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PubMed1983

Dark vergence and dark accommodation in human infants.

Vergence angle and accommodative state were assessed photographically in 3-, 6-, and 12-month old infants. In the dark, fluctuations of vergence and accommodation were generally uncorrelated among all groups. The vergence-accommodation functions obtained in the dark had a mean slope of 0.04. These findings provide evidence in infants for an uncoupling of vergence and accommodation in the absence of patterned retinal input.

Accommodation, Ocular↗
PubMed1987

Motion aftereffects associated with pursuit eye movements.

Contrary to an earlier report [Anstis and Gregory, Q. Jl exp. Psychol. 17, 173-174 (1965)], we find that the sustained retinal motion caused by tracking a moving target over a stationary grating does not result in a motion aftereffect (MAE) which is equivalent to that resulting from comparable retinal motion caused by actual motion of a grating. The MAE associated with tracking generally occurs in elements falling on areas not previously exposed to retinal motion. It is in the same direction as the previous retinal motion in the display and is apparently an induced MAE caused by a weak, below threshold MAE in the elements stimulating areas that were previously exposed to retinal motion. Based on an analysis of eye movement records, we do not believe that the weakness of the tracking MAE is primarily a function of the poor quality of the tracking eye movements. Other possible reasons for the weakness of the MAE are suggested.

Adaptation, Ocular↗
PubMed1987

Appearance of steadily viewed lights.

An interocular matching technique was used to investigate the variation of chromaticity and brightness following steady viewing of a chromatic test light (identical adapting and testing color). Adaptation times were of sufficient duration to ensure stable matches. Following chromatic adaptation we found changes in hue, saturation and brightness. The spectral colors appeared desaturated. The hue shift for the spectral region 546 to 570 nm was towards green and for 586 to 670 nm was towards red. The brightness decrease, independent of chromaticity, was 0.8 log unit at 150 td and 0.3 log unit at 8 td. Data were analyzed within a two-process framework of brightness. Bezold-Brücke effect measurements showed chromaticity shifts in the same direction as for dimming caused by continuous adaptation. Changes in saturation were also observed but were usually in the opposite direction from those found for adaptation.

Adaptation, Ocular↗
PubMed1988

The nature of sensory compensation during fusional response.

Simultaneous objective (based on binocular eye movement recording) and subjective (nonius line displacement) measurements of horizontal and vertical fusional response were carried out in order to examine the nature of sensory fusional compensation. It was found that the presence of sensory compensation in one retinal region affects the sensory representations of neighboring regions. Unlike motor compensation, however, sensory compensation affects fusible and nonfusible contours differently. The implication of these results is examined for the reliability of subjective determinants of binocular status.

Adult↗
PubMed1991

Visual resolution limits in human albinism.

The effects of the involuntary ocular oscillations on visual resolution was examined in 22 albinos and 11 idiopaths with congenital nystagmus. The idiopaths showed a linear relationship between the proportion of the slow phase spent at low velocities (less than or equal to deg/sec) and the log of the minimum angle of resolution; such that long dwell times were compatible with good resolution. For the albinos there appeared to be a critical duration of low retinal slip velocities above which there was no improvement in acuity. This supports the contention that factors other than the congenital nystagmus limit visual resolution in the albino.

Albinism, Ocular↗
PubMed1992

Chromatic adaptation to natural and incandescent illuminants.

A color CRT image display system was used to present adapting backgrounds that were spatially and temporally varied. Three observers adjusted the chromaticity of test stimuli to produce an achromatic appearance under a variety of adapting conditions. The achromatic-appearing chromaticities were used as measures of the observers' states of chromatic adaptation. The spatial configuration of the adapting background was varied to measure the spatial extent of the mechanisms responsible for chromatic adaptation. The temporal configuration of the adapting background was varied to measure the time-course of these mechanisms. The results show that chromatic adaptation is spatially localized with a time-course on the order of 10 sec. Since the mechanisms were shown to be spatially localized, the observed temporal integration across eye movements is required to allow these mechanisms to adjust to the spatially integrated scene chromaticity.

Adaptation, Ocular↗
PubMed1992

A visual nonlinearity fed by single cones.

An intensive nonlinearity in the visual system can produce distortion products, or difference frequency gratings, when observers view two high contrast, high spatial frequency interference fringes of slightly different frequency or orientation added together at the retina. These distortion products are visible even when the two fringes imaged on the retina are above the resolution limit. Our experiments take advantage of this nonlinearity to measure the spatial filtering in the visual system following the formation of the retinal image, but preceding the site of the nonlinearity. The point spread function corresponding to this spatial filter is so small that it can be entirely explained by light integration within the apertures of foveal and parafoveal cones. The small size of this point spread function implies that (1) laser interferometry avoids contrast losses inherent in the eye's optics at spatial frequencies as high as 130 c/deg, (2) retinal scatter causes negligible image degradation in the fovea and parafoveal retina, (3) eye movements have little or no effect on contrast sensitivity to the distortion product and (4) that there is no neural spatial summation in the visual system prior to the site of the nonlinearity. Distortion products could also be observed when a bright interference fringe was briefly flashed on the fovea and a test interference fringe was viewed through the resulting afterimage. Measurements of the point spread function at stages in the visual system that precede the generation of this distortion product were similar to those obtained with simultaneous presentation of the two fringes, implying that the aftereffect of light adaptation is extremely local, no larger than the dimensions of single cones.

Adaptation, Ocular↗
PubMed1994

Changes in ocular alignment and pointing accuracy after sustained passive rotation of one eye.

We have investigated the contribution of ocular muscle proprioception (OMP) to the long-term maintenance of ocular alignment in normal human beings. Using a scleral suction lens, one eye was rotated laterally 30 deg away from the position of the other eye. This procedure selectively affects OMP without altering the efferent copy of the ocular motor command. The passively displaced eye was covered while the unimpeded eye fixed upon a stationary target. The suction lens was removed after 6 or 10 min and the measures of alignment begun immediately. Three tests were used to determine the effects of the deviation on ocular alignment: the Lancaster red-green test; saccadic eye movement responses to stepping targets; and hand pointing to monocularly presented targets. All three tests indicated a change of ocular alignment of about 2-4 deg, lasting 5-10 min: sustained temporal deviation resulted in exophoria (relative divergence of the visual axis), and sustained nasal deviation induced esophoria (relative convergence). Binocular viewing rapidly abolished the effect. The hand pointing test showed a large shift in the perceived position of a target during monocular viewing with either eye and its amplitude was correlated with the change of ocular alignment. These results indicate that a sustained passive rotation of one eye can lead to a persistent change in ocular alignment even after the eye is released, without any disparity cues. We further suggest that central mechanisms, based upon ocular motor afferents, rather than passive orbital mechanical factors, are the main cause of this phenomenon.

Adult↗
PubMed1996

Direction-selective adaptation and simultaneous contrast induced by stereoscopic (cyclopean) motion.

Across four experiments, this study investigated direction-specific adaptation and simultaneous contrast induced by moving binocular disparity information (stereoscopic motion). The stimuli were moving arrays of stereoscopic dots created from dynamic random-element stereograms. Experiments 1 and 2 examined the effects of adaptation to motion in a given direction on the apparent direction of test motion. Results showed that the direction of test motion appeared repulsed away from the direction of adapting motion (repulsion aftereffect) by as much as 20 deg or more when directions of adapt and test were similar. Experiment 3 investigated transfer of the repulsion aftereffect across the stereoscopic and luminance domains by employing stereoscopic adapting motion and luminance test motion or vice versa. Results showed that the repulsion aftereffect transferred across the two stimulus domains. Experiment 4 investigated direction-specific contrast by measuring the perceived direction of two stereoscopic arrays presented simultaneously and moving in different directions. Results showed that the directions of the arrays appeared repulsed away from one another when their directions were similar. Taken together, these results suggest that the direction of stereoscopic motion is coded in the activity of directionally selective mechanisms, as is the case for luminance-domain motion. Transfer of the repulsion aftereffect between stereoscopic and luminance domains indicates the two kinds of motion perception are mediated by a common substrate.

Adaptation, Ocular↗
PubMed1996

Binocular eye movements caused by the perception of three-dimensional structure from motion.

We report that the perception of three-dimensional structure from monocular two-dimensional images changing over time--the kinetic depth effect (KDE)--can evoke binocular eye movements consistent with a three-dimensional percept. We used a monocular KDE stimulus that induced a vivid perception of a rigid three-dimensional sphere rotating in space. The gaze directions of both eyes were measured while observers pursued the motion of a patch on the surface of the perceived sphere as it went through a complete revolution. We found that the eyes converged when the patch was perceived on the front surface of the KDE sphere and diverged when the patch was perceived in the back. The pattern, magnitude and dynamics of binocular eye movements observed in the KDE experiment resembled those obtained when subjects viewed binocularly a light-emitting diode (LED) rotating in space and to the responses obtained with a dynamic stereogram simulating a rotating random dot sphere. Thus, the perception of three-dimensional structure from motion, stereopsis, or motion and stereopsis combined, were effective in guiding binocular eye movements.

Convergence, Ocular↗
PubMed1985

Binocular distance perception: egocentric distance tasks.

This study extends and tests a theory of binocular distance perception that has been shown to give a good account of performance in relative distance tasks. Here the theory is tested in two experiments in which the observer directly indicates perceived egocentric distance of targets (perceived distance from himself or herself) by means of a verbal report or manual pointing response. In the first, the distance to two targets is varied while maintaining a constant disparity between them. In the second, one target is held fixed while the distance to a second target is varied. In each case, the observer indicates the perceived distance of each target. Manual and verbal responses are found to agree with each other to within a linear transform. Both sets of data are shown to be consistent with the theory and are used to estimate the parameters of the theory. There is no other theory that predicts these results.

Adolescent↗