Lotfi Merabet

Massachusetts Eye and Ear Infirmary

Cerebral visual impairment (CVI) is a brain-based visual disorder associated with injury and/or maldevelopment of central visual pathways. Visuospatial processing impairments are a cardinal feature of the complex clinical profile of individuals with CVI. Here, we assessed visuospatial processing abilities using a classic conjunction search task. Tw...

Individuals with cerebral visual impairment (CVI) have difficulties identifying common objects, especially when presented as cartoons or abstract images. In this study, participants were shown a series of images of ten common objects, each from five possible categories ranging from abstract black & white line drawings to color photographs. Fifty in...

Aim: Using a visual psychophysical paradigm, we sought to assess motion and form coherence thresholds as indices of dorsal and ventral visual stream processing respectively, in individuals with cerebral visual impairment (CVI). We also explored potential associations between psychophysical assessments and brain lesion severity in CVI. Method: Tw...

Background Cerebral visual impairment (CVI) is a brain based visual disorder associated with the maldevelopment of central visual pathways. Individuals with CVI often report difficulties finding a target of interest in cluttered and crowded visual scenes. However, it remains unknown how manipulating task demands and other environmental factors infl...

Background Angelman syndrome (AS) is a rare neurogenetic disorder caused by altered expression of the maternal copy of the UBE3A gene. Together with motor, cognitive, and speech impairment, ophthalmological findings including strabismus, and ocular fundus hypopigmentation characterize the clinical phenotype. The aim of this study was to detail the...

Visuospatial processing deficits are commonly observed in individuals with cerebral visual impairment (CVI) and even in cases where visual acuity and visual field functions are intact. CVI is a brain-based visual disorder associated with the maldevelopment of central visual pathways and structures. However, the neurophysiological basis underlying h...

Vision is a primary and motivating sense. Early visual experience derived from the external world is known to have an important impact on the development of central visual pathways and, not surprisingly, visual impairment constitutes a risk factor for overall development. In light of the role of vision in early brain development, infants and young...

Cerebral visual impairment (CVI) is a brain-based disorder associated with the maldevelopment of central visual pathways. Individuals with CVI often report difficulties with daily visual search tasks such as finding a favorite toy or familiar person in cluttered and crowded scenes. We developed two novel virtual reality (VR)-based visual search tas...

Cerebral visual impairment (CVI) is associated with a wide range of visual perceptual deficits including global motion processing. However, the underlying neurophysiological basis for these impairments remain poorly understood. We investigated global motion processing abilities in individuals with CVI compared to neurotypical controls using a combi...

Cerebral visual impairment (CVI) often presents with deficits associated with higher order visual processing. We report a case of an individual with CVI who uses a verbal mediation strategy to perceive and interact with his visual surroundings. Visual perceptual performance was assessed using a virtual reality based visual search task combined with...

Individuals with cerebral visual impairment (CVI) often present with deficits related to visuospatial processing. However, the neurophysiological basis underlying these higher order perceptual dysfunctions have not been clearly identified. We assessed visual search performance using a novel virtual reality based task paired with eye tracking to sim...

Aim To evaluate the effectiveness of early visual training and environmental adaptation on visual function and neurological development in infants with visual impairment. Method This was a pilot intervention clinical trial study. Thirty infants (mean age 5.9mo, SD 2.1mo, range 4–11mo; 16 males, 14 females) with peripheral visual impairment (PVI, n...

Daily activities require the constant searching and tracking of visual targets in dynamic and complex scenes. Classic work assessing visual search performance has been dominated by the use of simple geometric shapes, patterns, and static backgrounds. Recently, there has been a shift toward investigating visual search in more naturalistic dynamic sc...

Cerebral (cortical) visual impairment (CVI) is associated with perinatal damage to retrochiasmatic pathways and cerebral structures. Individuals with CVI often present with impairments in visual spatial processing and attention. However, the neural correlates associated with these higher order perceptual deficits remain unknown. In this study, we i...

The human cerebral cortex is asymmetrically organized with hemispheric lateralization pervading nearly all neural systems of the brain. Whether the lack of normal visual development affects hemispheric specialization subserving the deployment of visuospatial attention asymmetries is controversial. In principle, indeed, the lack of early visual expe...

There remains great interest in understanding the relationship between visual impairment (VI) and autism spectrum disorder (ASD) due to the extraordinarily high prevalence of ASD in blind and visually impaired children. The broad variability across individuals and assessment methodologies have made it difficult to understand whether autistic-like s...

Cerebral visual impairment (CVI) results from perinatal injury to visual processing structures and pathways and is the most common individual cause of pediatric visual impairment and blindness in developed countries. While there is mounting evidence demonstrating extensive neuroplastic reorganization in early onset, profound ocular blindness, how t...

As humans, we rely heavily on our vision to interact with the world. Therefore, it is not surprising that individuals who are profoundly blind must make remarkable adjustments in order to pursue education, secure employment, and remain socially integrated. According to the World Health Organization (WHO), approximately 285 million people are visual...

The complete assessment of vision-related abilities should consider visual function (the performance of components of the visual system) and functional vision (visual task-related ability). Assessment methods are highly dependent upon individual characteristics (eg, the presence and type of visual impairment). Typical visual function tests assess f...

Mirror therapy (MT) has been proposed as an effective rehabilitative strategy to alleviate pain symptoms in amputees with phantom limb pain (PLP). However, establishing the neural correlates associated with MT therapy have been challenging given that it is difficult to administer the therapy effectively within a magnetic resonance imaging (MRI) sca...

Prior studies have shown that strabismic amblyopes do not exhibit pseudoneglect in visual line bisection, suggesting that the right-hemisphere dominance in the control of spatial attention may depend on a normally developing binocular vision. In this study, we aimed to investigate whether an abnormal binocular childhood experience also affects spat...

Little is known about how the brain processes information while navigating without visual cues. Technical limitations recording brain activity during real-world navigation have impeded research in this field. We have developed a study paradigm that benefits from wireless EEG recording technology. Participants heard a sequence of directional command...

Vision loss due to ocular diseases such as glaucoma, optic neuropathy, macular degeneration, or diabetic retinopathy, are generally considered an exclusive affair of the retina and/or optic nerve. However, the brain, through multiple indirect influences, has also a major impact on functional visual impairment. Such indirect influences include intra...

The spatial representation of numerical and temporal information is thought to be rooted in our multisensory experiences. Accordingly, we may expect visual or auditory deprivation to affect the way we represent numerical magnitude and time spatially. Here, we systematically review recent findings on how blind and deaf individuals represent abstract...

Children with cerebral palsy often present with cognitive‐visual dysfunctions characterized by visuo‐perceptual and/or visuo‐spatial deficits associated with a malfunctioning of visual‐associative areas. The neurofunctional model of this condition remains poorly understood due to the lack of a clear correlation between cognitive‐visual deficit and...

Virtual reality (VR) can provide robust assessment of cognitive spatial processing skills in individuals with visual impairment. VR combined with objective measures of behavioral performance, such as eye and hand tracking, affords a high degree of experimental control, task flexibility, participant engagement, and enhanced data capture. Individuals...

A growing body of evidence demonstrates that the brain can reorganize dramatically following sensory loss. Although the existence of such neuroplastic crossmodal changes is not in doubt, the functional significance of these changes remains unclear. The dominant belief is that reorganization is compensatory. However, results thus far do not unequivo...

Virtual reality (VR) can provide robust assessment of cognitive spatial processing skills in individuals with visual impairment. VR combined with objective measures of behavioral performance (i.e., eye tracking) affords a high degree of experimental control, task flexibility, participant engagement, and enhanced data capture. Individuals with visua...

Objective The impact of visuospatial attention on perception with supraliminal stimuli and stimuli at the threshold of conscious perception has been previously investigated. In this study, we assess the cross-modal effects of visuospatial attention on conscious perception for near-threshold somatosensory stimuli applied to the face. Methods Fiftee...

Selecting a research question is the first step of any research project. This chapter discusses how to formulate a specific research question from a variety of scientific interests. The reader will learn that a good research question needs to consider several aspects, such as feasibility, innovation, and significance, and that merging all these asp...

Converging evidence suggests that the perception of auditory pitch exhibits a characteristic spatial organization. This pitch–space association can be demonstrated experimentally by the Spatial Musical Association of Response Codes (SMARC) effect. This is characterized by faster response times when a low-positioned key is pressed in response to a l...

Growing evidence demonstrates dramatic structural and functional neuroplastic changes in individuals born with early onset blindness. For example, crossmodal sensory processing at the level of the occipital cortex appears to be associated with adaptive behaviors in the blind. However, detailed studies examining the structural properties of key whit...

In many cultures, humans conceptualize the past as behind the body and the future as in front. Whether this spatial mapping of time depends on visual experience is still not known. Here, we addressed this issue by testing early-blind participants in a space–time motor congruity task requiring them to classify a series of words as referring to the p...

Learning to read causes the development of a letter- and word-selective region known as the visual word form area (VWFA) within the human ventral visual object stream. Why does a reading-selective region develop at this anatomical location? According to one hypothesis, the VWFA develops at the nexus of visual inputs from retinotopic cortices and li...

Investigating the impact of early visual deprivation on evaluations related to social trust has received little attention to date. This is despite consistent evidence suggesting that early onset blindness may interfere with the normal development of social skills. In this study, we investigated whether early blindness affects judgments of trustwort...

Background and Aim: Diabetic macular edema (DME) is one of the leading causes of visual impairment among working-aged people responsible for more than 10,000 new cases of blindness per year. Although there are some therapeutical options for this disease, most of them are invasive, expensive, subject to a range of side effects, and may not be access...

Background: Deterministic diffusion tractography obtained from high angular resolution diffusion imaging (HARDI) requires user-defined quantitative anisotropy (QA) thresholds. Most studies employ a common threshold across all subjects even though there is a strong degree of individual variation within groups. We sought to explore whether it would...

This paper presents an ongoing work on methods for usability evaluation of audio- and haptic-based video games for learners who are blind. We report a Standard Usability Problem List which we envision to be the basis for comparison of the Usability Evaluation Methods (UEM) in this context. In addition, we present a preliminary analysis of evidence...

p class="abstract">Phantom limp pain (PLP) was first described in 1551. To date, its mechanisms and novel interventions remain mostly untested. Only limited conclusions can be drawn from few and small sized randomized clinical trials (RCTs) on PLP. In this scenario, enhanced recruitment strategies are crucial in order to overcome inherent challenge...

Cortical/cerebral visual impairment (CVI) results from perinatal injury to visual processing structures and pathways of the brain and is the most common cause of severe visual impairment/blindness in children in developed countries. Children with CVI display a wide range of visual deficits including decreased visual acuity, impaired visual field fu...

In the setting of profound ocular blindness, numerous lines of evidence demonstrate the existence of dramatic anatomical and functional changes within the brain. However, previous studies based on a variety of distinct measures have often provided inconsistent findings. To help reconcile this issue, we used a multimodal magnetic resonance (MR)-base...

Morphometry. Surface based morphometry analysis comparing differences in A) cortical volume and B) cortical thickness between early blind and sighted controls (corrected for multiple comparisons). Decreases in cortical volume (shown in blue) were evident within the left pericalcalcarine region, while increases (shown in red) were evident in right i...

Surface Based Morphometry Analysis (uncorrected). (DOCX)

Analysis of Quantitative Anisotropy (QA) values. Quantitative anisotropy (QA) values revealed by HARDI. A) Exploratory analysis of ROI-pairs revealed an overall tendency for both increases and decreases in QA in ocular blind compared to sighted controls. Decreases were spread throughout both inter- and intra-hemispheric connections, whereas increas...

HARDI QA (corrected). (DOCX)

Objective: Emotion processing is known to be mediated by a complex network of cortical and subcortical regions with evidence of specialized hemispheric lateralization within the brain. In light of prior evidence indicating that lateralization of cognitive functions (such as language) may depend on normal visual development, we investigated whether...

Cortical/cerebral visual impairment (CVI) is clinically defined as significant visual dysfunction caused by injury to visual pathways and structures occurring during early perinatal development. Depending on the location and extent of damage, children with CVI often present with a myriad of visual deficits including decreased visual acuity and impa...

Top-down influences allow the visual system to perceive globally meaningful structures in spatial patterns that may be locally noisy. This has been demonstrated in classic effects such as the Dalmation dog picture and black-and-white thresholded Mooney images (Gregory, 1970; Mooney, 1957). Yet, in the case of vision, global spatial organization is...

We are investigating cognitive spatial mapping skills in people who are blind through the use of virtual navigation and assessing the transference of acquired spatial knowledge in large-scale, real-world navigation tasks. Training is carried out with a user-centered, computer-based, navigation software platform called Haptic Audio Game Application...

Background: Despite the multiple available pharmacological and behavioral therapies for the management of chronic phantom limb pain (PLP) in lower limb amputees, treatment for this condition is still a major challenge and the results are mixed. Given that PLP is associated with maladaptive brain plasticity, interventions that promote cortical reor...

Advances in neuroimaging technology have been instrumental in uncovering the dramatic neurological changes that result from blindness, as well as revealing the inner workings of the human brain. Specifically, modern imaging techniques enable us to examine how the brain adapts and “re-wires” itself as a result of changes in behavior, the environment...

Recent evidence suggests that in representing numbers blind individuals might be affected differently by proprioceptive cues (e.g., hand positions, head turns) than are sighted individuals. In this study, we asked a group of early blind and sighted individuals to perform a numerical bisection task while executing hand movements in left or right per...

It is well known that in the case of blindness, the visual cortex is implicated in the processing of non-visual sensory processing [1]. These neuroplastic adaptations may be related to changes in structural and functional connectivity however, few studies have taken a multimodal approach in examining both diffusion based and resting state whole bra...

Symmetry is an organizational principle that is ubiquitous throughout the visual world. However, this property can also be detected through non-visual modalities such as touch. The role of prior visual experience on detecting tactile patterns containing symmetry remains unclear. We compared the behavioral performance of early blind and sighted (bli...

In the so-called McGurk illusion, when the synchronized presentation of the visual stimulus /ga/ is paired with the auditory stimulus /ba/, people in general hear it as /da/. Multisensory integration processing underlying this illusion seems to occur within the Superior Temporal Sulcus (STS). Herein, we present evidence demonstrating that bilateral...

Cortical (cerebral) visual impairment (CVI) is characterized by visual dysfunction associated with damage to the optic radiations and/or visual cortex. Typically it results from pre- or perinatal hypoxic damage to postchiasmal visual structures and pathways. The neuroanatomical basis of this condition remains poorly understood, particularly with re...

IntroductionThe International Neuromodulation Society (INS) has identified a need for evaluation and analysis of the practice of neurostimulation of the brain and extracranial nerves of the head to treat chronic pain.Methods The INS board of directors chose an expert panel, the Neuromodulation Appropriateness Consensus Committee (NACC), to evaluate...

With advances in assistive technology, the development of retinal prostheses, and the use of stem cells for retinal and corneal repair, the paradigm of vision rehabilitation is evolving. Now more than ever, clinicians need novel strategies for rehabilitative treatment, assessing outcomes, and determining overall rehabilitative success. The capacity...

Graphical information, such as illustrations, graphs, and diagrams, are an essential complement to text for conveying knowledge about the world. Although graphics can be communicated well via the visual modality, conveying this information via touch has proven to be challenging. The lack of easily comprehensible tactile graphics poses a problem for...

Symmetry detection is impaired by abnormal binocular vision development such as in amblyopia. However, the detection of symmetry has never been investigated in cases where input from one eye is profoundly compromised. Testing monocularly blind (MB) individuals represents a unique opportunity to investigate whether symmetry salience relies on a norm...

Navigating is a complex cognitive task that places high demands on spatial abilities, particularly in the absence of sight. Significant advances have been made in identifying the neural correlates associated with various aspects of this skill; however, how the brain is able to navigate in the absence of visual experience remains poorly understood....

To explain the biological foundations of art appreciation is to explain one of our species' distinctive traits. Previous neuroimaging and electrophysiological studies have pointed to the prefrontal and the parietal cortex as two critical regions mediating aesthetic appreciation of visual art. In this study, we applied transcranial magnetic stimulat...

For profoundly blind individuals, navigating in an unfamiliar building can represent a significant challenge. We investigated the use of an audio-based, virtual environment called Audio-based Environment Simulator (AbES) that can be explored for the purposes of learning the layout of an unfamiliar, complex indoor environment. Furthermore, we compar...

Consistent evidence suggests that pitch height may be represented in a spatial format, having both a vertical and a horizontal representation. The spatial representation of pitch height results into response compatibility effects for which high pitch tones are preferentially associated to up-right responses, and low pitch tones are preferentially a...

For individuals who are blind, navigating independently in an unfamiliar environment represents a considerable challenge. Inspired by the rising popularity of video games, we have developed a novel approach to train navigation and spatial cognition skills in adolescents who are blind. Audio-based Environment Simulator (AbES) is a software applicati...