Stereo-anomaly is found more frequently in tasks that require discrimination between depths.

Within the population of humans with otherwise normal vision, there exists some proportion whose ability to perceive depth from binocular disparity is poor or absent. The prevalence of this "stereo-anomaly" has been reported to be as small as 2%, or as great as 30%. We set out to investigate this discrepancy. We used a digital tool to measure stereoacuity in tasks requiring either the detection of disparity or the discrimination of the direction of disparity. In a cohort of 228 participants, we found that 98% were able to consistently perform the detection task. Of these, only 69% consistently performed the discrimination task. The 31% of participants who had difficulty with the discrimination task could further be divided into 17% who were consistently unable to perform the task and 14% who showed limited ability. This suggests that identification of the direction of disparity requires further processing beyond merely detecting its presence.

Binocular function in the aging visual system: fusion, suppression, and stereoacuity.

Introduction: Changes in vision that occur in normal healthy aging can be seen in fundamental measures of monocular vision. However, the nature of the changes in binocular vision with age remain unclear. Methods: A total of 28 older (53-66 years) and 28 younger adults (20-31 years) were enrolled in this study. We performed a battery of tests to assess differences in monocular contrast thresholds and various binocular visual functions including dichoptic masking weight and strength, the binocular balance point for fused stimuli, and stereoacuity in the aging and control groups. Results: Aging significantly increased monocular contrast thresholds (p < 0.001). Although this suggests that aging reduces the effective "input gain" to vision, we also found a significantly elevated contribution of those weaker signals to interocular suppression (p < 0.001). Consequently, there was no significant net difference in the strength of interocular suppression (p = 0.065). We did not find a significant difference of absolute balance point between the two groups (p = 0.090). Lastly, the mean stereoacuity was worse in the older group compared to the younger group (p = 0.002). Discussion: Our findings confirm previous results showing differences in contrast sensitivity and stereoacuity with aging. Furthermore, we find a change in interocular suppression that is a possible consequence of the change in contrast sensitivity. It is suggestive of a cortical system that maintains a homeostatic balance in interocular suppression across the lifespan.

Amblyopic stereo vision is efficient but noisy.

People with amblyopia demonstrate a reduced ability to judge depth using stereopsis. Our understanding of this deficit is limited, as standard clinical stereo tests may not be suited to give a quantitative account of the residual stereo ability in amblyopia. In this study we used a stereo test designed specifically for that purpose. Participants identified the location of a disparity-defined odd-one-out target within a random-dot display. We tested 29 amblyopic (3 strabismic, 17 anisometropic, 9 mixed) participants and 17 control participants. We obtained stereoacuity thresholds from 59% of our amblyopic participants. There was a factor of two difference between the median stereoacuity of our amblyopic (103 arcsec) and control (56 arcsec) groups. We used the equivalent noise method to evaluate the role of equivalent internal noise and processing efficiency in amblyopic stereopsis. Using the linear amplifier model (LAM), we determined the threshold difference was due to a greater equivalent internal noise in the amblyopic group (238 vs 135 arcsec), with no significant difference in processing efficiency. A multiple linear regression determined 56% of the stereoacuity variance within the amblyopic group was predicted by the two LAM parameters, with equivalent internal noise predicting 46% alone. Analysis of control group data aligned with our previous work, finding that trade-offs between equivalent internal noise and efficiency play a greater role. Our results allow a better understanding of what is limiting amblyopic performance in our task. We find this to be a reduced quality of disparity signals in the input to the task-specific processing.

Exercise does not enhance short-term deprivation-induced ocular dominance plasticity: evidence from dichoptic surround suppression.

The input from the two eyes is combined in the brain. In this combination, the relative strength of the input from each eye is determined by the ocular dominance. Recent work has shown that this dominance can be temporarily shifted. Covering one eye with an eye patch for a few hours makes its contribution stronger. It has been proposed that this shift can be enhanced by exercise. Here, we test this hypothesis using a dichoptic surround suppression task, and with exercise performed according to American College of Sport Medicine guidelines. We measured detection thresholds for patches of sinusoidal grating shown to one eye. When an annular mask grating was shown simultaneously to the other eye, thresholds were elevated. The difference in the elevation found in each eye is our measure of relative eye dominance. We made these measurements before and after 120 min of monocular deprivation (with an eye patch). In the control condition, subjects rested during this time. For the exercise condition, 30 min of exercise were performed at the beginning of the patching period. This was followed by 90 min of rest. We find that patching results in a shift in ocular dominance that can be measured using dichoptic surround suppression. However, we find no effect of exercise on the magnitude of this shift. We further performed a meta-analysis on the four studies that have examined the effects of exercise on the dominance shift. Looking across these studies, we find no evidence for such an effect.

A psychophysical performance-based approach to the quality assessment of image processing algorithms.

Image processing algorithms are used to improve digital image representations in either their appearance or storage efficiency. The merit of these algorithms depends, in part, on visual perception by human observers. However, in practice, most are assessed numerically, and the perceptual metrics that do exist are criterion sensitive with several shortcomings. Here we propose an objective performance-based perceptual measure of image quality and demonstrate this by comparing the efficacy of a denoising algorithm for a variety of filters. For baseline, we measured detection thresholds for a white noise signal added to one of a pair of natural images in a two-alternative forced-choice (2AFC) paradigm where each image was selected randomly from a set of n = 308 on each trial. In a series of experimental conditions, the stimulus image pairs were passed through various configurations of a denoising algorithm. The differences in noise detection thresholds with and without denoising are objective perceptual measures of the ability of the algorithm to render noise invisible. This was a factor of two (6dB) in our experiment and consistent across a range of filter bandwidths and types. We also found that thresholds in all conditions converged on a common value of PSNR, offering support for this metric. We discuss how the 2AFC approach might be used for other algorithms including compression, deblurring and edge-detection. Finally, we provide a derivation for our Cartesian-separable log-Gabor filters, with polar parameters. For the biological vision community this has some advantages over the more typical (i) polar-separable variety and (ii) Cartesian-separable variety with Cartesian parameters.

The effects of optically and digitally simulated aniseikonia on stereopsis.

PURPOSE: To simulate both lens-induced and screen-induced aniseikonia, and to assess its influence on stereopsis. Additionally, to determine if screen-based size differences could neutralise the effects of lens-induced aniseikonia. METHOD: A four-circle (4-C) paradigm was developed, where one circle appears in front or behind the others because of crossed or uncrossed disparity. This stereotest was used for three investigations: (1) Comparison with the McGill modified random dot stereogram (RDS), with anisometropia introduced with +2 D spheres and cylinders, and with aniseikonia introduced with 6% overall and 6% meridional (×180, ×90) magnifiers before the right eye; (2) Comparison of lens-induced and screen-induced 6% overall and meridional magnifications and (3) Determining if lens and screen effects neutralised, by opposing 6% lens-induced magnification to the right eye with screen-inducements of either 6% left eye magnification or 6% right eye minification. A pilot study of the effect of masking versus not masking the surround was also conducted. RESULTS: The 4-C test gave higher stereo-thresholds than the RDS test by 0.5 ± 0.2 log units across both anisometropic and aniseikonic conditions. However, variations in power, meridian and magnification affected the two tests similarly. The pilot study indicated that surround masking improved neutralisation of screen and lens effects. With masking, lens-induced and screen-induced magnifications increased stereo-thresholds similarly. With lens and screen effects opposed, for most participants stereo-thresholds returned to baseline for overall and ×180 magnifications, but not for ×90 magnification. Only three of seven participants showed good compensation for ×90 magnification. CONCLUSIONS: Effects of lens-induced aniseikonia on stereopsis cannot always be successfully simulated with a screen-based method. The ability to neutralise refractive aniseikonia using a computer-based method, which is the basis of digital clinical measurement, was reasonably successful for overall and ×180 meridional aniseikonia, but not very successful for ×90 aniseikonia.

Balanced Binocular Inputs Support Superior Stereopsis.

Purpose: Our visual system compares the inputs received from the two eyes to estimate the relative depths of features in the retinal image. We investigated how an imbalance in the strength of the input received from the two eyes affects stereopsis. We also explored the level of agreement between different measurements of sensory eye imbalance. Methods: We measured the sensory eye imbalance and stereoacuity of 30 normally sighted participants. We made our measurements using a modified amblyoscope. The sensory eye imbalance was assessed through three methods: the difference between monocular contrast thresholds, the difference in dichoptic masking weight, and the contribution of each eye to a fused binocular percept. We referred them as the "threshold imbalance," "masking imbalance," and "fusion imbalance," respectively. The stereoacuity threshold was measured by having subjects discriminate which of four circles were displaced in depth. All of our tests were performed using stimuli of the same spatial frequency (2.5 cycles/degree). Results: We found a relationship between stereoacuity and sensory eye imbalance. However, this was only the case for fusion imbalance measurement (ρ = 0.52; P = 0.003). Neither the threshold imbalance nor the masking imbalance was significantly correlated with stereoacuity. We also found the threshold imbalance was correlated with both the fusion and masking imbalances (r = 0.46, P = 0.011 and r = 0.49, P = 0.005, respectively). However, a nonsignificant correlation was found between the fusion and masking imbalances. Conclusions: Our findings suggest that there exist multiple types of sensory eye dominance that can be assessed by different tasks. We find only imbalances in dominance that result in biases to fused percepts are correlated with stereoacuity.

Some psychophysical tasks measure ocular dominance plasticity more reliably than others.

In the recent decade, studies have shown that short-term monocular deprivation strengthens the deprived eye's contribution to binocular vision. However, the magnitude of the change in eye dominance after monocular deprivation (i.e., the patching effect) has been found to be different between different methods and within the same method. There are three possible explanations for the discrepancy. First, the mechanisms underlying the patching effect that are probed by different measurement tasks might exist at different neural sites. Second, the test-retest variability of the same test can produce inconsistent results. Third, the magnitude of the patching effect itself within the same observer can vary across separate days or experimental sessions. To explore these possibilities, we assessed the test-retest reliability of the three most commonly used tasks (binocular rivalry, binocular combination, and dichoptic masking) and the repeatability of the shift in eye dominance after short-term monocular deprivation for each of the task. Two variations for binocular phase combination were used, at one and many contrasts of the stimuli. Also, two variations for dichoptic masking were employed; the orientation of the mask grating was either horizontal or vertical. Thus, five different tasks were evaluated. We hoped to resolve some of the inconsistencies reported in the literature concerning this form of visual plasticity. In this study, we also aimed to recommend a measurement method that would allow us to better understand its physiological basis and the underpinning of visual disorders.

Shifting eye balance using monocularly directed attention in normal vision.

In binocular vision, even without conscious awareness of eye of origin, attention can be selectively biased toward one eye by presenting a visual stimulus uniquely to that eye. Monocularly directed visual cues can bias perceptual dominance, as shown by studies using discrete measures of percept changes in continuous-flash suppression. Here, we use binocular rivalry to determine whether eye-based visual cues can modulate eye balance using continuous percept reporting. Using a dual-task versus single-task paradigm, we investigated whether the attentional load of these cues differentially modulates eye balance. Furthermore, both color-based and motion-based cue stimuli, non-overlaid and peripheral to the rivalry grating stimuli, were used to determine whether shifts in eye balance were stimulus specific. Aligned to cue stimulus onset, time series of percept reports were constructed and averaged across trials and participants. Specifically, for the monocular attention conditions, we found a significant shift in eye balance toward the cued eye and a significant difference in the time taken to switch from the dominating percept, regardless of whether the attention stimuli is color based or motion based. Although we did not find a significant main effect of attentional load, we found a significant interaction effect between the attentionally cued eye and attentional load on the shift in eye balance, indicating an influence of monocular attention on the shift in eye balance.

Comparison of blur and magnification effects on stereopsis: overall and meridional, monocularly- and binocularly-induced.

PURPOSE: To determine whether monocularly- and binocularly-induced spherical and meridional blur and aniseikonia had similar effects on stereopsis thresholds. METHODS: Twelve participants with normal binocular vision viewed McGill modified random dot stereograms to determine stereoacuities in a four-alternative forced-choice procedure. Astigmatism was induced by placing trial lenses in front of the eyes. Twenty-three conditions were used, consisting of zero (no lens), +1 D and +2 D spheres and cylinders at axes 180, 45 and 90 in front of the right eye, and the following binocular combinations of both lens powers: R × 180/L × 180, R × 45/L × 45, R × 90/L × 90, R sphere/L sphere, R × 180/L × 90, R × 45/L × 135, R × 90/L × 180. Aniseikonia was induced by placing magnifying lenses in front of the eyes. Twenty-three conditions were used, consisting of zero, 6% and 12% overall magnification and both magnifications at axes 180, 45 and 90 in front of the right eye only, and the following binocular combinations using 3% and 6% lenses: R × 90/L × 90, R × 45/L × 45, R × 180/L × 180, R overall/L overall, R × 90/L × 180, R × 45/L × 135, and R × 180/L × 90. RESULTS: Stereopsis losses for binocular blur effects with parallel axes (non-anisometropic) were the same as for monocular blur effects of the same axes, and these were strongly dependent on axis (spherical blur and ×90 had the greatest effects). Binocular blur effects with orthogonal axes had greater effects than with parallel axes, with the axis combination of the former having no effect (e.g. R × 90/L × 180 was similar to R × 45/L × 135). For induced aniseikonia, splitting the magnifications between the eyes improved stereopsis slightly, and the effects were not dependent on axis. CONCLUSION: Binocular blur affects stereopsis similarly to monocular meridional blur if axes in the two eyes are parallel, whereas the effect is greater if the axes are orthogonal. In meridional aniseikonia, splitting magnification between the right and left lenses produces a small improvement in stereopsis that is independent of axis direction and right/left combination.

Integration of contours defined by second-order contrast-modulation of texture.

Boundaries in the visual world can be defined by changes in luminance and texture in the input image. A "contour integration" process joins together local changes into percepts of lines or edges. A previous study tested the integration of contours defined by second-order contrast-modulation. Their contours were placed in a background of random wavelets. Participants performed near chance. We re-visited second-order contour integration with a different task. Participants distinguished contours with "good continuation" from distractors. We measured thresholds in different amounts of external orientation or position noise. This gave two noise-masking functions. We also measured thresholds for contours with a baseline curvature to assess performance with more curvy targets. Our participants were able to discriminate the good continuation of second-order contours. Thresholds were higher than for first-order contours. In our modelling, we found this was due to multiple factors. There was a doubling of equivalent internal noise between first- and second-order contour integration. There was also a reduction in efficiency. The efficiency difference was only significant in our orientation noise condition. For both first- and second-order stimuli, participants were also able to perform our task with more curved contours. We conclude that humans can integrate second-order contours, even when they are curved. There is however reduced performance compared to first-order contours. We find both an impaired input to the integrating mechanism, and reduced efficiency seem responsible. Second-order contour integration may be more affected by the noise background used in the previous study. Difficulty segregating that background may explain their result.

Suppression Rather Than Visual Acuity Loss Limits Stereoacuity in Amblyopia.

Purpose: To investigate the influence of interocular suppression and visual acuity loss on stereoacuity in observers with and without abnormal vision development from strabismus or amblyopia. To determine whether stereoacuity improves in amblyopic observers when suppression is neutralized. Methods: Experiment 1: Visual acuity (VA), depth of suppression (contrast ratio [CR]), and stereoacuity (digital random-dot) were tested in adult amblyopic observers (n = 21; age 27 ± 11 years). Experiment 2: VA, stereoacuity, and CR were measured at baseline and through a series of monocular contrast attenuation and Bangerter filter conditions that degrade visual input in participants with normal binocular vision (n = 19; age 31 ± 13 years). Multiple regression models were used to determine relative contribution of VA and CR to stereoacuity in both groups. Experiment 3: stereoacuity was retested in a subsample of amblyopic observers (n = 7) after contrast reduction of the stimulus presented to dominant eye to neutralize suppression. Results: In amblyopic observers, stereoacuity significantly correlated with CR (P < 0.001), but not with interocular VA difference (P = 0.863). In participants with normal vision development, stereoacuity, VA, and CR declined with introduction of monocular Bangerter filter (P < 0.001), and stereoacuity reduced with monocular attenuation of stimulus contrast (P < 0.001). Reduction in stereoacuity correlated with both VA decrement and degraded CR. Stereoacuity significantly improved in amblyopic observers when the contrast to the dominant eye was adjusted based on the contrast ratio. Conclusions: Suppression rather than visual acuity loss limits stereoacuity in observers with abnormal vision development. Stereopsis can be improved when interocular sensory dominance is neutralized.

Factors limiting sensitivity to binocular disparity in human vision: Evidence from a noise-masking approach.

Our visual system uses the disparity between the images received by the two eyes to judge three-dimensional distance to surfaces. We can measure this ability by having subjects discriminate the disparity of rendered surfaces. We wanted to know the basis of the individual differences in this ability. We tested 53 adults with normal vision using a relative disparity detection task. Targets were wedge-shaped surfaces formed from random dots. These were presented in either crossed or uncrossed disparity relative to a random dot background. The threshold disparity ranged from 24 arc seconds in the most-able subject to 275 arc seconds in the least-able subject. There was a small advantage for detecting crossed-disparity targets. We used the noise-masking paradigm to partition subject performance into two factors. These were the subject's equivalent internal noise and their processing efficiency. The parameters were estimated by fitting the linear amplifier model. We found both factors contributed to the individual differences in stereoacuity. Within subjects, those showing an advantage for one disparity direction had enhanced efficiency for that direction. Some subjects had a higher equivalent internal noise for one direction that was balanced out by an increased efficiency. Our approach provides a more thorough account of the stereo-ability of our subjects compared with measuring thresholds alone. We present a normative set of results that can be compared with clinical populations.

Effects of simulated anisometropia and aniseikonia on stereopsis.

PURPOSE: Stereopsis depends on horizontally disparate retinal images but otherwise concordance between eyes. Here we investigate the effect of spherical and meridional simulated anisometropia and aniseikonia on stereopsis thresholds. The aims were to determine effects of meridian, magnitude and the relative effects of the two conditions. METHODS: Ten participants with normal binocular vision viewed McGill modified random dot stereograms through synchronised shutter glasses. Stereoacuities were determined using a four-alternative forced-choice procedure. To induce anisometropia, trial lenses of varying power and axes were placed in front of right eyes. Seventeen combinations were used: zero (no lens) and both positive and negative, 1 and 2 D powers, at 45, 90 and 180 axes; spherical lenses were also tested. To induce aniseikonia 17 magnification power and axis combinations were used. This included zero (no lens), and 3%, 6%, 9% and 12% at axes 45, 90 and 180; overall magnifications were also tested. RESULTS: For induced anisometropia, stereopsis loss increased as cylindrical axis rotated from 180° to 90°, at which the loss was similar to that for spherical blur. For example, for 2 D meridional anisometropia threshold increased from 1.53 log sec arc (i.e. 34 sec arc) for x 180 to 1.89 log sec arc (78 sec arc) for x 90. Anisometropia induced with either positive or negative lenses had similar detrimental effects on stereopsis. Unlike anisometropia, the stereopsis loss with induced meridional aniseikonia was not affected by axis and was about 64% of that for overall aniseikonia of the same amount. Approximately, each 1 D of induced anisometropia had the same effect on threshold as did each 6% of induced aniseikonia. CONCLUSION: The axes of meridional anisometropia but not aniseikonia affected stereopsis. This suggests differences in the way that monocular blur (anisometropia) and interocular shape differences (aniseikonia) are processed during the production of stereopsis.

Assessment of stereovision with digital testing in adults and children with normal and impaired binocularity.

New digital approaches allow stereovision to be assessed with greater precision than current clinical stereo tests. Those current tests present a relatively narrow range of stimulus disparities in coarsely quantized steps. With dichoptic treatments for amblyopia emerging, more accurate assessment of especially coarse stereopsis becomes increasingly important for verifying their aim to improve 3D vision. We used digital testing in subjects of a large age range (4-59 years), with groups having both normal (n = 34) and impaired binocular vision due to unilateral amblyopia, with or without strabismus (n = 27). Random-dot stimuli were presented on a 3D monitor with shutter glasses. The test applies adaptive procedures to measure psychometric functions and provides thresholds with associated confidence intervals. Digital thresholds for controls (range 11-160 arcsec) and stereodeficient subjects (range 43-911 arcsec) were compared to the TNO, a standard clinical test which uses similar random-dot targets presented with anaglyph glasses. Agreement between digital and TNO thresholds varied with the level of stereopsis. Stereoacuity was measurable in several subjects who failed on the TNO. With the digital test we found good repeatability for both groups, with the indication of a small learning effect for subjects with coarse stereopsis. Thus, assessment of all target groups for new tests is important, and repeated testing before therapy may avoid confusing learning and treatment effects. Our digital approach supplies a large range of accurate stereo data in children and adults; together with its associated measure of variability, it will be useful in longitudinal treatment studies.

Increased Noise in Cortico-Cortical Integration After Mild TBI Measured With the Equivalent Noise Technique.

The bulk of deficits accompanying mild traumatic brain injury (mTBI) is understood in terms of cortical integration-mnemonic, attentional, and cognitive disturbances are believed to involve integrative action across brain regions. Independent of integrative disturbances, mTBI may increase cortical noise, and this has not been previously considered. High-level integrative deficits are exceedingly difficult to measure and model, motivating us to utilize a tightly-controlled task within an established quantitative model to separately estimate internal noise and integration efficiency. First, we utilized a contour integration task modeled as a cortical-integration process involving multiple adjacent cortical columns in early visual areas. Second, we estimated internal noise and integration efficiency using the linear amplifier model (LAM). Fifty-seven mTBI patients and 24 normal controls performed a 4AFC task where they had to identify a valid contour amongst three invalid contours. Thresholds for contour amplitude were measured adaptively across three levels of added external orientation noise. Using the LAM, we found that mTBI increased internal noise without affecting integration efficiency. mTBI also caused hemifield bias differences, and efficiency was related to a change of visual habits. Using a controlled task reflecting cortical integration within the equivalent noise framework empowered us to detect increased computational noise that may be at the heart of mTBI deficits. Our approach is highly sensitive and translatable to rehabilitative efforts for the mTBI population, while also implicating a novel hypothesis of mTBI effects on basic visual processing-namely that cortical integration is maintained at the cost of increased internal noise.

Ocular dominance plasticity: A binocular combination task finds no cumulative effect with repeated patching.

Short-term monocular deprivation strengthens the contribution of the deprived eye to binocular vision. This change has been observed in adults with normal vision or amblyopia. The change in ocular dominance is transient and recovers over approximately one hour. This shift has been measured with various visual tasks, including binocular rivalry and binocular combination. We investigated whether the ocular dominance shift could be accumulated across multiple periods of monocular deprivation over consecutive days. We used a binocular phase combination task to measure the shift in eye dominance. We patched the dominant eye of ten adults with normal vision for two hours across five consecutive days. Our results show no cumulative effect after repeated sessions of short-term monocular deprivation.

Visual plasticity and exercise revisited: No evidence for a "cycling lane".

Experiments using enriched environments have shown that physical exercise modulates visual plasticity in rodents. A recent study (Lunghi & Sale, 2015) investigated whether exercise also affects visual plasticity in adult humans. The plastic effect they measured was the shift in ocular dominance caused by 2 hr of monocular deprivation (e.g., by an eye patch). They used a binocular rivalry task to measure this shift. They found that the magnitude of the shift was increased by exercise during the deprivation period. This effect of exercise was later disputed by a study that used a different behavioral task (Zhou, Reynaud, & Hess, 2017). Our goal was to determine whether the difference in task was responsible for that study's failure to find an exercise effect. We set out to replicate Lunghi and Sale (2015). We measured ocular dominance with a rivalry task before and after 2 hr of deprivation. We measured data from two conditions in 30 subjects. On two separate days, they either performed exercise or rested during the deprivation period. Contrary to the previous study, we find no significant effect of exercise. We hypothesize that exercise may affect rivalry dynamics in a way that interacts with the measurement of the deprivation effect.

Cholinergic Potentiation Alters Perceptual Eye Dominance Plasticity Induced by a Few Hours of Monocular Patching in Adults.

A few hours of monocular deprivation with a diffuser eye patch temporarily strengthens the contribution of the deprived eye to binocular vision. This shift in favor of the deprived eye is characterized as a form of adult visual plasticity. Studies in animal and human models suggest that neuromodulators can enhance adult brain plasticity in general. Specifically, acetylcholine has been shown to improve certain aspects of visual function and plasticity in adulthood. We investigated whether a single administration of donepezil (a cholinesterase inhibitor) could further augment the temporary shift in perceptual eye dominance that occurs after 2 h of monocular patching. Twelve healthy adults completed two experimental sessions while taking either donepezil (5 mg, oral) or a placebo (lactose) pill. We measured perceptual eye dominance using a binocular phase combination task before and after 2 h of monocular deprivation with a diffuser eye patch. Participants in both groups demonstrated a significant shift in favor of the patched eye after monocular deprivation, however our results indicate that donepezil significantly reduces the magnitude and duration of the shift. We also investigated the possibility that donepezil reduces the amount of time needed to observe a shift in perceptual eye dominance relative to placebo control. For this experiment, seven subjects completed two sessions where we reduced the duration of deprivation to 1 h. Donepezil reduces the magnitude and duration of the patching-induced shift in perceptual eye dominance in this experiment as well. To verify whether the effects we observed using the binocular phase combination task were also observable in a different measure of sensory eye dominance, six subjects completed an identical experiment using a binocular rivalry task. These results also indicate that cholinergic enhancement impedes the shift that results from short-term deprivation. In summary, our study demonstrates that enhanced cholinergic potentiation interferes with the consolidation of the perceptual eye dominance plasticity induced by several hours of monocular deprivation.

The shift in ocular dominance from short-term monocular deprivation exhibits no dependence on duration of deprivation.

Deprivation of visual information from one eye for a 120-minute period in normal adults results in a temporary strengthening of the patched eye's contribution to binocular vision. This plasticity for ocular dominance in adults has been demonstrated by binocular rivalry as well as binocular fusion tasks. Here, we investigate how its dynamics depend on the duration of the monocular deprivation. Using a binocular combination task, we measure the magnitude and recovery of ocular dominance change after durations of monocular deprivation ranging from 15 to 300 minutes. Surprisingly, our results show that the dynamics are of an all-or-none form. There was virtually no significant dependence on the duration of the initial deprivation.