Early Binocular Input Is Critical for Development of Audiovisual but Not Visuotactile Simultaneity Perception

Altered development of face recognition among infants born amid the COVID-19 pandemic

To effectively contain the spread of COVID-19, public health agencies mandated special regulations. Although they protected us from COVID-19, these restrictions have inevitably changed the environment around us. It remains unclear how these changes may have affected early cognitive development among infants born during the pandemic. Thus, this study examined how the COVID-19 restrictions have affected infants' face recognition ability, a hallmark of their cognitive capacities. Specifically, we used the familiarization and visual pair comparison paradigm to examine face recognition performance among infants aged 6 to 14 months amid the second wave of the pandemic (February to July 2021). Experiment 1 investigated the recognition of unmasked faces and found that only younger infants, but not older infants, recognized faces by showing a novelty preference. Experiment 2 examined the recognition of faces wearing masks and found that only older infants, but not younger ones, recognized faces by exhibiting a familiarity preference. These results suggest that with limited interactions during the pandemic, infants could have developed an overly specialized face processing ability that failed to recognize the faces of strangers. Moreover, infants could have obtained more information on masked faces during the pandemic and adapted to the current situation. In Expreiment 3, we further confirmed the restriction on infants' interpersonal experiences with a survey conducted both before and during the pandemic. Overall, these findings demonstrated how the pandemic altered early perceptual development and further confirmed that interpersonal experiences during infancy are critical in their cognitive development.

Synchrony perception across senses: A systematic review of temporal binding window changes from infancy to adolescence in typical and atypical development

Sensory integration is increasingly acknowledged as being crucial for the development of cognitive and social abilities. However, its developmental trajectory is still little understood. This systematic review delves into the topic by investigating the literature about the developmental changes from infancy through adolescence of the Temporal Binding Window (TBW) - the epoch of time within which sensory inputs are perceived as simultaneous and therefore integrated. Following comprehensive searches across PubMed, Elsevier, and PsycInfo databases, only experimental, behavioral, English-language, peer-reviewed studies on multisensory temporal processing in 0-17-year-olds have been included. Non-behavioral, non-multisensory, and non-human studies have been excluded as those that did not directly focus on the TBW. The selection process was independently performed by two Authors. The 39 selected studies involved 2859 participants in total. Findings indicate a predisposition towards cross-modal asynchrony sensitivity and a composite, still unclear, developmental trajectory, with atypical development associated to increased asynchrony tolerance. These results highlight the need for consistent and thorough research into TBW development to inform potential interventions.

The fusion point of temporal binding: Promises and perils of multisensory accounts

Performing an action to initiate a consequence in the environment triggers the perceptual illusion of temporal binding. This phenomenon entails that actions and following effects are perceived to occur closer in time than they do outside the action-effect relationship. Here we ask whether temporal binding can be explained in terms of multisensory integration, by assuming either multisensory fusion or partial integration of the two events. We gathered two datasets featuring a wide range of action-effect delays as a key factor influencing integration. We then tested the fit of a computational model for multisensory integration, the statistically optimal cue integration (SOCI) model. Indeed, qualitative aspects of the data on a group-level followed the principles of a multisensory account. By contrast, quantitative evidence from a comprehensive model evaluation indicated that temporal binding cannot be reduced to multisensory integration. Rather, multisensory integration should be seen as one of several component processes underlying temporal binding on an individual level.

Audiovisual simultaneity windows reflect temporal sensory uncertainty

The ability to judge the temporal alignment of visual and auditory information is a prerequisite for multisensory integration and segregation. However, each temporal measurement is subject to error. Thus, when judging whether a visual and auditory stimulus were presented simultaneously, observers must rely on a subjective decision boundary to distinguish between measurement error and truly misaligned audiovisual signals. Here, we tested whether these decision boundaries are relaxed with increasing temporal sensory uncertainty, i.e., whether participants make the same type of adjustment an ideal observer would make. Participants judged the simultaneity of audiovisual stimulus pairs with varying temporal offset, while being immersed in different virtual environments. To obtain estimates of participants' temporal sensory uncertainty and simultaneity criteria in each environment, an independent-channels model was fitted to their simultaneity judgments. In two experiments, participants' simultaneity decision boundaries were predicted by their temporal uncertainty, which varied unsystematically with the environment. Hence, observers used a flexibly updated estimate of their own audiovisual temporal uncertainty to establish subjective criteria of simultaneity. This finding implies that, under typical circumstances, audiovisual simultaneity windows reflect an observer's cross-modal temporal uncertainty.

Crossmodal plasticity following short-term monocular deprivation

A brief period of monocular deprivation (MD) induces short-term plasticity of the adult visual system. Whether MD elicits neural changes beyond visual processing is yet unclear. Here, we assessed the specific impact of MD on neural correlates of multisensory processes. Neural oscillations associated with visual and audio-visual processing were measured for both the deprived and the non-deprived eye. Results revealed that MD changed neural activities associated with visual and multisensory processes in an eye-specific manner. Selectively for the deprived eye, alpha synchronization was reduced within the first 150 ms of visual processing. Conversely, gamma activity was enhanced in response to audio-visual events only for the non-deprived eye within 100-300 ms after stimulus onset. The analysis of gamma responses to unisensory auditory events revealed that MD elicited a crossmodal upweight for the non-deprived eye. Distributed source modeling suggested that the right parietal cortex played a major role in neural effects induced by MD. Finally, visual and audio-visual processing alterations emerged for the induced component of the neural oscillations, indicating a prominent role of feedback connectivity. Results reveal the causal impact of MD on both unisensory (visual and auditory) and multisensory (audio-visual) processes and, their frequency-specific profiles. These findings support a model in which MD increases excitability to visual events for the deprived eye and audio-visual and auditory input for the non-deprived eye.

Noise-rearing precludes the behavioral benefits of multisensory integration

Concordant visual-auditory stimuli enhance the responses of individual superior colliculus (SC) neurons. This neuronal capacity for "multisensory integration" is not innate: it is acquired only after substantial cross-modal (e.g. auditory-visual) experience. Masking transient auditory cues by raising animals in omnidirectional sound ("noise-rearing") precludes their ability to obtain this experience and the ability of the SC to construct a normal multisensory (auditory-visual) transform. SC responses to combinations of concordant visual-auditory stimuli are depressed, rather than enhanced. The present experiments examined the behavioral consequence of this rearing condition in a simple detection/localization task. In the first experiment, the auditory component of the concordant cross-modal pair was novel, and only the visual stimulus was a target. In the second experiment, both component stimuli were targets. Noise-reared animals failed to show multisensory performance benefits in either experiment. These results reveal a close parallel between behavior and single neuron physiology in the multisensory deficits that are induced when noise disrupts early visual-auditory experience.

The development of audio-visual temporal precision precedes its rapid recalibration

Through development, multisensory systems reach a balance between stability and flexibility: the systems integrate optimally cross-modal signals from the same events, while remaining adaptive to environmental changes. Is continuous intersensory recalibration required to shape optimal integration mechanisms, or does multisensory integration develop prior to recalibration? Here, we examined the development of multisensory integration and rapid recalibration in the temporal domain by re-analyzing published datasets for audio-visual, audio-tactile, and visual-tactile combinations. Results showed that children reach an adult level of precision in audio-visual simultaneity perception and show the first sign of rapid recalibration at 9 years of age. In contrast, there was very weak rapid recalibration for other cross-modal combinations at all ages, even when adult levels of temporal precision had developed. Thus, the development of audio-visual rapid recalibration appears to require the maturation of temporal precision. It may serve to accommodate distance-dependent travel time differences between light and sound.

Calibrating Vision: Concepts and Questions

The idea that visual coding and perception are shaped by experience and adjust to changes in the environment or the observer is universally recognized as a cornerstone of visual processing, yet the functions and processes mediating these calibrations remain in many ways poorly understood. In this article we review a number of facets and issues surrounding the general notion of calibration, with a focus on plasticity within the encoding and representational stages of visual processing. These include how many types of calibrations there are - and how we decide; how plasticity for encoding is intertwined with other principles of sensory coding; how it is instantiated at the level of the dynamic networks mediating vision; how it varies with development or between individuals; and the factors that may limit the form or degree of the adjustments. Our goal is to give a small glimpse of an enormous and fundamental dimension of vision, and to point to some of the unresolved questions in our understanding of how and why ongoing calibrations are a pervasive and essential element of vision.

Compensation Mechanisms May Not Always Account for Enhanced Multisensory Illusion in Older Adults: Evidence from Sound-Induced Flash Illusion

Sound-induced flash illusion (SiFI) is typical auditory dominance phenomenon in multisensory illusion. Although a number of studies have explored the SiFI in terms of age-related effects, the reasons for the enhanced SiFI in older adults are still controversial. In the present study, older and younger adults with equal visual discrimination were selected to explore age differences in SiFI effects, and to explore the neural indicators by resting-state functional magnetic resonance imaging (rs-fMRI) signals. A correlation analysis was calculated to examine the relationship between regional homogeneity (ReHo) and the SiFI. The results showed that both younger and older adults experienced significant fission and fusion illusions, and fission illusions of older adults were greater than that of younger adults. In addition, our results showed ReHo values of the left middle frontal gyrus (MFG), the right inferior frontal gyrus (IFG) and right superior frontal gyrus (SFG) were significantly positively correlated with the SiFI in older adults. More importantly, the comparison between older and younger adults showed that ReHo values of the right superior temporal gyrus (STG) decreased in older adults, and this was independent of the SiFI. The results indicated that when there was no difference in unisensory ability, the enhancement of multisensory illusion in older adults may not always be explained by compensation mechanisms.

Critical Periods in Vision Revisited

For four decades, investigations of the biological basis of critical periods in the developing mammalian visual cortex were dominated by study of the consequences of altered early visual experience in cats and nonhuman primates. The neural deficits thus revealed also provided insight into the origin and neural basis of human amblyopia that in turn motivated additional studies of humans with abnormal early visual input. Recent human studies point to deficits arising from alterations in all visual cortical areas and even in nonvisual cortical regions. As the new human data accumulated in parallel with a near-complete shift toward the use of rodent animal models for the study of neural mechanisms, it is now essential to review the human data and the earlier animal data obtained from cats and monkeys to infer general conclusions and to optimize future choice of the most appropriate animal model. Expected final online publication date for the Annual Review of Vision Science, Volume 8 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Brief Postnatal Visual Deprivation Triggers Long-Lasting Interactive Structural and Functional Reorganization of the Human Cortex

Patients treated for bilateral congenital cataracts provide a unique model to test the role of early visual input in shaping the development of the human cortex. Previous studies showed that brief early visual deprivation triggers long-lasting changes in the human visual cortex. However, it remains unknown if such changes interact with the development of other parts of the cortex. With high-resolution structural and resting-state fMRI images, we found changes in cortical thickness within, but not limited to, the visual cortex in adult patients, who experienced transient visual deprivation early in life as a result of congenital cataracts. Importantly, the covariation of cortical thickness across regions was also altered in the patients. The areas with altered cortical thickness in patients also showed differences in functional connectivity between patients and normally sighted controls. Together, the current findings suggest an impact of early visual deprivation on the interactive development of the human cortex.

Multisensory spatial perception in visually impaired infants

Congenitally blind infants are not only deprived of visual input but also of visual influences on the intact senses. The important role that vision plays in the early development of multisensory spatial perception1, 2, 3, 4, 5, 6, 7 (e.g., in crossmodal calibration8, 9, 10 and in the formation of multisensory spatial representations of the body and the world^1,2) raises the possibility that impairments in spatial perception are at the heart of the wide range of difficulties that visually impaired infants show across spatial,8, 9, 10, 11, 12 motor,13, 14, 15, 16, 17 and social domains.^8,18,19 But investigations of early development are needed to clarify how visually impaired infants’ spatial hearing and touch support their emerging ability to make sense of their body and the outside world. We compared sighted (S) and severely visually impaired (SVI) infants’ responses to auditory and tactile stimuli presented on their hands. No statistically reliable differences in the direction or latency of responses to auditory stimuli emerged, but significant group differences emerged in responses to tactile and audiotactile stimuli. The visually impaired infants showed attenuated audiotactile spatial integration and interference, weighted more tactile than auditory cues when the two were presented in conflict, and showed a more limited influence of representations of the external layout of the body on tactile spatial perception.²⁰ These findings uncover a distinct phenotype of multisensory spatial perception in early postnatal visual deprivation. Importantly, evidence of audiotactile spatial integration in visually impaired infants, albeit to a lesser degree than in sighted infants, signals the potential of multisensory rehabilitation methods in early development.

Video abstract

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Visually impaired infants have a distinct phenotype of audiotactile perception

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Infants with severe visual impairment (SVI) place more weight on tactile locations

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SVI infants show attenuated audiotactile spatial integration and interference

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SVI infants do not show an influence of body representations on tactile space

The size-weight illusion is unimpaired in individuals with a history of congenital visual deprivation

Visual deprivation in childhood can lead to lifelong impairments in multisensory processing. Here, the Size-Weight Illusion (SWI) was used to test whether visuo-haptic integration recovers after early visual deprivation. Normally sighted individuals perceive larger objects to be lighter than smaller objects of the same weight. In Experiment 1, individuals treated for dense bilateral congenital cataracts (who had no patterned visual experience at birth), individuals treated for developmental cataracts (who had patterned visual experience at birth, but were visually impaired), congenitally blind individuals and normally sighted individuals had to rate the weight of manually explored cubes that differed in size (Small, Medium, Large) across two possible weights (350 g, 700 g). In Experiment 2, individuals treated for dense bilateral congenital cataracts were compared to sighted individuals in a similar task using a string set-up, which removed haptic size cues. In both experiments, indistinguishable SWI effects were observed across all groups. These results provide evidence that early aberrant vision does not interfere with the development of the SWI, and suggest a recovery of the integration of size and weight cues provided by the visual and haptic modality.

Binocular Enhancement of Multisensory Temporal Perception

Purpose

The goal of this study was to examine the behavioral effects and to suggest possible underlying mechanisms of binocularity on audiovisual temporal perception in normally-sighted individuals.

Methods

Participants performed two audiovisual simultaneity judgment tasks-one using simple flashes and beeps and the other using audiovisual speech stimuli-with the left eye, right eye, and both eyes. Two measures, the point of subjective simultaneity (PSS) and the temporal binding window (TBW), an index for audiovisual temporal acuity, were derived for each viewing condition, stimulus type, and participant. The data were then modeled using causal inference, allowing us to determine whether binocularity affected low-level unisensory mechanisms (i.e., sensory noise level) or high-level multisensory mechanisms (i.e., prior probability of interring a common cause, pC=1).

Results

Whereas for the PSS there was no significant effect of viewing condition, for the TBW, a significant interaction between stimulus type and viewing condition was found. Post hoc analyses revealed a significantly narrower TBW during binocular than monocular viewing (average of left and right eyes) for the flash-beep condition but no difference between the viewing conditions for the speech stimuli. Modeling results showed no significant difference in pC=1 but a significant reduction in sensory noise during binocular performance on flash-beep trials.

Conclusions

Binocular viewing was found to enhance audiovisual temporal acuity as indexed by the TBW for simple low-level audiovisual stimuli. Furthermore, modeling results suggest that this effect may stem from enhanced sensory representations evidenced as a reduction in sensory noise affecting the measurement of physical asynchrony during audiovisual temporal perception.

Brief period of monocular deprivation drives changes in audiovisual temporal perception

The human brain retains a striking degree of plasticity into adulthood. Recent studies have demonstrated that a short period of altered visual experience (via monocular deprivation) can change the dynamics of binocular rivalry in favor of the deprived eye, a compensatory action thought to be mediated by an upregulation of cortical gain control mechanisms. Here, we sought to better understand the impact of monocular deprivation on multisensory abilities, specifically examining audiovisual temporal perception. Using an audiovisual simultaneity judgment task, we discovered that 90 minutes of monocular deprivation produced opposing effects on the temporal binding window depending on the eye used in the task. Thus, in those who performed the task with their deprived eye there was a narrowing of the temporal binding window, whereas in those performing the task with their nondeprived eye there was a widening of the temporal binding window. The effect was short lived, being observed only in the first 10 minutes of postdeprivation testing. These findings indicate that changes in visual experience in the adult can rapidly impact multisensory perceptual processes, a finding that has important clinical implications for those patients with adult-onset visual deprivation and for therapies founded on monocular deprivation.

Early maturation of the social brain: How brain development provides a platform for the acquisition of social-cognitive competence

Across the last century psychology has provided a lot of insight about social-cognitive competence. Recognizing facial expressions, joint attention, discrimination of cues and experiencing empathy are just a few examples of the social skills humans acquire from birth to adolescence. However, how very early brain maturation provides a platform to support the attainment of highly complex social behavior later in development remains poorly understood. Magnetic Resonance Imaging provides a safe means to investigate the typical and atypical maturation of regions of the brain responsible for social cognition in as early as the perinatal period. Here, we first review some technical challenges and advances of using functional magnetic resonance imaging on developing infants to then describe current knowledge on the development of diverse systems associated with social function. We will then explain how these characteristics might differ in infants with genetic or environmental risk factors, who are vulnerable to atypical neurodevelopment. Finally, given the rapid early development of systems necessary for social skills, we propose a new framework to investigate sensitive time windows of development when neural substrates might be more vulnerable to impairment due to a genetic or environmental insult.

Sensory experience during early sensitive periods shapes cross-modal temporal biases

Typical human perception features stable biases such as perceiving visual events as later than synchronous auditory events. The origin of such perceptual biases is unknown. To investigate the role of early sensory experience, we tested whether a congenital, transient loss of pattern vision, caused by bilateral dense cataracts, has sustained effects on audio-visual and tactile-visual temporal biases and resolution. Participants judged the temporal order of successively presented, spatially separated events within and across modalities. Individuals with reversed congenital cataracts showed a bias towards perceiving visual stimuli as occurring earlier than auditory (Expt. 1) and tactile (Expt. 2) stimuli. This finding stood in stark contrast to normally sighted controls and sight-recovery individuals who had developed cataracts later in childhood: both groups exhibited the typical bias of perceiving vision as delayed compared to audition. These findings provide strong evidence that cross-modal temporal biases depend on sensory experience during an early sensitive period.

The Detrimental Effect of Noisy Visual Input on the Visual Development of Human Infants

We followed visual development in a rare yet large sample of patients with congenital bilateral cataract for 4 years. We divided the patients into two groups: a complete deprivation group with no response to a flashlight pointing to either of their eyes and otherwise an incomplete deprivation group. All the patients received cataract surgery at age of 3 months. From 27 months onward, the complete deprivation group showed better developmental outcomes in acuity and eyeball growth than the incomplete deprivation group. Such a seemingly counterintuitive finding is consistent with research on visually deprived animals. Plasticity is better preserved in animals receiving a short period of complete visual deprivation from birth than in animals who saw diffuse light. The current finding that plasticity in visual development is better preserved in human infants with complete visual deprivation than in those who can see diffuse light but not patterned visual input has important clinical implications.

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Infants with complete deprivation have developed better acuity than incomplete ones

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Plasticity is better preserved in complete deprivation infants than in incomplete ones

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Infants with complete deprivation have less myopic shift than incompletes ones

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Early noisy input has the detrimental effect on human visual development

Alteration in binocular fusion modifies audiovisual integration in children

Background: In the field of multisensory integration, vision is generally thought to dominate audiovisual interactions, at least in spatial tasks, but the role of binocular fusion in audiovisual integration has not yet been studied.

Methods: Using the Maddox test, a classical ophthalmological test used to subjectively detect a latent unilateral eye deviation, we checked whether an alteration in binocular vision in young patients would be able to change audiovisual integration. The study was performed on a group of ten children (five males and five females aged 11.3±1.6 years) with normal binocular vision, and revealed a visual phenomenon consisting of stochastic disappearanceof part of a visual scene caused by auditory stimulation.

Results: Indeed, during the Maddox test, brief sounds induced transient visual scotomas (VSs) in the visual field of the eye in front of where the Maddox rod was placed. We found a significant correlation between the modification of binocular vision and VS occurrence. No significant difference was detected in the percentage or location of VS occurrence between the right and left eye using the Maddox rod test orbetween sound frequencies.

Conclusion: The results indicate a specific role of the oculomotor system in audiovisual integration in children. This convenient protocol may also have significant interest for clinical investigations of developmental pathologies where relationships between vision and hearing are specifically affected.

The role of multisensory development in early language learning

In typical development, communicative skills such as language emerge from infants' ability to combine multisensory information into cohesive percepts. For example, the act of associating the visual or tactile experience of an object with its spoken name is commonly used as a measure of early word learning, and social attention and speech perception frequently involve integrating both visual and auditory attributes. Early perspectives once regarded perceptual integration as one of infants' primary challenges, whereas recent work suggests that caregivers' social responses contain structured patterns that may facilitate infants' perception of multisensory social cues. In the current review, we discuss the regularities within caregiver feedback that may allow infants to more easily discriminate and learn from social signals. We focus on the statistical regularities that emerge in the moment-by-moment behaviors observed in studies of naturalistic caregiver-infant play. We propose that the spatial form and contingencies of caregivers' responses to infants' looks and prelinguistic vocalizations facilitate communicative and cognitive development. We also explore how individual differences in infants' sensory and motor abilities may reciprocally influence caregivers' response patterns, in turn regulating and constraining the types of social learning opportunities that infants experience across early development. We end by discussing implications for neurodevelopmental conditions affecting both multisensory integration and communication (i.e., autism) and suggest avenues for further research and intervention.

Impaired Spatial Hearing in Amblyopia: Evidence for Calibration of Auditory Maps by Retinocollicular Input in Humans

Purpose

Evidence from animals and blind humans suggests that early visual experience influences the developmental calibration of auditory localization. Hypothesizing that unilateral amblyopia may involve cross-modal deficits in spatial hearing, we measured the precision and accuracy of sound localization in humans with amblyopia.

Methods

All participants passed a standard hearing test. Experiment 1 measured sound localization precision for click stimuli in 10 adults with amblyopia and 10 controls using a minimum audible angle (MAA) task. Experiment 2 measured sound localization error (i.e., accuracy) for click train stimuli in 14 adults with amblyopia and 16 controls using an absolute sound localization task.

Results

In Experiment 1, the MAA (mean ± SEM) was significantly greater in the amblyopia group compared with controls (2.75 ± 0.30° vs. 1.69 ± 0.09°, P = 0.006). In Experiment 2, the overall sound localization error was significantly greater in the amblyopia group compared with controls (P = 0.047). The amblyopia group also showed significantly greater sound localization error in the auditory hemispace ipsilateral to the amblyopic eye (P = 0.036). At a location within this auditory hemispace, the magnitude of sound localization error correlated significantly with deficits in stereo acuity (P = 0.036).

Conclusions

The precision and accuracy of sound localization are impaired in unilateral amblyopia. The asymmetric pattern of sound localization error suggests that amblyopic vision may interfere with the development of spatial hearing via the retinocollicular pathway.

Faces in early visual environments are persistent not just frequent

The regularities in very young infants' visual worlds likely have out-sized effects on the development of the visual system because they comprise the first-in experience that tunes, maintains, and specifies the neural substrate from low-level to higher-level representations and therefore constitute the starting point for all other visual learning. Recent evidence from studies using head cameras suggests that the frequency of faces available in early infant visual environments declines over the first year and a half of life. The primary question for the present paper concerns the temporal structure of face experiences: Is frequency the key exposure dimension distinguishing younger and older infants' face experiences, or is it the duration for which faces remain in view? Our corpus of head-camera images collected as infants went about their daily activities consisted of over a million individually coded frames sampled at 0.2 Hz from 232 h of infant-perspective scenes, recorded from 51 infants aged 1 month to 15 months. The major finding from this corpus is that very young infants (1-3 months) not only have more frequent face experiences but also more temporally persistent ones. The repetitions of the same very few face identities presenting up-close and frontal views are exaggerated in more persistent runs of the same face, and these persistent runs are more frequent for the youngest infants. The implications of early experiences consisting of extended repeated exposures of up-close frontal views for visual learning are discussed.

The Developing Infant Creates a Curriculum for Statistical Learning

New efforts are using head cameras and eye-trackers worn by infants to capture everyday visual environments from the point of view of the infant learner. From this vantage point, the training sets for statistical learning develop as the sensorimotor abilities of the infant develop, yielding a series of ordered datasets for visual learning that differ in content and structure between timepoints but are highly selective at each timepoint. These changing environments may constitute a developmentally ordered curriculum that optimizes learning across many domains. Future advances in computational models will be necessary to connect the developmentally changing content and statistics of infant experience to the internal machinery that does the learning.

Alterations in audiovisual simultaneity perception in amblyopia

Amblyopia is a developmental visual impairment that is increasingly recognized to affect higher-level perceptual and multisensory processes. To further investigate the audiovisual (AV) perceptual impairments associated with this condition, we characterized the temporal interval in which asynchronous auditory and visual stimuli are perceived as simultaneous 50% of the time (i.e., the AV simultaneity window). Adults with unilateral amblyopia (n = 17) and visually normal controls (n = 17) judged the simultaneity of a flash and a click presented with both eyes viewing. The signal onset asynchrony (SOA) varied from 0 ms to 450 ms for auditory-lead and visual-lead conditions. A subset of participants with amblyopia (n = 6) was tested monocularly. Compared to the control group, the auditory-lead side of the AV simultaneity window was widened by 48 ms (36%; p = 0.002), whereas that of the visual-lead side was widened by 86 ms (37%; p = 0.02). The overall mean window width was 500 ms, compared to 366 ms among controls (37% wider; p = 0.002). Among participants with amblyopia, the simultaneity window parameters were unchanged by viewing condition, but subgroup analysis revealed differential effects on the parameters by amblyopia severity, etiology, and foveal suppression status. Possible mechanisms to explain these findings include visual temporal uncertainty, interocular perceptual latency asymmetry, and disruption of normal developmental tuning of sensitivity to audiovisual asynchrony.