Martin J. Steinbach

Pursuing the perceptual rather than the retinal stimulus

Abstract In the first experiment, subjects were able to successfully track a perceptually completed contour that was extrapolated from peripheral retinal information. In the second experiment, subjects successfully pursued an object that moved horizontally behind a narrow slit in such a way that the only visible stimuli were the edges of the object moving vertically in the slit. In the third experiment, subjects successfully tracked the invisible center of a rolling wheel when all that could be seen were points of light travelling in a cycloidal path on the rim of the wheel. It is argued that the stimulus for pursuit eye movements is the appreciation of an object in motion with respect to the observer, regardless of the retinal stimulation, and in some cases regardless of the sense modality through which the motion is detected.

Fixation characteristics of patients with macular degeneration recorded with the mp-1 microperimeter.

Purpose: The authors examined the fixation stability patterns of people with age-related macular degeneration (AMD) using the MP-1 microperimeter and describe a method to bypass some calibration artifacts that can influence the fixation results. Method: The preferred retinal locus (PRL) and fixation patterns of 37 eyes with AMD and the foveas location relative to the middle of the optic disc of 10 experienced controls were measured. For the patients, fixation characteristics such as the former foveas location, PRL distance, and fixation stability were analyzed. Results: For the controls, the mean foveal distance temporal to the middle of the optic disc was 15.5 deg ± 0.86 deg horizontally and –1.33 deg ± 0.71 deg vertically. Thirty-one out of 37 PRLs occurred in the upper and right quadrants of the retina. There were significant positive correlations between fixation stability and PRL distance from the former fovea. Time since diagnosis and acuity also showed positive correlations with fixation stability and PRL distance from the fovea. Conclusions: The authors recommend that fixation stability recorded with the MP-1 be analyzed based on the raw data. Most of the fixation parameters obtained agree with those reported in the literature, if proper calibration is used.

Eye movements of the owl

Abstract : The tubular shape and tightly encapsulating orbit of the owls eye would seem to make horizontal and vertical eye rotations impossible. The amazing flexibility of the neck, allowing the head to rotate 270 degrees on the torso, would seem to make eye movements unnecessary. These two characteristics have led to the claim that the owl eye is immobile. The authors report the presence of small eye movements (less than 1.5 degrees) in awake, unanesthetized owls, occurring both spontaneously and elicited by visual and vestibular stimuli.

Nonadditivity of vergence and saccadic eye movement

Abstract We measured durations, peak velocities and magnitudes of the eye movements consisting of saccadic and vergence components. While duration and direction of the combined eye movements were the same for both eyes, we found reliable differences between the magnitudes and peak velocities of the two which were too large to be understood by an additivity hypothesis.

Eye Position Stability in Amblyopia and in Normal Binocular Vision

PURPOSE We investigated whether the sensory impairments of amblyopia are associated with a decrease in eye position stability (PS). METHODS The positions of both eyes were recorded simultaneously in three viewing conditions: binocular, monocular fellow eye viewing (right eye for controls), and monocular amblyopic eye viewing (left eye for controls). For monocular conditions, movements of the covered eye were also recorded (open-loop testing). Bivariate contour ellipses (BCEAs), representing the region over which eye positions were found 68.2% of the time, were calculated and normalized by log transformation. RESULTS For controls, there were no differences between eyes. Binocular PS (log(10)BCEA = -0.88) was better than monocular PS (log(10)BCEA = -0.59) indicating binocular summation, and the PS of the viewing eye was better than that of the covered eye (log(10)BCEA = -0.33). For patients, the amblyopic eye exhibited a significant decrease in PS during amblyopic eye (log(10)BCEA = -0.20), fellow eye (log(10)BCEA = 0.0004), and binocular (log(10)BCEA = -0.44) viewing. The PS of the fellow eye depended on viewing condition: it was comparable to controls during binocular (log(10)BCEA = -0.77) and fellow eye viewing (log(10)BCEA = -0.52), but it decreased during amblyopic eye viewing (log(10)BCEA = 0.08). Patients exhibited binocular summation during fellow eye viewing, but not during amblyopic eye viewing. Decrease in PS in patients was mainly due to slow eye drifts. CONCLUSIONS Deficits in spatiotemporal vision in amblyopia are associated with poor PS. PS of amblyopic and fellow eyes is differentially affected depending on viewing condition.

Monocular stereopsis with and without head movement

Random dots moving with various velocity gradients were presented to observers; the motion was yoked to head movement in one condition and to no head movement in another. In Experiment 1, 12 observers were shown motion gradients with sine, triangle, sawtooth, and square waveforms with amplitudes (equivalent disparities) of 12′ and 1° 53′. In Experiment 2, 48 observers were shown only the sinewave or square-wave gradient of 1° 53′ disparity either with or without head movement so that the observers’ expectation to see depth in one condition did not transfer to another. The main findings were: (1) with 12′ disparity, the head-movement condition produced perceived depth but almost no perceived motion, whereas the no-head-movement condition produced both perceived depth and perceived motion; (2) with 1° 53′ disparity, both conditions produced perceived depth and perceived motion; and (3) when the expectation to see depth was removed, the no-head-movement condition with the square-wave gradient produced no perceived depth, only motion. We suggest that monocular stereopsis with head movement can be achieved without perception of motion but monocular stereopsis without head movement requires perception of motion.

Vision with one eye: a review of visual function following unilateral enucleation.

What happens to vision in the remaining eye following the loss of vision in the fellow eye? Does the one-eyed individual have supernormal visual ability with the remaining eye in order to adapt and compensate for the loss of binocularity and the binocular depth cue, stereopsis? There are subtle changes in visual function following the complete loss of one eye from unilateral enucleation. Losing binocularity early in life results in a dissociation in form perception and motion processing: some aspects of visual spatial ability are enhanced, whereas motion processing and oculomotor behaviour appear to be adversely affected suggesting they are intrinsically linked to the presence of binocularity in early life. These differential effects may be due to a number of factors, including plasticity through recruitment of resources to the remaining eye; the absence of binocular inhibitory interactions; and/or years of monocular practice after enucleation. Finally, despite this dissociation of spatial vision and motion processing, research that has examined visual direction and performance on monocular tasks shows adaptive effects as a result of the loss of one eye. Practically speaking, one-eyed individuals maintain perfectly normal lives and are not limited by their lack of binocularity.

Additivity of fuslonal vergence and pursuit eye movements

Abstract We measured binocular eye movements photoelectrically while subjects tracked a target moving smoothly along a horizontal path in the fronto-parallel plane, with interpolated step changes in depth. By measuring eye movement speeds when only fusional vergence or only pursuit was required we were able to ascertain how the vergence and pursuit movements combined when called out together. When the two were in opposite directions the net eye movement speed was equal to the difference of the vergence and pursuit components, reflecting perfect additivity. When vergence and pursuit were in the same direction a significant deviation from strict additivity was found, i.e. the combined eye movements were on average 11% slower than expected. We speculate that this attenuation may be peripheral in origin.

The development of optokinetic nystagmus in strabismic and monocularly enucleated subjects

Assymmetries of monocular optokinetic nystagmus (OKN) following anomalous visual experience are thought to be due to disruption at the cortical level. Visual disruption usually results from eye suture (in animals), unilateral dense and central cataracts or strabismus (in humans). Many form-deprived animals and humans frequently show a residual strabismus after lid opening (animals) or cataract extraction and optical correction (humans). We wanted to determine whether strabismus was unique in causing monocular asymmetries of OKN. Two independent observers rated eye movement videotapes of 20 normal subjects, the non-deviating eye of 25 unilateral strabismic subjects and 29 unilaterally eye-enucleated subjects, who were watching either a nasally directed square wave grating, a temporally directed square wave grating, or a blank field. Observers rated the proportion of trials where OKN occurred, the duration of OKN in each trial and the number of beats of OKN within each trial. Monocular OKN was symmetrical in normal subjects for the proportion and duration measures, but half the normal group showed small but significant asymmetries for the beats measure. Subjects in both enucleate and strabismic groups showed asymmetries of OKN favouring nasally directed stimulation, but only the early onset strabismics (as a group) showed asymmetries that were significantly greater (P less than 0.05) than the normal group. Asymmetry scores correlated significantly with age of diagnosis of strabismus for the strabismic group but not with age of enucleation for the enucleate group. The results are discussed in terms of binocular competition.

Fixation stability using radial gratings in patients with age-related macular degeneration

BACKGROUND The fixation stability of patients with macular atrophy is generally worse than that of people without pathology. METHODS The effects of 2 types of high-contrast fixation stimuli on fixation stability were compared between patients with longstanding age-related macular degeneration (AMD) and control subjects with normal vision. One stimulus was a 9-cycle square-wave radial grating measuring 5 degrees in diameter and the other a white 0.5 degrees disc. A video-based infrared eye tracker with remote optics was used to record eye position while participants fixated the stimuli in primary position of gaze for 6 to 7 s. Fixation stability was measured with a bivariate contour ellipse area (BCEA). RESULTS For patients with AMD, fixation stability for the radial grating was largely independent of visual acuity, whereas fixation stability for the disc diminished with acuity. For the control observers, there were no differences in fixation stability for the 2 kinds of stimuli. INTERPRETATION In clinical and research settings, radial gratings can be useful targets for fixation for patients with macular disease since they provide enough visual information to help maintain fixation stability. These findings have important implications for the design of clinical tests and procedures such as perimetry, multifocal electroretinography, and optical coherence tomography for patients with macular atrophies.