scholarly journals Eye Morphology and Retinal Topography in Hummingbirds (Trochilidae: Aves)

2015 ◽  
Vol 86 (3-4) ◽  
pp. 176-190 ◽  
Author(s):  
Thomas J. Lisney ◽  
Douglas R. Wylie ◽  
Jeffrey Kolominsky ◽  
Andrew N. Iwaniuk
Keyword(s):  
Visual Fields ◽  
High Density ◽  
Resolving Power ◽  
Transverse Diameter ◽  
Density Region ◽  
Temporal Area ◽  
Eye Morphology ◽  
Neuron Density ◽  
Retinal Topography ◽  
Central High

Hummingbirds are a group of small, highly specialized birds that display a range of adaptations to their nectarivorous lifestyle. Vision plays a key role in hummingbird feeding and hovering behaviours, yet very little is known about the visual systems of these birds. In this study, we measured eye morphology in 5 hummingbird species. For 2 of these species, we used stereology and retinal whole mounts to study the topographic distribution of neurons in the ganglion cell layer. Eye morphology (expressed as the ratio of corneal diameter to eye transverse diameter) was similar among all 5 species and was within the range previously documented for diurnal birds. Retinal topography was similar in Amazilia tzacatl and Calypte anna. Both species had 2 specialized retinal regions of high neuron density: a central region located slightly dorso-nasal to the superior pole of the pecten, where densities reached ∼45,000 cells·mm-2, and a temporal area with lower densities (38,000-39,000 cells·mm-2). A weak visual streak bridged the two high-density areas. A retina from Phaethornis superciliosus also had a central high-density area with a similar peak neuron density. Estimates of spatial resolving power for all 3 species were similar, at approximately 5-6 cycles·degree-1. Retinal cross sections confirmed that the central high-density region in C. anna contains a fovea, but not the temporal area. We found no evidence of a second, less well-developed fovea located close to the temporal retina margin. The central and temporal areas of high neuron density allow for increased spatial resolution in the lateral and frontal visual fields, respectively. Increased resolution in the frontal field in particular may be important for mediating feeding behaviors such as aerial docking with flowers and catching small insects.

Retinal Topography in Two Species of Baleen Whale (Cetacea: Mysticeti)

2018 ◽  
Vol 92 (3-4) ◽  
pp. 97-116 ◽  
Author(s):  
Thomas J. Lisney ◽  
Shaun P. Collin
Keyword(s):  
Ganglion Cells ◽  
Feeding Strategy ◽  
Visual Fields ◽  
Humpback Whale ◽  
High Density ◽  
Resolving Power ◽  
Temporal Area ◽  
Baleen Whales ◽  
Axial Diameter ◽  
Retinal Topography

Little is known about the visual systems of large baleen whales (Mysticeti: Cetacea). In this study, we investigate eye morphology and the topographic distribution of retinal ganglion cells (RGCs) in two species of mysticete, Bryde’s whale (Balaenoptera edeni) and the humpback whale (Megaptera novaeanglia). Both species have large eyes characterised by a thickened cornea, a heavily thickened sclera, a highly vascularised fibro-adipose bundle surrounding the optic nerve at the back of the eye, and a reflective blue-green tapetum fibrosum. Using stereology and retinal whole mounts, we estimate a total of 274,268 and 161,371 RGCs in the Bryde’s whale and humpback whale retinas, respectively. Both species have a similar retinal topography, consisting of nasal and temporal areas of high RGC density, suggesting that having higher visual acuity in the anterior and latero-caudal visual fields is particularly important in these animals. The temporal area is larger in both species and contains the peak RGC densities (160 cells mm–2 in the humpback whale and 200 cells mm–2 in Bryde’s whale). In the Bryde’s whale retina, the two high-density areas are connected by a weak centro-ventral visual streak, but such a specialisation is not evident in the humpback whale. Measurements of RGC soma area reveal that although the RGCs in both species vary substantially in size, RGC soma area is inversely proportional to RGC density, with cells in the nasal and temporal high-density areas being relatively more homogeneous in size compared to the RGCs in the central retina and the dorsal and ventral retinal periphery. Some of the RGCs were very large, with soma areas of over 2,000 µm2. Using peak RGC density and eye axial diameter (Bryde’s whale: 63.5 mm; humpback whale: 48.5 mm), we estimated the peak anatomical spatial resolving power in water to be 4.8 cycles/degree and 3.3 cycles/degree in the Bryde’s whale and the humpback whale, respectively. Overall, our findings for these two species are very similar to those reported for other species of cetaceans. This indicates that, irrespective of the significant differences in body size and shape, behavioural ecology and feeding strategy between mysticetes and odontocetes (toothed whales), cetacean eyes are adapted to vision in dim light and adhere to a common “bauplan” that evolved prior to the divergence of the two cetacean parvorders (Odontoceti and Mysticeti) over 30 million years ago.

Review lecture: Apposition eyes of large diurnal insects as organs adapted to seeing

1980 ◽  
Vol 207 (1168) ◽  
pp. 287-309 ◽  
Keyword(s):  
Nodal Point ◽  
Visual Fields ◽  
Photoreceptor Cells ◽  
Resolving Power ◽  
Field Size ◽  
Correct Position ◽  
Anatomical Arrangement ◽  
Angular Coordinates ◽  
And Function ◽  
Facet Size

(1) The fields of view of the photoreceptor cells are determined by the dimensions and anatomical arrangement of the optical part of the ommatidium. The dimensions, and therefore the fields of view of the ommatidia are also related across the eye. In the relation between structure and function there are many points that invite discussion, but the intention is to order our knowledge so that the gaps become obvious. (2) The first step has been to make maps of the eyes showing the maximum theoretical resolving power of the facets and also the interommatidial angle, the reciprocal of which is the maximum spatial resolution of combinations of facets. The ratio of these two resolutions at each point shows the minimum overlap of the visual fields. These maps can be made from the outside of the eye; they show the main types of eye. (3) The next step is to work out the optics of individual ommatidia so that the focal lengths and receptor widths can be measured. The field width can then be predicted from the facet size and the subtense of the receptor at the posterior nodal point. The final step is to measure the field widths of individual ommatidia experimentally as a test of the optical theory, and to make maps of the actual fields in their correct position on the eye in angular coordinates. (4) Three examples of maps of actual fields are given, and their anato­mical and diffraction components are separated. The maps are an essential step towards the electrophysiological analysis of the ganglia behind the eye. A theory of the origin of the fields in terms of anatomy and optics also opens the way to an analysis of mechanisms that change the field size upon adaptation to light. A comparative study of the fields in different eye regions and in different species can also be related to visual habits and behaviour.

Recovery of function after lesions in the superior temporal sulcus in the monkey

1991 ◽  
Vol 66 (3) ◽  
pp. 651-673 ◽  
Author(s):  
D. S. Yamasaki ◽  
R. H. Wurtz
Keyword(s):  
Smooth Pursuit ◽  
Visual Motion ◽  
Visual Fields ◽  
Ibotenic Acid ◽  
Superior Temporal Sulcus ◽  
Position Error ◽  
Eye Position ◽  
Motion Information ◽  
Temporal Area ◽  
Rate Of Recovery

1. Ibotenic acid lesions in the monkey's middle temporal area (MT) and the medial superior temporal area (MST) in the superior temporal sulcus (STS) have previously been shown to produce a deficit in initiation of smooth-pursuit eye movements to moving visual targets. The deficits, however, recovery within a few days. In the present experiments we investigated the factors that influence that recovery. 2. We tested two aspects of the monkey's ability to use motion information to acquire moving targets. We used eye-position error as a measure of the monkey's ability to make accurate initial saccades to the moving target. We measured eye speed within the first 100 ms after the saccade to evaluate the monkey's initial smooth pursuit. 3. We determined that pursuit recovery was not dependent specifically on the use of neurotoxic lesions. Although the rate of recovery was slightly altered by replacing the usual neurotoxin (ibotenic acid) with another neurotoxin [alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)] or with an electrolytic lesion, pursuit recovery still occurred within a period of days to weeks. 4. There was a relationship between the size and location of the lesion and the recovery time. The time to recovery for eye-position error and initial eye speed increased with the fraction of MT removed. Whether the rate of recovery and size of lesions within regions on the anterior bank were related was unresolved. 5. We found that a large AMPA lesion within the STS that removed all of MT and nearly all of MST drastically altered the rate of recovery. Recovery was incomplete more than 7 mo after the lesion. Even with this lesion, however, the monkey's ability to use motion information for pursuit was not completely eliminated. 6. The large lesion also included parts of areas V1, V2, V3, and V4, but analysis of the visual fields associated with this lesion indicated that these areas probably did not have a substantial effect on recovery. 7. We tested whether visual motion experience of the monkey after a lesion was necessary for recovery by limiting the monkey's experience either by using a mask or by using 4-Hz stroboscopic illumination. In one monkey the eye-position error component of pursuit was prolonged to greater than 2 wk, but recovery of eye speed was not. Reduced motion experience had little effect on recovery in the other two monkeys. These results suggest that such visual motion experience is not necessary for the recovery of pursuit.(ABSTRACT TRUNCATED AT 400 WORDS)

The variation of resolution and of ommatidial dimensions in the compound eyes of the fiddler crab Uca lactea annulipes (Ocypodidae, Brachyura, Decapoda)

1996 ◽  
Vol 199 (7) ◽  
pp. 1569-1577 ◽  
Author(s):  
J Zeil ◽  
M Al-Mutairi
Keyword(s):  
Visual Field ◽  
Fiddler Crab ◽  
Visual Fields ◽  
Horizontal Resolution ◽  
Resolving Power ◽  
Compound Eyes ◽  
Vertical Resolution ◽  
Histological Techniques ◽  
Uca Lactea

We studied variations in the optical properties of the compound eyes of Uca lactea annulipes using in vivo optical and histological techniques. The distribution of resolving power in the eyes of this fiddler crab species is typical for arthropods that inhabit flat environments: the eyes possess a panoramic equatorial acute zone for vertical resolution and a steep decrease of resolution away from the eye equator in the dorsal and ventral visual fields. The dimensions of the cellular components of the ommatidia vary accordingly: in the equatorial part of the eyes, facets are larger, and crystalline cones and rhabdoms are longer than in the dorsal and ventral parts of the eyes. Along the eye equator, horizontal resolution is low compared with vertical resolution and varies little throughout the visual field. The eyes of Uca lactea annulipes are unusual in that the gradient of vertical anatomical and optical resolution is steeper in the dorsal than in the ventral visual field. We interpret this difference as indicating that the information content of the world as seen by the crabs differs above and below the horizon line in specific and predictable ways.

scholarly journals Early Shaping of Asymmetric Planetary Nebulae

1989 ◽  
Vol 106 ◽  
pp. 232-232
Author(s):  
Noam Soker
Keyword(s):  
Planetary Nebula ◽  
Binary Star ◽  
Symmetry Plane ◽  
Planetary Nebulae ◽  
High Density ◽  
Close Binary ◽  
Density Region ◽  
Short Period ◽  
Fast Wind ◽  
High Density Region

We suggest that the shape of a young asymmetric planetary nebulae may be influenced by a close binary star located at its center. This binary is a relic of the common envelope phase, presumably through which the asymmetric planetary nebula evolved. We assume that for a short period of time, shortly after the cession of the slow wind and long before the fast wind becomes effective, the binary ejects a small amount of mass, mainly in the equatorial plane. In this work we do not discuss the exact mechanism for the ejection of this pulse of mass. In the case in which the cooling is very efficient, (i.e., high-Mach-number isothermal flow), we can solve the problem analytically by using a few simplifying assumptions. In this case the high density region is shaped like a ring. We use two-dimensional hydrodynamics for the more general case. We find that at late times the high density region has a “horseshoe” shape, as viewed in the symmetry plane. There is an instability in the maximum density region. Finally we compare our results with the shape of the planetary nebula M2-9.

Do American Goldfinches See Their World Like Passive Prey Foragers? A Study on Visual Fields, Retinal Topography, and Sensitivity of Photoreceptors

2014 ◽  
Vol 83 (3) ◽  
pp. 181-198 ◽  
Author(s):  
Patrice E. Baumhardt ◽  
Bret A. Moore ◽  
Megan Doppler ◽  
Esteban Fernández-Juricic
Keyword(s):  
Visual Fields ◽  
Retinal Topography

Gettering Effect in Low and High Density Structural Defect Regions of the Cast Multi-Crystalline-Silicon Wafer

2007 ◽  
Vol 994 ◽  
Author(s):  
Yongkook Park ◽  
Jinggang Lu ◽  
G. A. Rozgonyi
Keyword(s):  
Solar Cell ◽  
Structural Defect ◽  
Crystalline Silicon ◽  
High Density ◽  
Low Density ◽  
Density Region ◽  
Recombination Lifetime ◽  
Cell Processing ◽  
Defect Sites ◽  
Before And After

AbstractTwo cast multi-crystalline silicon (mc-Si) sister wafers before and after solar cell processing were investigated to explore the gettering effect in low and high density structural defect regions. For the processed wafer, the minority carrier recombination lifetime was correlated to the structural defect distribution. For the low density region of as-grown wafer, Cr impurities were 3.28x1013cm-3 and they were reduced to 1.74×1012cm−3 for the processed wafer. The isolated Cr impurities dissolved from the precipitates at 900°C which is the typical gettering temperature in the solar cell processing are getterd effectively in the low density regions. Our current understanding for the gettering effect in the high density regions is that the segregated Cr impurities at defect sites are not released to the silicon matrix at 900°C resulting in the poor gettering effect.

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