Opaque Screen Research Articles

Changes in the darkness of four body features of bluegill sunfish ( Lepomis macrochirus Rafinesque) during aggressive encounters

The darkness of four body features (general body surface, GBS; lateral stripe pattern, LSP; opercular flap spot, OFS; and dorsal fin-ray spot, DFRS) was observed during the formation of 16 pairwise status relationships among bluegill sunfish (Lepomis macrochirus Rafinesque). In eight cases (Method A) an intruder fish was placed into a 110 liter aquarium occupied for 7 previous days by a resident fish. In eight additional cases (Method B) two fish lived on opposite sides of a 110 liter aquarium divided by an opaque screen for 7 days prior to removal of the screen. Dominance was established by one of the fish in all but two cases (both were Method B) and aggressive encounters proceeded through five clearly identifiable stages: (1) a stage of inactivity just after pair formation, (2) a stage in which the fish oriented and approached each other tentatively and without further interaction, (3) a stage in which threat displays are emitted, often by both fish, but no actual body contact occurs, (4) a stage of vigorous attacks, and (5) a stage where one fish is clearly emitting all attacks and where the other fish is fleeing and/or hiding. Darkness of each feature in each fish was evaluated with a statistically reliable three-point scale at each stage during the contest. GBS increased in darkness equally for dominant and submissive fish. LSP, OFS and DFRS became darker in dominant fish and lighter in submissives, suggesting that these three features may have status-related signal value. Method of pair formation did not interact with these effects.

Optical-diffraction methods of studying the electron-diffraction patterns of thin films of copper–gold alloys

Superlattice formation in thin films of copper–gold alloys has been studied by the use of optical-diffraction analogues. Fraunhofer diffraction patterns of arrangements of holes in opaque screens have been compared with electron-diffraction patterns of the alloy films. It has been found possible to draw some general conclusions about the ways in which the antiphase domains fit together to produce certain characteristics of the electron-diffraction patterns. Some ideas are put forward about the growth of superlattices.

Measurement of capillary basement membrane thickness by magnification on a rear opaque projection screen

2190 measurements of capillary basement membrane thickness were obtained from the images of magnified micrographs using a rear opaque projection screen. This method proved to be reproducible and reliable. The electron microscope magnification used, 2500x, permits sharp definition of structures in the resulting micrographs. Projection on the opaque rear screen magnified the image 16x, yielding a final magnification of 40,000x. This high final magnification of micrographs of good quality minimized the error in measurement. The use of a special dial caliper with pins attached allows an open field and decreases the subjective components of measurements. Moreover, this technique results in less stress for the persons performing the measurements.

Two new optical techniques to measure strain

A grating engraved on the surface to be analyzed is utilized to measure strain. The grating is illuminated by a monochromatic, plane wavefront. A lens produces the diffraction spectrum of the grating, and an opaque screen is located in the plane of the spectrum. A window allows a single diffraction order to go through the screen. Two techniques are presented.

One-dimensional Optical Fourier Transforms of Line Tracings

An optical Fourier transforming system is used to produce the transform of a one-dimensional signal recorded as a transparent oscillogram on an opaque screen. If the tracing is illuminated with light whose amplitude varies linearly perpendicular to the tracing axis, then the exact transform is obtained along one axis of the output plane. Spectra with small error terms are obtained by superimposing a phase plate, or a knife edge or a special binary mask over the line tracing. The theory of the methods is presented and verified experimentally. Multichannel operation is demonstrated.

On the Propagation of a Pulse through a Dispersive Medium

The problem of the behavior of a pulse when propagating through a dispersive medium has been treated in terms of Fourier transforms. For a linearly dispersive medium the evaluation of the integrals is trivial, but when the dispersion relation contains a significant quadratic term the integrals can be evaluated using the properties of Fresnel integrals. The advantage of this treatment is that it shows that there is a very strong analogy between the pulse shape and the diffraction pattern produced when light passes through a small hole in an opaque screen.

Determination of Atmospheric Structure Function by Using a Single Coherent Detector

The wave structure function associated with atmospheric turbulence is important in the effective design of telescopes for coherent optical receivers. This paper describes a method of measurement of the wave structure function by employing an already existing optical receiver. The aperture of this receiver's telescope is masked by an opaque screen with two small holes. It is then shown that when the incident beam obeys Gaussian statistics, the receiver's A.M. output can be simply related to the wave structure function of the incident beam.

Diffraction of a plane electromagnetic wave by a slit in a thick screen placed between two different media

The diffraction pattern due to a plane H-polarized electromagnetic wave is investigated, when this wave is incident upon an infinitely long slit of finite width in an opaque screen of non-vanishing thickness. The screen is located between the plane boundaries of two media with different electromagnetic properties. A Green's function formulation of the problem is employed, leading to a system of four coupled integral equations in which the field distributions in the slit occur as unknowns. Numerical results are presented for the field just below the screen as well as for the far field pattern.

Two-point Resolution in Partially Coherent Light

The classical approach to the study of two-point resolution has considered the case of two infinitesimal pinholes in an opaque screen. Since partially coherent imagery is non-linear with respect to either intensity or amplitude, the question of resolution needs to be re-examined for a pair or point-like particles embedded in a medium of finite but different transmission. This paper deals with this situation in ordinary microscopy. It has been found that the limit of resolution may be expressed as  0 + j , where  0 is the limit obtainable on the basis of the Sparrow criterion, and is seen to be independent of the original object contrast. The second term j  is an incremental term that depends on the object contrast and the final required image contrast. Both terms, however, depend on the degree of coherence between the object particles. A simple semi-empirical expression K s =  0 sin f / u = 0·475 + 0·26 o gives the Sparrow limit of resolution, where o is the coherence between the pair of points. Curv...

Pecten of the pigeon's eye as an inter-ocular eye shade.

THE eyes Of all birds have a black pleated structure, known as the pecten, which projects from the retinal surface into the vitreal space, towards the lens. This remarkable structure has provoked many speculations about its function1,2, but only one has so far been widely accepted : the pecten has a copious blood supply and this is thought to function as a replacement for the capillary bed that, in many other vertebrates, supplies the vitreal surface of the retina3,4. Its size, shape, and heavy black pigmentation have suggested optical functions, some of which centre around its shadow casting potentialities5,6, but many of these theories do not seem to take account of the way the pecten is placed in the optical system. It is oriented nearly parallel to light entering the centre of the pupil, so that it presents the minimum area to the converging rays forming the retinal image, and the folded free border that is its most striking gross anatomical feature approaches close behind the lens. Thus the shadow cast by the incoming light, which we here call the “primary shadow”, will be as small as possible and very blurred. It is, furthermore, centred on the pecten's own base, which is the elongated optic disk or “blind spot”, devoid of receptors, where optic nerve fibres leave the eye. Thus we think the primary shadow has no beneficial functional significance; on the contrary, it is remarkable that such a large nutrient structure can be inserted into a small optical system with so little disturbance to its normal image forming function. There is, however, an optical function that can be performed by an opaque screen in the position of the pecten.

Photoinhibition of arousal in the stick insect Carausius

1. The phasmid Carausius assumes a stick posture (thanatosis) during the day but becomes active and feeds at night. Animals placed in darkness during the day start to arouse after a latency of 8–10 minutes, and about half are active after 12 minutes. 2. Light inhibits arousal. A flux of 4×109 hν sec-1 cm−2 at 483 nm increases the latency to the first arousal to about 12 minutes and the half-time to about 26 minutes. 3. The action spectrum for the inhibition of arousal peaks at 510–520 nm. Sensitivity falls gently toward the blue, more steeply to longer wavelengths, and is down 2 log units at 620 nm. 4. Animals with opaque screens on their eyes arouse quickly when placed in dim test lights that inhibit activity in normal controls. Therefore the eyes are the principal receptors. 5. Animals with eyes surgically removed show residual sensitivity to light. Therefore a higher-threshold, extra-optic receptor is also present. 6. Normally the insects integrate intensity over large areas of the visual field, for if they are placed on a reflecting substrate, illumination of the posterior half of the body is as effective in inhibiting arousal as light on the anterior end.

Optical Fourier Transformation of Area-Modulated Spatial Functions

A one-dimensional function may be represented spatially as an aperture in an opaque screen where the aperture's width is proportional to the function. When such an area-modulated screen is the input to a standard coherent optical fourier transformer, the amplitude of the light along one axis on the output plane is proportional to the fourier transform of the original function. Continuous and sampled area modulation for single and multichannel operation are discussed. Experimental agreement with the expected results is obtained. Hybrid configurations combining area and optical-density modulation are discussed.

Perception and knowledge of the world

An experiment was performed in order to test Köhler's satiation hypothesis. It was hypothesized that an object, when seen in the upper half of the visual field would tend to be perceived as differing in size from when seen in the lower half of the visual field. Thirty male and female college undergraduates were required to make size judgements on pairs of circles which were projected on an opaque screen. The design employed a two-choice Method of Constant Stimuli, with controls for response bias and position effects. Significant results were found (binomial test, p = 0.013) for the field effect, with upper visual field stimuli judged larger than lower visual field stimuli. The implications for man's knowledge of the world were discussed.

Concealment of Stimuli during Delay in the Delayed-Response Problem

Unless their level of performance on delayed-response problems is very high, monkeys show a decrement when the opaque screen of the WGTA is lowered. This did not occur when the objects were concealed for a comparable period by a small hand screen, suggesting the deficit was due to the signal that lowering the screen meant trial termination.

Temporal estimation in the perception of occluded motion.

Ss were shown a rectangular object which moved transversely across their field of view and passed behind an opaque screen. The purpose was to investigate some of the factors affecting estimates of the time required for the occluded moving object to travel a given distance behind the screen. The factors selected for study were (1) method of viewing the moving object (pursuit, static fixation), (2) background structure (homogeneous, textured), and (3) object size. According to previous studies, these variables affect the perceived speed of a moving object and might therefore be expected to affect estimates of the duration of occluded traversal. The results did not show statistically significant differences among experimental groups, although data trends are discussed. An additional finding was that Ss significantly overestimated the duration of occluded traversal, consistent with a tendency to overestimate traversal distance. The experiment is related to Michotte's studies of “amodal perception” and discussed in terms of Gibson's stimulus information approach to perception.

DISCRIMINATION LEARNING IN LANGURS AND RHESUS MONKEYS

Our previous studies have demonstrated that langurs (Presbytis entellus) differ from rhesus monkeys (Macaca mulatta) in some forms and frequencies of social behavior (Manocha, 1966) and also in reactions to novel situations and objects (Singh & Manocha, 1966). The present study concerns possible differences in cognitive ability. Method.-Ss were Indian Langurs (Presbytis entellus), 2 males and 2 females with a mean estimated age of 7 yr. and 4 male and 2 female rhesus monkeys (Macaca mzrlatfa) whose mean estimated age was 8 yr. Ss were caught near urban areas. They were housed individually in metal cages measuring 3 ft. by 3 ft. by 3 ft. Previously they had been tested for reactions to novel situations. Discrimination learning tests were given in a modified Wisconsin General Test Apparatus (WGTA) as described in detail elsewhere (Singh, 1966). It consisted of a table measuring 395 ft. by 5 ft. with a superstructure supporting the opaque and one-way vision screen. A moveable test tray containing two foodwells was mounted on the table. Instead of the usual restraining cage, 3%-ft.-high side walls projected in front by 3 ft.; these also covered the sides of the living cage when the apparatus was set in place. Each S was trained to displace a gray wooden block placed on one of the foodwells and take a raisin until S responded within 5 sec. of the presentation of the test tray. Each trial for visual pattern discrimination began with the opaque screen down; the foodwell was baited with one raisin and the visual panerns, mounted on rhe wooden blocks, were placed at right angles over the two foodwells. The tray was then pushed ro S's side, the one-way vision screen lowered, and the opaque screen raised. Once S re

Indirect delayed reactions under various testing conditions in normal and midlateral frontal monkeys

A group of nine rhesus monkeys with bilateral ablation of the cortex in and around the sulcus principalis were unimpaired relative to a group of xeven control animals when tested for the retention of a preoperatively learned indirect delayed reaction based upon a sign-differentiated position discrimination. Introduction of longer durations of delay and a change in the basic discrimination task also failed to reveal any deficit. A significant but transient loss appeared in frontals when an opaque screen was used during delays. The results were discussed in terms of certain anatomical and methodological features of the research.

A diffraction size-frequency analyser with automatic recording of size-frequency distributions and total and respirable surface areas

A simple non-rigorous account of the theory of the diffraction size-frequency analyser, an instrument for determining particle size-frequency distributions, is given. A vacuum metallizing technique is used to obtain an opaque diffraction screen in which each particle is represented by an aperture of the same size and shape as the projection of the particle on to the screen. It is shown that by using illumination coherent in one plane it is possible to obtain an unambiguous length-frequency distribution of aperture chords parallel to the plane of coherence. The size-frequency distribution of the apertures can be obtained from a knowledge of their shape distribution or by assuming a shape distribution which may be regarded as defining the particle size parameter. An instrument, based on this theory, which records the size-frequency distributions or the total and respirable surface areas of dust samples at the rate of 10 samples per min has been developed. The required information is obtained by modulating the far-field diffraction spectrum by means of wave vector filters and integrating the transmitted light with a photomultiplier. The results are recorded either as curves on a recorder chart or printed out in digital form.

Evidence Supporting an Intratrial Interpretation of Delayed Response Performance of Monkeys

Eight 4-yr.-old lab-reared Ss received delayed response problems which were factorial combinations of 3 intertrial intervals (8, 16, and 24 sec.) and 3 intratrial delay intervals (0, 10, and 20 sec.). Errors were directly related to delay duration, but no effect of intertrial interval was measured. Errors were not correlated with general activity during delay intervals, but errors were related to bodily positioning. In a second experiment 6 of the same Ss were given 18-sec. delay trials interrupted by lowering the opaque screen at 1, 6, and 11 sec. for durations of 1, 4, and 7 sec. While both onset time and duration were significant dimensions of screen lowering, only the combination of earliest and longest screen interruption increased errors significantly. Activity increased directly with interruption duration. These results were interpreted as supporting an intratrial performance analysis of the delayed response.

Optical Properties and Uses of the Conical Mirror

A conical mirror offers a means of magnifying the image of an object on an opaque screen, so that it may be viewed from a position directly in front of the screen, and the projecting distance necessary to produce the magnification is much less than that required by present methods. An experiment shows that the conical mirror gives high resolution when used in a specific projecting system. It may provide a convenient means with which to obtain high magnification for many optical systems. The magnification is shown by theory and experiment to be equal to the secant of the conical mirror angle.