Orthogonal Gratings Research Articles

Incipient cutting and transient stresses in a cutting tool using Moire method

In the present paper the Moire method of stress analysis has been successfully used for the study of transient stresses in a single point cutting tool during incipient cutting process. Isothermal orthogonal planing of lead was carried out using a transparent plastic tool. A 500 lines/in. orthogonal Moire grating was used. Cine photography was used for the fringe measurement. Results indicate that during tool entry the tool-chip contact stress distribution varies from instant to instant before reaching the steady state values. However, the observed variation of the maximum free rake tensile stresses during tool entry appear to be of importance from the point of view of brittle failure of tool-tip during entry or exit. Peak tensile stresses are observed in the early stages of entry (within 20% of the steady state time) and the results are in agreement with the data on transient strain in the work material during incipient cutting already reported in published literature.

The effect of contrast on the completeness of binocular rivalry suppression.

Binocular rivalry between orthogonal sine wave gratings was studied by asking subjects to indicate when they saw just one or the other grating, as opposed to a composite. Using this measure, it was found that the completeness of rivalry (1) usually increased with grating contrast; (2) increased as a trial progressed, up to about 40 sec; and (3) depended on spatial frequency, with the optimal spatial frequency being lower than that at which contrast sensitivity was maximal. These findings supplement what has been learned about rivalry by other methods.

Fluctuations of visibility during dichoptic viewing: Preliminary report.

Detection rates were determined for multiple flashes (20-msec duration, 7.5 arc min dia) presented foveally to one eye while the other eye had either a uniform target (the "monocular" condition), a congruent grating (fusion), or an orthogonal grating (rivalry). Average detection rates were highest in the monocular condition, and they were about the same in fusion and rivalry. In all conditions, the typical error (some 70% of all errors) was one stimulus missed out of several simultaneously presented. It was concluded that sensitivity fluctuates over the fovea, even in the absence of contours in the other eye. In two observers, the ratio of detection rates for the two eyes was about the same for all conditions; in two other observers, this ratio decreased (eye dominance increased) in fusion, and especially in rivalry, relative to the monocular condition. The question is raised whether a common link exists between spontaneous fluctuations of sensitivity and those induced by dichoptic contours.

Clues to the site of origin of the complementary image

PATTERNS of near-parallel black-and-white lines induce an anomalous state of the visual system, in which a superimposed test field of dynamic noise (such as the ‘snowstorm’ on a detuned TV receiver) seems to stream in directions roughly perpendicular to the inducing contours1. The illusory streamers form a ‘complementary image’ (CI) which for the stimulus of Fig. 1a comprises a family of wavy circles, as sketched by J. P. Wilson2 in Fig. 1b. When two orthogonal gratings are superimposed, the streamers lie at 45° to both, as if the resulting bias obeys the rule of vector summation3. J. P. Wilson4 has observed rudimentary signs of directional bias and streaming even at a single black/white contour; and M. E. Wilson5, using only simple pairs of test spots illuminated in sequence, found that the illusory ‘phi’ motion seen between the spots was enhanced for directions orthogonal to the contours of a superimposed grating. When the inducing pattern is presented to one eye and the noise field to the other, however, little or no CI is observed1,6. It has seemed logical1 to attribute these phenomena to some form of adaptive cooperative activity among orientation-sensitive cells of the visual system, leading to a kind of ‘simultaneous contrast’ in the orientation domain, that is, a bias of the signalling system for motion and contour orientation in favour of the orientation(s) not present in the inducing stimulus.

Induction of the McCollough effect II: two different mechanisms.

An orientation-specific chromatic aftereffect was observed when a single colored grating was used as an induction stimulus. The magnitude of the aftereffect was compared to that obtained when alternating orthogonal gratings in complementary hues were used as induction stimuli. The two-stimulus condition produced a stronger aftereffect than a single-stimulus condition. This facilitation was also obtained when a colored plain square with no grating was substituted for the second colored grating in the two-stimulus condition. The results suggest that the McCollough effect involves adaptation of two different mechanisms, one which is orientation-specific and one which is not.

Multiple orientation-contingent chromatic after-effects.

McCollough's (1965) original demonstration of an orientation-contingent chromatic after-effect (OCCA) used two orthogonal inducing gratings in complementary colours. Fidell (1970) has shown that inducing gratings whose orientations are separated by less than 90° give progressively smaller OCCAs, becoming ineffective below 20° or so. Stromeyer (1969) found that with only a single inducing grating, orthogonal test fields still appeared tinted in complementary hues, and claimed that these hues could be “neutralized” by rotating the inducing grating by 90°. These results raise the question whether (A) the neural representations of orthogonal orientations are coupled with respect to colour in “opponent” fashion, so that red-horizontal has similar effects to green-vertical; or (B) the representations of orientations separated by some minimum angle are chromatically independent, and can develop substantially independent OCCAs. We report the following results which favour hypothesis (B): (1) With a single coloured inducing grating à la Stromeyer (1969), the measured OCCA at right angles shows no signs of “opponent processing”, if the hue of the test grating is compared against that of a plain field rather than an orthogonal grating. (2) With inducing gratings at several orientations, the resultant OCCA has an angular distribution which is the algebraic sum of those for each grating separately. (3) It is possible to associate the same colour with two orientations at right angles without mutual cancellation. (4) Multiple OCCAs show independent time-courses of decay, and can be induced and retained for at least eight orientations at once.

Interocular generalization of orientation specific color aftereffects

McCollough effects were generated by monocular exposure to alternating red vertical and green horizontal gratings, and observed with achromatic orthogonal gratings that formed concentric square bands. Chromatic aftereffects on appropriately oriented gratings viewed by the contralateral eye were obtained when binocular scanning of the test pattern preceded testing with the contralateral eye. The red-green configuration was reversed between the two eyes. The chromatic aftereffects that appear with the contralateral eye are proposed to be “second order McCollough Effects”.

Pattern alternation: Effects of spatial frequency and orientation

Campbell and Howell (1972) reported an effect called “monocular pattern alternation.” They found that a pattern composed of two orthogonal sinusoidal gratings, one horizontal and the other vertical, underwent rivalry when viewed monocularly for a period of time. In the present study, it has been shown that monocular pattern alternation depends upon the orientation of the pattern and the spatial frequency of its components. Fewer reversals were found for an obliquely oriented pattern than for a pattern with components in the horizontal and vertical meridians. Alternation rate was higher when the gratings were similar in frequency but differed in orientation than when the components of the pattern differed in both dimensions. It was concluded that pattern alternation reflects an antagonistic interaction between interdependent channels in the human visual system that respond to orientation and spatial frequency.

Moiré techniques for measuring strains during welding

The present work measures dynamic strains near welds using a projected-grating moire technique. Experimental procedures are described for producing the orthogonal submaster gratings and etched heat-resistant specimen gratings necessary for this work. A modification of the gridanalyzer method allows all strain information to be obtained from a single photograph. A mathematical procedure combines fringe patterns from small adjacent sections of a surface into a larger continuous pattern. Computerized regression techniques enable more rapid and accurate analysis of the data. Results from welds in an Al−Mg alloy show the feasibility of dynamic welding-strain analysis using this approach. Welding deformation is found to be almost entirely shear straining, which explains the nature and orientation of high-temperature cracks sometimes found near welds.