Alternatives to superposition images in clear-zone compound eyes

1971 ◽  
Vol 179 (1055) ◽  
pp. 97-124 ◽  
Keyword(s):  
Scattered Light ◽  
Retinula Cell ◽  
Compound Eyes ◽  
Clear Zone ◽  
Light Effect ◽  
Angular Sensitivity ◽  
Dim Light ◽  
Optical Pathway ◽  
Receptor Layer

The clear zone between the cones and the receptor layer in dark -adapted eyes of insects that are active in dim light has formerly been explained as a space to allow formation of a superposition image. Although erect images have been seen in Ephestia (Lepidoptera) and Hydrophilus (Coleoptera), new experiments show that they are accompanied by scattered light and that the angular sensitivity of individual receptors must be wide in the dark-adapted state. Alternatives to the superposition theory are examined, and it is concluded that in eyes with crystalline cones the clear zone (in general, in the numerous shapes and sizes of eyes of nocturnally active insects) enables light entering by many facets to sum upon individual receptors on the far side of the clear zone. In addition to the scattered light effect, light is carried across the clear zone in crystalline tracts or retinula cell columns, which provide a separate optical pathway for each ommatidium also in the light-adapted state.

Theory of the summation of scattered light in clear zone compound eyes

1972 ◽  
Vol 181 (1063) ◽  
pp. 137-156 ◽  
Keyword(s):  
Normal Distribution ◽  
Null Hypothesis ◽  
Scattered Light ◽  
Compound Eyes ◽  
Sectional Area ◽  
Clear Zone ◽  
Acceptance Angle ◽  
Cross Sectional ◽  
Layer 4 ◽  
Receptor Layer

1. The clear zone between the cones and the receptors of dark-adapted nocturnal insects and crustaceans is considered as a region across which light entering the eye by many facets can sum upon the receptors beyond the clear zone. 2. In the model, light is admitted through each facet as a normal distribution. This amount of light spreads out from the cone tip as another normal distribution unrelated to the first except in total energy. The direction of arrival of a ray on the receptor is therefore minimally related to its direction of origin. 3. At the expense of acuity the geometry of summation across the clear zone increases the sensitivity of the eye in the ratio R 2 1 / R 2 2 where R 1 and R 2 are the radii from the centre of the eye to the cone tips and to the receptor layer. 4. The existence of a clear zone permits a further increase in sensitivity in the dark-adapted state by allowing an increase in the acceptance angle of the facets and in cross-sectional area of the receptors, without prejudice to the acuity of the light-adapted eye. 5. In this model of the clear zone eye, a minimum of parameters and optical properties are assumed. An intensity at the receptor greater than that given by this ‘null hypothesis’ would then point to additional optical mechanisms.

Two models of the partially focused clear zone compound eye

1973 ◽  
Vol 183 (1071) ◽  
pp. 141-158 ◽  
Keyword(s):  
Direct Measurement ◽  
Gaussian Distribution ◽  
Compound Eye ◽  
Angle Of Incidence ◽  
Clear Zone ◽  
Angular Sensitivity ◽  
Layer 2 ◽  
Radial Axis ◽  
Ray Paths ◽  
Receptor Layer

1. The theory of the unfocused clear zone eye is extended to cover cases where rays are partially focused upon the receptor layer. 2. Light is admitted through facets according to a Gaussian distribution of angle of incidence defined with respect to the axis of the facet. 3. The same light crosses the clear zone in an average direction related to its direction of origin outside the eye, so that it tends to be concentrated around that receptor on the radial axis pointing towards the source of light. This effect, defined as focusing in contrast to the unfocused eye, allows a simultaneous improvement in sensitivity and acuity. 4. An eye can be focused partially because rays diverge from each cone tip or because, on average, they converge above or below the receptor layer on the radial axis pointing towards their source. The two situations are analysed quantitatively. 5. In a partially focused eye neither the measured angular sensitivity nor the absolute sensitivity allow a prediction of the ray paths because many different distributions from the cone tips produce a given final result. Therefore the optics of partially focused clear zone eyes must be analysed by direct measurement of light distribution from the cone tips.

scholarly journals The Nature of Light: What Hidden Behind Young's Double-Slit Experiment?

2021 ◽  
Author(s):  
X. Q. Huang
Keyword(s):  
Scattered Light ◽  
Exchange Property ◽  
Field Energy ◽  
Light Effect ◽  
Light Phase ◽  
Conventional View ◽  
Experimental Diffraction Pattern ◽  
Wave Particle Duality ◽  
Double Slit Experiment ◽  
Double Slit

We experimentally prove that the famous single- and double-slit experimentsare the scattered-light phase transition by slit edges rather thanthe conventional view of the transmitted-light effect by slits. Thenature of the wave-particle duality of light quanta can be well understoodwith the help of the dynamic hypothesis of the quantized chiral photons havingan intrinsic dual-energy (implicit electric field energy and hiddenmagnetic field energy) cyclic exchange property. With the suggestedtheoretical framework, the experimental diffraction pattern of thesingle slit is analytically determined and numerically confirmed.

The ommatidium of the lacewing Chrysopa (Neuroptera)

1976 ◽  
Vol 192 (1108) ◽  
pp. 259-271 ◽  
Keyword(s):  
Signal To Noise Ratio ◽  
Visual Fields ◽  
Neural Mechanism ◽  
Retinula Cell ◽  
Cell Nuclei ◽  
Clear Zone ◽  
Parallel Beam ◽  
Cell Column ◽  
Spatial Frequencies ◽  
Different Levels

The eye is a clear zone eye with extensive movement of retinula cells on adaptation to light. The ommatidium has three types of rhabdomere, at different levels, so that the eye necessarily abstracts at least three kinds of information simultaneously from the incoming rays. In the lightadapted state light can enter each ommatidium only via a crystalline tract that is surrounded by dense pigment grains. A small distal rhabdomere (cell 7) always lies at the end of this tract. In the dark-adapted eye the retinula cell nuclei and distal rhabdomere move to the cone tip and the crystalline tract is drawn into the cone. There is then a region of the retinula cell column, between cone tip and proximal rhabdoms, across which there is no structure that could act as a light guide. A key question, therefore, is how the light is focused across this clear zone in the darkadapted state. As shown by the wide angular distribution of eyeshine when a parallel beam is incident on the dark-adapted eye, rays are poorly focused upon the columns of the large rhabdoms. The wide visual fields of receptors 1-6 in the dark-adapted eye, inferred from the observation of eyeshine, are seen as a way of narrowing the bandwidth of spatial frequencies, so that only the largest objects in the visual field contribute to motion-detection. This would improve the signal-to-noise ratio, not in the receptors themselves, but in the neural mechanism, by simplifying the incoming signal.

The dorsal eye of the mayfly Atalophlebia (Ephemeroptera)

1978 ◽  
Vol 200 (1139) ◽  
pp. 137-150 ◽  
Keyword(s):  
Visual Pigment ◽  
Current Flow ◽  
Yellow Pigment ◽  
The Other ◽  
Retinula Cell ◽  
Clear Zone ◽  
Large Size ◽  
Sharp Focus ◽  
Pigment Distribution ◽  
Light Guides

The dorsal eye of Atalophlebia has two unusual features, the sensitivity only to ultraviolet (u. v.) light, and the candelabra-shaped rhabdom. In addition, the crystalline cone is surrounded to its tip by a yellow pigment, and the tip tapers gradually as a dense fibre. These details, particularly the pigment distribution, indicate that a superposition image cannot be formed by u. v. light. Also, there is no refracting or reflecting structure that could form a sharp superposition image. Instead, it is suggested that u. v. rays are sharply focused on the cone tip and conducted by the retinula cell columns acting as light guides across the clear zone. Light of longer wavelength, on the other hand, is partially focused through the yellow pigment, and, although it is not seen by the insect, it is available to photoregenerate the visual pigment. This method of boosting sensitivity is appropriate for a pure u. v. eye and does not require a sharp focus of the regenerative rays, although the clear zone is an essential part of the mechanism. The rhabdom has an extraordinary shape like a flat 5-armed candelabra in cross section, with five posteriorly directed arms which are formed by six retinula cells. There is also a 7th retinula cell without a rhabdomere. This cell penetrates laterally the rhabdom of the other six, and also forms a sheath around half of its own ommatidium and half of the the adjacent ommatidium. The exceptional relations between this cell, and the other six, together with the orientated candelabra pattern of the rhabdom, and the large size of the 7th retinula axon, is interpreted as a way of enhancing the current flow down the 7th axon which runs direct to the medulla, bypassing the lamina.

scholarly journals The remarkable visual capacities of nocturnal insects: vision at the limits with small eyes and tiny brains

2017 ◽  
Vol 372 (1717) ◽  
pp. 20160063 ◽  
Author(s):  
Eric J. Warrant
Keyword(s):  
Temporal Summation ◽  
Optic Lobe ◽  
Night Vision ◽  
Visual Signals ◽  
Compound Eyes ◽  
Begging The Question ◽  
Light Levels ◽  
Dim Light ◽  
Control Flight ◽  
Light Capture

Nocturnal insects have evolved remarkable visual capacities, despite small eyes and tiny brains. They can see colour, control flight and land, react to faint movements in their environment, navigate using dim celestial cues and find their way home after a long and tortuous foraging trip using learned visual landmarks. These impressive visual abilities occur at light levels when only a trickle of photons are being absorbed by each photoreceptor, begging the question of how the visual system nonetheless generates the reliable signals needed to steer behaviour. In this review, I attempt to provide an answer to this question. Part of the answer lies in their compound eyes, which maximize light capture. Part lies in the slow responses and high gains of their photoreceptors, which improve the reliability of visual signals. And a very large part lies in the spatial and temporal summation of these signals in the optic lobe, a strategy that substantially enhances contrast sensitivity in dim light and allows nocturnal insects to see a brighter world, albeit a slower and coarser one. What is abundantly clear, however, is that during their evolution insects have overcome several serious potential visual limitations, endowing them with truly extraordinary night vision. This article is part of the themed issue ‘Vision in dim light’.

Movement on dark–light adaptation in beetle eyes of the neuropteran type

1971 ◽  
Vol 179 (1054) ◽  
pp. 73-85 ◽  
Keyword(s):  
Outer Layer ◽  
Light Adaptation ◽  
Pigment Cells ◽  
Retinula Cell ◽  
Clear Zone ◽  
Dark Light ◽  
Light Guides

Beetles of several species belonging to the families Carabidae, Dytiscidae, Gyrinidae and Hydrophilidae have an eye of the neuropteran type which is characterized as follows. In the dark-adapted state a long column formed by retinula cells (in these families numbering seven) stretches from the cone tip to the rhabdom layer. In the light a crystalline tract, formed from the outer layer of the cone, extends about 100 µ m from the cone and is surrounded by pigment cells. Scarabaeid beetles examined are similar but lack the distal rhabdomere always found in the above groups. All have a basal retinula cell with rhabdomere. In the scarabaeids the retinula cell columns have a content of solids greater than the surrounding cells, suggesting that they act as light guides across the clear zone.

Possible role of the central retinular cells in the ommatidia of male black flies (Diptera: Simuliidae)

1987 ◽  
Vol 65 (12) ◽  
pp. 3186-3188 ◽  
Author(s):  
Susan B. McIver ◽  
Gail E. O'Grady
Keyword(s):  
Sensory Receptor ◽  
Compound Eyes ◽  
Black Flies ◽  
Dorsal Region ◽  
Blue Range ◽  
Retinular Cells ◽  
Dioptric Apparatus ◽  
Receptor Layer ◽  
Swarm Formation

In Cnephia dacotensis, a species that mates on rocks and plants without swarm formation, the eyes of the males are separate and undivided. Each ommatidium consists of two general regions: a distal dioptric apparatus and a sensory receptor layer with eight retinular cells. Six of these cells (R1–6) are located peripherally and two centrally; R7 occurs distally and R8 basally. In males of previously studied species in which females are detected as they fly above a male swarm, the compound eyes are holoptic and divided into distinct dorsal and ventral regions. Ommatidia in the dorsal region lack the R7 cell. If in black flies R7 is a blue receptor and R8 a uv receptor, then the absence of R7 means that swarm-forming males see the females against a background that provides a sharper contrast than a background of a uv to blue range. This would sharpen the visibility of the dark female against the background skylight, enabling the male to perceive her more swiftly.

The eye of the firefly Photuris

1969 ◽  
Vol 171 (1025) ◽  
pp. 445-463 ◽  
Keyword(s):  
Basement Membrane ◽  
Optical Axis ◽  
Retinula Cell ◽  
Axis Light ◽  
Receptor Layer

1. The pseudocone eye of Photuris has long corneal cones that are laminated in a series of concentric paraboloids which have the effect of bending rays towards the optical axis within the cone. 2. Between the proximal end of each cone and the receptor layer is a crystalline thread which conducts light by internal reflexion to the receptors. Not all light travels by this path in the dark-adapted eye. 3. The receptor layer has proximal and distal rhabdomeres in a pattern unlike that of any other known eye. The enormously developed rhabdoms form two superimposed continuous sheets across the eye. 4. The eighth retinula fibre in each bundle at the basement membrane comes from the basal retinula cell. 5. Off-axis light which escapes the route down the crystalline thread in the dark-adapted eye is refracted by the curved end of the cone in such a direction that it tends towards a receptor in the ommatidium which points towards the origin of the light. There is no functional superposition image at the level of the receptors.

The eye of Anoplognathus (Coleoptera, Scarabaeidae)

1975 ◽  
Vol 188 (1090) ◽  
pp. 1-30 ◽  
Keyword(s):  
Refractive Index ◽  
Point Source ◽  
Dark Adaptation ◽  
Compound Eye ◽  
Visual Fields ◽  
Optomotor Response ◽  
Clear Zone ◽  
Acceptance Angle ◽  
Single Plane ◽  
Receptor Layer

The night flying scarabaeid beetle Anoplognathus provides an example of a dark-adapted clear-zone compound eye in which rays from a distant point source, entering by a large patch of facets, are imperfectly focused upon the receptor layer. The optical system of the eye was investigated by six methods, all of which give similar results: (1) ray tracing through structures of known refractive index, (2) measurement of visual fields of single receptors, (3) measurement of the divergence of eyeshine, and (4) of the optomotor response to stripes of decreasing width, and (5) by direct observation of distribution of light within the eye. Finally (6) anatomically there is no single plane upon which an image could be focused. In each ommatidium, beneath the thick cornea, with its short corneal cone, lies a non-homogeneous crystalline cone (range of r. i. 1.442-1.365) that is significant in partially focusing rays across the wide clear zone (340 μm) in the dark-adapted eye. On the proximal side of the clear zone the rhabdoms form 7-lobed columns, isolated from each other over half their length by a tracheal tapetum. In the light-adapted eye the cone cells extend to form a crystalline tract (70-90 μm long) which is sur­rounded by dense pigment, and the optical path across the clear zone is completed by retinula cell columns that are of higher density than the surrounding cells. Pigment movement upon adaptation takes about 10 min to complete. Dark adaptation can be induced only at night on account of a strong diurnal rhythm. Eyeshine can be seen in the dark-adapted eye so long as the distal pig­ment leaves free the tips of the crystalline cones. Eyeshine falls to 50% at an angle of 12° from the direction of a parallel beam shining on the eye, as is consistent with a partial focus in which the distribution of light on the receptor layer is 18°-24° wide at the 50% contour. This distribution was confirmed by direct examination of the inside of the eye and by measure­ment of receptor fields as follows. The mean acceptance angle for 13 light-adapted units was 12.57° ± 1.97° s. d. and that of 10 dark-adapted ones 20.3° ± 3.36° s. d. The sensi­tivity to a point source on axis is increased at least 1000 fold by dark adaptation. Rays traced through a scale drawing of the eye, with refractive index measured for each component, show how the eye as a whole comes to be partially focused, and predicts an acceptance angle of 12° in the light-adapted and 20°-24° in the dark-adapted eye. In optomotor experiments dark-adapted Anoplognathus does not respond to stripes narrower than 18° repeat period, but light-adapted beetles respond down to 10°. The optomotor experiments also show a 1000 fold increase in sensitivity when dark-adapted at night. The eye has poor acuity that goes with wide visual fields of its recep­tors, and this is surprising when other excellently focused clear zone eyes are known. A possible compensation for the poor acuity is that the aperture of the eye can be larger, so that sensitivity although only to large objects, is that much increased.

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