects of omnidirectional excess light reaching the receptors of the pigment deficient mutants can be simulated in less translucent eyes: when certain amounts of background illumination were combined with the optomotor stimulus in the visual fields of the wild-type receptors it was possible to elicit the predicted “mutant behavior”.

Virtual-Reality Techniques Resolve the Visual Cues Used by Fruit Flies to Evaluate Object Distances

Insects can estimate distance or time-to-contact of surrounding objects from locomotion-induced changes in their retinal position and/or size. Freely walking fruit flies (Drosophila melanogaster) use the received mixture of different distance cues to select the nearest objects for subsequent visits. Conventional methods of behavioral analysis fail to elucidate the underlying data extraction. Here we demonstrate first comprehensive solutions of this problem by substituting virtual for real objects; a tracker-controlled 360 degrees panorama converts a fruit flys changing coordinates into object illusions that require the perception of specific cues to appear at preselected distances up to infinity. An application reveals the following: (1) en-route sampling of retinal-image changes accounts for distance discrimination within a surprising range of at least 8-80 body lengths (20-200 mm). Stereopsis and peering are not involved. (2) Distance from image translation in the expected direction (motion parallax) outweighs distance from image expansion, which accounts for impact-avoiding flight reactions to looming objects. (3) The ability to discriminate distances is robust to artificially delayed updating of image translation. Fruit flies appear to interrelate self-motion and its visual feedback within a surprisingly long time window of about 2 s. The comparative distance inspection practiced in the small fruit fly deserves utilization in self-moving robots.