Stereopsis and the random element in the organization of the striate cortex.

Receptive field position and orientation disparities are both properties of binocularly discharged striate neurons. Receptive field position desparities have been used as a key element in the neural theory for binocular depth discrimination. Since most striate cells in the cat are binocular, these position disparities require that cells immediately adjacent to one another in the cortex should show a random scatter in their monocular receptive field positions. Superimposed on the progressive topographical representation of the visual field on the striate cortex there is experimental evidence for a localized monocular receptive field position scatter. The suggestion is examined that the binocular position disparities are built up out of the two monocular position scatters. An examination of receptive field orientation disparities and their relation to the random variation in the monocular preferred orientations of immediately adjacent striate neurons also leads to the conclusion that binocular orientation disparities are a consequence of the two monocular scatters. As for receptive field position, the local scatter in preferred orientation is superimposed on a progressive representation of orientation over larger areas of the cortex. The representation in the striate cortex of visual field position and of stimulus orientation is examined in relation to the correlation between the disparities in receptive field position and preferred orientation. The role of orientation disparities in binocular vision is reviewed.     

Polarized fluorescence in an electric field: comparison with other electrooptical effects for rodlike fragments of DNA and the problem of the saturation of the induced moment in polyelectrolytes

Electrical birefringence, electrical dichroism and polarisation of fluorescence in an electric field experiments have been performed at high fields on sonicated fragments of DNA labelled with Acridine Orange. The latter electrooptical effect gives access to the field dependence of the fourth moment of the orientation function while the two former give access to the field dependence of the second moment. The origin of the large departure from an E2 dependence at rather low degrees of orientation is extensively discussed. Following a suggestion of Shirai on the calculation of orientational averages for a saturated induced moment, we can show that this model rationalizes the existence of a linear E dependence of the orientation factor at intermediate fields and explains very well our experimental results. When applied to previous dichroic data at higher fields it shows that the low value of the dichroism at saturation introduced to fit with other models, in contradiction with the absence of base tilting in the B form of DNA, is not required for a quantitative fit with this new orientation mechanism. The transition from an E2 dependence at low fields to an E dependence at intermediate fields gives an estimate of the field required for the saturation of the ionic polarisation E approximately 6 kV/cm.     

视网膜神经节细胞感受野的一种新模型 II.神经节细胞方位选择性中心周边相互作用机制

在前文建立的二维视网膜神经节细胞含大周边感受野模型基础上 ,结合生理实验结果模拟了神经节细胞的方位选择性特性。文中采用椭圆感受野的观点解释了方位选择性的成因。并通过中心区以外区域对中心区方位选择性的复杂调制组合 ,展示了感受野不同亚单元对方位选择性的影响作用 ;指出方位选择性的成因是感受野椭圆亚单元的存在;感受野复杂的方位选择性是由于中心和周边在不同刺激条件下竞争的不同结果造成的;同时指出对椭圆感受野 ,倍频反应也会有相应的方位选择性。     

Effect of pulsed and reversing electric fields on the orientation of linear and supercoiled DNA molecules in agarose gels

When linear or supercoiled DNA molecules are imbedded in agarose gels and subjected to electric fields, they become oriented in the gel matrix and give rise to an electric birefringence signal. The sign of the birefringence is negative, indicating that the DNA molecules are oriented parallel to the electric field lines. If the DNA molecules are larger than about 1.5 kilobase pairs, a delay is observed before the birefringence signal appears. This time lag, which is roughly independent of DNA molecular weight, decreases with increasing electric field strength. The field-free decay of the birefringence is much slower for the DNA molecules imbedded in agarose gels than observed in free solution, indicating that orientation in the gel is accompanied by stretching. Both linear and supercoiled molecules become stretched, although the apparent change in conformation is much less pronounced for supercoiled molecules. When the electric field is rapidly reversed in polarity, very little change in the birefringence signal is observed for linear or supercoiled DNAs if the equilibrium orientation (i.e., birefringence) had been reached before field reversal. Apparently, completely stretched, oriented DNA molecules are able to reverse their direction of migration with little or no loss of orientation. If the steady-state birefringence had not been reached before the field reversal, complicated orientation patterns are observed after field reversal. Very large, partially stretched DNA molecules exhibit a rapid decrease in orientation at field reversal. The rate of decrease of the birefringence signal in the reversing field is faster than the field-free decay of the birefringence and is approximately equal to the rate of orientation in the field (after the lag period).(ABSTRACT TRUNCATED AT 250 WORDS)     

Application of the paramagnetic dipole field for solution NMR active site structure determination in low-spin, cyanide-inhibited ferric hemoproteins

The principles for the application of the paramagnetic dipolar field of low-spin, cyanide-inhibited ferrihemoproteins for determining active site structure are briefly described. The ubiquitous dipolar shifts for assigned residues, together with crystal coordinates of some appropriate structural homolog, allow determination of the orientation and anisotropies of the paramagnetic dipolar tensor. The orientation of chi uniquely defines the orientation of the Fe-CN unit, which is tilted variably and sensitively monitors distal steric and H-bond interactions. The mapped dipolar field, in turn, can be used to determine the orientation of mutated residues. Case studies involving unusual genetic variants and point mutants of myoglobins, human hemoglobins, horseradish peroxidase and its substrate complex of heme oxygenase are presented as examples.     

The light sensitivity of the human visual system depends on the direction of view

The near-stable North-South orientation of the natural geomagnetic field provides an ideal basis for navigation. Sailors have used it since ancient times, animals for much longer. Various mechanisms have developed for this purpose. Experiments have pointed to a connection between orientation in the geomagnetic field and light perception. Such observations are supported by theoretical considerations. The underlying interaction should also modulate the light sensitivity of the visual system. Recently we demonstrated the effect of an oscillating field. Here we report the existence of a weak influence of the static field on visual sensitivity in man. By comparison with control experiments, if the directions of view line and field vector coincide the perception threshold of a light stimulus is slightly but significantly increased. This significance is lost if the view line deviates by 10 degrees from the field direction.     

Magnetic compass sense in the large yellow underwing moth, Noctua pronuba L.

Many animals are now known to have a magnetic sense which they use when moving from one place to another. Among insects, this sense has only been studied in any detail in the honey bee. A role for a magnetic compass sense in cross-country migration has not so far been demonstrated for any insect. On clear nights the large yellow underwing moth, Noctua pronuba, has been shown to orientate by both the moon and the stars. However, radar studies have shown moths to be well-oriented on overcast nights as well as clear nights. We report here that when large yellow underwings are placed in an orientation cage on overcast nights and the Earth's normal magnetic field is reversed, there is a corresponding reversal in the orientation of the moth. We conclude that this species makes use of the Earth's magnetic field in maintaining compass orientation on overcast nights. We also show that the preferred compass orientation to the Earth's magnetic field is the same as the compass direction that results from orientation to the moon and stars.     

Transient orientation of linear DNA molecules during pulsed-field gel electrophoresis.

The transient orientation of lambda DNA and lambda-DNA oligomers has been measured during pulsed field gel electrophoresis. The DNA becomes substantially aligned parallel to the electric field E. In response to a single rectangular pulse, orientation shows an overshoot with a peak at 1 second, then a small undershoot, and finally a plateau. When the field is turned off, the orientation dissipates in two distinct exponential phases. Field inversion leads to periods of orientation with intervening periods of reduced orientation as the chains reverse direction. Field inversion pulses applied to linear oligomers of lambda-DNA show that orientation responses slow down but increase in amplitude as molecular weight increases, for a given field. Because DNA stretching and alignment parallel to E are expected to correlate with DNA velocity, the velocity in response to a pulsed field is also expected to exhibit an overshoot.     

Brownian diffusion and electrophoretic transport of double‐stranded DNA in agarose gels

The field free diffusion constant and the electric field dependence of the electrophoretic mobility and molecular orientation of DNA samples from 5 to 164 kilobase pairs in agarose gels from 0.5 to 2% have been measured by fluorescence recovery after photobleaching and birefringence. In conditions where the reptation predictions hold for the field free diffusion, they partially fail for the DNA size dependence of the low field limit of the electrophoretic mobility. The linear field dependencies of the electrophoretic mobility and orientation factor seem to favor the biased reptation model with fluctuations over the standard biased reptation model, which predicts a quadratic field dependence. The quantitative analysis of the molecular parameters shows, however, that most experiments have been carried out at values of the field where the difference between the two models may be less conclusive. The pore size dependence of the different quantities has been given a particular attention and the role of the distribution of pore sizes in the departures from the reptation predictions is discussed. © 1999 John Wiley & Sons, Inc. Biopoly 50: 45–59, 1999     

Behavioural evidence for the use of geomagnetic cue in Japanese glass eel <Emphasis Type="Italic">Anguilla japonica</Emphasis> orientation

Japanese eel is already magnetosensitive at the glass eel phase. However, currently, there is no evidence that they can use geomagnetic cues for orientation. We examined orientation behaviour in a radially symmetrical test arena in which the horizontal component of the geomagnetic field could be manipulated. Groups of glass eels released at the centre of the arena showed a mean orientation angle significantly biased to the south of 198° in the ambient geomagnetic field, but showed random orientation in the geomagnetic field when its horizontal component was cancelled in a solenoid. Results showed that they use geomagnetic cues for orientation.     

Influence of magnetic field alignment of cellulose whiskers on the mechanics of all-cellulose nanocomposites

Orientation of cellulose nanowhiskers (CNWs) derived from tunicates, in an all-cellulose nanocomposite, is achieved through the application of a magnetic field. CNWs are incorporated into a dissolved cellulose matrix system and during solvent casting of the nanocomposite a magnetic field is applied to induce their alignment. Unoriented CNW samples, without the presence of a magnetic field, are also produced. The CNWs are found to orient under the action of the magnetic field, leading to enhanced stiffness and strength of the composites, but not to the level that is theoretically predicted for a fully aligned system. Lowering the volume fraction of the CNWs is shown to allow them to orient more readily in the magnetic field, leading to larger relative increases in the mechanical properties. It is shown, using polarized light microscopy, that the all-cellulose composites have a domain structure, with some domains showing pronounced orientation of CNWs and others where no preferred orientation occurs. Raman spectroscopy is used to both follow the position of bands located at ～1095 and ～895 cm(-1) with deformation and also their intensity as a function rotation angle of the specimens. It is shown that these approaches give valuable independent information on the respective molecular deformation and orientation of the CNWs, and the molecules in the matrix phase, in oriented and nonoriented domains of all-cellulose composites. These data are then related to an increase in the level of molecular deformation in the axial direction, as revealed by the Raman technique. Little orientation of the matrix phase is observed under the action of the magnetic field indicating the dominance of the stiff CNWs in governing mechanical properties.     

The orientation of the primary donor in bacterial photosynthesis.

The triplet state EPR spectra of magnetically aligned whole cells of Rhodopseudomonas viridis and Rhodopseudomonas palustris display a marked dependence on the orientation of the static EPR field with respect to the alignment field direction. This observation implies that the primary donor species on which the triplets are localized are ordered within the membranes. We have developed a theoretical model for the system to enable calculation of the orientation of the magnetic axes of the primary donor species with respect to the membranes in which they reside. The triplet state spectra are generated by an ensemble of partially ordered magnetic systems and a computer simulation of the experimental results. The triplet orientation is very similar for the two organisms studied, where one axis lies predominantly in the plane of the membrane and the other two axes have approximately equal projections onto the normal to the membrane.     

Mapping of contextual modulation in the population response of primary visual cortex

We review the evidence of long-range contextual modulation in V1. Populations of neurons in V1 are activated by a wide variety of stimuli outside of their classical receptive fields (RF), well beyond their surround region. These effects generally involve extra-RF features with an orientation component. The population mapping of orientation preferences to the upper layers of V1 is well understood, as far as the classical RF properties are concerned, and involves organization into pinwheel-like structures. We introduce a novel hypothesis regarding the organization of V1’s contextual response. We show that RF and extra-RF orientation preferences are mapped in related ways. Orientation pinwheels are the foci of both types of features. The mapping of contextual features onto the orientation pinwheel has a form that recapitulates the organization of the visual field: an iso-orientation patch within the pinwheel also responds to extra-RF stimuli of the same orientation. We hypothesize that the same form of mapping applies to other stimulus properties that are mapped out in V1, such as colour and contrast selectivity. A specific consequence is that fovea-like properties will be mapped in a systematic way to orientation pinwheels. We review the evidence that cytochrome oxidase blobs comprise the foci of this contextual remapping for colour and low contrasts. Neurodynamics and motion in the visual field are argued to play an important role in the shaping and maintenance of this type of mapping in V1.     

Orientation in pied flycatchers: the relative importance of magnetic and visual information at dusk

We investigated the orientation of juvenile pied flycatchers, Ficedula hypoleuca, during autumn migration in south Sweden using orientation cage experiments, to study the relative importance of visual and magnetic information at sunset. We performed cage tests under 12 experimental conditions that manipulated the geomagnetic and visual sunset cues available for orientation: natural clear skies in the local or a vertical magnetic field; simulated total overcast in the local or a vertical magnetic field; natural pattern of skylight polarization and directional information from stars screened off, with the sun's position as normal or shifted 120 degrees anticlockwise with mirrors; reduced polarization in the local or a vertical magnetic field; directions of polarization (e-vector) NE/SW and NW/SE, respectively, in the local or a vertical magnetic field. The pied flycatchers were significantly oriented towards slightly south of west when they could use a combination of skylight and geomagnetic cues. The mean orientation was significantly shifted along with the deflection of the sunset position by mirrors. Reduced polarization had no significant effect on orientation either in the local, or in a vertical, magnetic field. The birds tended to orient parallel with the axis of polarization, but only when the artificial e-vector was aligned NW/SE. The mean orientation under simulated total overcast in a vertical, and in the local, magnetic field was not significantly different from random. It is difficult to rank either cue as dominant over the other and we conclude that both visual and magnetic cues seem to be important for the birds' orientation when caught and tested during active migration. Copyright 1999 The Association for the Study of Animal Behaviour.     

Orientation-sensitive Neurons in the Brain of the Honey Bee (Apis mellifera)

Recent behavioural experiments have shown that bees are able to distinguish vertically presented patterns with orientation cues, although the locations of areas of black are randomized. To discriminate between two orientations, the bees must possess more than one orientation-sensitive neuron type. Therefore, the aim is to search for different types of orientation-sensitive cells of the honey bee, and measure their receptive field, velocity sensitivity and contrast sensitivity. Orientation-sensitive cells with two different types of orientation tuning-curves were recorded intracellularly in the mid-brain of the honey bee when the stimulus was a narrow bar (bar width = 5 degrees ). These cells are sensitive to bar movement within their large receptive field, which covers the visual field of one eye. They are quite distinct from the well-known directional motion detectors. The contrast sensitivity of the orientation-sensitive cells recorded in this study corresponds to results from behavioural experiments. The velocity-sensitivity curves of the orientation-sensitive cells differ from those of the direction-sensitive cells. Measurements of orientation sensitivity and contrast sensitivity when the stimulus is a wide bar (bar width = 10 degrees ), done in different eye regions, suggest that each orientation-sensitive cell receives visual signals from an array of orientational subunits within its receptive field. The correspondence between these physiological results and the results of recent behavioural experiments are discussed. Copyright 1997 Elsevier Science Ltd. All rights reserved     

Orientational behavior of phosphatidylcholine bilayers in the presence of aromatic amphiphiles and a magnetic field.

A number of aromatic-containing additives which can influence the orientation of fragments of lipid bilayer membranes by a magnetic field have been investigated. Two properties of these additives prove important: (1) sufficient detergency to facilitate reorganization of bilayer components and (2), sufficient anisotropy in magnetic susceptibility the preferred direction of fragment orientation. Triton X-100 is identified as effective in terms of facilitating magnetic field ordering of bilayer fragments but does not alter the preferred direction of orientation. A combination of the detergent CHAPSO (3-[(3-cholamidopropyl)-dimethylammonio]-1-propane sulfonate) and the aromatic alcohol 1-naphthol facilitates both ordering and alters the preferred direction of bilayer orientation. As mixtures of dimyristoylphosphatidylcholine (DMPC) and CHAPSO, which orient with bilayer normals perpendicular to the magnetic field, were titrated with 1-naphthol, the assemblies underwent transitions, first to random orientation, and then to an orientation with bilayer normals parallel to the field. Based on temperature-induced phase transitions and the extent of motional averaging of the 31P shielding tensor of the DMPC headgroup, the DMPC in these oriented samples appears to maintain a bilayer morphology during transitions. The insight provided in this study regarding factors which influence fragment stability and orientation lays the groundwork for the design of improved field-oriented media for spectroscopic investigation of membrane components.     

Avian orientation: effects of cue-conflict experiments with young migratory songbirds in the high Arctic

The migratory orientation of juvenile white-crowned sparrows, Zonotrichia leucophrys gambelli, was investigated by orientation cage experiments in manipulated magnetic fields performed during the evening twilight period in northwestern Canada in autumn. We did the experiments under natural clear skies in three magnetic treatments: (1) in the local geomagnetic field; (2) in a deflected magnetic field (mN shifted −90°); and (3) after exposure to a deflected magnetic field (mN −90°) for 1 h before the cage experiment performed in the local geomagnetic field at dusk. Subjects showed a mean orientation towards geographical east in the local geomagnetic field, north of the expected migratory direction towards southeast. The sparrows responded consistently to the shifted magnetic field, demonstrating the use of a magnetic compass during their first autumn migration. Birds exposed to a cue conflict for 1 h on the same day before the experiment, and tested in the local geomagnetic field at sunset, showed the same northerly orientation as birds exposed to a shifted magnetic field during the experiment. This result indicates that information transfer occurred between magnetic and celestial cues. Thus, the birds' orientation shifted relative to available sunset and geomagnetic cues during the experimental hour. The mean orientation of birds exposed to deflected magnetic fields prior to and during testing was recorded up to two more times in the local geomagnetic field under natural clear and overcast skies before release, resulting in scattered mean orientations.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .     

Magnetic Orientation in Solenopsis sp. Ants

It is known that magnetic fields affect ants behavior. It has been shown that Solenopsis ants are sensitive to magnetic fields but there is no experimental evidence for magnetic orientation. In this paper experiments were done to verify the magnetic orientation of Solenopsis sp. ants. The spontaneous orientation of ants in a circular arena was studied in two different magnetic conditions: in the natural geomagnetic field and under an altered magnetic field, with the horizontal geomagnetic axis shifted in 90?o. Our results show that ants consistently change their orientation direction when the magnetic field was altered. Axial circular statistics analysis showed that, in the absence of other cues, ants orient spontaneously to the horizontal geomagnetic field axis. The present paper shows for the first time magnetic orientation in Solenopsis sp. ants.     

Does assignment of orientation to dot patterns reveal optimization processes in the visual system?

Sixty subjects were tested to assign orientation to ten dot patterns differing in their overall form and the number of dots in the pattern. The patterns were presented in four different positions in the visual field and their orientation was estimated in two ways. It was demonstrated that the assignment of orientation did not depend on the position of the pattern in the visual field as well as on the method of estimation used. A quantitative measure for the elongation of a dot pattern is proposed which correlates with the degree of ambiguity in orientation estimation. The greater the elongation the smaller the standard deviation of the estimates given. The distributions of the estimates for the ten patterns were analyzed. It was shown that they can be presented as superpositions of two or more groups of normally distributed estimates determined by some salient characteristics of the stimuli. Data are discussed from the point of view that assignment of orientation to dot patterns reveals the existence of optimization mechanisms in human brain that extract perceptual invariants from external stimulation.     

Celestial orientation in the marbled newt (Triturus marmoratus)

Orientation toward breeding ponds plays an important role in the seasonal movements of amphibians. In this study, adult marbled newts were tested in a circular arena to determine sensory cues used to locate breeding ponds. Animals were collected from a temporary pond situated in northern Spain, taken to the experimental site 340 m distant, and tested for orientation under a variety of conditions (i.e., orientation under a clear night sky, orientation under an overcast night sky, and orientation under a clear night sky in the presence of an altered geomagnetic field). These investigations have demonstrated that the marbled newt is able to orient using celestial cues. Animals chose a compass course in the direction of their breeding pond only when celestial cues were available. Conversely, the ambient geomagnetic field does not seem to be relevant to orientation of marbled newts since they were unable to orient themselves using the ambient geomagnetic field in the absence of celestial cues. Electronic Publication