Gratings Of Different Orientations Research Articles

Orientation bandwidth: The effect of spatial and temporal frequency

Te orientation bandwidths of psychophysically defined channels of human vision were estimated by two techniques for a wide range of spatial and temporal frequencies. The first technique was an adaptation paradigm, where the subjects' ability to see patterns of various orientations was measured before and after adapting to a high contrast pattern. The second technique evaluated subjects' ability to discriminate between two gratings of different orientations in relation to their ability to detect the patterns. Bandwidths were unaffected by temporal frequency at high spatial frequencies but increased with temporal frequency at low spatial frequencies. Bandwidths increased modestly with decreasing spatial frequency at low temporal frequencies but more drastically at high temporal frequencies. Both techniques gave similar results except for patterns with very low spatial and high temporal frequencies. In this region the stimulus appears “spatial-frequency doubled” which may be used as a cue for the orientation discrimination task.

The influence of stimulus length on the oblique effect of contrast sensitivity

Contrast sensitivity for gratings of different orientations was measured at various stimulus lengths. The oblique effect of contrast sensitivity was observed to increase in magnitude as the length of the truncated gratings was increased from 0.5 to 5.6deg. This finding refutes a purported distinction between the contrast sensitivity oblique effect and the orientation discrimination oblique effect. Thus, these results are consistent with the idea that the contrast sensitivity oblique effect and the orientation discrimination oblique effect share the same common underlying anisotropic basis. These results also show that grating summation differs at oblique and nonoblique orientations in terms of length summation as well as in terms of width summation.

The Visual Acuity of Octopuses For Gratings of Different Orientations

ABSTRACT A recent study has shown that the minimum separable angle of visual acuity of Octopus pallidus and O. australis lies between 4·4′ and 9·7′ when vertical and horizontal gratings are used as test objects (Muntz & Gwyther, 1988). In view of other observations - the horizontal rectangular shape of octopus pupils, the pronounced astigmatism of the lens of Eledone cirrhosa (SroczyŃski & Muntz, 1985), the difficulty that O. vulgaris has in discriminating between oblique rectangles (Sutherland, 1957), and the vertically and horizontally arranged rectilinear organization of both retina and neurones in the optic lobe of O. vulgaris (Young, 1960) - it seemed worthwhile testing the effect of grating orientation on visual acuity in more detail, and in particular extending the measurements to include oblique gratings oriented at 45° with respect to gravity.

Role of Inhibition in the Specification of Orientation Selectivity of Cells in the Cat Striate Cortex

Mechanisms supporting orientation selectivity of cat striate cortical cells were studied by stimulation with two superimposed sine-wave gratings of different orientations. One grating (base) generated a discharge of known amplitude which could be modified by the second grating (mask). Masks presented at nonoptimal orientations usually reduced the base-generated response, but the degree of reduction varied widely between cells. Cells with narrow orientation tuning tended to be more susceptible to mask presence than broadly tuned cells; similarly, simple cells generally showed more response reduction than did complex cells. The base and mask stimuli were drifted at different temporal frequencies which, in simple cells, permitted the identification of individual response components from each stimulus. This revealed that the reduction of the base response by the mask usually did not vary regularly with mask orientation, although response facilitation from the mask was orientation selective. In some sharply tuned simple cells, response reduction had clear local maxima near the limits of the cell's orientation-tuning function. Response reduction resulted from a nearly pure rightward shift of the response versus log contrast function. The lowest mask contrast yielding reduction was within 0.1-0.3 log unit of the lowest contrast effective for excitation. The temporal-frequency bandpass of the response-reduction mechanism resembled that of most cortical cells. The spatial-frequency bandpass was much broader than is typical for single cortical cells, spanning essentially the entire visual range of the cat. These findings are compatible with a model in which weak intrinsic orientation-selective excitation is enhanced in two stages: (1) control of threshold by nonorientation-selective inhibition that is continuously dependent on stimulus contrast; and (2) in the more narrowly tuned cells, orientation-selective inhibition that has local maxima serving to increase the slope of the orientation-tuning function.

Orientation-selective visual loss in patients with Parkinson's disease.

Visual contrast sensitivity was measured using 2 cycle/deg sinewave gratings of different orientations in 10 patients with Parkinson's disease and in 15 age-matched controls. Loss of visual contrast sensitivity was found in 6 patients, all of whom had normal visual acuity. Visual loss depended on grating orientation; in all cases the maximum sensitivity loss was for the horizontal. Sensitivity loss was most marked at a temporal frequency of 4 to 8 Hz. Visual fields gave no hint of the orientation selectivity. We conclude that orientation selectivity implicates visual cortical cells in Parkinson's disease. We tentatively suggest that a preferential loss of contrast sensitivity to horizontal gratings might be due to a functional abnormality in the striate cortex that relatively spares the extrastriate cortex. The dependence of visual loss on temporal frequency combined with the sparing of visual acuity might possibly be understood if Parkinson's disease preferentially affects the visual pathway leading from the retina to cortex via the magnocellular layer of the lateral geniculate nucleus. There is an intriguing similarity between the pattern of visual loss in Parkinson's disease and in multiple sclerosis.

Discrimination of flicker gratings of different orientations in the rabbit

Discrimination of flicker gratings of different orientations in the rabbit

Visual evoked potentials to binocular stimulation with disparate patterns.

Experiments with VEP to checkerboard stimulation in 4 subjects with normal stereoscopic vision showed that binocular interaction was the same for fused images and for linear pattern displacement induced by horizontal and vertical prisms, as long as the patterns were projected on the macular areas of both eyes. Also in a stereo-blind subject the impaired binocular VEP interaction remained unchanged during linear displacement of the patterns. Thus the previously reported differences in binocular VEP interaction between stereo-normal stereoblind subjects cannot be explained by binocular stimulation with unfused patterns in the latter group. With patterns displaced to different hemifields in the 2 eyes, no binocular interaction was recorded. Experiments with black-and-white gratings of different orientations to the 2 eyes showed that binocular VEP reactions remained the same even with patterns perpendicular to each other. However, the binocular interaction was disrupted when the subject viewed the perpendicular patterns through coloured filters.

Anisotropies of perceived contrast and detection speed

Gratings of different orientations were compared in terms of both apparent contrast and detection speed. Magnitude estimates demonstrated that oblique gratings appear perceptually to have lower contrasts than horizontal or vertical gratings of the same physical contrast. This anisotropy of perceived contrast holds across a wide supratheshold range of physical contrasts. Even when gratings of the different orientations are equated in terms of perceived contrast, an oblique effect of detection time remains. The magnitude of this residual anisotropy of detection speed decreases as contrast is increased from threshold, such that this second anisotropy is observed only at a restricted range of lower contrasts.

Discrimination of orientation by human infants.

Successive discrimination of suprathreshold gratings of different orientations by two-month-old infants was tested with the use of a type of familiarization-novelty paradigm. Infants showed clear discrimination between horizontally and vertically oriented gratings. Infants failed, however, to discriminate mirror-image obliques from each other and also failed to discriminate nonmirror-image obliques. Considered along with previous demonstrations in children and adults of a greater confusability of oblique grating pairs relative to that of the horizontal and vertical pair, these findings indicate that this differential confusability of orientation is, at least in part, manifest in humans by two months of age.

Importance of orientation on visual and neuronal resolution (author's transl)

Spatial resolution of gratings of different orientation has been evaluated in 39 patients, by means of projected slides and by laser interference fringes. Both methods reveal a significantly higher resolution (about 12%) for vertical or horizontal bars compared to oblique ones. The similarity of findings for both methods is indicative of the neuronal origin of this orientation-dependent effect and exclude an optical origin.

Visual cortex ablation and thresholds for successively presented stimuli in rhesus monkeys: I. Orientation.

Rhesus monkeys were trained to discriminate gratings of different orientation presented one at a time. The smallest difference they could reliably detect was determined before and after removal of either inferotemporal, foveal prestriate or lateral striate cortex. Four animals with inferotemporal lesions had significantly higher thresholds after operation, which did not improve after extensive practice. Two monkeys with lateral striate ablation, and 1 out of 3 animals with foveal prestriate lesions were also impaired, but improved with practice. Monkeys without inferotemporal cortex may have imprecise internal templates for stimulus orientation, in accordance with the categorisation hypothesis of the inferotemporal defect.

Early and permanent effects of monocular deprivation on pattern discrimination and visuomotor behavior in cats

Visuomotor behavior and pattern discrimination were studied in a group of cats raised with one eye closed by eyelid suturing 7–10 days after birth. At the age of 8–10 months the animals were forced to use their deprived eye by reversal of eye closure (closing the normal eye and opening the deprived one). Visuomotor behavior and pattern discrimination were tested before as well as after reverse closure, to compare performances of the deprived eye with those of the non-deprived eye. In order to get optimal visuomotor experience, the animals were kept in large playrooms for at least 4 h each day. Except for normal tactile placing responses, visually triggered extension responses and uncertain jumping, 2 years after reverse closure all other tests (visually guided reaching, visual cliff behavior, obstacle avoidance, tracking, jumping, and visual blink responses) still showed impairments; the optokinetic nystagmus was asymmetric. In contrast with this partial behavioral recovery, pattern discrimination in a simple nose-push training ☐ requiring no complicated visuomotor coordination was found to be positive. Discriminations of gratings of different orientations, starting 4 weeks after reverse closure, appeared to be normal, in comparison with performance using the non-deprived eye of the same cats tested before reverse closure. Form discrimination was also found to be positive; some monocularly deprived cats required more trials than normal cats in upright vs. reversed solid triangles discrimination, but succeeding form problems were mastered within the same range as found in normal cats. Apparently behavioral defects after monocular deprivation are due to deficiencies in visuomotor control rather than in pattern identification.

Behavioral deficits in cats following early selected visual exposure to contours of a single orientation

The ability of adult cats, whose early visual experience was confined to contours of a single orientation (either vertical or horizontal), to resolve gratings of different orientations was studied by operant methods. Following selective visual exposure during part or all of the first 4 months of life, the cats were trained on a simultaneous discrimination between gratings of various orientations and blank fields of the same mean luminance. The spatial frequency of the gratings was systematically altered in order to obtain an estimate of acuity based upon extrapolation to chance levels of performance. Selectively deprived cats performed as well as normally reared cats on gratings having the same orientation as that of the stripes they saw as kittens, but their performance on gratings orthogonal to these was poorer. The deficits in acuity for gratings perpendicular to the experienced orientation varied between 0.26 and 0.87 of an octave. On the other hand, control cats whose early visual experience alternated between vertical and horizontal stripes, or who were reared in an environment containing randomly oriented contours, failed to show any difference in their acuity for vertical and horizontal gratings. the acuity deficits shown by the selectively deprived animals are long-standing since they remain unchanged even after 30 months of normal visual exposure. It is argued that these perceptual deficits are a consequence of the changes in cortical physiology that other investigators 8,20 have described in cats who had undergone similar early visual deprivation. Taken together, these findings provide a basis for explaining a number of human perceptual disorders.

The effect of orientation in binocular contour rivalry of real images and afterimages

Binocular rivalry was investigated using gratings of different orientations in three experiments. No consistent effects of orientation were found for predominance measures of rivalry between real images. Rivalrous afterimages, on the other hand, did exhibit orientation selectivity: vertical gratings were visible for longer than were 45-deg gratings. This effect was compared to the similar orientation selectivity found for monocular observation of grating afterimages. Comparisons of binocular rivalry between real images and afterimages were made in terms of the frequency distributions of the dominance periods.