Journal of the Optical Society of America最新文献

Fender and Julesz [J. Opt. Soc. Am. 57, 819 (1967)] found that fused retinally stabilized binocular line targets could be misaligned on the two retinas in the temporalward direction by at least 30 min of arc without loss of fusion and stereopsis and that random-dot stereograms could be misaligned 2 deg before fusion was lost. To test these results in normal vision, we recorded eye motions of four observers while they viewed a random-dot stereogram that subtended about 10 deg. The observers misaligned overlaid vectograph stereo images by moving them apart in a temporalward direction until fusion was lost. They then returned the vectographs to the overlaid position. Throughout this cycle the observers reported at frequent intervals if they could perceive strong or weak depth, loss of depth, or loss of fusion. For some observers the image separation could be increased to 5 deg beyond parallel before fusion was lost. The visual axes diverged to follow the image centers and varied from overconverged to overdiverged with respect to the image centers while the observers still reported depth and fusion. We call the difference between the image separation and eye vergence the vergence error. If a vergence error persisted for at least 10 sec without loss of the percepts of fusion and depth, we postulate that neutral remapping occurred that compensated for the retinal misalignment. We found that the average maximum neural remapping was 3.0 deg.(ABSTRACT TRUNCATED AT 250 WORDS)

This study of form vision explores the relationships between orientation and spatial frequency in suprathreshold discrimination tasks. Orientation discrimination thresholds for sine-wave gratings were 0.3-0.5 deg, much less than the roughly 10-24-deg orientational bandwidth of channels; spatial-frequency discrimination thresholds were 3-7%, much less than the roughly 1.2-octave spatial-frequency bandwidth of channels. We find that spatial-frequency discrimination between two gratings was as acute when the two gratings were orthogonal as when they were parallel. Orientation discrimination between two gratings was as acute when the two gratings had the same spatial frequencies as when they had different spatial frequencies. Thus orientation and spatial frequency are independent dimensions at the discrimination stage of spatial information processing.

A new measure called color-rendering capacity is developed, by applying some of the concepts used in communication engineering, to describe another aspect of the color-rendering properties of illumination, i.e., the maximum possible number of different colors that can be displayed by a given illumination. It is a relative measure expressed as a dimensionless parameter between zero and unity, depending only on the spectral power distribution of the illumination. The computer program involved in calculating this parameter and calculated examples for several different light-source types are presented. By reference to this parameter, the prediction for four different fluorescent lamps about the extent to which a lamp can make an average chromatic environment appear colorful and bright is in general agreement with the existing observation. Another potential use of this parameter, in collaboration with the luminous efficacy, as a relevant indicator of the visual efficiency of illumination is also discussed.

We studied the detection of coherent motion in stroboscopically moving random-dot patterns for foveal vision and at eccentricities of 6, 12, 24, and 48 deg in the temporal visual field. Threshold signal-to-noise ratios (SNR's) were determined as a function of velocity for a range of stimulus sizes. It was found that the motion-detection performance is roughly invariant throughout the temporal visual field, provided that the stimuli are scaled according to the cortical magnification factor to obtain equivalent cortical sizes and velocities at all eccentricities. The maximum field velocity compatible with the percept of coherent motion increased about linearly with the width of the square stimuli. At this high-velocity threshold any pixel crossed the field in five to nine equal steps with a constant total crossing time of 50-90 msec, regardless of stimulus size or eccentricity. The lowest SNR values were reached at the optimal or tuning velocity V0. They approached the amazingly low values of 0.04-0.05 for large stimuli and at all eccentricities. Regardless of stimulus size, the parameter V0 increased about linearly with eccentricity from roughly 1 deg sec-1 at the fovea to some 8 deg sec-1 at 48 deg in the temporal visual field.

We found that inspecting a sine-wave grating elevated threshold for spatial-frequency discrimination as it does for contrast detection, but discrimination threshold was maximally elevated at about twice the adapting frequency, where detection threshold was little affected; and detection threshold was maximally elevated at the adapting frequency, where discrimination threshold was not elevated at all. Orientation tuning was roughly similar for contrast and for discrimination threshold elevations; elevations fell by half at between 7 and 17 deg from the adapting orientation. We compared our findings with the predictions of three models of discrimination: (1) The data are inconsistent with the idea that the most strongly stimulated channels are the most important channels for discrimination. (2) With an additional assumption, the Hirsch-Hylton scaled-lattice model could account for our finding that discrimination threshold elevations are asymmetric. (3) With no additional assumptions, the idea that discrimination is determined by the relative activities of multiple overlapping spatial-frequency channels or size-tuned neurons can account for our finding that discrimination thresholds are asymmetric. We propose a physiologically based discrimination model: Asymmetrically tuned cortical cells feed a ratio-tuned neural mechanism whose properties are formally analogous to those of ratio-tuned neurons that have recently been found in cat visual cortex. The linear relation between firing frequency and contrast can explain why discrimination threshold is substantially independent of contrast.

Detection thresholds of sinusoidal gratings in the simultaneous presence of high-contrast peripheral masking stimuli partially overlapping the test gratings were determined as a function of the separation between the center of the test grating and the peripheral stimulus by a two-alternative forced-choice method. The results showed that the threshold-elevating effect of simultaneously present peripheral masking stimuli depends on how much of the test grating is left unexposed. An additional experiment, in which the detection thresholds in the absence of the peripheral stimulus were determined as a function of the number of cycles of the test grating, enabled us to show that the threshold-elevating effect is somewhat higher than the effect of simply cutting the test grating down in size. The threshold-elevating effects caused by high-contrast peripheral masking stimuli can be explained in terms of a lateral inhibition and a probability summation across space, taking into account the nonuniform sensitivity across the visual field.

Analysis of the optics of photorefractively computed ray tracing shows that, for short camera-to-subject distances, the function relating image size to defocus of the eye is not symmetrical for errors of focus in front of and behind the camera. This asymmetry is exploited in the new method of isotropic photorefraction, in which the supplementary cylinder lenses of the original orthogonal photorefractors are replaced by defocusing of the camera lens itself. By comparing photographs taken with the camera focused in front of and behind the subject, the sign of the eyes' defocus (myopic or hyperopic relative to the camera) can be determined. The axis of any astigmatism is readily apparent as the direction in which the photorefractive images are elongated. The method is well adapted for the refractive screening of infants and young children.

In a theoretical eye with spherical and aspheric surfaces, the retinal illumination is calculated if a Ganzfeld luminance field is used. The resulting retinal light distribution is nearly homogeneous over the whole retina. The homogeneity is not much influenced by the size of the optical surfaces. The corresponding retinal area and the luminous flux entering the eye are calculated as functions of the size of the visual field. The values of the length of the light path through the crystalline lens and of the angle of incidence on the retina are described as functions of the angle in the visual field.