Orientation Of Gratings Research Articles

Electrophysiological and Psychophysical Measures of Interocular Suppression

ABSTRACTPrevious studies of the effect of interocular suppression on VEP amplitude have shown that gratings presented steadily to one eye result in a significant reduction in the amplitude of VEPs elicited by flashed gratings in the other eye when orientation and spatial frequency of gratings presented to each eye are similar. The present study reveals that psychophysical thresholds for flashed gratings are significantly elevated when subjects view checkerboards having fundamental Fourier components of the same spatial frequency and orientation in the contralateral eye. This effect is greater in the periphery than in the fovea. Checkerboard stimuli of different orientation had no differential interocular suppressing effects on VEPs to flashed gratings. These results suggest that while psychophysical detection of patterned stimuli relies most on the fundamental Fourier components, VEP amplitude is equally influenced by the fundamental and higher harmonic spatial frequency components. The VEP to patterned stimuli derives, for the most part, from macular stimulation, but the influence of the fundamental Fourier components on the psychophysical threshold is greater in retinal areas adjacent to the macula.

The perceived spatial frequency, contrast, and orientation of illusory gratings.

Illusory vertical gratings (V) and diagonal gratings (D) can be seen on a uniform field after inspection of a vertical grating. When using simultaneous and successive matching techniques the spatial frequencies of the V effect were found to be about 2 octaves below and 1-2 octaves above the adapting spatial frequency, but to be invariant with temporal frequency. At high adapting frequencies the D effect dominated, and was about 0.8 octave below the adapting spatial frequency, oriented about +/-35 degrees from vertical. The apparent contrast of V was about twice the value of the contrast threshold at its apparent spatial frequency. D effects seen during adaptation were about 60 degrees from vertical and 3 octaves below the adapting frequency. The results are interpreted in terms of inhibition and disinhibition in an organized matrix of tuned channels, and the dominant pattern of inhibition in the matrix is inferred. Supporting evidence from neurophysiology, neuroanatomy, and psychophysics is briefly reviewed. An appendix deals with the question of interocular transfer of the aftereffect.

Grating acuity along the vertical meridian as a function of grating orientation

Visual acuity was measured for horizontal, vertical, and oblique grating target orientations in the fovea and at various retinal eccentricities along the vertical meridian. Acuity was higher in the fovea, higher for vertical and horizontal target orientations, and higher in the superior retinal regions. The difference between acuities for vertical and oblique targets was greater in the superior retinal regions. It was concluded that the oblique effect is channel-size dependent.

Visual resolution, contrast sensitivity, and the cortical magnification factor.

This study shows that photopic contrast sensitivity and resolution can be predicted by means of simple functions derived by using the cortical magnification factor M as a scale factor of mapping from the visual field into the striate cortex. We measured the minimum contrast required for discriminating the direction of movement or orientation of sinusoidal gratings, or for detecting them in central and peripheral vision. No qualitative differences were found between central and peripheral vision, and almost all quantitative differences observed could be removed by means of a size compensation derived from M. The results indicated specifically that (1) visual patterns can be made equally visible if they are scaled so that their calculated cortical representations become equivalent; (2) contrast sensitivity follows the same power function of the cortical area stimulated by a grating at any eccentricity; (3) area and squared spatial frequency are reciprocally related as determinants of contrast sensitivity; and (4) acuity and resolution are directly proportional to M, and the minimum angle of resolution is directly proportional to M-1. The power law of spatial summation expressed in (2) and (3) suggests the existence of a central integrator that pools the activity of cortical neurons. This summation mechanism makes the number of potentially activated visual cells the most important determinant of visibility and contrast sensitivity. The functional homogeneity of image processing across the visual field observed here agrees with the assumed anatomical and physiological uniformity of the visual cortex.

Frequency and orientation interactions in the mccollough effect: Interchannel effects?

Abstract Previous explanations of the McCollough effect propose that the colour changes are due to neural adaptation of detectors in the visual system tuned to specific spatio-chromatic parameters. In particular, the effect is known to be induced by either spatial frequency components or orientations of bar gratings of complementary colours. However, recent evidence indicates that the effect is not restricted to grating stimuli and that, in these circumstances, it may be induced by joint occurrences of orientation, curvature and frequency conditions. This experiment was conducted to investigate whether the orientation and frequency parameters have an additive effect on inducing the phenomena, or whether both parameters interact or suppress each other in inducing the effect. The results indicate that both channels can induce the aftereffect in complex patterns, but that orientation specificity seems to be largely enhanced or inhibited by frequency components of the stimulus.

Visual stimuli for strabismic suppression.

The effects of orientation and spatial frequency of grating stimuli upon suppression were examined with a binocular rivalry paradigm in a group of ten strabismic patients and in a control normal group. Duration, frequency, and period of rivalry were examined as functions of differences in orientation and spatial frequency of dichoptic achromatic sinusoidal gratings. Records were made of responses by the sighting and by the nonsighting eye as well as responses during periods of combined binocular vision. Strabismic subjects reported normal binocular rivalry when presented with gratings of dissimilar orientation. Suppression of the deviating eye in strabismic subjects occurred with stimuli of similar orientation and was unaffected by spatial-frequency differences between dichoptic stimuli. Suppression was most intense under conditions that normally stimulate stereopsis and sensory fusion.

Visual discriminations during eyelid closure in the cat

We were able to train cats raised with sutured eyelids to perform simple brightness discriminations before their lids were parted. If, and only if, a small hole was present in a lid, could some of the cats also perform a grating orientation discrimination. By establishing their thresholds for the brightness discrimination before and after dark adaptation and before and after the lids were opened, we reached three main conclusions. (1) During dark adaptation (with pupils maximally dilated and retinae most sensitive, regardless of lid suture), the cats were 3–4 log units more sensitive with the lids open than with the lids closed. This indicates a 3–4 log unit attenuation for the lids which is in agreement with our photometric measurements. (2) During light adaptation, the sensitivity difference between the conditions of opened and closed lids was only 1–2 log units. We concluded that factors (such as pupil dilatation and retinal sensitivity) partially compensated for the lid attenuation, since the open eye could have a smaller pupil and less sensitive retina during light adaptation. (3) Given these potential compensatory features of the pupil and assuming consensual pupil sizes, the deprived eye of a monocularly sutured cat may suffer more photic deprivation (since the pupil behind the closed lid would be as constricted as the pupil in the open eye) than would either eye of a binocularly sutured cat (where both pupils can be relatively large).

Spatial properties of binocular neurones in the human visual system.

The spatial properties of human binocular mechanisms were investigated using the technique of subthreshold summation. Isolation of binocular mechanisms was achieved by means of interocular stimulus presentation. The contrast detection threshold for a sinusoidal test grating viewed by one eye was found to be reduced by a subthreshold grating of the same spatial frequency and orientation seen by the other eye. The interaction between the gratings was approximately linear. Threshold increased as the spatial frequencies or orientations of test and subthreshold gratings were made increasingly different. Spatial stimulus specificities measured in this way were as great for interocular presentation as for simultaneous monocular presentation. The results suggest that human contrast sensitivity for gratings may depend upon binocularly-activated neurones similar to those found in cat and monkey visual cortex.

Plasticity of orientation specific chromatic aftereffects

Changes in the orientation of McCollough effects were explored with and without prolonged exposure to prismatic tilt and subsequent viewing of chromatic inducing stimuli. Prolonged exposure to prism adaptation generates a reduction in the optically induced tilt and thus a disparity between the perceived and the retinal orientation of the chromatic inducing stimuli. Saturated chromatic aftereffects, following prism adaptation and subsequent induction of the McCollough effect, were obtained when the orientation of the achromatic test gratings matched the perceived, rather than the retinal, orientation of the inducing chromatic gratings.

Contrast sensitivity in humans with abnormal visual experience.

1. Grating contrast sensitivities have been determined over a range of spatial frequencies for a normal subject and for subjects who are visually biased in that they have a lower resolution capacity for targets of specific orientations. The bias si only found in astigmatic subjects and the grating orientation yielding poorest acuity coincides with the most defocused astigmatic meridian. However this resolution anisotropy remains when optical factors are accounted for. 2. For the normal subject, high and low frequency attenuation is found and a typical reduction in contrast sensitivity is exhibited for oblique target orientations. 3. The biased subjects, called meridional amblyopes because they have reduced acuity for a given grating orientation, show markedly abnormal contrast sensitivity functions. Their cut-off spatial frequencies are different for various target orientations and this difference applies also to contrast sensitivity over nearly the entire spatial frequency range tested (0-5-16 cycles/deg). The differences are of about the same magnitude for most frequencies and they are found in all types of meridional amblyopes. 4. Optical explanations of these differences are ruled out by laser-interference fringe tests and by varying effective pupil size. 5. Theoretical effects of defocus have been calculated to compare predicted visual deprivation with performance. Results indicate that reduced contrast sensitivity functions can be equivalent to a small defocus effect. 6. To examine the results in the spatial domain, inverse Fourier transforms of representative contrast sensitivity functions have been computed. The optical portion of the resulting spatial weighting functions has been parcelled out to obtain neural spatial weighting functions.

Contour-Contingent Color Aftereffects: Retinal Area Specificity

Once an area of the retina was adapted to colored gratings, the aftereffect colors were judged to be most saturated when the test grating approximately coincided with the adapted area, less so as the overlap was reduced. The colors disappeared when the grating was moved just off the area and reappeared when the grating was moved very near it. In brief, the McCollough effect is highly area specific. McCollough demonstrated a color aftereffect specific to the orientation of gratings of light and dark bars (1965). The aftereffect was built up by alternating a vertical grating of black stripes on one color with a horizontal grating on another color. Negative color aftereffects were seen on test gratings of black and white stripes, in a retinal orientation like that of the adaptation gratings. The question in the present paper is whether the aftereffect is area specific. That is, does adapting a small area of the retina to colored gratings produce a color aftereffect that can be elicited by a small test grating placed almost anywhere on the retina, or must the grating fall on the originally exposed area? A nonlocalized aftereffect might reflect a learning process (an association between edge orientation and color) or, alternatively, an adaptation process involving cells with very large receptive fields. A localized aftereffect, on the other hand, might suggest that the effect depends on cells with small receptive fields -and would be consistent with the findings on many other sensory aftereffects. Two classes of area-specific (localized) aftereffects may be distinguished. One class requires that the adaptation, or inducing, stimulus remain quite fixed on the retina. The afterimage is the typical case: a sharp afterimage is seen only when the inducing stimulus is not smeared