Fly eyes are not still: a motion illusion in Drosophila flight supports parallel visual processing.

Most animals shift gaze by a 'fixate and saccade' strategy, where the fixation phase stabilizes background motion. A logical prerequisite for robust detection and tracking of moving foreground objects, therefore, is to suppress the perception of background motion. In a virtual reality magnetic tether system enabling free yaw movement, Drosophila implemented a fixate and saccade strategy in the presence of a static panorama. When the spatial wavelength of a vertical grating was below the Nyquist wavelength of the compound eyes, flies drifted continuously and gaze could not be maintained at a single location. Because the drift occurs from a motionless stimulus - thus any perceived motion stimuli are generated by the fly itself - it is illusory, driven by perceptual aliasing. Notably, the drift speed was significantly faster than under a uniform panorama, suggesting perceptual enhancement as a result of aliasing. Under the same visual conditions in a rigid-tether paradigm, wing steering responses to the unresolvable static panorama were not distinguishable from those to a resolvable static pattern, suggesting visual aliasing is induced by ego motion. We hypothesized that obstructing the control of gaze fixation also disrupts detection and tracking of objects. Using the illusory motion stimulus, we show that magnetically tethered Drosophila track objects robustly in flight even when gaze is not fixated as flies continuously drift. Taken together, our study provides further support for parallel visual motion processing and reveals the critical influence of body motion on visuomotor processing. Motion illusions can reveal important shared principles of information processing across taxa

Visual control of flight speed in Drosophila melanogaster

Flight control in insects depends on self-induced image motion (optic flow), which the visual system must process to generate appropriate corrective steering maneuvers. Classic experiments in tethered insects applied rigorous system identification techniques for the analysis of turning reactions in the presence of rotating pattern stimuli delivered in open-loop. However, the functional relevance of these measurements for visual free-flight control remains equivocal due to the largely unknown effects of the highly constrained experimental conditions. To perform a systems analysis of the visual flight speed response under free-flight conditions, we implemented a `one-parameter open-loop' paradigm using `TrackFly' in a wind tunnel equipped with real-time tracking and virtual reality display technology. Upwind flying flies were stimulated with sine gratings of varying temporal and spatial frequencies, and the resulting speed responses were measured from the resulting flight speed reactions. To control flight speed, the visual system of the fruit fly extracts linear pattern velocity robustly over a broad range of spatio–temporal frequencies. The speed signal is used for a proportional control of flight speed within locomotor limits. The extraction of pattern velocity over a broad spatio–temporal frequency range may require more sophisticated motion processing mechanisms than those identified in flies so far. In Drosophila, the neuromotor pathways underlying flight speed control may be suitably explored by applying advanced genetic techniques, for which our data can serve as a baseline. Finally, the high-level control principles identified in the fly can be meaningfully transferred into a robotic context, such as for the robust and efficient control of autonomous flying micro air vehicles

Miniature curved artificial compound eyes.

International audienceIn most animal species, vision is mediated by compound eyes, which offer lower resolution than vertebrate single-lens eyes, but significantly larger fields of view with negligible distortion and spherical aberration, as well as high temporal resolution in a tiny package. Compound eyes are ideally suited for fast panoramic motion perception. Engineering a miniature artificial compound eye is challenging because it requires accurate alignment of photoreceptive and optical components on a curved surface. Here, we describe a unique design method for biomimetic compound eyes featuring a panoramic, undistorted field of view in a very thin package. The design consists of three planar layers of separately produced arrays, namely, a microlens array, a neuromorphic photodetector array, and a flexible printed circuit board that are stacked, cut, and curved to produce a mechanically flexible imager. Following this method, we have prototyped and characterized an artificial compound eye bearing a hemispherical field of view with embedded and programmable low-power signal processing, high temporal resolution, and local adaptation to illumination. The prototyped artificial compound eye possesses several characteristics similar to the eye of the fruit fly Drosophila and other arthropod species. This design method opens up additional vistas for a broad range of applications in which wide field motion detection is at a premium, such as collision-free navigation of terrestrial and aerospace vehicles, and for the experimental testing of insect vision theories

A computational analysis of separating motion signals in transparent random dot kinematograms

When multiple motion directions are presented simultaneously within the same region of the visual field human observers see motion transparency. This perceptual phenomenon requires from the visual system to separate different motion signal distributions, which are characterised by distinct means that correspond to the different dot directions and variances that are determined by the signal and processing noise. Averaging of local motion signals can be employed to reduce noise components, but such pooling could at the same time lead to the averaging of different directional signal components, arising from spatially adjacent dots moving in different directions, which would reduce the visibility of transparent directions. To study the theoretical limitations of encoding transparent motion by a biologically plausible motion detector network, the distributions of motion directions signalled by a motion detector model (2DMD) were analysed here for Random Dot Kinematograms (RDKs). In sparse dot RDKs with two randomly interleaved motion directions, the angular separation that still allows us to separate two directions is limited by the internal noise in the system. Under the present conditions direction differences down to 30 deg could be separated. Correspondingly, in a transparent motion stimulus containing multiple motion directions, more than eight directions could be separated. When this computational analysis is compared to some published psychophysical data, it appears that the experimental results do not reach the predicted limits. Whereas the computer simulations demonstrate that even an unsophisticated motion detector network would be appropriate to represent a considerable number of motion directions simultaneously within the same region, human observers usually are restricted to seeing not more than two or three directions under comparable conditions. This raises the question why human observers do not make full use of information that could be easily extracted from the representation of motion signals at the early stages of the visual system

The effects of target contrast on Drosophila courtship

Many animals use visual cues such as object shape, color and motion to detect and pursue conspecific mates. Contrast is another possibly informative visual cue, but has not been studied in great detail. In this study, we presented male Drosophila melanogaster with small, fly-sized, moving objects painted either black, white or gray to test whether they use contrast cues to identify mates. We found that males frequently chased gray objects and rarely chased white or black objects. Although males started chasing black objects as often as gray objects, the resulting chases were much shorter. To test whether the attraction to gray objects was mediated via contrast, we fabricated black and gray behavioral chambers. However, wild-type males almost never chased any objects in these darkly colored chambers. To circumvent this limitation, we increased baseline levels of chasing by thermogenetically activating P1 neurons to promote courtship. Males with thermogenetically activated P1 neurons maintained a similar preference for gray objects despite elevated levels of courtship behavior. When placed in a black chamber, males with activated P1 neurons switched their preference and chased black objects more than gray objects. We also tested whether males use contrast cues to orient to particular parts of the female's body during courtship. When presented with moving objects painted two colors, males positioned themselves next to the gray half regardless of whether the other half was painted black or white. These results suggest that males can use contrast to recognize potential mates and to position themselves during courtship

Chirped refractive microlens arrays

The presented thesis deals with the design, the fabrication, and the characterization of nonregular microlens arrays that are referred to as "chirped microlens array" (cMLA) in accordance to other non-periodical structures. In contrast to conventional, regular microlens arrays that consist of a repetitive arrangement of a unit cell on a fixed, equidistantly sectioned grid, a cMLA contains similar but not identical lenses that are defined by a parametric description. The parameters of each cell can be defined by analytical functions, by using numerical optimization techniques, or by a combination of the both. Dependency on the position of the cell within the array is the most characteristic property of these functions. Overcoming the inflexibility of a regular arrangement leads to the enhancement of the classical array concept and enables new degrees of freedom in the design of micro-optical systems. The focus of this thesis is to point out the potentials of these new design possibilities which are explained by example systems built as prototypes. Fields of application are amongst others the improvement of the system's integration and the optimization of the optical performance of a system. Applications in the field of beam shaping and miniaturized imaging optics are discussed in detail as example systems. The latter enables extremely thin imaging objectives with a track length shorter than 250µm that have their natural antetype in the compound eyes of insects. The use of a cMLA allows the correction of off-axis aberrations and consequently the extension of the field of view of the objective, whereas the array describing function can be derived analytically. For the rst time, the use of a cMLA with individually adapted lenses allows the fabrication of objectives based on the well-known imaging principle that are compliant to the demands of industrial applications rather than just being proof-of-principle demonstrators. Furthermore, a fly's eye condenser setup based on cMLAs is discussed. In contrast to the application examples mentioned before, here the focus is on the collective interaction of all lenses of the array that leads to novel coherent effects. The periodic intensity peaks appearing in the plane of homogenization which are typical when using regular arrays can be avoided by employing non-periodic arrays. This leads to an improved homogeneity of the radiation. Fly's eye condensers based on cMLAs are especially advantageous when dealing with short pulse applications such as in sensing or material processing since otherwise applicable homogeneity improving measures are not suitable. The microlens arrays are fabricated using reflow of photoresist or laser lithography which had to be adapted to the specifics of cMLAs. This concerns especially software tools for the generation of mask layouts for the reflow of photoresist as well as profile data for laser lithography which had to be developed beforehand the prototyping and are now available as universal tools.Die vorliegende Arbeit befasst sich mit Aspekten des Designs, der Herstellung und der Charakterisierung nichtregulärer Mikrolinsenarrays, für die in Anlehnung an weitere nichtperiodische Strukturen der englischsprachige Begriff "chirped microlens array" (cMLA) eingeführt wurde. Im Gegensatz zu klassischen - regulären - Mikrolinsenarrays, die aus identischen Linsen mit konstantem Abstand zueinander gebildet werden, bestehen cMLAs aus ähnlichen, jedoch nicht identischen Linsen, die mittels parametrischer Beschreibung deniert sind. Die Zelldefinition kann durch analytische Funktionen, numerische Optimierungsverfahren oder eine Kombination aus beiden gewonnen werden. Bei allen gechirpten Arrays hängen die Funktionen von der Position der jeweiligen Zelle im Array ab.insen mit konstantem Abstand zueinander gebildet werden, bestehen cMLAs aus ähnlichen, jedoch nicht identischen Linsen, die mittels parametrischer Beschreibung deniert sind. Die Zelldefinition kann durch analytische Funktionen, numerische Optimierungsverfahren oder eine Kombination aus beiden gewonnen werden. Bei allen gechirpten Arrays hängen die Funktionen von der Position der jeweiligen Zelle im Array ab. Die Loslösung von der starren Geometrie regulärer Arrays führt zu einer Erweiterung des klassischen Arraybegriffes und ermöglicht neue Freiheitsgrade im Design mikrooptischer Systeme. Der Schwerpunkt der Arbeit ist auf das Aufzeigen der neuen Designmöglichkeiten gerichtet, welche anhand von prototypenhaft umgesetzten Beispielsystemen erläutert werden. Anwendungsgebiete sind hierbei unter anderem die Verbesserung der Integrationsmöglichkeiten und die Optimierung der Funktionsparameter optischer Systeme. Exemplarisch werden hierzu optische Designs und Prototypen diskutiert, die unter anderem Anwendungen in der Strahlformung und der miniaturisierten Abbildungsoptik besitzen. Letzteres betrifft ein ultra-dünnes Kamerasystem, welches auf einem Sehprinzip von Insekten basiert und Baulängen kleiner als 250um ermöglicht. Hierbei findet ein cMLA Einsatz, welches die Korrektur außeraxialer Bildfehler und damit die Vergrößerung des Gesichtsfeldes der Kamera ermöglicht. Die das Array beschreibenden Funktionen können hierbei vollständig analytisch abgeleitet werden. Die Nutzung eines cMLA aus individuell angepassten Linsen ermöglicht damit erstmals, das bekannte Abbildungsprinzip von akademischen Prinzipprototypen zu Systemen mit optischen Parametern zu erweitern, die den Einsatzbedingungen industrieller Anwendungen genügen. Weiterhin wird ein Wabenkondensoraufbau auf Basis von cMLAs zur Strahlhomogenisierung behandelt. Im Gegensatz zu den zuvor aufgeführten Anwendungsbereichen von cMLAs steht hierbei die Interaktion der Gesamtheit aller Linsen des Arrays im Mittelpunkt, was im Besonderen zu neuartigen kohärenten Effekten führt. Die Nutzung nichtregulärer Arrays ermöglicht die Vermeidung der ansonsten auftretenden periodischen Intensitätsmaxima und -minima in der Homogenisierungsebene, was mit einer Verbesserung der Homogenität einhergeht. Wabenkondensoren auf Basis von cMLAs sind im Speziellen für Kurzpulsanwendungen in der Sensorik und Materialbearbeitung von Interesse, da andere homogenitätsverbessernde Maßnahmen nicht angewendet werden können. Für die Herstellung der Arraystrukturen werden das Reflow von Fotolack und die Laserlithographie genutzt, die an die Besonderheiten der cMLAs anzupassen waren. Dies betrifft im Speziellen Softwaretools zur Erstellung von Maskendaten für den Reflowprozess und von profilbeschreibenden Daten für die Laserlithographie, die im Vorfeld der Prototypenfertigung entwickelt wurden und als universelle Werkzeuge zur Verfügung stehen

The first and second neural projections of the insect eye

1. The patterns of projection of some of the perpendicular neurones between the retina and medulla of the optic lobes of various insects have been studied. Axon paths have been studied from consecutive semi-thin plastic sections cut transversely and stained with toluidine blue. The termination positions and the paths of axons are both highly ordered and predictable. 2. In all insects with fused-rhabdomere eyes the axons of one ommatidium project to one cartridge of the lamina and the array of cartridges duplicates the array of ommatidia. In insects with open-rhabdomere eyes visual information is distributed amongst a number of lamina cartridges so that each cartridge receives information originating from one visual axis. 3. In both open- and fused-rhabdomere types the cartridge, array of the lamina is exactly duplicated in the medulla but by the intervention of the chiasma is reversed about a dorso-ventral plane. The axons of one lamina cartridge contribute to one medulla cartridge. Thus, in all insects studied, the visual field is projected exactly from retina to medulla. 4. Most of the retinula axons from one ommatidium terminate in the lamina but usually one pair passes directly to the medulla. These are from the central retinula cells (open-rhabdomere eyes) or from the small retinula cells (apposition type fused-rhabdomere eyes). Retinal responses are known mainly only for the short retinula axons so that visual information delivered to the medulla cartridge is still largely unresolved. 5. The lamina neuropile probably contains the elements responsible for the lateral correlation between parallel receptor inputs which is necessary for movement perception, but units with long lasting responses which could act as the delay circuit of movement perception are unknown. 6. The occurrence of errors in termination of the first projection of the optic lobe of the fly, which are reported for the first time in this work, provide no direct clues to the developmental processes by which such a morphologically complex system arises. Nevertheless errors may arise within a sequence of growth processes which are fundamentally quite simple and not obvious from knowledge of the generalized perfect pattern of connections

On the performance of the visual system in the nocturnal hunting spider Cupiennius salei

Die vorliegende Arbeit beschäftigt sich mit dem visuellen System von Cupiennius salei, einer nachtaktiven Jagdspinne, die als Modellorganismus für die Neuroethologie etabliert ist. In zwei Studien wurde die Muskelaktivität der Hauptaugen aufgezeichnet und eine signifikante Erhöhung als Indikator für visuelle Perzeption in den Nebenaugen herangezogen. In der ersten Studie wurde die höchste räumliche Frequenz eines Streifenmusters gemessen, für die bei Bewegung der Streifen noch eine signifikante Muskelaktivitätserhöhung nachweisbar war. Für vertikale Streifenmuster lag dieses Limit bei einer Wellenlänge von 2°, für horizontale Streifenmuster bei 2.7°. Der Unterschied in den Reaktionsschwellen war aber kleiner als es die Interrezeptorwinkel in den beiden Orientierungen vermuten ließen. Das führte zu der Annahme, dass die Spinnen auch auf rein zeitliche Intensitätsschwankungen reagieren. Diese Hypothese konnte in einer Folgestudie mit Hilfe von Flimmer-Stimuli bestätigt werden. Die Flimmerfusionsfrequenz der Nebenaugen lag bei wenigen Perioden pro Sekunde. Unsere Verhaltensdaten passen gut zu anatomischen und elektrophysiologischen Arbeiten, welche ein relativ gutes räumliches aber ein relativ schlechtes zeitliches Auflösungsvermögen von Cupiennius salei nahelegen. Cupiennius salei ist dafür bekannt, dass sie ohne jeglichen visuellen Input erfolgreich jagen kann. In einer dritten Studie ließ sich nun erstmals nachweisen, dass es auch mit rein visuellen Stimuli möglich ist, Angriffe der Spinnen auszulösen. Eine vierte Studie untersucht Pigmentringe, die in den Augen von frisch gehäuteten Spinnen auftreten und sich anschließend langsam zurückbilden. Mit Hilfe von Micro-CT-Aufnahmen konnten wir zeigen, dass Pigmentringe jene Teile der Cornea abdecken, welche zunächst noch nicht von der wachsenden Linse ausgefüllt sind. Die Funktion der Pigmentringe könnte es sein, das Auge gegen störende, periphere Lichtstrahlen abzuschirmen, die nicht von der Linse auf die Retina gebündelt würdenThe present thesis deals with the visual system of Cupiennius salei, a nocturnal hunting spider established as model organism in neuroethology. In two studies the temporal and spatial cut-off frequencies were investigated. For that purpose, the activity of the eye muscles that move the retinae of the principal eyes was monitored. An increase in that activity indicates visual perception in the secondary eyes. To determine the spatial cut-off frequency we confronted the spiders with sinusoidally modulated gratings. Vertical gratings elicited a significant increase down to a wavelength of 2 deg, horizontal gratings down to a wavelength of 2.7 deg. The difference in the limiting frequencies for the two orientations was less pronounced than the corresponding interreceptor angles would suggest. Thus we assumed that Cupiennius might also respond to temporal intensity modulations with an increase in eye muscle activity. We could confirm this hypothesis in a follow-up study using flicker stimuli. We subsequently measured the temporal cut-off frequency to be in the range of a few cycles per second. Our data were in line with anatomical and electrophysiological studies suggesting a relatively high spatial and a relatively low temporal resolution in these spiders. Cupiennius salei was known to be able to hunt successfully relying exclusively on its excellent mechanosensory systems. In a third study we were now able to show that it is also possible to elicit attack behaviour with visual stimuli alone, in the absence of any mechanosensory input. In a fourth study we describe the appearance and subsequent decrease of enlarged pigment rings in the eyes of freshly moulted spiders. Using micro CT scans we could confirm our hypothesis that the pigment rings are linked to the maturation of the lens. The pigment rings might maintain vision in postecdysal animals by shielding light rays that could otherwise enter beside the growing lens and degrade the image on the retina