Spots Of Different Sizes Research Articles

Centrifugal organization of direction preferences in the cat's lateral suprasylvian visual cortex and its relation to flow field processing

The cerebral cortex of the cat contains between 1 and 2 dozen representations of the visual field with different functional specializations. Six visual field maps lie along both banks of the suprasylvian sulcus, lateral and anterior to the visual areas in the occipital cortex. We have studied single-unit receptive field properties and their global organization across the visual field in 2 of these lateral suprasylvian areas, PMLS (essentially the Clare-Bishop area) and PLLS. Most neurons in PMLS and PLLS display selectivity for the direction of a light stimulus moving across their receptive fields with various degrees of directional tuning. We have used light spots of different size and velocity projected on a tangent screen in order to determine the direction preference of cells in these 2 areas. A strong tendency was found for neurons to respond best to centrifugal directions, i.e., to movement away from the area centralis. Thus, for these cells direction preference depends on the location of their receptive fields within the visual field. Velocity preference and binocular interaction in these neurons is also globally organized: Velocity preference increases with eccentricity, binocular synergism is strongest in the center of the visual field. Cluster analysis of recording tracks with respect to "radial" and "circular" cell categories reveals a grouping of cells with like properties in the lateral suprasylvian cortex. These new categories are formed by combining "centrifugal" and "centripetal" cells on the one hand and cells with direction preferences orthogonal to these on the other. The radial or centrifugal organization of direction preferences in conjunction with the global arrangement of velocity preference and binocular interaction suggests that PMLS and PLLS are involved in the processing of expanding visual flow fields of motion. Such flow fields are commonly encountered when a visual object moves towards an observer or during forward locomotion.

Two-Spot Modeling of Synoptic Light Curves of II PEG

The light curve (LC) of the single-line spectroscopic binary system II Peg (K2-3, IV-III) generally shows an asymmetrical and highly variable shape (Fig.l, left). Therefore, single circular spot models can be successfully applied only to symmetric LCs, as the 1977 one by Vogt (1981). When asymmetrical or almost flat LCs develop, as appears to be the rule for II Peg, at leasts two-spot modeling is required (Bopp and Noah 1980, Dorren and Guinan 1982).From classical single-spot models (Torres and Ferraz Mello 1973, Friedman and Gurtler 1975, Bopp and Evans 1973) we have developed a computer code including two separate circular spots of different size which are allowed to assume any relative location on the stellar surface. The model is symmetric with respect to the equator. The spots are assumed to radiate as back bodies with temperature ranging from 100 to 2000 degree lower than the temperature of the unspotted photosphere (4500°K).

Chromatic properties of bipolar cells in the carp retina

AbstractIn order to analyze the receptive‐field arrangement of color‐opponent bipolar cells, the intracellular responses to monochromatic light spots of different sizes and shapes were recorded from the isolated retina of the carp (Cyprinus carpio) under photopic conditions. Out of 72 bipolar cells identified, 39 color‐opponent cells were classified into three types: the spatially segregated color‐opponent type, the surround color‐opponent type, and the center coloropponent type. The spectral responses of the second type in the surround receptive field were similar to those of their chromatic counterparts in the horizontal cells, suggesting a close relationship to the horizontal‐cell feedback mechanism. The third type was characterized by a small center area of less than 100 μm in diameter. For each type, the mirror images of the spectral response curves were obtained from on and off bipolar cells. This fact strongly suggests that the four basic color channels originate in the bipolar cells.

Some aspects of electromigration in D.C. electroluminescent ZnS devices

The stabilization with time of light emission from electroluminescent (EL) structures still requires investigation. Microscope observations of the EL structure show that the brightness is inhomogeneous and that the light emission is localized on many spots of different sizes. We investigated the distribution of the brightness along the active region of the sample and its dependence on time. The localized emission disappears with increasing time, and the brightness of the sample becomes more homogeneous although its intensity is reduced. This degration of the light emission is tentatively explained in terms of copper ion migration. The migration of copper ions affects the properties of the layer close to the positive electrode which appears bright. Some changes in the electrode surface and the precipitation of substantial amounts of copper were observed.

Physiological studies of single retinal cells and their morphological identification

Intracellular recordings were made from various types of cells in goldfish retina. Receptive fields of these cells were studied with light spots of different sizes. After recording, the cells were identified morphologically by injecting dyes from the recording electrode: thus correlation was made between cell types and their characteristic responses. Receptors were hyperpolarized by illumination. No obvious spatial summation was seen in these responses. Regardless of wavelength, receptors were always hyperpolarized. They were classified into three types according to response maxima at red, green and blue region of the spectrum. External and internal horizontal cells were identified as the origin of S-potentials. Both L- and C-type responses were seen from two types of horizontal cells. Electrical coupling was demonstrated between neighboring external horizontal cells; presumably this accounts for large spatial summation of S-potentials. Bipolar cells had center-surround type receptive field. The size of the center was about 100 μ, the same order of magnitude as the dendritic field. The surround was large, extending to about 1.5 mm dia. The majority of bipolar cells were color-coded; in these cells the center always received input from red cones and the surround from green cones. Amacrine cells showed two types of responses, transient and sustained. Their receptive field was at least 2.5 mm dia. All the sustained type amacrine cells showed opponent color responses; hyperpolarization to red and depolarization to green. No spatial segregation was seen between red sensitive and green sensitive areas. It was suggested that a double opponent ganglion cell receives inputs from bipolar cells in the center and from amacrine cells in the surround.

Further studies on the velocity function of movement detecting class-2 neurons in the frog retina

The responses of the class 2 movement-detecting neurons of the frog's retina were recorded and analyzed in order to determine the extent of the validity of the previously described power function of exponent 0.7 which relates response to stimulus velocity. It was found that the power function is capable of describing the responses to linear, non-linear, discontinuous and completely irregular movements; to apparent motion stroboscopic illumination and to movements of spots of different sizes and different stimulus background contrast. A change of the luminance of the stimulus pattern within the photopic and upper scotopic level did not change the exponent of the power function; neither did illumination with monochromatic light of different wave lengths.

Automatic Particle-sizing by Successive Counting

THE development of automatic apparatus, generally employing optical scanning systems in conjunction with electronic counters, for determining the number and size of a population of small particles randomly dispersed in one plane has aroused considerable interest during recent years. Walton1 has summarized some of the chief trends and methods used in the design and operation of such apparatus. Hawksley2 has pointed out that, whereas counting can be carried out by relatively simple instruments, all proposals for methods of size determination have involved the measurement of pulse-heights or pulse-lengths from the records obtained from photoelectric scanning devices. He showed, however, that it is possible to derive a value for the mean diameter of the particles from a series of counts made with scanning spots of different sizes, so that sizing can be carried out with simple counting apparatus. He also implies that similar results could be obtained if the ‘response-level’ of the detecting device is altered during successive counts, but fails to follow up this suggestion.

On the factors influencing the appearance of placques of bacterial lysis.

If the activity of “bacteriophage” is studied upon agar cultures spots or so-called placques of lysis are seen to appear, instead of a homogeneous growth. As a rule, these clear spots stand out quite distinctly against the background of agar, but occasionally one observes among them a certain number of spots which may be considerably less distinct than others. The variations among the spots are even more marked as regards their size. The placques may vary in the same plate from the size of a pin-prick to that of a size larger than the head of the pin. A number of authors have succeeded in demonstrating that by isolating and propagating each of the variants one can obtain pure strains of “bacteriophage”—showing very little if any variation in the size or distinctness of the placques (or spots). In their opinion the co-existence in one plate of spots of different size is indicative of impurity of the lytic strain. Having in our possession a strain of “bacteriophage” which showed a tendency to give rise to spots of lysis of various sizes, we considered it impure and attempted to isolate the several component strains by the usual method of daily transfers. When we found that pure strains of “bacteriophage” thus secured would unexpectedly show marked changes in respect to the average size of spots or their distinctness, we attempted to ascertain the cause of the changes. 1. Within certain limits, the average size of the placque changes inversely with the number of bacteria susceptible to lysis present in each cc. of agar. 2. The average size of the placque depends upon the relative concentration of young and old individuals in the culture—the greater the number of old bacteria, the smaller the spots.