Altered white matter structure in the visual system following early monocular enucleation.

Partial visual deprivation from early monocular enucleation (the surgical removal of one eye within the first few years of life) results in a number of long-term morphological adaptations in adult cortical and subcortical visual, auditory, and multisensory brain regions. In this study, we investigated whether early monocular enucleation also results in the altered development of white matter structure. Diffusion tensor imaging and probabilistic tractography were performed to assess potential differences in visual system white matter in adult participants who had undergone early monocular enucleation compared to binocularly intact controls. To examine the microstructural properties of these tracts, mean diffusion parameters including fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) were extracted bilaterally. Asymmetries opposite to those observed in controls were found for FA, MD, and RD in the optic radiations, the projections from primary visual cortex (V1) to the lateral geniculate nucleus (LGN), and the interhemispheric V1 projections of early monocular enucleation participants. Early monocular enucleation was also associated with significantly lower FA bidirectionally in the interhemispheric V1 projections. These differences were consistently greater for the tracts contralateral to the enucleated eye, and are consistent with the asymmetric LGN volumes and optic tract diameters previously demonstrated in this group of participants. Overall, these results indicate that early monocular enucleation has long-term effects on white matter structure in the visual pathway that results in reduced fiber organization in tracts contralateral to the enucleated eye. Hum Brain Mapp 39:133-144, 2018. © 2017 Wiley Periodicals, Inc.

Vestibular-somatosensory interactions affect the perceived timing of tactile stimuli.

Passive rotation has been shown to alter temporal-order judgments for tactile stimuli delivered to the hands giving an advantage to the leading hand. Here we measure thresholds for detecting stimulus onset asynchrony for touches on the hands during tilt to the left or right and during galvanic vestibular stimulation (GVS) that evoked illusory tilt. During tilt to one side, the effect of gravity on the otoliths is equivalent to a physical acceleration away from that side (e.g., tilt left is equivalent to accelerating rightwards). We therefore predicted a "leading hand advantage" for the hand opposite to the tilt direction. Thresholds for detecting asynchronicity for left-hand-first and right-hand-first touches (defined as correct detection 75% of the time) were measured separately using interleaved adaptive staircases for 15 participants. For both physical and illusory tilt there was a temporal advantage for stimuli presented to the hand contralateral to the tilt-equivalent to the "leading hand" during passive rotation. That is, there was a temporal advantage for the upward hand (for physical tilt) and for the anodal-side hand (for illusory tilt caused by GVS). These results are discussed in terms of attention and direct sensory components evoking the "leading hand" bias. These findings add to the emerging understanding of the pervasive role of vestibular activity in many aspects of cognitive processing.

Normal temporal binding window but no sound-induced flash illusion in people with one eye.

Integrating vision and hearing is an important way in which we process our rich sensory environment. Partial deprivation of the visual system from the loss of one eye early in life results in adaptive changes in the remaining senses (e.g., Hoover et al. in Exp Brain Res 216:565-74, 2012). The current study investigates whether losing one eye early in life impacts the temporal window in which audiovisual events are integrated and whether there is vulnerability to the sound-induced flash illusion. In Experiment 1, we measured the temporal binding window with a simultaneity judgement task where low-level auditory and visual stimuli were presented at different stimulus onset asynchronies. People with one eye did not differ in the width of their temporal binding window, but they took longer to make judgements compared to binocular viewing controls. In Experiment 2, we measured how many light flashes were perceived when a single flash was paired with multiple auditory beeps in close succession (sound induced flash illusion). Unlike controls, who perceived multiple light flashes with two, three or four beeps, people with one eye were not susceptible to the sound-induced flash illusion. In addition, they took no longer to respond compared to both binocular and monocular (eye-patched) viewing controls. Taken together, these results suggest that the lack of susceptibility to the sound-induced flash illusion in people with one eye cannot be accounted for by the width of the temporal binding window. These results provide evidence for adaptations in audiovisual integration due to the reduction of visual input from the loss of one eye early in life.

Assessment of implicit COVID-19 attitudes using affective priming for pro-vaccine and vaccine-hesitant individuals.

The COVID-19 pandemic has resulted in the introduction of pharmaceutical and non-pharmaceutical interventions such as precautionary behaviours. The current study used affective priming to evaluate COVID-19 attitudes in vaccine-hesitant and pro-vaccine participants. Explicitly, both groups rated their overall perception of risk associated with contracting COVID-19 significantly lower compared to their perception of necessary precautions and overall adherence to public health measures. Pro-vaccine participants rated their perception of necessary precautions higher compared to vaccine-hesitant participants. During baseline measures, both groups classified COVID-19 affiliated words as unpleasant. Affective priming was observed for congruent prime-target pleasant and unpleasant word pairs but was not observed for COVID-19 related word pairs. Differences between groups in the perception of necessary public health precautions points to different underlying pathways for reduced perceived risk and lack of affective priming. These results refine previous findings indicating that implicit attitudes towards COVID-19 can be measured using the affective priming paradigm.

Perception of the McGurk effect in people with one eye depends on whether the eye is removed during infancy or adulthood.

Background: The visual system is not fully mature at birth and continues to develop throughout infancy until it reaches adult levels through late childhood and adolescence. Disruption of vision during this postnatal period and prior to visual maturation results in deficits of visual processing and in turn may affect the development of complementary senses. Studying people who have had one eye surgically removed during early postnatal development is a useful model for understanding timelines of sensory development and the role of binocularity in visual system maturation. Adaptive auditory and audiovisual plasticity following the loss of one eye early in life has been observed for both low-and high-level visual stimuli. Notably, people who have had one eye removed early in life perceive the McGurk effect much less than binocular controls. Methods: The current study investigates whether multisensory compensatory mechanisms are also present in people who had one eye removed late in life, after postnatal visual system maturation, by measuring whether they perceive the McGurk effect compared to binocular controls and people who have had one eye removed early in life. Results: People who had one eye removed late in life perceived the McGurk effect similar to binocular viewing controls, unlike those who had one eye removed early in life. Conclusion: This suggests differences in multisensory compensatory mechanisms based on age at surgical eye removal. These results indicate that cross-modal adaptations for the loss of binocularity may be dependent on plasticity levels during cortical development.

No Colavita effect: equal auditory and visual processing in people with one eye.

Previous research has shown that people with one eye have enhanced spatial vision implying intra-modal compensation for their loss of binocularity. The current experiments investigate whether monocular blindness from unilateral eye enucleation may lead to cross-modal sensory compensation for the loss of one eye. We measured speeded detection and discrimination of audiovisual targets presented as a stream of paired objects and familiar sounds in a group of individuals with monocular enucleation compared to controls viewing binocularly or monocularly. In Experiment 1, participants detected the presence of auditory, visual or audiovisual targets. All participant groups were equally able to detect the targets. In Experiment 2, participants discriminated between the visual, auditory or bimodal (audiovisual) targets. Both control groups showed the Colavita effect, that is, preferential processing of visual over auditory information for the bimodal stimuli. The monocular enucleation group, however, showed no Colavita effect, and further, they demonstrated equal processing of visual and auditory stimuli. This finding suggests a lack of visual dominance and equivalent auditory and visual processing in people with one eye. This may be an adaptive form of sensory compensation for the loss of one eye and could result from recruitment of deafferented visual cortical areas by inputs from other senses.

Virtual reality hope machines in a curative imaginary: recommendations for neurorehabilitation research from a critical disability studies perspective.

PURPOSE: This paper provides recommendations for neurorehabilitative research informed by insights from critical disability studies (CDS) and a research study that tested an augmented neurorehabilitative technology prototype. METHODS: The methodology combines critical reflection, feminist science studies and CDS to analyze how neurorehabilitation and disability studies conceptualize notions of disability and cure. It offers recommendations for reconciling the conflicting ideologies of cure that operate within neurorehabilitative research. RESULTS: The prototype acted as a kind of virtual reality hope machine that tapped into different emotions and language games regarding disability and cure. The result is five recommendations about the ways that a CDS perspective might inform neurorehabilitation research: (I) ensure clarity in recruitment materials to account for dominant social views on disability and the possibility of cure; (II) build "strong objectivity" into research methods through attention to social context and multiple meanings of terms; (III) engage in critical reflection about research processes and findings; (IV) incorporate principles of crip technoscience; and (V) include CDS perspectives in neurorehabilitation education. CONCLUSIONS: Bridging a conversation between neurorehabilitative research and CDS can address the discrepancies between ideologies of cure, and situate rehabilitation within the wider concerns of social determinants of health and disability justice.Implications for rehabilitationBridging connections between rehabilitation studies and critical disability studies can generate productive insights that open up conversations with disabled people and a commitment to disability justice.Disability and cure are social constructs and may have different meanings for patients and rehabilitation professionals.Clinicians should be mindful of the conflicting ideological constructs and socio-political dimensions of disability and cure that are operating below the surface in the rehabilitation profession and in interactions between clinicians and patients.As technology continues to transform clinical rehabilitation care through virtual reality and other innovative paradigms, rehabilitation clinicians should recognize the potential for these technologies to become "hope machines," generating patient expectations that are idealized constructions of hoped-for outcomes of returning to a previous state or level of functionality rather than predictive expectations of likely results.

Lack of affective priming indicates attitude-behaviour discrepancy for COVID-19 affiliated words.

The ongoing novel coronavirus (COVID-19) pandemic has resulted in the enforcement of national public health safety measures including precautionary behaviours such as border closures, movement restrictions, total or partial lockdowns, social distancing, and face mask mandates in order to reduce the spread of this disease. The current study uses affective priming, an indirect behavioural measure of implicit attitude, to evaluate COVID-19 attitudes. Explicitly, participants rated their overall risk perception associated with contracting COVID-19 significantly lower compared to their perception of necessary precautions and overall adherence to public health measures. During baseline trials, participants explicitly rated COVID-19 affiliated words as unpleasant, similar to traditional unpleasant word stimuli. Despite rating the COVID-19 affiliated words as unpleasant, affective priming was not observed for congruent prime-target COVID-19 affiliated word pairs when compared to congruent prime-target pleasant and unpleasant words. Overall, these results provide quantitative evidence that COVID-19 affiliated words do not invoke the same implicit attitude response as traditional pleasant and unpleasant word stimuli, despite conscious explicit rating of the COVID-19 words as unpleasant. This reduction in unpleasant attitude towards COVID-19 related words may contribute towards decreased fear-related behaviours and increased incidences of risky-behaviour facilitating the movement of the virus.

Brain Activation for Audiovisual Information in People With One Eye Compared to Binocular and Eye-Patched Viewing Controls.

Blindness caused by early vision loss results in complete visual deprivation and subsequent changes in the use of the remaining intact senses. We have also observed adaptive plasticity in the case of partial visual deprivation. The removal of one eye, through unilateral eye enucleation, results in partial visual deprivation and is a unique model for examining the consequences of the loss of binocularity. Partial deprivation of the visual system from the loss of one eye early in life results in behavioral and structural changes in the remaining senses, namely auditory and audiovisual systems. In the current study we use functional neuroimaging data to relate function and behavior of the audiovisual system in this rare patient group compared to controls viewing binocularly or with one eye patched. In Experiment 1, a whole brain analysis compared common regions of cortical activation between groups, for auditory, visual and audiovisual stimuli. People with one eye demonstrated a trend for increased activation for low-level audiovisual stimuli compared to patched viewing controls but did not differ from binocular viewing controls. In Experiment 2, a region of interest (ROI) analysis for auditory, visual, audiovisual and illusory McGurk stimuli revealed that people with one eye had an increased trend for left hemisphere audiovisual activation for McGurk stimuli compared to binocular viewing controls. This aligns with current behavioral analysis and previous research showing reduced McGurk Effect in people with one eye. Furthermore, there is no evidence of a correlation between behavioral performance on the McGurk Effect task and functional activation. Together with previous behavioral work, these functional data contribute to the broader understanding of cross-sensory effects of early sensory deprivation from eye enucleation. Overall, these results contribute to a better understanding of the sensory deficits experienced by people with one eye, as well as, the relationship between behavior, structure and function in order to better predict the outcome of early partial visual deafferentation.

Short and long-term visual deprivation leads to adapted use of audiovisual information for face-voice recognition.

Person identification is essential for everyday social interactions. We quickly identify people from cues such as a person's face or the sound of their voice. A change in sensory input, such as losing one's vision, can alter how one uses sensory information. We asked how people with only one eye, who have had reduced visual input during postnatal maturation of the visual system, use faces and voices for person identity recognition. We used an old/new paradigm to investigate unimodal (visual or auditory) and bimodal (audiovisual) identity recognition of people (face, voice and face-voice) and a control category, objects (car, horn and car-horn). Participants learned the identity of 10 pairs of faces and voices (Experiment 1) and 10 cars and horns (Experiment 2) and were asked to identify the learned face/voice or car/horn among 20 distractors. People with one eye were more sensitive to voice identification compared to controls viewing binocularly or with an eye-patch. However, both people with one eye and eye-patched viewing controls use combined audiovisual information for person identification more equally than binocular viewing controls, who favour vision. People with one eye were no different from controls at object identification. The observed visual dominance for binocular controls is larger for person compared to object identification, indicating that faces (vision) play a larger role in person identification and that person identity processing is unique from that for objects. People with long-term visual deprivation from the loss of one eye may have adaptive strategies, such as placing less reliance on vision to achieve intact performance, particularly for face processing.

Altered white matter structure in auditory tracts following early monocular enucleation.

PURPOSE: Similar to early blindness, monocular enucleation (the removal of one eye) early in life results in crossmodal behavioral and morphological adaptations. Previously it has been shown that partial visual deprivation from early monocular enucleation results in structural white matter changes throughout the visual system (Wong et al., 2018). The current study investigated structural white matter of the auditory system in adults who have undergone early monocular enucleation compared to binocular control participants. METHODS: We reconstructed four auditory and audiovisual tracts of interest using probabilistic tractography and compared microstructural properties of these tracts to binocularly intact controls using standard diffusion indices. RESULTS: Although both groups demonstrated asymmetries in indices in intrahemispheric tracts, monocular enucleation participants showed asymmetries opposite to control participants in the auditory and A1-V1 tracts. Monocular enucleation participants also demonstrated significantly lower fractional anisotropy in the audiovisual projections contralateral to the enucleated eye relative to control participants. CONCLUSIONS: Partial vision loss from early monocular enucleation results in altered structural connectivity that extends into the auditory system, beyond tracts primarily dedicated to vision.

Intact Dynamic Visual Capture in People With One Eye.

Observing motion in one modality can influence the perceived direction of motion in a second modality (dynamic capture). For example observing a square moving in depth can influence the perception of a sound to increase in loudness. The current study investigates whether people who have lost one eye are susceptible to audiovisual dynamic capture in the depth plane similar to binocular and eye-patched viewing control participants. Partial deprivation of the visual system from the loss of one eye early in life results in changes in the remaining intact senses such as hearing. Linearly expanding or contracting discs were paired with increasing or decreasing tones and participants were asked to indicate the direction of the auditory stimulus. Magnitude of dynamic visual capture was measured in people with one eye compared to eye-patched and binocular viewing controls. People with one eye have the same susceptibility to dynamic visual capture as controls, where they perceived the direction of the auditory signal to be moving in the direction of the incongruent visual signal, despite previously showing a lack of visual dominance for audiovisual cues. This behaviour may be the result of directing attention to the visual modality, their partially deficient sense, in order to gain important information about approaching and receding stimuli which in the former case could be life-threatening. These results contribute to the growing body of research showing that people with one eye display unique accommodations with respect to audiovisual processing that are likely adaptive in each unique sensory situation.

Audiovisual plasticity following early abnormal visual experience: Reduced McGurk effect in people with one eye.

Previously, we have shown that people who have had one eye surgically removed early in life during visual development have enhanced sound localization [1] and lack visual dominance, commonly observed in binocular and monocular (eye-patched) viewing controls [2]. Despite these changes, people with one eye integrate auditory and visual components of multisensory events optimally [3]. The current study investigates how people with one eye perceive the McGurk effect, an audiovisual illusion where a new syllable is perceived when visual lip movements do not match the corresponding sound [4]. We compared individuals with one eye to binocular and monocular viewing controls and found that they have a significantly smaller McGurk effect compared to binocular controls. Additionally, monocular controls tended to perceive the McGurk effect less often than binocular controls suggesting a small transient modulation of the McGurk effect. These results suggest altered weighting of the auditory and visual modalities with both short and long-term monocular viewing. These results indicate the presence of permanent adaptive perceptual accommodations in people who have lost one eye early in life that may serve to mitigate the loss of binocularity during early brain development.

Evidence of multisensory plasticity: Asymmetrical medial geniculate body in people with one eye.

UNLABELLED: The medial geniculate body (MGB) plays a central role in auditory processing with both efferent and afferent tracts to primary auditory cortex. People who have lost one eye early in life have enhanced sound localization, lack visual over auditory dominance and integrate auditory and visual information optimally, similar to controls, despite taking longer to localize unimodal visual stimuli. Compared to controls, people with one eye have decreased lateral geniculate nuclei (LGN) volume as expected given the 50% deafferentation of the visual system. However, LGN volume is larger than predicted contralateral to the remaining eye, indicating altered structural development likely through recruitment of deafferented LGN cells. PURPOSE: the current study investigated whether structural MGB changes are also present in this group given the changes they exhibit in auditory processing. METHODS: MGB volumes were measured in adults who had undergone early unilateral eye enucleation and were compared to binocularly intact controls. RESULTS: unlike controls, people with one eye had a significant asymmetry with a larger left compared to right MGB, independent of eye of enucleation. MGB volume correlated positively with LGN volume in people with one eye. CONCLUSIONS: volume asymmetry in the MGB in people with one eye may represent increased interactions between the left MGB and primary auditory cortex. This interaction could contribute to increased auditory and other left hemisphere-dominant processing, including language, as compensation for the loss of one half of visual inputs early in life. The positive correlation between MGB and LGN volume is not due to space constraints but rather indicates increased plasticity in both auditory and visual sensory systems following early eye enucleation.

Optimal audiovisual integration in people with one eye.

People with one eye show altered sensory processing. Such changes might reflect a central reweighting of sensory information that might impact on how multisensory cues are integrated. We assessed whether people who lost an eye early in life differ from controls with respect to audiovisual integration. In order to quantify the relative weightings assigned to each sensory system, participants were asked to spatially localize audiovisual events that have been previously shown to be optimally combined and perceptually fused from the point of view of location in a normal population, where the auditory and visual components were spatially disparate. There was no difference in the variability of localizing unimodal visual and auditory targets by people with one eye compared to controls. People with one eye did however, demonstrate slower reaction times to localize visual stimuli compared to auditory stimuli and were slower than binocular and eye-patched control groups. When localizing bimodal targets, the weightings assigned to each sensory modality in both people with one eye and controls were predictable from their unimodal performance, in accordance with Maximum Likelihood Estimation and the time it took all three groups to localize the bimodal targets was faster than for vision alone. Regardless of demonstrating a longer response time to visual stimuli, people with one eye appear to integrate the auditory and visual components of multisensory events optimally when determining spatial location.

No Colavita effect: increasing temporal load maintains equal auditory and visual processing in people with one eye.

We investigate whether the loss of one eye leads to enhanced multisensory processing. Previously, we measured discrimination of auditory, visual and audiovisual targets in people with one eye compared to controls viewing binocularly or with one eye patched. Both control groups demonstrated typical visual dominance (the Colavita effect) whereas people with one eye show no Colavita effect, and instead show equal preference for visual and auditory stimuli. Here, we loaded temporal processing in an attempt to favour audition and thereby reverse Colavita visual dominance with a modified repetition blindness paradigm. The Colavita effect was reduced for controls however, people with one eye continued to show no Colavita effect, reversed or otherwise. People with one eye display equal auditory and visual processing in this context, suggesting unbiased multisensory processing, likely as a form of cross-modal adaptation and compensation for their loss of binocularity.