Interocular Delay Research Articles

No correlation between interocular delay and stereosensitvity in healthy adults

No correlation between interocular delay and stereosensitvity in healthy adults

Continuous psychophysics shows millisecond-scale visual processing delays are faithfully preserved in movement dynamics.

Image differences between the eyes can cause interocular discrepancies in the speed of visual processing. Millisecond-scale differences in visual processing speed can cause dramatic misperceptions of the depth and three-dimensional direction of moving objects. Here, we develop a monocular and binocular continuous target-tracking psychophysics paradigm that can quantify such tiny differences in visual processing speed. Human observers continuously tracked a target undergoing Brownian motion with a range of luminance levels in each eye. Suitable analyses recover the time course of the visuomotor response in each condition, the dependence of visual processing speed on luminance level, and the temporal evolution of processing differences between the eyes. Importantly, using a direct within-observer comparison, we show that continuous target-tracking and traditional forced-choice psychophysical methods provide estimates of interocular delays that agree on average to within a fraction of a millisecond. Thus, visual processing delays are preserved in the movement dynamics of the hand. Finally, we show analytically, and partially confirm experimentally, that differences between the temporal impulse response functions in the two eyes predict how lateral target motion causes misperceptions of motion in depth and associated tracking responses. Because continuous target tracking can accurately recover millisecond-scale differences in visual processing speed and has multiple advantages over traditional psychophysics, it should facilitate the study of temporal processing in the future.

Measuring the Interocular Delay and its Link to Visual Acuity in Amblyopia.

Research on interocular synchronicity in amblyopia has demonstrated a deficit in synchronization (i.e., a neural processing delay) between the two eyes. Current methods for assessing interocular delay are either costly or ineffective for assessments in severe amblyopia. In this study, we adapted a novel protocol developed by Burge and Cormack based on continuous target tracking to measure the interocular delay on a wide range of amblyopes. Our main aims were to assess the accessibility of this protocol and to investigate the relationship between interocular delay and visual acuity. This protocol, which consists of tracking a target undergoing random lateral motion with the mouse cursor, is performed both binocularly and monocularly. The processing speed of a given eye is computed by comparing the changes in velocity of the target and mouse via cross-correlation. The difference in processing speed between the eyes defines the interocular delay. Cross-correlations revealed that the amblyopic eye tends to be delayed in time compared with the fellow eye. Interocular delays fell in the range of 0.6 to 114.0ms. The magnitude of the delay was positively correlated with differences in interocular visual acuity (R2 = 0.484; P = 0.0002). These results demonstrate the accessibility of this new protocol and further support the link between interocular synchronicity and amblyopia. Furthermore, we determine that the interocular delay in amblyopia is best explained by a deficit in the temporal integration of the amblyopic eye.

Retinal eccentricity strongly modulates how interocular delays are impacted by image differences

Retinal eccentricity strongly modulates how interocular delays are impacted by image differences

Perceptual learning based on a temporal stimulus enhances visual function in adult amblyopic subjects

Studies have shown that Perceptual Learning (PL) can lead to enhancement of spatial visual functions in amblyopic subjects. Here we aimed to determine whether a simple flickering stimulus can be utilized in PL to enhance temporal function performance and whether enhancement will transfer to spatial functions in amblyopic subjects. Six adult amblyopic and six normally sighted subjects underwent an evaluation of their performance of baseline psychophysics spatial functions (Visual acuity (VA), contrast sensitivity (CS), temporal functions (critical fusion frequency (CFF) test), as well as a static and flickering stereopsis test, and an electrophysiological evaluation (VEP). The subjects then underwent 5 training sessions (on average, a total of 150 min over 2.5 weeks), which included a task similar to the CFF test using the method of constant stimuli. After completing the training sessions, subjects repeated the initial performance evaluation tasks. All amblyopic subjects showed improved temporal visual performance (CFF) in the amblyopic eye (on average, 17%, p << 0.01) following temporal PL. Generalization to spatial, spatio-temporal, and binocular tasks was also found: VA increased by 0.12 logMAR (p = 0.004), CS in backward masking significantly increased (by up to 19%, p = 0.003), and flickering stereopsis increased by 85 arcsec (p = 0.048). These results were further electrophysiologically manifested by an increase in VEP amplitude (by 43%, p = 0.03), increased Signal-to-Noise ratio (SNR) (by 39%, p = 0.024) to levels not different from normally sighted subjects, along with an improvement in inter-ocular delay (by 5.8 ms, p = 0.003). In contrast, no significant effect of training was found in the normally sighted group. These results highlight the potential of PL based on a temporal stimulus to improve the temporal and spatial visual performance in amblyopes. Future work is needed to optimize this method for clinical applications.

Assessing the interocular delay in amblyopia and its link to visual acuity

Assessing the interocular delay in amblyopia and its link to visual acuity

Interocular Transfer: The Dichoptic Flash-Lag Effect in Controls and Amblyopes.

PurposeThe mammalian brain can take into account the neural delays in visual information transmission from the retina to the cortex when accurately localizing the instantaneous position of moving objects by motion extrapolation. In this study, we wanted to investigate whether such extrapolation mechanism operates in a comparable fashion between the eyes in normally sighted and amblyopic observers.MethodsTo measure interocular extrapolation, we adapted a dichoptic version of the flash-lag effect (FLE) paradigm, in which a flashed bar is perceived to lag behind a moving bar when their two positions are physically aligned. Twelve adult subjects with amblyopia and 12 healthy controls participated in the experiment. We measured the FLE magnitude of the subjects under binocular, monocular, and dichoptic conditions.ResultsIn controls, the FLE magnitude of binocular condition was significantly smaller than that of monocular conditions (P ≤ 0.023), but there was no difference between monocular and dichoptic conditions. Subject with amblyopia exhibited a smaller FLE magnitude in the dichoptic condition when the moving bar was presented to the amblyopic eye and the flash to the fellow eye (DA condition) compared to the opposite way around (DF condition), consistent with a delay in the processing of the amblyopic eye (P = 0.041).ConclusionsOur observations confirm that trajectory extrapolation mechanisms transfer between the eyes of normal observers. However, such transfer may be impaired in amblyopia. The smaller FLE magnitude in DA compared to DF in patients with amblyopia could be due to an interocular delay in the amblyopic visual system. The observation that normal controls present a smaller FLE in binocular conditions raises the question whether a larger FLE is or is not an indicator of better motion processing and extrapolation.

Contributed Session III: Target tracking shows that millisecond-scale visual delays are faithfully preserved in the movement of the hand

Image differences between the eyes can cause millisecond-scale interocular differences in processing speed. For moving objects, these differences can cause dramatic misperceptions of distance and 3D direction. Here, we develop a continuous target-tracking paradigm that shows these tiny differences are preserved in the movement dynamics of the hand. Human observers continuously tracked a target undergoing Brownian motion with various luminance differences between the eyes. From this data, we recover the time course of the visuomotor response. The difference in the visuomotor response across luminance conditions reveals temporal differences in visual processing between the eyes. Next, using traditional psychophysical methods, we measure interocular processing speed differences in equivalent conditions using a paradigm developed to study the Pulfrich effect. Target tracking and traditional psychophysics provide estimates of interocular delays that agree to within a fraction of a millisecond. Thus, despite the myriad signal transformations occurring between early visual and motor responses, millisecond-scale visual delays are preserved in the movement of the hand. This paradigm provides the potential for new predictive power, the application of analytical techniques from computational neuroscience, and rapid measurements in populations in which traditional psychophysics might be impractical. Further implications for future research will be discussed.

Contributed Session III: Global Luminance and Local Contrast Modulate Interocular Delay in Virtual Reality

Virtual reality (VR) systems take advantage of depth cues to create immersive environments that simulate a three-dimensional world. Most often these cues provide consistent information about depth, but on occasion, such cues conflict with each other to create compelling phenomena that illustrate the function of underlying mechanisms. Here we examine the interaction of depth produced by local contrast, global luminance, and interocular luminance differences (i.e., a Pulfrich effect). We measure depth perception with two adjustment tasks. 1: Two moving streams of balls, one upwards (the standard) and the other sideways; the observer adjusts the depth of the sideways stream to lie in the same plane as the upward stream. 2: Balls move sinusoidally back and forth in the frontal plane; if depth is perceived, the pattern appears as a rotating helix. The observer adjusts the helical path until the balls appear to move in a single depth plane. We report that at low luminance levels dark balls are more effective at creating depth than bright balls; at higher luminance levels the effectiveness of dark balls decreases but the effectiveness of bright balls remains constant. Based on these data, we demonstrate how changes in the luminance of the background (or balls) can lead to shifts in the apparent depth order and the apparent direction of helical rotation. The results suggest a method for investigating potentially conflicting contributions of contrast and Pulfrich depth information.

TeleParallax: Low-Motion-Blur Stereoscopic System With Correct Interpupillary Distance for 3D Head Rotations

Binocular parallax provides cues for depth information when a scene is viewed with both eyes. In visual telepresence systems, stereo cameras are commonly used to simulate human eyes. However, motion blur occurs when these cameras are rotated quickly. The use of omnidirectional cameras can reduce the motion blur, but does not provide the correct interpupillary distance (IPD) when viewers tilt or turn their heads sideways. We propose a method called TeleParallax, in which two omnidirectional cameras are separated by the IPD and the direction of the lenses are kept constant in world coordinates by robotic arms during three-dimensional head rotations. TeleParallax can suppress the increase in image buffering during head rotations because each camera can capture an omnidirectional image with the lens direction fixed. We conducted three user studies to evaluate the perceptual effect of head tilt, eye asynchrony, and delays in IPD correction for a particular rotation. The results indicate that TeleParallax can provide depth perception that is independent of the head movement with less visual discomfort. Although the results show that the users were sensitive to the asynchrony between their eyes and to camera motion during IPDs, they retained the feeling of depth perception within interocular delays of 70 ms and motion velocity of 75°/s. These results imply that TeleParallax has remarkable potential for visual telepresence systems.

Measuring the monocular interocular delay in amblyopia

Measuring the monocular interocular delay in amblyopia

Short-term monocular deprivation induces an interocular delay

Short term monocular deprivation modulates ocular dominance, such that the previously deprived eye’s contribution to the binocular percept increases, supposedly as a result of changes in contrast-gain. Therefore, the processing time of the previously patched eye would be expected to speed up as a result of an increase in contrast gain. In order to test this hypothesis, this study examines the effects of short-term monocular deprivation on interocular synchronicity. The present study uses a paradigm based on the Pulfrich phenomenon. The stimulus used for testing consists of elements defining a cylinder rotating in depth, that allows measurement of any interocular delay. The interocular delay was measured at baseline before patching and at outcome, after one hour of monocular deprivation with an opaque or translucent patch. Contrary to expectations, short-term monocular deprivation induces an interocular delay, albeit not always significant, in the previously patched eye. The amplitude of this effect is larger with opaque patching compared to translucent patching. These results are the first report of a non-beneficial effect – i.e. a slowing down in the processing time of the previously patched-eye. They indicate that the plasticity effects of monocular deprivation are not exclusively mediated by contrast gain mechanisms and that light adaptation mechanisms might also be involved in the plasticity resulting from short-term monocular deprivation.

Interocular Differences in Spatial Frequency Influence the Pulfrich Effect

The Pulfrich effect is a stereo-motion phenomenon. When the two eyes are presented with visual targets moving in fronto-parallel motion at different luminances or contrasts, the perception is of a target moving-in-depth. It is thought that this percept of motion-in-depth occurs because lower luminance or contrast delays the speed of visual processing. Spatial properties of an image such as spatial frequency and size have also been shown to influence the speed of visual processing. In this study, we use a paradigm to measure interocular delay based on the Pulfrich effect where a structure-from-motion defined cylinder, composed of Gabor elements displayed at different interocular phases, rotates in depth. This allows us to measure any relative interocular processing delay while independently manipulating the spatial frequency and size of the micro elements (i.e., Gabor patches). We show that interocular spatial frequency differences, but not interocular size differences of image features, produce interocular processing delays.

Two Patterns of Interocular Delay Revealed by Spontaneous Motion-in-Depth Pulfrich Phenomenon in Amblyopes with Stereopsis.

PurposeTo assess interocular delays in amblyopes with stereopsis and to evaluate the relationship between interocular delays and the clinical characteristics.MethodsTwenty amblyopes with stereopsis (median, 400 arcseconds) and 20 controls with normal or corrected to normal visual acuity (≤0 logMAR) and normal stereopsis (≤60 arcseconds) participated. Using a rotating cylinder defined by horizontally moving Gabor patches, we produced a spontaneous Pulfrich phenomenon in order to determine the interocular delays, that is, the interocular phase difference at which ambiguous motion in plane was perceived. Two spatial frequencies—a low (0.95 cycles/degree [c/d]) and a medium (2.85 c/d) spatial frequency—were tested.ResultsThe absolute interocular delays of the amblyopic group was significantly longer than that of the controls at both low or medium spatial frequencies (P < 0.01). However, the interocular delays was not always in favor of the fellow eye: 35% of the amblyopes (7/20) showed a faster processing of the amblyopic eye than that of the fellow eye at 0.95 c/d and 29.5% (5/17) at 2.85 c/d. No significant correlation was found between interocular delays and the clinical characteristics (e.g., age, treatment history, stereoacuity, and magnitude of anisometropia) in this amblyopic cohort.ConclusionsThe interocular delays in amblyopes with stereopsis might result from either a faster or slower processing of the amblyopic eye relative to the fellow eye. This work provides important additional information for binocular processing of dynamic visual stimuli in amblyopia. However, the special role between this form of interocular delays and patients’ clinical characteristics remains unknown.

An Unexpected Spontaneous Motion-In-Depth Pulfrich Phenomenon in Amblyopia.

The binocular viewing of a fronto-parallel pendulum with a reduced luminance in one eye results in the illusory tridimensional percept of the pendulum following an elliptical orbit in depth, the so-called Pulfrich phenomenon. A small percentage of mild anisometropic amblyopes who have rudimentary stereo are known to experience a spontaneous Pulfrich phenomenon, which posits a delay in the cortical processing of information involving their amblyopic eye. The purpose of this study is to characterize this spontaneous Pulfrich phenomenon in the mild amblyopic population. In order to assess this posited delay, we used a paradigm where a cylinder rotating in depth, defined by moving Gabor patches at different disparities (i.e., at different interocular phases), generates a strong to ambiguous depth percept. This paradigm allows one to accurately measure a spontaneous Pulfrich phenomenon and to determine how it depends on the spatio-temporal properties of stimulus. We observed a spontaneous Pulfrich phenomenon in anisometropic, strabismic, and mixed amblyopia, which is posited to be due to an interocular delay associated with amblyopic processing. Surprisingly, the posited delay was not always observed in the amblyopic eye, was not a consequence of the reduced contrast sensitivity of the amblyopic eye, and displayed a large variability across amblyopic observers. Increasing the density, decreasing the spatial frequency, or increasing the speed of the stimulus tended to reduce the observed delay. The spontaneous Pulfrich phenomenon seen by some amblyopes was variable and depended on the spatio-temporal properties of the stimulus. We suggest it could involve two conflicting components: an amblyopic delay and a blur-based acceleration.

An overview of depth distortion in stereoscopic 3D displays

This article reviews how different presentation techniques of stereoscopic 3D (S3D) TVs affect depth perception. Many S3D TVs employ various interlacing techniques to present two eye views using one screen. The spatial or temporal interocular offsets introduced by these interlacing techniques can affect the image's perceived depth, resulting in depth distortion. Temporal interlacing delivers the two eye views with an interocular delay, which can be interpreted by the visual system as a horizontal disparity. Spatial interlacing presents the two eye views in alternating fashion on every other pixel row, thereby creating a vertical interocular offset, which can induce an additional horizontal disparity while the visual system performs binocular matching. Recently, novel S3D presentation techniques were introduced to improve depth perception. Spatiotemporal hybrid interlacing combines spatial interlacing and temporal interlacing: it presents the two eye views as spatial interlacing does, but each pixel row switches between the two views overtime. This hybrid technique has been proven to be free from depth distortion. By contrast, color interlacing presents the two eye views with an interocular delay, but the sign of the delay differs among the color channels. Such a configuration effectively decreases the interocular delay and improves the depth perception.

The Limits of Human Stereopsis in Space and Time

To encode binocular disparity, the visual system determines the image patches in one eye that yield the highest correlation with patches in the other eye. The computation of interocular correlation occurs after spatiotemporal filtering of monocular signals, which leads to restrictions on disparity variations that can support depth perception. We quantified those restrictions by measuring humans' ability to see disparity variation at a wide range of spatial and temporal frequencies. Lower-disparity thresholds cut off at very low spatiotemporal frequencies, which is consistent with the behavior of V1 neurons. Those thresholds are space-time separable, suggesting that the underlying neural mechanisms are separable. We also found that upper-disparity limits were characterized by a spatiotemporal, disparity-gradient limit; to be visible, disparity variation cannot exceed a fixed amount for a given interval in space-time. Our results illustrate that the disparity variations that humans can see are very restricted compared with the corresponding luminance variations. The results also provide insight into the neural mechanisms underlying depth from disparity, such as why stimuli with long interocular delays can still yield clear depth percepts.

Pulfrich autostereo display with micro-prism array

A micro-prism film, with spectral characteristics, is attached on a display panel to show images appearing with + 10° ~ + 50° and -10° ~-50° bright regions and with a + 10° ~-10° dark region. When both eyes separately receive the bright region and the dark region of an image, interocular delay would appear to generate a stereo perception. With the optical simulation software, LightTools 7.3.0, to simulate the brightness change, the light with lower brightness appears on the 0° region and the light with the highest brightness appears on the ± 10° region. The optimal viewing distance of 25 cm could accurately deliver the image with shading parallax to both eyes. The actual measurement of brightness presents the shading distribution, achieving the condition of binocular retinal illumination, and the angle of visibility appears on the ± 50° region, causing interocular delay so that the viewer generates the stereo perception.

Integration of Alternating Monocular Samples During Goal-Directed Aiming

The current study examined the effect of interocular delay in a manual aiming task that required accurate end-point placement, but not precise control of a grip aperture. Participants aimed in binocular, monocular, or alternating monocular vision conditions. For the latter, 25ms monocular samples were provided to alternate eyes without delay (0ms), or a delay of 25 or 50ms. The interocular delay resulted in a longer movement time, caused by a longer time-to-peak and time-after-peak velocity, and a reduction in peak velocity. We suggest that the change in kinematics reflect a strategic response to preserve terminal aiming accuracy and variability when faced with an informational perturbation. These findings indicate that the response to the interocular delay between alternating monocular samples depends on the task-specific information used to control that behavior.

The effect of interocular delays on the perception of 3D movies

The effect of interocular delays on the perception of 3D movies