Altered Perception of the Bistable Motion Quartet in Albinism

Abstract

Purpose: Perception of the motion quartet (MQ) alternates between horizontal and vertical motion, with a bias toward vertical motion. This vertical bias has been explained by the dominance of intrahemispheric processing. In albinism, each hemisphere receives input from both visual hemifields owing to enhanced crossing of the optic nerves at the optic chiasm. This might affect the perception of the ambiguous MQ and particularly the vertical bias.

Methods: The effect of optic nerve misrouting in persons with albinism and nystagmus (PWA, n = 14) on motion perception for MQ was compared with healthy controls (HC; n = 11) and with persons with nystagmus in the absence of optic nerve misrouting (PWN; n = 12). We varied the ratio of horizontal and vertical distances of MQ dots (aspect ratio [AR]) between 0.75 and 1.25 and compared the percentages of horizontal and vertical motion percepts as a function of AR between groups.

Results: For HC, the probability of vertical motion perception increased as a sigmoid function with increasing AR exhibiting the expected vertical percept bias (mean, 58%; median, 54%; vertical motion percepts). PWA showed a surprisingly strong horizontal bias independent of the AR with a mean of 11% (median, 10%) vertical motion percepts. The PWN was in between PWA and HC, with a mean of 34% (median, 47%) vertical perception. Nystagmus alone is unlikely to explain this pattern of results because PWA and PWN had comparable fixation stabilities.

Conclusions: The strong horizontal bias observed in PWA and PWN might partly result from the horizontal nystagmus. The even stronger horizontal bias in PWA indicates that the intrahemispherical corepresentation of both visual hemifields may play an additional role. The altered perception of the MQ in PWA opens opportunities to (i) understand the interplay of stability and plasticity in altered visual pathway conditions and (ii) identify visual pathway abnormalities with a perception-based test using the MQ.

Normally, the line of decussation separating the retinal ganglion cells that project to the contralateral hemisphere from those that project to the ipsilateral hemisphere coincides with the fovea. In human albinism, the line of decussation is, on average, shifted by 8° into the temporal retina.^1,2 As a consequence, for the corresponding visual field (VF) portion, the primary visual cortex (V1) does not comprise the usual binocular retinotopic maps of the contralateral VF. Instead, it receives input from both VFs. Specifically, it comprises, in addition to the normal map of the contralateral visual hemifield, a map of the ipsilateral hemifield. In persons with albinism (PWA), the atypically routed ipsilateral and the typically routed contralateral representations are organized as retinotopic overlays, such that VF positions that are mirror symmetrical along the vertical meridian are represented in close cortical vicinity to each other.^3,4 

The visual system abnormality in albinism clearly affects visual function, including loss of binocular vision, nystagmus, and reduced visual acuity. In contrast, the abnormal ipsilateral VF representation is made available for visual perception, indicating developmental plasticity in the albinotic visual system.⁵ Importantly, such plasticity is mandatory to avoid that sensory conflicts arise from the representation abnormality in albinism. Normally, the information held in the ocular dominance columns is integrated to yield stereovision. However, the integration of the information across the corresponding hemifield columns in albinism would give rise to a major sensory conflict. The cells receiving the integrated information would have bilateral receptive fields arranged mirror symmetrically along the central vertical meridian. This would predict facilitating the interaction of visual information across the visual hemifields and has been addressed for the cross-talk of visual adaptation. Interestingly, for the example of orientation adaptation (tilt aftereffect) no cross-talk between hemifields has been reported,⁶ which indicates that the input from both hemifields is processed separately in albinism, at least for V1-dominated pattern processing. Facilitated interaction of visual information across the visual hemifields, however, might take action at higher visual areas of PWA, which tend to have receptive fields that partly also include the ipsilateral VF, even in healthy controls (HC). To address these higher areas, we investigated interhemifield interactions in visual motion perception, as motion perception engages a greater network of visual areas including those with ipsilateral representations in HC (e.g., the human middle temporal visual area (MT) + complex). 

In bistable motion perception, ambiguous sensory information is presented such that two perceptual states alternate, despite unchanged visual input, such as, von Schiller's ambiguous stroboscopic alternation motion, which is or alternatively called the “apparent motion quartet” stimulus (MQ).^7–9 This presentation of a single stimulus resulting in two alternating perceptual states (bistable perception) might provide leverage for the investigation of the neural processes that determine how persons perceive the world from fragmentary or ambiguous information.^10–12 The MQ consists of two pairs of dots located on the diagonal corners of an imaginary rectangle, which alternatively appear and disappear. It is perceived as two dots moving either horizontally or vertically—in opposite directions—as a function of the ratio between horizontal and vertical dot distances (aspect ratio [AR]). At an AR of 1 (the dots form a square), perception should be ambiguous, alternating spontaneously between horizontal and vertical motion.^13,14 However, previous studies indicate a vertical bias, that is, a prevalence of the perception for vertical motion.^13–15 This perceptual asymmetry for the square version of the MQ is assumed to be due to the perception of horizontal motion requiring integration across hemispheres, whereas perception of vertical motion requires only intrahemispheric processing (interhemispheric integration hypothesis).^13–15 This process prompts albinism on the stage, as here, the representations of the ipsilateral and contralateral visual hemifields are organized as retinotopic overlays in each hemisphere, such that VF positions that are mirror symmetrical along the vertical meridian are represented in close cortical vicinity to each other.^3,4 

As a consequence, no or less interhemispheric integration might be required for a horizontal motion percept in albinism. If plastic mechanisms give enough room for an interaction of both hemifield representations, horizontal motion perception might be more frequent in PWA than in HC. Taken together, the intrahemispherical corepresentation of both visual hemifields should be expected to lead to a decreased or even eliminated vertical bias in albinism, if (a) interhemispherical connections are the limiting factor and (b) intracortical plastic mechanisms in albinism provide sufficient scope for a meaningful interaction of the two hemifields. 

Methods

This study was conducted at the ophthalmology department of the Otto-von-Guericke University after approval from the Otto-von-Guericke University ethical committee adhering to the tenets of the declaration of Helsinki. Written informed consent was obtained from all participants. 

Participants

All participants received a complete ophthalmological examination and were classified into three groups. 

• (i) Albinism (PWA; n = 14; 7 female; mean age, 39.4 years): Participants with an established albinism diagnosis.^16,17 Optic nerve misrouting was confirmed using visual evoked potentials (VEPs).
• (ii) Nystagmus (PWN; n = 12; 6 female; mean age, 36.3 years): Participants with either infantile (n = 9) or acquired nystagmus (n = 3); absence of optic nerve misrouting was confirmed using VEPs (misrouting-VEP, Hoffmann et al.²).
• (iii) HC (n = 11; 6 female; mean age, 44.5 years): Participants with best-corrected visual acuity (BCVA) of ≤0.0 logMAR and no eye diseases were included.

Participants with other neurological diseases unrelated to nystagmus, any retinal diseases affecting the measurements, such as diabetic retinopathy, or any other eye diseases were excluded from the study. Only one eye per subject was included for data acquisition and data analysis (Table 1). All participants had corrections for refractive errors at the tested distance. To rule out the confound effect of astigmatism (usually around the 0° axis) on motion perception and probable distortion effects on the dot pairs, vertical motion perception was compared between albinism patients with high versus low astigmatism. Both groups had nonsignificant differences of vertical motion perception (mean ± SD of vertical percept for high vs. low astigmatism: 9.4 ± 8.9% vs. 15.9 ± 17.4%; P = 0.4). 

Table 1.

 

Participants Characteristics

 

Fixation Stability Assessment

Fixation stability of participants was quantified with a fundus-controlled microperimeter (MP-1 Microperimeter, Nidek, Padua, Italy). The participants were instructed to fixate a central fixation target and retinal fixation locations were tracked for 30 seconds at 25 Hz. Subsequently, the percentage of fixations within the central 2° and 4° radius were determined via a built-in feature of the MP-1 microperimeter. 

Misrouting VEP

The EP2000 Evoked potentials system¹⁸ was used to record conventional pattern-pulse VEPs to a checkerboard stimulus (stimulus contrast, 98%; check sizes, 0.5°, 1.0°, and 2.0°) for each eye separately following Hoffmann et al.^19,20 For the subsequent analyses, the VEP differences were determined between VEP traces recorded for electrode sites at opposing hemispheres (interhemispheric VEP difference traces). The correlation coefficient of the interhemispheric VEP difference traces between the two eyes was determined (interocular correlation coefficient). The interocular correlation-coefficients range between positive and negative values (+1 and −1), indicating more normal (i.e., partial) and abnormal (i.e. enhanced) optic nerve crossing, respectively. 

Perception of the Bistable MQ

Rationale

MQ stimulus is composed of two white (200 cd/m²), pairs of dots (width and height = 3°) alternating at the diagonal corners of an imaginary rectangle on a dark background (0.40 cd/m²), as depicted in the schematic given in Figure 1. The observers perceived the MQ as two dots moving forward and backward in opposite directions. The perceived motion direction changes from horizontal to vertical as a function of the ratio between horizontal and vertical dot distances (AR = horizontal/vertical point distance), with an AR of less than 1 biasing motion perception to horizontal and an AR of greater than 1 to vertical motion perception. At an AR of 1, perception should be ambiguous, alternating spontaneously between horizontal and vertical motion. 

Figure 1.

 

Testing paradigm of motion perception for the MQ display. (A) Schematic of the test sequence and (B) percepts to be reported. See Methods for details and Supplementary Table S1 for the specific geometry of the stimuli including the different ARs applied. The red dashed rectangle indicates one observation sequence.

Stimuli and Experimental Paradigm

In the present study, we presented the MQ with nine different ARs (see Supplementary Table S1) in a randomized order using PsychoPy v1.83.04 at a viewing distance of 114cm. Each of the 9 different MQ variants was presented 20 times. To estimate the deviation of motion direction percepts from symmetry around an AR of 1, the analysis and statistics were based 6 ARs arranged symmetrically around an AR of 1.00: 0.75, 0.85, and 0.95 versus 1.05, 1.15, and 1.25. An experimental observation sequence started by presenting one pair of dots positioned at opposing diagonal corners of an imaginary rectangle for 150 ms, followed the second pair of dots at the remaining diagonal corners also for 150 ms. The observation sequence ends with a blank screen presentation for 1500 ms, during which the participant indicated via key press whether the motion was perceived in a horizontal or in vertical direction. Within an observation sequence, the ARs stayed unchanged, but changed from one observation sequence to the next. One measurement block comprised nine observation sequences with nine MQ, with different ARs respectively, presented in random order. Participants had to execute 20 repetitions of such a measurement block. The experiment was executed with two different conditions. In one condition, the different ARs were realized by varying the horizontal dot distance, while keeping the vertical distance constant, termed the “vertical distance constant,” and vice versa, termed the “horizontal distance constant.” During the experiment, participants were instructed to fixate at a central fixation target, while they viewed the presentation of the succession of the two dot pairs. Between the measurement blocks, a dialog box was presented explaining the key assignments to the two possible motion directions. The start of each measurement block was self-paced by the participant, allowing to introduce beaks when needed. Before MQ measurements, participants were familiarized with horizontal and vertical motion percepts in a practice trial. 

Statistics

We fit a generalized logistic regression model with a binomial error distribution and logit link using maximum likelihood estimation to predict the perceived motion in each individual. These models included random effects on the intercept to account for the multiple responses within individuals. Fixed effects or predictor variables included group, AR (with a focus on six of nine different ARs), and condition (direction of constant dot distance either vertical or horizontal). To determine whether an interaction model might be better incorporated in the analysis, sequential interactions were added to the main effects model retaining all factors. The Akaike information criterion (AIC) was used to compare between models; a lower AIC indicates better goodness fit and a less complex model.^21,22 

Here, only Group × AR interaction significantly improved the goodness of fit of the model with AIK (6880.8) in comparison with the fixed effects only model (AIC = 7014.5), χ² (10) = 153.7, P < 0.001. A three-way interaction model minimized the AIC (6894.4) in comparison with the fixed effects only model and was selected owing to the best combination of goodness of fit and complexity, χ² (27) = 174.13, P < 0.001. The effects of different factors and their interaction on motion perception was evaluated by likelihood ratio tests based on type III sum of squares tests. Post hoc analyses for contrasts were conducted for the significant effects indicated by the model using emmeans package in R²³ and odds ratio were calculated accordingly for contrasts of interests. 

For continuous variables, parametric or nonparametric tests were conducted, based on normality Shapiro–Wilk tests, to summarize differences and characteristics between groups. For the response variable of motion perception, the percentage of vertical motion perception relative to all responses for each individual was calculated. Arcsine transformation of these percentages allowed a normal distribution assumption of data and parametric testing:²⁴ 

\begin{eqnarray*} && \;{\rm{arcsine\;transformation\;}}\left( {{\rm{Vertical\;response}}} \right) \nonumber \\ && = {\sin ^{ - 1}}\sqrt {Vertical\;response\left[ \% \right]/100} .\end{eqnarray*}

 

The means and medians of proportions for each participant group were also reported and compared between groups. Vertical response proportions were also correlated with other functional measures using Spearman rho (ρ) correlations. P values were corrected after Holm²⁵ for multiple comparisons/tests. All analysis were conducted in R.²⁶ 

Results

In Figure 2, the percentage of vertical motion percepts in the MQ is depicted as a function of AR (AR = dot – distance_Horizontal/dot – distance_Vertical). For all groups, the percentage of vertical motion percepts increased with increasing AR—that is, the greater the horizontal dot distance (or smaller the vertical dot distance), the higher the frequency of vertical motion percepts. Only for the HC group the probability of vertical motion percepts eventually exceeded that of horizontal motion percepts. Importantly, in HC the frequency of vertical motion percepts of 50% or greater was reached already for an AR of less than 1.0, which is termed vertical bias (see Introduction). Remarkably, we did observe this well-known vertical bias only for HC. In clear contrast, for PWN and PWA we found a strong horizontal bias, that is, the mean percentage of vertical percepts of the total presented trials was 34% (median, 47%) and 11% (median, 10%, in contrast with 58% (median, 54%) for HC. For the PWN and PWA groups, the frequency of vertical motion percepts failed to exceed 50% for any of the used ARs, even for the largest AR of 1.25. The strong dominance of the horizontal motion percepts was clearly visible in PWN, but it was most pronounced for PWA. This pattern of findings was observed for both experimental conditions, the vertical distance constant and the horizontal distance constant. 

Figure 2.

 

Results of the generalized linear mixed-effect binary logistic regression model displaying the predicted probabilities (mean ± SEM) of vertical motion perception across varied AR and two different ways to vary the AR (vertical or horizontal dot distance constant). Red (horizontal) dashed line indicates chance level, black (vertical) dotted line indicates equal vertical and horizontal dot distances of the MQ stimulus, AR = 1. Larger than 50% vertical motion percepts at AR = 1 in the HC group indicates the vertical bias of the MQ, as known from the literature. In contrast, a strong bias toward horizontal motion percepts can be observed in the two patient groups. Analysis and statistics were based on only 6 (out of 9) horizontal/vertical AR around 1: 0.75–1.25. Data points not included in the analysis (AR 0.45–0.65) are grayed out.

In fact, the vertical bias decreased for both conditions from HC to PWN down to PWA, where we observed a distinct horizontal bias instead. This qualitative account (see Fig. 2 for generalized linear mixed-effect binary logistic regression model and Supplementary Fig. S1 for raw data) is corroborated by the statistical analysis, which comprised an analysis of variance with a generalized linear binary logistic regression mixed model (see Methods). As detailed in Table 2, there was a significant effect of group and AR, and importantly an interaction of both, that is, the probability of perceiving vertical motion differs in a differential manner between the participant groups and for the different ARs. This is further supported by post hoc tests for the different ARs that demonstrated significant differences between the different groups as detailed in Table 3. It should be noted that the two patient groups, PWN and PWA, not only differed from the controls, but also, for all ARs tested, from each other. The PWN versus PWA difference is also evident for responses collapsed across AR (0.75–1.25). This finding is further visualized in Figure 3, depicting the overall median proportions of the percentage of the mean vertical motion perception to be 58% (median, 54%), 34% (median, 47%), and 11 (median, 10%), for HC, PWN, and PWA, respectively. It appears, therefore, that (i) nystagmus (PWN and PWA) decreases the frequency of vertical motion percepts and that (ii) there is a further reduction for PWA compared with PWN. 

Table 2.

 

Analysis of Variance of Generalized Linear Binary Logistic Regression Mixed Model

 

Table 3.

 

Results of Generalized Mixed-effect Binary Logistic Regression Model, Comparing the Odds in Different Groups of Perceiving a Vertical Motion Across Varied Dot ARs

 

Figure 3.

 

Comparison of percentage of vertical motion perception averaged for each subject across all trials. ω², partial omega squared effect size; CI, confidence interval. The median value is given with untransformed % tag. Analysis and statistics were based on only six horizontal/vertical AR around 1: 0.75–1.25. Small filled circles indicate individual data points. The large filled circles indicate within-group means.

To test whether this finding might be related to stronger nystagmus in PWA than in PWN, we tested whether fixation instabilities differed between the two groups. Across 35 participants, Kruskal–Wallis test (P < 0.001) showed only significant differences between HC versus PWA and HC versus PWN with a median proportion of fixation within 2° (4°): 100% (100%) versus 49% (87.5%) and 66% (90.5%), respectively (P < 0.01) (see Table 4). This finding affirms that the driving force of any distinctive motion percept of PWA might not be related to the fixation instability. To probe this idea further, two raters inspected the pattern of gaze directions on MP-1 perimetry printouts, owing to the absence of a detailed quantitative output. Based on the microperimetry fixation examination, fixation location patterns were inspected, where the raters had to decide whether most of points lie central or laterally displaced from fovea. Subsequently, for each patient group, the motion percept for those fixating laterally versus centrally was compared with identified lateralization of fixation as a possible mechanism to explain differences in motion perception. In fact, the laterally versus centrally fixating subjects had a comparable vertical motion percept of 47.4% (n = 3) versus 45.9% (n = 9) for PWN and 4.8% (n = 2) versus 10.6% (n = 10) for PWA. Taken together, compared with the main effects, the effect of gaze lateralization seemed to be negligible. 

Table 4.

 

Differences of Visual Readouts Between Groups

 

Because the degree of nystagmus-induced fixation instability did not differ between PWN and PWA, it seems that other factors distinguishing these two patient groups were driving the further decrease of vertical motion perception in PWA. Consequently, candidate factors, which are potentially related to altered perception of the bistable MQ in albinism, are BCVA, fixation stability, and optic nerve misrouting. We assessed this via correlation analyses that included all three participant groups. Higher fixation stability within 4° correlated significantly with higher proportions of vertical motion perception (ρ = –0.52; P < 0.001). There was also a correlation of better BCVA estimates with vertical motion perception, which might, at least partly, be due to its association with fixation instability. The optic nerve misrouting index, that is, VEP coefficients of interocular correlations, was also significantly correlated with the median frequency of the vertical motion percept (ρ = 0.60; P < 0.001) (see Fig. 4). 

Figure 4.

 

Correlation between vertical motion perception and the VEP-based optic nerve misrouting index of checksize 0.5° (interocular correlation of the interhemispheric VEP difference detailed in Methods). Dashed line indicates cutoff for misrouting versus no-misrouting coefficients (<0.0 [left], misrouting; >0.0 [right], no misrouting). Black regression line (behind gray dashed) and its confidence interval are shown for the VEP checksize 0.5°. For comparison purposes, dark gray dashed line for VEP checksize 1.0° and dotted line for VEP checksize 2° are also shown in the figure.

PWA demonstrated indeed distinct functional and structural readouts of vision compared with PWN and HC. BCVA, a surrogate measure of visual function, was lowest in PWA versus PWN and HC (0.65 logMAR vs. 0.1 and –0.07 logMAR; P < 0.01). 

Discussion

This study investigated whether PWA had distinctive patterns of motion perception using bistable motion stimulus, that is, MQ, and the possible underlying physiological mechanisms. As per the literature, HC were biased toward vertical motion perception. In contrast, for the patient groups, we found a pronounced bias toward horizontal motion percepts, which was strongest in the PWA group and weaker in the PWN group, despite comparable fixation instabilities in both groups. This finding is taken as evidence for specifically altered perception of bistable motion in the albinotic visual system. 

Group Differences in the Horizontal Bias

The bistable perception of stroboscopic alternation motion, where a single sensory stimulus might result in two percepts, represents a simple psychophysical experiment, but provides nuanced and valuable insights about cognitive and perceptual processes.^27,28 Previous studies using MQ indicated that the vertical bias seen in HC might be related to the efficient intrahemispheric processing of vertical motion compared with more demanding interhemispheric processing during horizontal motion perception.^13–15,29 In addition to the behavioral evidence, this result was further supported, for example, by magnetic resonance imaging^29,30 and electrophysiological studies.¹⁵ Indeed, Genç et al.²⁹ indicated that the microstructural integrity of callosal pathways between motion centers (human motion complex) was predictive of MQ bias in HC. In PWA, enhanced crossing of optic nerve fibers at the optic chiasm results in a mirror symmetrical overlay of opposing visual hemifields.^3,5 As a consequence, in PWA relating activations from horizontally mirror symmetrical visual locations does not require interhemispheric transfer. This factor is a likely cause of the horizontal MQ bias observed in PWA. The presence of horizontal bias, albeit to a lesser extent, in PWN warrants further investigation into other associated driving forces of nystagmus. 

Relation of Horizontal Bias to Fixation Instability, Visual Acuity, and Misrouting Coefficient

The horizontal bias was not only strongest for the PWA group, but also correlated most strongly with measures that are specifically affected in PWA, such as misrouting VEP index and BCVA, owing to optic nerve misrouting and foveal hypoplasia in PWA. This finding supports the view that visual system abnormalities typical for albinism enhance the horizontal bias. Another trait that is known to influence motion perception is fixation instability that was evident in both PWA and PWN. Previous studies, for example, have demonstrated abnormal motion detection and higher discrimination thresholds in individuals with abnormal eye movement (i.e., nystagmus).^31,32 However, this finding is unlikely to explain the stronger horizontal bias in PWA versus PWN, as the observed fixation instabilities were comparable between the two patient groups and we did not observe a correlation of horizontal bias with fixation instability. In this regard, further inspection of fixation preferences of the microperimetry fixation statistics did not reveal any notable differences of gaze lateralization in both groups. In line with this finding, previous research puts the role of eye movements for perceptual alternations of ambiguous figures into perspective, as perceptual alternations still takes place during fixated gaze (e.g., Zhou et al.³³). Yet, the nature of nystagmus behavior in PWA versus PWN might play a role in driving differences in MQ perception. In this context, it was shown that the frequency of nystagmus was significantly lower in PWA than PWN (3.3 Hz vs. 4.3 Hz,³⁴ respectively), a potentially plausible mechanism for MQ perception warranting further investigations in future studies. 

Relevance of MQ Findings for Albinism Research

Previous magnetic resonance imaging studies in albinism demonstrated abnormal processing at lower and higher motion-related visual brain areas in PWA. For example, visual motion areas and superior colliculus were reported to be activated during stationary stimuli presentation,³⁵ in the absence of conscious perception of oscillopsia. The horizontal bias to MQ observed in PWA might also relate to abnormalities in areas driving MQ perception,^30,36 which overlap with the abovementioned areas. Specifically, the horizontal bias in PWA might indicate a stronger interaction between visual hemifields than normal owing to the superimposed cortical representations of opposing visual hemifields in PWA. Previously, we did not find evidence for such an interhemifield crosstalk of visual processing for orientation adaptation (tilt aftereffect: after perception of a patch of lines rotated away from cardinals axis, another patch of lines at the cardinal axis, presented afterward, would seem to be rotated in the opposition direction)⁶ believed to manifest in early visual areas, such as V1. Consequently, such an increased interaction between visual hemifields might be reserved to higher visual areas, such as those specialized for motion processing, like the human MT–complex. Clearly, the observed bias to horizontal motion perception in PWA warrants further investigation. Functional magnetic resonance imaging–based localizations of the involved networks in the processing of the MQ stimulus are of promise to contribute to our understanding of the related changes to motion perception in albinism. 

Limitations and Outlook

At present, we cannot be certain about the mechanism by which nystagmus affects the perception of ambiguous motion in the two patient groups investigated (i.e., PWA and PWN) or about the exact nature of the differences between them. The difference between horizonal and vertical motion perception in the different groups are likely related to an interplay of (i) the nystagmus-related (predominantly horizontal) retinal image shift and (ii) the different postretinal VF representations in the patient groups. The exact mechanisms cannot be identified at present. Future studies that allow determining the exact location of the stimuli in the VF and their cortical representations in patients with nystagmus might provide a key to resolve this issue. Such studies might include approaches that provide detailed characterizations of the individual nystagmus patterns, stimulus locked eye tracking, fundus-controlled stimulation, and/or functional magnetic resonance imaging monitoring of the cortical representations of the presented stimuli. Further, it is not clear, whether our finding of a horizontal bias in albinism can be generalized to other patient groups where opposing hemifields are corepresented on the same hemisphere (i.e., achiasma).^5,37,38 

Conclusions

We report the frequency of horizontal motion percepts for an ambiguous motion stimulus to increase steadily from controls to participants with nystagmus (PWN) and eventually participants with albinism (PWA). This increase is likely related to an interplay of nystagmus (PWN and PWA) and abnormal VF representations in PWA. The large effect sizes of our findings stimulate future research detailing the relevance of nystagmus and the involved cortical networks in PWA, PWN, and HC for motion perception in ambiguous stimuli. 

Acknowledgments

Supported by funding of the German Research Foundation (DFG; #655841) to MBH (HO-2002/10-3). 

This work was presented as a poster presentation at the society of neuroscience (SFN) meeting 2023. 

Disclosure: K.O. Al-Nosairy, None; E.V. Quanz, None; C.M. Eick, None; M.B. Hoffmann, None; J. Kornmeier, None