K Kirschfeld

Die Projektion der optischen Umwelt auf das Raster der Rhabdomere im Komplexauge von Musca

SummaryThe dioptrics of the Musca ommatidium acts as an inverting lens system. The distal endings of the rhabdomeres at the basis of the dioptric apparatus are separated and arranged in a typical asymmetric pattern. The optical axes of the individual rhabdomeres of one ommatidium are the geometric projections of the distal rhabdomere endings into the environment, inverted by 180° by the dioptric apparatus. The divergence angles between the optical axes of the rhabdomeres of one ommatidium correspond to divergence angles between the appropriate set of ommatidia in such a way, that seven rhabdomeres of seven ommatidia are looking at one point in the environment (in the intermediate region between dorsal and ventral part of the eye: eight to nine rhabdomeres of a set of eight to nine ommatidia). These facts were established from sections of living eyes and confirmed by using special optical methods in the intact animal.The pattern of the decussation of individual retinulacell axons between retina and lamina was predicted adopting the hypothesis that the fibres of retinulacells number one to six, whose rhabdomers are looking at one point in the environment, project into a single “cartridge” in the lamina. These predicted connections were confirmed by other investigators. We have therefore a one to one correspondence between a lattice of points in the environment and the lattice of “cartridges” in the lamina.It is shown that the unfused rhabdomeric structure of the Musca ommatidium increases the effective entrance pupil of the eye by a factor of seven (resp. eight to nine in the intermediate region between dorsal and ventral part of the eye) compared to the classical apposition eye. —The Musca compound eye can be regarded as a “neural superposition eye”.

Ein Mechanismus zur Steuerung des Lichtflusses in den Rhabdomeren des Klomplexauges von Musca

SummaryIn the ommatidia of Musca, the light flux transmitted by each one of the rhabdomeres of sense cells no. 1 to 6 decreases as a function of time if light falls onto these rhabdomeres. With a similar time course the light flux reflected from these rhabdomeres increases. These changes take place within a few seconds following illumination. The results have been established in the intact animal using changes in the appearance of the pseudopupil as indicator and also in surviving preparations of the eye with direct inspection of the rhabdomeres.The changes are interpreted as a consequence of interactions between pigment granules in the sense cells and electromagnetic fields induced outside the rhabdomeres by light travelling on the inside: In the dark adapted situation the granules are quite distant from the rhabdomeres, the interaction is negligible. During light adaptation the granules move close to the rhabdomeres, and as a consequence, total reflection of the light in the rhabdomere is frustrated. The relatively rapid changes in the optical characteristics of the rhabdomeres are explained by the fact that the distance, the granules have to move in order to switch from one condition to the other is in principle on the order of the wavelength of light.The results indicate, that the changes in the position of the granules are induced by the excitation of the respective sense cells themselves, for instance by the degree of their depolarisation. No interaction between the sense cells of one ommatidium nor between those of different ommatidia could be found.The function of the movement of the pigment granules is interpreted as a means to protect the sense cells no. 1 to 6 against strong illumination. — Movement of pigment granules is not induced in sense cells no. 7 and 8 with light intensities which give maximal response in sense cells no. 1 to 6.

The Resolution of Lens and Compound Eyes

Two distinctly different types of eyes have been highly developed in evolution: lens eyes (= camera eyes) in vertebrates, some molluscs and arachnids and compound eyes in arthropods. Based on his comparative studies of the optical properties of compound and lens eyes, Exner (1891) concluded that both types of eyes are optimally adapted for different functions: lens eyes with their high angular resolution seem to more useful for pattern recognition, whereas the compound eyes, with their poor resolution, are thought to be specialized for movement perception. This view is still generally accepted (see the textbooks of Scheer, 1969, Kaestner, 1972). Furthermore, the small facet diameters of the ommatidia in compound eyes seem to cause a poor absolute sensitivity (Exner, 1891; Barlow, 1952; Kirschfeld, 1966; Prosser and Brown, 1969; Snyder et al., 1973). Some insects are said, however, to have higher temporal resolution than humans (Autrum, 1948).

Optische Eigenschaften der Ommatidien im Komplexauge von Musca

SummaryOptical characteristics of the dioptric system in the ommatidia of Musca have been analysed by use of “antidromic illumination” of the eye. The results indicate that the distal endings of the rhabdomers terminate near the focal plane of the dioptrics and that the quality of the lens is high enough to resolve some details of their shape. — Using optical methods it has been possible to confirm directly that the optical axes of 7 individual rhabdomers from 7 different ommatidia all converge to a common point in the distant surroundings. This is a characteristic for compound eyes of the “neural superposition” type. — The results are discussed on the basis of the hypothesis that the Musca eye is composed of two functionally different subsystems: One system (D) with high absolute sensitivity and low spatial resolution consisting of the sense cells no. 1 to 6, and a second system (H) with high spatial resolution and low absolute sensitivity composed of cells no. 7 and 8.

Etude optique in vivo des éléments photorécepteurs dans l‘oeil composé de Drosophila.

SummaryThanks to a technique of optical neutralisation associated with a transilluinination of the eye, it is possible to study the photoreceptor endings (rhabdomere tips) in the compound eye of live and intact Drosophilae.The success of the neutralisation process directly confirms the idea that the convergence of the dioptric system in each ommatidium is essentially due to the refraction at the corneal outer surface. The remarkable regularity of the asymmetrical receptor pattern throughout the eye (fig. 7) is of functional importance. The divergence angle between the optical axis of neighbouring receptors, and their farfield radiation pattern are shown to depend respectively on the spacing and the diameter of the rhabdomere distal endings (fig. 8). The tip of the centrally located rhabdomere number 7 (fig. 5) is found to have a smaller optical diameter than its six neighbours and the extinction spectrum of this rhabdomere is different from those of the other ones. Modal patterns are observed at the distal tip of the rhabdomeres (fig. 9), confirming the waveguide properties of these components. The eye of Drosophila is morphologically composed of two equal parts, dorsal and ventral, in which the rhabdomere patterns are symmetrical (fig. 7). Sporadic irregularities are found in the border between these two parts (fig. 10).Actually the main importance of this neutralisation technique lies in its possible applications. The simultaneous visualization of a lot of receptors, in transmitted light, allows a precise stimulation, in incident light, of single and known cells in the eye of live insects. This method combined with other in vivo techniques such as those using the phenomenons of “corneal pseudopupil” (Kirschfeld and Franceschini, 1968) and “deep pseudopupil” (Franceschini and Kirschfeld, 1971a) may simplify further studies regarding the nervous integration of visual stimuli in the facet eye.

A photostable pigment within the rhabdomere of fly photoreceptors no. 7

SummaryThe population of the centrally located rhabdomeres no. 7 in the ommatidia of flies (Musca, Calliphora, Drosophila) is inhomogeneous: approximately 2/3 of them contain — besides a photoisomerizable rhodopsin — a photostable pigment. Its extinction spectrum has a maximum at 460 nm and two shoulders at 430 and 485 nm respectively. Extinction is maximal for theE-vector perpendicular to the microvilli. Whereas the functional role of the photostable pigment for receptor 7 has still to be worked out, its functional consequence for receptors no. 8, which are located proximal to receptors 7, is obvious: it modifies their spectral sensitivity by selectively absorbing blue light. Due to this “screening”-effect, a shift of the maximal sensitivity of receptors no. 8 is predicted from 490 nm (maximal sensitivity of unscreened receptor 8, Harris et al., 1976) to 520 to 540 nm. This is in agreement with recent electrophysiological data (Hardie, 1977). The results show that spectral sensitivities of receptors no. 8, as determined by means of the ERG of white-eyed mutants or of mutants lacking receptor 7, do not represent the spectral sensitivities of most of these receptors in wild-type flies.

Chemical identity of the chromophores of fly visual pigment

vanced that nickel inhibits either the synthesis of SMM or the transaminase of homocysteine or its precursors. Synthesis of cysteine [7] and hence homocysteine occurs in leaves. If vase solutions containing nickel ions inhibit the leaf synthesis of cysteine and homocysteine that explains why our leafy Chrysanthemum blooms responded to nickel by delayed flower senescence, whereas the leafless blooms of Papaver nudicaule did not. Our thanks are expressed to Dr. V.J. Bofinger of the Department of Mathematics for statistical advice. Received December 8, 1983

The absolute sensitivity of lens and compound eyes

Abstract The numbers of light quanta available to photoreceptors of lens-and different types of com pound eyes are calculated on the basis of photometric considerations. It is shown that the results depend upon the situation in the optical environment: For point-like lightsources such as stars receptors in compound eyes generally receive considerably less numbers of light quanta compared n. g. with the human eye. This is due to the small sizes of the ommatidial facets. For extended optical surroundings, however, the numbers of quanta reaching the receptors in typical insect compound eyes of the apposition type are comparable to those in the human eye. In this respect the optical superposition eye of nocturnal insects like E ph estia is an exceptional case, where there is an improvement in the numbers of quanta reaching the receptors by a factor 100 to 1000 com pared to the eyes of bee or man

The Visual System of Musca: Studies on Optics, Structure and Function

Experiments were performed in order to obtain information on the function of receptive and neural structures, and to relate this to the histology. The study of the optical properties of the ommatidia, and the “wiring diagram” of the first optic ganglion as evaluated by means of histological methods (BRAITENBERG, 1967; TRUJILLO-CENOZ and MELAMED, 1966), lead to the hypothesis that the unfused rhabdoms of the Dipteran eye, combined with the special neural connexions between retina and lamina are a means of increasing the light gathering power in this type of compound eye by “neural superposition” of the output of receptors nos. 1 to 6. The concept of neural superposition predicts functional differences between the system composed of receptors 1 to 6 and, the other composed of receptors 7 and 8. These differences, concerning absolute and spectral sensitivity, sensitivity to polarized light, and contrast transfer, have been demonstrated by means of optomotor experiments. One other consequence of the concept of neural superposition is that one ommatidium alone should be able to analyze movement. This has been verfified by stimulation of pairs of receptors within one single ommatidium. By means of this technique it has been shown, furthermore, that movement detectors in the upper front region of the eye are arranged in two orthogonal directions. This information has been used in order to draw a network of connexions which are the least necessary and sufficient to explain the experimental results. These connexions are also the minimal ones that must be found in the histology of the information carrying channels.

The Frohlich effect: a consequence of the interaction of visual focal attention and metacontrast

Usually we assume that the central nervous system preserves temporal sequences. Here we show that moving objects--in the context of behaviour often dangerous ones--are seen with a shorter latency than stationary (flashed) objects. In addition moving objects are deblurred. Two mechanisms contribute to this functional specialisation: cue-induced visual focal attention and metacontrast. Under unnatural conditions these mechanisms lead to an optical illusion first described by Fröhlich [Fröhlich, F. W. (1923). Uber die Messung der Empfindungszeit. Zeitschrift für Sinnesphysiologie, 54, 58-78].