Do blind people hear better?

Altered visual cortex excitatory/inhibitory ratio following transient congenital visual deprivation in humans

Non-human animal models have indicated that the ratio of excitation to inhibition (E/I) in neural circuits is experience dependent, and changes across development. Here, we assessed 3T Magnetic Resonance Spectroscopy (MRS) and electroencephalography (EEG) markers of cortical E/I ratio in 10 individuals who had been treated for dense bilateral congenital cataracts, after an average of 12 years of blindness, to test for dependence of the E/I ratio on early visual experience in humans. First, participants underwent MRS scanning at rest with their eyes open and eyes closed, to obtain visual cortex Gamma-Aminobutyric Acid (GABA+) concentration, Glutamate/Glutamine (Glx) concentration, and the concentration ratio of Glx/GABA+, as measures of inhibition, excitation, and E/I ratio, respectively. Subsequently, EEG was recorded to assess aperiodic activity (1-20 Hz) as a neurophysiological measure of the cortical E/I ratio, during rest with eyes open and eyes closed, and during flickering stimulation. Across conditions, congenital cataract-reversal individuals demonstrated a significantly lower visual cortex Glx/GABA+ ratio, and a higher intercept and steeper aperiodic slope at occipital electrodes, compared to age-matched sighted controls. In the congenital cataract-reversal group, a lower Glx/GABA+ ratio was associated with better visual acuity, and Glx concentration correlated positively with the aperiodic intercept in the conditions with visual input. We speculate that these findings result from an increased E/I ratio of the visual cortex as a consequence of congenital blindness, which might require commensurately increased inhibition in order to balance the additional excitation from restored visual input. The lower E/I ratio in congenital cataract-reversal individuals would thus be a consequence of homeostatic plasticity.

Ageing of adults who are blind: A scoping review

The ageing process of adults with a disability may differ from the typical ageing process, yet few studies have addressed ageing of adults who are blind. However, a broad scope of literature exists on ageing with a visual impairment that includes adults who are blind. People who are blind may age differently than people with a visual impairment. Furthermore, it cannot be inferred from studies on the ageing of visually impaired adults that changes are due to the ageing process alone, since vision may decline further as well. This article presents a scoping review of studies on the ageing of adults who are blind, examining the areas of decline due to ageing, differences compared to non-blind adults, additional contributing factors and support. A systematic literature search was performed from inception up to July-October 2023 in Scopus, Medline, Embase, CINAHL, APA PsycInfo and Web of Science. Thirteen articles met the eligibility criteria. Analysis led to four broad areas: physical, sensory, cognitive and psychological. In several of these areas, the decline due to ageing was similar for people who were blind or non-blind. Declines specific to people who were blind were in spatial memory and engagement to the outer world. Two abilities were identified where blind people outperformed sighted people: attention and working memory and active tactile acuity. Overall, ageing blind adults were shown to have additional risks and hence need extra support. Interventions may focus on physical and cognitive exercise, braille training, risk screening, education and social activities. More research is needed to replicate studies and disambiguate results, to include areas that have not been investigated specifically for this group, to differentiate between different types of blindness and to investigate systematically the needs and support of blind adults who are ageing.

Volumetric alterations in auditory and visual subcortical nuclei following perinatal deafness in felines

In response to sensory deprivation, the brain adapts to efficiently navigate a modified perceptual environment through a process referred to as compensatory crossmodal plasticity, allowing the remaining senses to repurpose deprived regions and networks. A mechanism that has been proposed to contribute to this plasticity involves adaptations within subcortical nuclei that trigger cascading effects throughout the brain. The current study uses 7T MRI to investigate the effect of perinatal deafness on the volumes of subcortical structures in felines, focusing on key sensory nuclei within the brainstem and thalamus. Using both ROI-based and morphometric approaches, the regional macrostructure of four auditory and two visual nuclei were studied, as well as the corresponding volumetric asymmetries within and across groups. In the auditory pathway, significant bilateral volumetric reductions were revealed within the lower-level structures (cochlear nucleus, superior olivary complex, and inferior colliculus), alongside a shrinkage of solely the left medial geniculate body. Within the visual pathway, a significant bilateral volumetric reduction was found in the lateral geniculate nucleus, with the superior colliculus largely unaffected. These regional alterations, along with an extensive loss of volume throughout the brainstem of deprived cats, were attributed to disuse-driven atrophy corresponding to evolved functional demands reflective of a modified perceptual environment. Furthermore, the left-right volumetric symmetries of the control subcortex were preserved following deafness. Overall, the current study reinforces the notion that subcortical structures likely contribute to compensatory crossmodal plasticity prior to cortical processing, and that these deafness-induced adaptations appear to be influenced by both the level of the affected structure within its respective sensory processing hierarchy and the specifics of its afferent profile.

Motion-onset visually evoked potentials are amplified in the deaf

The loss of a sensory modality triggers a phenomenon known as cross-modal plasticity, where areas of the brain responsible for the lost sensory modality are reorganized and repurposed to the benefit of the remaining modalities. After perinatal or congenital deafness, superior visual motion detection abilities have been psychophysically identified in both humans and cats, and this advantage has been causally demonstrated to be mediated by reorganized auditory cortex. In our study, we investigated visually evoked potentials (VEPs) in response to motion-onset stimuli of varying speeds in both hearing and perinatally deafened cats under light anesthesia. Although the peak latencies did not differ between the two groups, we observed significantly greater VEP amplitudes in deaf cats, specifically in the P1 component and the signal power of the overall waveform. Through sigmoidal modeling, we identified that the speed offset and steepness at the threshold for 50% maximum neural activity was unchanged, showing that neuronal activity was modulated by motion speeds in a comparable manner between the hearing and deaf subjects and the deaf had greater potentials at all dot speeds. Our results suggest that the increased cortical activity by the auditory and visual cortices of deaf cats may account for their superior behavioral advantage in motion detection and indicates that cross-modal plasticity plays a significant role in the cortical processing of motion. NEW & NOTEWORTHY The present study investigated cross-modal plasticity after perinatal deafness in cats using motion-onset visually evoked potentials. Deaf animals were observed to have significantly greater evoked potentials in both peak components and the signal power of the overall waveforms. These results are discussed in relation to prior studies on deaf subjects in both human and animal research on evoked potentials and psychophysics.

Top-down and emotional attention in blind and sighted individuals

There is evidence that congenitally blind individuals possess superior auditory perceptual skills compared to sighted people. However, relatively little is known about the auditory-specific cortical correlates of spatial attention in the blind and how task-irrelevant emotional stimulus features could further modulate such neural processes. This study tested blind and sighted participants in a challenging auditory discrimination task. All participants were blindfolded and seated between loudspeakers at 45-degree angles, while pseudowords were randomly presented. The task was to identify target sounds from either the left or the right speaker while ignoring nontarget stimuli, the irrelevant loudspeaker, and irrelevant speaker identity. Emotional valence-neutral, happy, fearful, threatening-of pseudowords was task-irrelevant, focusing solely on syllable detection. Our focus was on measuring the moment-to-moment deployment of auditory-selective attention. This was achieved using the lateralized N2ac event-related potential component characterised by greater negativity at anterior electrodes on the side contralateral to an attended auditory stimulus and observed 75 to 250 ms after stimulus onset. We observed that blind individuals showed better behavioural performance and reduced N2ac amplitudes than sighted individuals. Furthermore, for both groups, N2ac amplitudes were increased for the target compared to nontarget stimuli and stimuli appearing at spatially relevant versus irrelevant locations. Our study highlights the superiority of auditory processing capabilities in blind individuals. The results also highlight the N2ac component's sensitivity to top-down attentional engagement and emotional attention, offering new insights into how blind and sighted individuals process auditory information.

Evidence for early encoding of speech in blind people

Blind listeners rely more on their auditory skills than the sighted to adapt to unavailable visual information. However, it is still unclear whether the blind has stronger noise-related modulation compared with the sighted when speech is presented under adverse listening conditions. This study aims to address this research gap by constructing noisy conditions and syllable contrasts to obtain auditory middle-latency response (MLR) and long-latency response (LLR) in blind and sighted adults. We found that blind people showed higher MLR (Na, Nb, and Pa) and N1 amplitudes compared with sighted, while this phenomenon was not observed for mismatch negativity (MMN) during auditory discrimination in both quiet and noisy backgrounds, which might eventually affect stream segregation and facilitate the understanding of speech in complex environments, contributing to their more sensitive speech detection ability of blind people. These results had important implications regarding the interpretation of noise-induced changes in the early encoding of speech in blind people.

Brief periods of visual deprivation in adults increase performance on auditory tasks

Plastic changes in the brain are primarily limited to early postnatal periods. Recovery of adult brain plasticity is critical for the effective development of therapies. A brief (1-2 weeks) duration of visual deprivation (dark exposure, DE) in adult mice can trigger functional plasticity of thalamocortical and intracortical circuits in the primary auditory cortex suggesting improved sound processing. We tested if DE enhances the ability of adult mice to detect sounds. We trained and continuously evaluated the behavioral performance of mice in control and DE conditions using automated home-cage training. Consistent with age-related peripheral hearing loss present in C57BL/6J mice, we observed decreased performance for high-frequency sounds with age, which was reduced by DE. In CBA mice with preserved peripheral hearing, we also found that DE showed modest auditory performance improvements in low and mid frequencies over time compared to the control.

Gray matter volume of the feline cerebral cortex and structural plasticity following perinatal deafness

In response to sensory deprivation, the brain adapts according to contemporary demands to efficiently navigate a modified perceptual environment. This reorganization may result in improved processing of the remaining senses-a phenomenon referred to as compensatory crossmodal plasticity. One approach to explore this neuroplasticity is to consider the macrostructural changes in neural tissue that mirror this functional optimization. The current study is the first of its kind to measure MRI-derived gray matter (GM) volumes of control felines (n=30), while additionally identifying volumetric differences in response to perinatal deafness (30 ototoxically-deafened cats). To accomplish this purpose, regional and morphometric methods were performed in parallel. The regional analysis evaluated volumetric alterations of global GM, as well as the volumes of 146 regions of interest (ROIs) and 12 functional subgroupings of these ROIs. Results revealed whole-brain GM preservation; however, somatosensory and visual cortices exhibited an overall increase in volume. On a smaller scale, this analysis uncovered two auditory ROIs (second auditory cortex, A2, and ventral auditory field, VAF) that decreased in volume alongside two visual regions (anteromedial lateral suprasylvian area, AMLS and splenial visual area, SVA) that increased-all localized within the right hemisphere. Comparatively, the findings of tensor-based morphometry (TBM) generally aligned with those of the ROI-based method, as this voxel-wise approach demonstrated clusters of expansion coincident with visual- and somatosensory-related loci; although, it failed to detect any GM reductions following deafness. As distinct differences were identified in each analysis, the current study highlights the importance of employing multiple methods when exploring MRI volumetry. Overall, this study proposes that volumetric alterations within sensory loci allude to a redistribution of cortical space arising from modified perceptual demands following auditory deprivation.

Perception and discrimination of real-life emotional vocalizations in early blind individuals

Introduction

The capacity to understand others' emotions and react accordingly is a key social ability. However, it may be compromised in case of a profound sensory loss that limits the contribution of available contextual cues (e.g., facial expression, gestures, body posture) to interpret emotions expressed by others. In this study, we specifically investigated whether early blindness affects the capacity to interpret emotional vocalizations, whose valence may be difficult to recognize without a meaningful context.

Methods

We asked a group of early blind (N = 22) and sighted controls (N = 22) to evaluate the valence and the intensity of spontaneous fearful and joyful non-verbal vocalizations.

Results

Our data showed that emotional vocalizations presented alone (i.e., with no contextual information) are similarly ambiguous for blind and sighted individuals but are perceived as more intense by the former possibly reflecting their higher saliency when visual experience is unavailable.

Disussion

Our study contributes to a better understanding of how sensory experience shapes ememotion recognition.

Dark exposure reduces high-frequency hearing loss in C57BL/6J mice

Plastic changes in the brain are primarily limited to early postnatal periods. Recovery of adult brain plasticity is critical for the effective development of therapies. A brief (1-2 week) duration of visual deprivation (dark exposure, DE) in adult mice can trigger functional plasticity of thalamocortical and intracortical circuits in the primary auditory cortex suggesting improved sound processing. We tested if DE enhances the ability of adult mice to detect sounds. We trained and continuously evaluated the behavioral performance of mice in control and DE conditions using automated home-cage training. Consistent with age-related peripheral hearing loss present in C57BL/6J mice, we observed decreased performance for high-frequency sounds with age, which was reduced by DE. In CBA mice with preserved peripheral hearing, we also found that DE enhanced auditory performance in low and mid frequencies over time compared to the control.

The impact of early and late blindness on language and verbal working memory: A brain-constrained neural model

Neural circuits related to language exhibit a remarkable ability to reorganize and adapt in response to visual deprivation. Particularly, early and late blindness induce distinct neuroplastic changes in the visual cortex, repurposing it for language and semantic processing. Interestingly, these functional changes provoke a unique cognitive advantage - enhanced verbal working memory, particularly in early blindness. Yet, the underlying neuromechanisms and the impact on language and memory-related circuits remain not fully understood. Here, we applied a brain-constrained neural network mimicking the structural and functional features of the frontotemporal-occipital cortices, to model conceptual acquisition in early and late blindness. The results revealed differential expansion of conceptual-related neural circuits into deprived visual areas depending on the timing of visual loss, which is most prominent in early blindness. This neural recruitment is fundamentally governed by the biological principles of neural circuit expansion and the absence of uncorrelated sensory input. Critically, the degree of these changes is constrained by the availability of neural matter previously allocated to visual experiences, as in the case of late blindness. Moreover, we shed light on the implication of visual deprivation on the neural underpinnings of verbal working memory, revealing longer reverberatory neural activity in 'blind models' as compared to the sighted ones. These findings provide a better understanding of the interplay between visual deprivations, neuroplasticity, language processing and verbal working memory.

Connectome alterations following perinatal deafness in the cat

Following sensory deprivation, areas and networks in the brain may adapt and reorganize to compensate for the loss of input. These adaptations are manifestations of compensatory crossmodal plasticity, which has been documented in both human and animal models of deafness-including the domestic cat. Although there are abundant examples of structural plasticity in deaf felines from retrograde tracer-based studies, there is a lack of diffusion-based knowledge involving this model compared to the current breadth of human research. The purpose of this study was to explore white matter structural adaptations in the perinatally-deafened cat via tractography, increasing the methodological overlap between species. Plasticity was examined by identifying unique group connections and assessing altered connectional strength throughout the entirety of the brain. Results revealed a largely preserved connectome containing a limited number of group-specific or altered connections focused within and between sensory networks, which is generally corroborated by deaf feline anatomical tracer literature. Furthermore, five hubs of cortical plasticity and altered communication following perinatal deafness were observed. The limited differences found in the present study suggest that deafness-induced crossmodal plasticity is largely built upon intrinsic structural connections, with limited remodeling of underlying white matter.

Noise Sensitivity in Cataract Patients: A Retrospective Study

BACKGROUND

Noise sensitivity results from a series of variables and processes, and it can be used to predict the annoyance caused by noise and health-related outcomes. This study aimed to compare the noise sensitivity between cataract patients and healthy subjects and explore the effect of high noise sensitivity on cataract patients.

METHODS

A retrospective analysis was conducted on the clinical data of 100 cataract patients and 78 healthy subjects who underwent physical examination in Jiaozhou Central Hospital of Qingdao from February 2020 to February 2023. Noise sensitivity was evaluated by adopting the 8-Item Weinstein Noise Sensitivity Scale (WNSS-8). Comparisons were conducted on the psychological state scores, blood pressure (BP), and heart rate (HR) of the high- (HG) and low-noise-sensitivity (LG) groups.

RESULTS

Cataract patients exhibited lower visual acuity (P < 0.001) and higher WNSS-8 scores than the healthy subjects (P < 0.05). On the basis of the median of WNSS-8, the cataract patients were divided into HG (n = 42) and LG (n = 58). Compared with the LG, the HG presented higher Generalized Anxiety Disorder-7 scores, Beck Depression Inventory scores, systolic BP, diastolic BP and HR (P < 0.05).

CONCLUSIONS

High noise sensitivity in cataract patients may be associated with vision disorders, and it may affect their BP and HR and damage physical and mental health.

Blindness influences emotional authenticity perception in voices: Behavioral and ERP evidence

The ability to distinguish spontaneous from volitional emotional expressions is an important social skill. How do blind individuals perceive emotional authenticity? Unlike sighted individuals, they cannot rely on facial and body language cues, relying instead on vocal cues alone. Here, we combined behavioral and ERP measures to investigate authenticity perception in laughter and crying in individuals with early- or late-blindness onset. Early-blind, late-blind, and sighted control participants (n = 17 per group, N = 51) completed authenticity and emotion discrimination tasks while EEG data were recorded. The stimuli consisted of laughs and cries that were either spontaneous or volitional. The ERP analysis focused on the N1, P2, and late positive potential (LPP). Behaviorally, early-blind participants showed intact authenticity perception, but late-blind participants performed worse than controls. There were no group differences in the emotion discrimination task. In brain responses, all groups were sensitive to laughter authenticity at the P2 stage, and to crying authenticity at the early LPP stage. Nevertheless, only early-blind participants were sensitive to crying authenticity at the N1 and middle LPP stages, and to laughter authenticity at the early LPP stage. Furthermore, early-blind and sighted participants were more sensitive than late-blind ones to crying authenticity at the P2 and late LPP stages. Altogether, these findings suggest that early blindness relates to facilitated brain processing of authenticity in voices, both at early sensory and late cognitive-evaluative stages. Late-onset blindness, in contrast, relates to decreased sensitivity to authenticity at behavioral and brain levels.

Sound suppresses earliest visual cortical processing after sight recovery in congenitally blind humans

Neuroscientific research has consistently shown more extensive non-visual activity in the visual cortex of congenitally blind humans compared to sighted controls; a phenomenon known as crossmodal plasticity. Whether or not crossmodal activation of the visual cortex retracts if sight can be restored is still unknown. The present study, involving a rare group of sight-recovery individuals who were born pattern vision blind, employed visual event-related potentials to investigate persisting crossmodal modulation of the initial visual cortical processing stages. Here we report that the earliest, stimulus-driven retinotopic visual cortical activity (<100 ms) was suppressed in a spatially specific manner in sight-recovery individuals when concomitant sounds accompanied visual stimulation. In contrast, sounds did not modulate the earliest visual cortical response in two groups of typically sighted controls, nor in a third control group of sight-recovery individuals who had suffered a transient phase of later (rather than congenital) visual impairment. These results provide strong evidence for persisting crossmodal activity in the visual cortex after sight recovery following a period of congenital visual deprivation. Based on the time course of this modulation, we speculate on a role of exuberant crossmodal thalamic input which may arise during a sensitive phase of brain development.

Dual Sensory Impairment: Impact of Central Vision Loss and Hearing Loss on Visual and Auditory Localization

Purpose

In the United States, AMD is a leading cause of low vision that leads to central vision loss and has a high co-occurrence with hearing loss. The impact of central vision loss on the daily functioning of older individuals cannot be fully addressed without considering their hearing status. We investigated the impact of combined central vision loss and hearing loss on spatial localization, an ability critical for social interactions and navigation.

Methods

Sixteen older adults with central vision loss primarily due to AMD, with or without co-occurring hearing loss, completed a spatial perimetry task in which they verbally reported the directions of visual or auditory targets. Auditory testing was done with eyes open in a dimly lit room or with a blindfold. Twenty-three normally sighted, age-matched, and hearing-matched control subjects also completed the task.

Results

Subjects with central vision loss missed visual targets more often. They showed increased deviations in visual biases from control subjects as the scotoma size increased. However, these deficits did not generalize to sound localization. As hearing loss became more severe, the sound localization variability increased, and this relationship was not altered by coexisting central vision loss. For both control and central vision loss subjects, sound localization was less reliable when subjects wore blindfolds, possibly due to the absence of visual contextual cues.

Conclusions

Although central vision loss impairs visual localization, it does not impair sound localization and does not prevent vision from providing useful contextual cues for sound localization.

The Topo-Speech sensory substitution system as a method of conveying spatial information to the blind and vision impaired

Humans, like most animals, integrate sensory input in the brain from different sensory modalities. Yet humans are distinct in their ability to grasp symbolic input, which is interpreted into a cognitive mental representation of the world. This representation merges with external sensory input, providing modality integration of a different sort. This study evaluates the Topo-Speech algorithm in the blind and visually impaired. The system provides spatial information about the external world by applying sensory substitution alongside symbolic representations in a manner that corresponds with the unique way our brains acquire and process information. This is done by conveying spatial information, customarily acquired through vision, through the auditory channel, in a combination of sensory (auditory) features and symbolic language (named/spoken) features. The Topo-Speech sweeps the visual scene or image and represents objects' identity by employing naming in a spoken word and simultaneously conveying the objects' location by mapping the x-axis of the visual scene or image to the time it is announced and the y-axis by mapping the location to the pitch of the voice. This proof of concept study primarily explores the practical applicability of this approach in 22 visually impaired and blind individuals. The findings showed that individuals from both populations could effectively interpret and use the algorithm after a single training session. The blind showed an accuracy of 74.45%, while the visually impaired had an average accuracy of 72.74%. These results are comparable to those of the sighted, as shown in previous research, with all participants above chance level. As such, we demonstrate practically how aspects of spatial information can be transmitted through non-visual channels. To complement the findings, we weigh in on debates concerning models of spatial knowledge (the persistent, cumulative, or convergent models) and the capacity for spatial representation in the blind. We suggest the present study's findings support the convergence model and the scenario that posits the blind are capable of some aspects of spatial representation as depicted by the algorithm comparable to those of the sighted. Finally, we present possible future developments, implementations, and use cases for the system as an aid for the blind and visually impaired.