Long-term deprivation affects visual perception and cortex

Pattern-reversal visual evoked potentials in prosthetic vision and simulated visual reduction

OBJECTIVE

To quantitatively evaluate visual evoked potentials (VEPs) in prosthetic vision and simulated visual reduction.

METHODS AND ANALYSIS

Four blind patients implanted with the Argus II retinal prosthesis and seven sighted controls participated. VEPs were recorded with pattern-reversal stimuli (2 cycles of a horizontal square wave grating, 0.1 cycle/degree) at 1.07 reversals per second (rps) for Argus II subjects and 3.37 rps for controls. Argus II patients had both eyes patched, viewing the pattern solely through their implant. Controls viewed the pattern monocularly, either with their best-corrected vision or with simulated visual reduction (field restriction, added blur or reduced display contrast).

RESULTS

VEPs recorded in Argus II patients displayed a similar shape to normal VEPs when controls viewed the pattern without simulated visual reduction. In sighted controls, adding blur significantly delayed the P100 peak time by 8.7 ms, 95% CI (0.9, 16.6). Reducing stimulus contrast to 32% and 6% of full display contrast significantly decreased P100 amplitude to 55% (37%, 82%) and 20% (13%, 31%), respectively. Restriction on the field of view had no impact on either the amplitude or the peak latency of P100.

CONCLUSION

The early visual cortex in retinal prosthesis users remains responsive to retinal input, showing a similar response profile to that of sighted controls. Pattern-reversal VEP offers valuable insights for objectively evaluating artificial vision therapy systems (AVTSs) when selecting, fitting and training implant users, but the uncertainties in the exact timing and location of electrode stimulation must be considered when interpreting the results.

Motion's privilege in recognizing facial expressions following treatment for blindness

In his 1872 monograph, Charles Darwin posited that "… the habit of expressing our feelings by certain movements, though now rendered innate, had been in some manner gradually acquired."1 Nearly 150 years later, researchers are still teasing apart innate versus experience-dependent contributions to expression recognition. Indeed, studies have shown that face detection is surprisingly resilient to early visual deprivation,2,3,4,5 pointing to plasticity that extends beyond dogmatic critical periods.6,7,8 However, it remains unclear whether such resilience extends to downstream processing, such as the ability to recognize facial expressions. The extent to which innate versus experience-dependent mechanisms contribute to this ability has yet to be fully explored.9,10,11,12,13 To investigate the impact of early visual experience on facial-expression recognition, we studied children with congenital cataracts who have undergone sight-correcting treatment14,15 and tracked their longitudinal skill acquisition as they gain sight late in life. We introduce and explore two potential facilitators of late-life plasticity: the availability of newborn-like coarse visual acuity prior to treatment16 and the privileged role of motion following treatment.4,17,18 We find that early visual deprivation does not preclude partial acquisition of facial-expression recognition. While rudimentary pretreatment vision is sufficient to allow a low level of expression recognition, it does not facilitate post-treatment improvements. Additionally, only children commencing vision with high visual acuity privilege the use of dynamic cues. We conclude that skipping typical visual experience early in development and introducing high-resolution imagery late in development restricts, but does not preclude, facial-expression skill acquisition and that the representational mechanisms driving this learning differ from those that emerge during typical visual development.

First-sight recognition of touched objects shows that chicks can solve Molyneux's problem

If a congenitally blind person learns to distinguish between a cube and a sphere by touch, would they immediately recognize these objects by sight once their vision is restored? This question, posed by Molyneux in 1688, has puzzled philosophers and scientists since then. To overcome ethical and practical difficulties in the investigation of cross-modal recognition, we studied inexperienced poultry chicks, which can be reared in darkness until the moment of a visual test with no detrimental consequences. After hatching chicks in darkness, we exposed them to either tactile smooth or tactile bumpy stimuli for 24 h. Immediately after the tactile exposure, chicks were tested in a visual recognition task, during their first experience with light. At first sight, chicks that had been exposed in the tactile modality to smooth stimuli approached the visual smooth stimulus significantly more than those exposed to the tactile bumpy stimuli. These results show that visually inexperienced chicks can solve Molyneux's problem, indicating cross-modal recognition does not require previous multimodal experience. At least in this precocial species, supra-modal brain areas appear functional already at birth. This discovery paves the way for the investigation of predisposed cross-modal cognition that does not depend on visual experience.

Short-term monocular pattern deprivation reduces the internal additive noise of the visual system

Previous studies have shown that short-term monocular pattern deprivation can shift perceptual dominance in favor of the deprived eye. However, little is known about the effect of monocular pattern deprivation on contrast sensitivity (CS) and its corresponding mechanisms. Here, contrast sensitivity function (CSF) in the nondominant eye of normal subjects was evaluated before and after 150 min of monocular pattern deprivation. To obtain a CSF with high precision and efficiency before deprivation effect washout, a quick CSF (qCSF) method was used to assess CS over a wide range of spatial frequencies and at two external noise levels. We found that (1) monocular pattern deprivation effectively improved the CS of the deprived eye with larger effect on high spatial frequencies, (2) CS improvement only occurred when external noise was absent and its amount was spatial frequency dependent, and (3) a perceptual template model (PTM) revealed that decreased internal additive noise accounted for the mechanism of the monocular pattern derivation effect. These findings help us better understand the features of short-term monocular pattern deprivation and shed light on the treatment of amblyopia.

From intermediate shape-centered representations to the perception of oriented shapes: response to commentaries

In this response paper, we start by addressing the main points made by the commentators on the target article's main theoretical conclusions: the existence and characteristics of the intermediate shape-centered representations (ISCRs) in the visual system, their emergence from edge detection mechanisms operating on different types of visual properties, and how they are eventually reunited in higher order frames of reference underlying conscious visual perception. We also address the much-commented issue of the possible neural mechanisms of the ISCRs. In the final section, we address more specific and general comments, questions, and suggestions which, albeit very interesting, were less directly focused on the main conclusions of the target paper.

New Approaches to 3D Vision

New approaches to 3D vision are enabling new advances in artificial intelligence and autonomous vehicles, a better understanding of how animals navigate the 3D world, and new insights into human perception in virtual and augmented reality. Whilst traditional approaches to 3D vision in computer vision (SLAM: simultaneous localization and mapping), animal navigation (cognitive maps), and human vision (optimal cue integration) start from the assumption that the aim of 3D vision is to provide an accurate 3D model of the world, the new approaches to 3D vision explored in this issue challenge this assumption. Instead, they investigate the possibility that computer vision, animal navigation, and human vision can rely on partial or distorted models or no model at all. This issue also highlights the implications for artificial intelligence, autonomous vehicles, human perception in virtual and augmented reality, and the treatment of visual disorders, all of which are explored by individual articles. This article is part of a discussion meeting issue 'New approaches to 3D vision'.

Minimal theory of 3D vision: new approach to visual scale and visual shape

Since Kepler and Descartes in the early-1600s, vision science has been committed to a triangulation model of stereo vision. But in the early-1800s, we realized that disparities are responsible for stereo vision. And we have spent the past 200 years trying to shoe-horn disparities back into the triangulation account. The first part of this article argues that this is a mistake, and that stereo vision is a solution to a different problem: the eradication of rivalry between the two retinal images, rather than the triangulation of objects in space. This leads to a 'minimal theory of 3D vision', where 3D vision is no longer tied to estimating the scale, shape, and direction of objects in the world. The second part of this article then asks whether the other aspects of 3D vision, which go beyond stereo vision, really operate at the same level of visual experience as stereo vision? I argue they do not. Whilst we want a theory of real-world 3D vision, the literature risks giving us a theory of picture perception instead. And I argue for a two-stage theory, where our purely internal 'minimal' 3D percept (from stereo vision) is linked to the world through cognition. This article is part of a discussion meeting issue 'New approaches to 3D vision'.

Do you hear what I see? How do early blind individuals experience object motion?

One of the most important tasks for 3D vision is tracking the movement of objects in space. The ability of early blind individuals to understand motion in the environment from noisy and unreliable auditory information is an impressive example of cortical adaptation that is only just beginning to be understood. Here, we compare visual and auditory motion processing, and discuss the effect of early blindness on the perception of auditory motion. Blindness leads to cross-modal recruitment of the visual motion area hMT+ for auditory motion processing. Meanwhile, the planum temporale, associated with auditory motion in sighted individuals, shows reduced selectivity for auditory motion. We discuss how this dramatic shift in the cortical basis of motion processing might influence the perceptual experience of motion in early blind individuals. This article is part of a discussion meeting issue 'New approaches to 3D vision'.

Testing geometry and 3D perception in children following vision restoring cataract-removal surgery

As neuroscience and rehabilitative techniques advance, age-old questions concerning the visual experience of those who gain sight after blindness, once thought to be philosophical alone, take center stage and become the target for scientific inquiries. In this study, we employ a battery of visual perception tasks to study the unique experience of a small group of children who have undergone vision-restoring cataract removal surgery as part of the Himalayan Cataract Project. We tested their abilities to perceive in three dimensions (3D) using a binocular rivalry task and the Brock string task, perceive visual illusions, use cross-modal mappings between touch and vision, and spatially group based on geometric cues. Some of the children in this study gained a sense of sight for the first time in their lives, having been born with bilateral congenital cataracts, while others suffered late-onset blindness in one eye alone. This study simultaneously supports yet raises further questions concerning Hubel and Wiesel's critical periods theory and provides additional insight into Molyneux's problem, the ability to correlate vision with touch quickly. We suggest that our findings present a relatively unexplored intermediate stage of 3D vision development. Importantly, we spotlight some essential geometrical perception visual abilities that strengthen the idea that spontaneous geometry intuitions arise independently from visual experience (and education), thus replicating and extending previous studies. We incorporate a new model, not previously explored, of testing children with congenital cataract removal surgeries who perform the task via vision. In contrast, previous work has explored these abilities in the congenitally blind via touch. Taken together, our findings provide insight into the development of what is commonly known as the visual system in the visually deprived and highlight the need to further empirically explore an amodal, task-based interpretation of specializations in the development and structure of the brain. Moreover, we propose a novel objective method, based on a simple binocular rivalry task and the Brock string task, for determining congenital (early) vs. late blindness where medical history and records are partial or lacking (e.g., as is often the case in cataract removal cases).

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.

Learning to see after early and extended blindness: A scoping review

PURPOSE

If an individual has been blind since birth due to a treatable eye condition, ocular treatment is urgent. Even a brief period of visual deprivation can alter the development of the visual system. The goal of our structured scoping review was to understand how we might better support children with delayed access to ocular treatment for blinding conditions.

METHOD

We searched MEDLINE, Embase and Global Health for peer-reviewed publications that described the impact of early (within the first year) and extended (lasting at least 2 years) bilateral visual deprivation.

RESULTS

Of 551 reports independently screened by two authors, 42 studies met our inclusion criteria. Synthesizing extracted data revealed several trends. The data suggests persistent deficits in visual acuity, contrast sensitivity, global motion, and visual-motor integration, and suspected concerns for understanding complex objects and faces. There is evidence for resilience in color perception, understanding of simple shapes, discriminating between a face and non-face, and the perception of biological motion. There is currently insufficient data about specific (re)habilitation strategies to update low vision services, but there are several insights to guide future research in this domain.

CONCLUSION

This summary will help guide the research and services provision to help children learn to see after early and extended blindness.

Face shape processing via visual-to-auditory sensory substitution activates regions within the face processing networks in the absence of visual experience

Previous evidence suggests that visual experience is crucial for the emergence and tuning of the typical neural system for face recognition. To challenge this conclusion, we trained congenitally blind adults to recognize faces via visual-to-auditory sensory-substitution (SDD). Our results showed a preference for trained faces over other SSD-conveyed visual categories in the fusiform gyrus and in other known face-responsive-regions of the deprived ventral visual stream. We also observed a parametric modulation in the same cortical regions, for face orientation (upright vs. inverted) and face novelty (trained vs. untrained). Our results strengthen the conclusion that there is a predisposition for sensory-independent and computation-specific processing in specific cortical regions that can be retained in life-long sensory deprivation, independently of previous perceptual experience. They also highlight that if the right training is provided, such cortical preference maintains its tuning to what were considered visual-specific face features.

Implications of Neural Plasticity in Retinal Prosthesis

Retinal degenerative diseases such as retinitis pigmentosa cause a progressive loss of photoreceptors that eventually prevents the affected person from perceiving visual sensations. The absence of a visual input produces a neural rewiring cascade that propagates along the visual system. This remodeling occurs first within the retina. Then, subsequent neuroplastic changes take place at higher visual centers in the brain, produced by either the abnormal neural encoding of the visual inputs delivered by the diseased retina or as the result of an adaptation to visual deprivation. While retinal implants can activate the surviving retinal neurons by delivering electric current, the unselective activation patterns of the different neural populations that exist in the retinal layers differ substantially from those in physiologic vision. Therefore, artificially induced neural patterns are being delivered to a brain that has already undergone important neural reconnections. Whether or not the modulation of this neural rewiring can improve the performance for retinal prostheses remains a critical question whose answer may be the enabler of improved functional artificial vision and more personalized neurorehabilitation strategies.

Brain Gray Matter Atrophy and Functional Connectivity Remodeling in Patients With Chronic LHON

Purpose

The aim of this study was to investigate the brain gray matter volume (GMV) and spontaneous functional connectivity (FC) changes in patients with chronic Leber's hereditary optic neuropathy (LHON), and their relations with clinical measures.

Methods

A total of 32 patients with chronic LHON and matched sighted healthy controls (HC) underwent neuro-ophthalmologic examinations and multimodel magnetic resonance imaging (MRI) scans. Voxel-based morphometry (VBM) was used to detect the GMV differences between the LHON and HC. Furthermore, resting-state FC analysis using the VBM-identified clusters as seeds was carried out to detect potential functional reorganization in the LHON. Finally, the associations between the neuroimaging and clinical measures were performed.

Results

The average peripapillary retinal nerve fiber layer (RNFL) thickness of the chronic LHON was significantly thinner (T = −16.421, p < 0.001), and the mean defect of the visual field was significantly higher (T = 11.28, p < 0.001) than the HC. VBM analysis demonstrated a significantly lower GMV of bilateral calcarine gyri (CGs) in the LHON than in the HC (p < 0.05). Moreover, in comparison with the HC, the LHON had significantly lower FC between the centroid of the identified left CG and ipsilateral superior occipital gyrus (SOG) and higher FC between this cluster and the ipsilateral posterior cingulate gyrus (p < 0.05, corrected). Finally, the GMV of the left CG was negatively correlated with the LHON duration (r = −0.535, p = 0.002), and the FC between the left CG and the ipsilateral posterior cingulate gyrus of the LHON was negatively correlated with the average peripapillary RNFL thickness (r = −0.522, p = 0.003).

Conclusion

The atrophied primary visual cortex of the chronic LHON may be caused by transneuronal degeneration following the retinal damage. Moreover, our findings suggest that the functional organization of the atrophied primary visual cortex has been reshaped in the chronic LHON.

Development of Visual Memory Capacity Following Early-Onset and Extended Blindness

It is unknown whether visual memory capacity can develop if onset of pattern vision is delayed for several years following birth. We had an opportunity to address this question through our work with an unusual population of 12 congenitally blind individuals ranging in age from 8 to 22 years. After providing them with sight surgery, we longitudinally evaluated their visual memory capacity using an image-memorization task. Our findings revealed poor visual memory capacity soon after surgery but significant improvement in subsequent months. Although there may be limits to this improvement, performance 1 year after surgery was found to be comparable with that of control participants with matched visual acuity. These findings provide evidence for plasticity of visual memory mechanisms into late childhood but do not rule out vulnerability to early deprivation. Our computational simulations suggest that a potential mechanism to account for changes in memory performance may be progressive representational elaboration in image encoding.

Congenitally blind adults can learn to identify face-shapes via auditory sensory substitution and successfully generalize some of the learned features

Unlike sighted individuals, congenitally blind individuals have little to no experience with face shapes. Instead, they rely on non-shape cues, such as voices, to perform character identification. The extent to which face-shape perception can be learned in adulthood via a different sensory modality (i.e., not vision) remains poorly explored. We used a visual-to-auditory Sensory Substitution Device (SSD) that enables conversion of visual images to the auditory modality while preserving their visual characteristics. Expert SSD users were systematically taught to identify cartoon faces via audition. Following a tailored training program lasting ~ 12 h, congenitally blind participants successfully identified six trained faces with high accuracy. Furthermore, they effectively generalized their identification to the untrained, inverted orientation of the learned faces. Finally, after completing the extensive 12-h training program, participants learned six new faces within 2 additional hours of training, suggesting internalization of face-identification processes. Our results document for the first time that facial features can be processed through audition, even in the absence of visual experience across the lifespan. Overall, these findings have important implications for both non-visual object recognition and visual rehabilitation practices and prompt the study of the neural processes underlying auditory face perception in the absence of vision.

Early visual exposure primes future cross-modal specialization of the fusiform face area in tactile face processing in the blind

The fusiform face area (FFA) is a core cortical region for face information processing. Evidence suggests that its sensitivity to faces is largely innate and tuned by visual experience. However, how experience in different time windows shape the plasticity of the FFA remains unclear. In this study, we investigated the role of visual experience at different time points of an individual's early development in the cross-modal face specialization of the FFA. Participants (n = 74) were classified into five groups: congenital blind, early blind, late blind, low vision, and sighted control. Functional magnetic resonance imaging data were acquired when the participants haptically processed carved faces and other objects. Our results showed a robust and highly consistent face-selective activation in the FFA region in the early blind participants, invariant to size and level of abstraction of the face stimuli. The cross-modal face activation in the FFA was much less consistent in other groups. These results suggest that early visual experience primes cross-modal specialization of the FFA, and even after the absence of visual experience for more than 14 years in early blind participants, their FFA can engage in cross-modal processing of face information.

Structural Differences Across Multiple Visual Cortical Regions in the Absence of Cone Function in Congenital Achromatopsia

Most individuals with congenital achromatopsia (ACHM) carry mutations that affect the retinal phototransduction pathway of cone photoreceptors, fundamental to both high acuity vision and colour perception. As the central fovea is occupied solely by cones, achromats have an absence of retinal input to the visual cortex and a small central area of blindness. Additionally, those with complete ACHM have no colour perception, and colour processing regions of the ventral cortex also lack typical chromatic signals from the cones. This study examined the cortical morphology (grey matter volume, cortical thickness, and cortical surface area) of multiple visual cortical regions in ACHM (n = 15) compared to normally sighted controls (n = 42) to determine the cortical changes that are associated with the retinal characteristics of ACHM. Surface-based morphometry was applied to T1-weighted MRI in atlas-defined early, ventral and dorsal visual regions of interest. Reduced grey matter volume in V1, V2, V3, and V4 was found in ACHM compared to controls, driven by a reduction in cortical surface area as there was no significant reduction in cortical thickness. Cortical surface area (but not thickness) was reduced in a wide range of areas (V1, V2, V3, TO1, V4, and LO1). Reduction in early visual areas with large foveal representations (V1, V2, and V3) suggests that the lack of foveal input to the visual cortex was a major driving factor in morphological changes in ACHM. However, the significant reduction in ventral area V4 coupled with the lack of difference in dorsal areas V3a and V3b suggest that deprivation of chromatic signals to visual cortex in ACHM may also contribute to changes in cortical morphology. This research shows that the congenital lack of cone input to the visual cortex can lead to widespread structural changes across multiple visual areas.

A review on various explanations of Ponzo-like illusions

This article reviews theoretical and empirical arguments for and against various theories that explain the classic Ponzo illusion and its variants from two different viewpoints concerning the role of perceived depth in size distortions. The first viewpoint argues that all Ponzo-like illusions are driven by perceived depth. The second viewpoint argues that the classic Ponzo illusion is unrelated to depth perception. This review will give special focus to the first viewpoint and consists of three sections. In the first section, the role of the number of pictorial depth cues and previous experience in the strength of all Ponzo-like illusions are discussed. In the second section, we contrast the first viewpoint against the theories that explain the classic Ponzo illusion with mechanisms that are unrelated to depth perception. In the last section, we propose a Bayesian-motivated reconceptualization of Richard Gregory's misapplied size constancy theory that explains Ponzo-variant illusions in terms of prior information and prediction errors. The new account explains why some studies have provided inconsistent evidence for misapplied size constancy theory.

Shape-centered representations of bounded regions of space mediate the perception of objects

We report the study of a woman who perceives 2D bounded regions of space ("shapes") defined by sharp edges of medium to high contrast as if they were rotated by 90, 180 degrees around their centre, mirrored across their own axes, or both. In contrast, her perception of 3D, strongly blurred or very low contrast shapes, and of stimuli emerging from a collection of shapes, is intact. This suggests that a stage in the process of constructing the conscious visual representation of a scene consists of representing mutually exclusive bounded regions extracted from the initial retinotopic space in "shape-centered" frames of reference. The selectivity of the disorder to shapes originally biased toward the parvocellular subcortical pathway, and the absence of any other type of error, additionally invite new hypotheses about the operations involved in computing these "intermediate shape-centered representations" and in mapping them onto higher frames for perception and action.

Traumatic Injury to the Developing Brain: Emerging Relationship to Early Life Stress

Despite the high incidence of brain injuries in children, we have yet to fully understand the unique vulnerability of a young brain to an injury and key determinants of long-term recovery. Here we consider how early life stress may influence recovery after an early age brain injury. Studies of early life stress alone reveal persistent structural and functional impairments at adulthood. We consider the interacting pathologies imposed by early life stress and subsequent brain injuries during early brain development as well as at adulthood. This review outlines how early life stress primes the immune cells of the brain and periphery to elicit a heightened response to injury. While the focus of this review is on early age traumatic brain injuries, there is also a consideration of preclinical models of neonatal hypoxia and stroke, as each further speaks to the vulnerability of the brain and reinforces those characteristics that are common across each of these injuries. Lastly, we identify a common mechanistic trend; namely, early life stress worsens outcomes independent of its temporal proximity to a brain injury.

Cortical Visual Mapping following Ocular Gene Augmentation Therapy for Achromatopsia

The ability of the adult human brain to develop function following correction of congenital deafferentation is controversial. Specifically, cases of recovery from congenital visual deficits are rare. CNGA3-achromatopsia is a congenital hereditary disease caused by cone-photoreceptor dysfunction, leading to impaired acuity, photoaversion, and complete color blindness. Essentially, these patients have rod-driven vision only, seeing the world in blurry shades of gray. We use the uniqueness of this rare disease, in which the cone-photoreceptors and afferent fibers are preserved but do not function, as a model to study cortical visual plasticity. We had the opportunity to study two CNGA3-achromatopsia adults (one female) before and after ocular gene augmentation therapy. Alongside behavioral visual tests, we used novel fMRI-based measurements to assess participants' early visual population receptive-field sizes and color regions. Behaviorally, minor improvements were observed, including reduction in photoaversion, marginal improvement in acuity, and a new ability to detect red color. No improvement was observed in color arrangement tests. Cortically, pretreatment, patients' population-receptive field sizes of early visual areas were untypically large, but were decreased following treatment specifically in the treated eye. We suggest that this demonstrates cortical ability to encode new input, even at adulthood. On the other hand, no activation of color-specific cortical regions was demonstrated in these patients either before or up to 1 year post-treatment. The source of this deficiency might be attributed either to insufficient recovery of cone function at the retinal level or to challenges that the adult cortex faces when computing new cone-derived input to achieve color perception.SIGNIFICANCE STATEMENT The possibility that the adult human brain may regain or develop function following correction of congenital deafferentation has fired the imagination of scientists over the years. In the visual domain, cases of recovery from congenital deficits are rare. Gene therapy visual restoration for congenital CNGA3-achromatopsia, a disease caused by cone photoreceptor dysfunction, gave us the opportunity to examine cortical function, to the best of our knowledge for the first time, both before and after restorative treatment. While behaviorally only minor improvements were observed post-treatment, fMRI analysis, including size algorithms of population-receptive fields, revealed cortical changes, specifically receptive field size decrease in the treated eyes. This suggests that, at least to some degree, the adult cortex is able to encode new input.

Learning to perceive shape from temporal integration following late emergence from blindness

Visual perception requires massive use of inference because the 3D structure of the world is not directly provided by the sensory input.¹ Particularly challenging is anorthoscopic vision-when an object moves behind a narrow slit such that only a tiny fraction of it is visible at any instant. Impressively, human observers correctly recognize objects in slit-viewing conditions by early childhood,^2,3 via temporal integration of the contours available in each sliver.^4,5 But can this capability be acquired if one has been effectively blind throughout childhood? We studied 23 Ethiopian children which had bilateral early-onset cataracts-resulting in extremely poor vision in infancy-and surgically treated only years later. We tested their anorthoscopic vision, precisely because it requires a cascade of demanding visual inference processes to perceive veridical shape. Failure to perform the task may allow mapping specific bottlenecks for late visual recovery. The patients' visual acuity typically improved substantially within 6 months post-surgery. Still, at this stage many were unable to recover shape under slit-viewing conditions, although they could infer the direction of global motion. However, when retested later, almost all patients could judge shape in slit-conditions necessitating temporal integration. This acquired capability often transferred to novel stimuli, in similar slit-viewing conditions. Thus, learning was not limited to the specific visual features of the original shapes. These results indicate that plasticity of sophisticated visual inference routines is preserved well into adolescence, and vision restoration after prolonged early-onset blindness is feasible to a greater extent than previously thought.

Advances in Neuroscience, Not Devices, Will Determine the Effectiveness of Visual Prostheses

Background: Innovations in engineering and neuroscience have enabled the development of sophisticated visual prosthetic devices. In clinical trials, these devices have provided visual acuities as high as 20/460, enabled coarse navigation, and even allowed for reading of short words. However, long-term commercial viability arguably rests on attaining even better vision and more definitive improvements in tasks of daily living and quality of life. Purpose: Here we review technological and biological obstacles in the implementation of visual prosthetics. Conclusions: Research in the visual prosthetic field has tackled significant technical challenges, including biocompatibility, signal spread through neural tissue, and inadvertent activation of passing axons; however, significant gaps in knowledge remain in the realm of neuroscience, including the neural code of vision and visual plasticity. We assert that further optimization of prosthetic devices alone will not provide markedly improved visual outcomes without significant advances in our understanding of neuroscience.

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.

Hierarchical Sparse Coding of Objects in Deep Convolutional Neural Networks

Recently, deep convolutional neural networks (DCNNs) have attained human-level performances on challenging object recognition tasks owing to their complex internal representation. However, it remains unclear how objects are represented in DCNNs with an overwhelming number of features and non-linear operations. In parallel, the same question has been extensively studied in primates' brain, and three types of coding schemes have been found: one object is coded by the entire neuronal population (distributed coding), or by one single neuron (local coding), or by a subset of neuronal population (sparse coding). Here we asked whether DCNNs adopted any of these coding schemes to represent objects. Specifically, we used the population sparseness index, which is widely-used in neurophysiological studies on primates' brain, to characterize the degree of sparseness at each layer in representative DCNNs pretrained for object categorization. We found that the sparse coding scheme was adopted at all layers of the DCNNs, and the degree of sparseness increased along the hierarchy. That is, the coding scheme shifted from distributed-like coding at lower layers to local-like coding at higher layers. Further, the degree of sparseness was positively correlated with DCNNs' performance in object categorization, suggesting that the coding scheme was related to behavioral performance. Finally, with the lesion approach, we demonstrated that both external learning experiences and built-in gating operations were necessary to construct such a hierarchical coding scheme. In sum, our study provides direct evidence that DCNNs adopted a hierarchically-evolved sparse coding scheme as the biological brain does, suggesting the possibility of an implementation-independent principle underling object recognition.

Brief localised monocular deprivation in adults alters binocular rivalry predominance retinotopically and reduces spatial inhibition

Short-term deprivation (2.5 h) of an eye has been shown to boost its relative ocular dominance in young adults. Here, we show that a much shorter deprivation period (3–6 min) produces a similar paradoxical boost that is retinotopic and reduces spatial inhibition on neighbouring, non-deprived areas. Partial deprivation was conducted in the left hemifield, central vision or in an annular region, later assessed with a binocular rivalry tracking procedure. Post-deprivation, dominance of the deprived eye increased when rivalling images were within the deprived retinotopic region, but not within neighbouring, non-deprived areas where dominance was dependent on the correspondence between the orientation content of the stimuli presented in the deprived and that of the stimuli presented in non-deprived areas. Together, these results accord with other deprivation studies showing V1 activity changes and reduced GABAergic inhibition.

The Consumer Contextual Decision-Making Model

Consumers can have difficulty expressing their buying intentions on an explicit level. The most common explanation for this intention-action gap is that consumers have many cognitive biases that interfere with rational decision-making. The current resource-rational approach to understanding human cognition, however, suggests that brain environment interactions lead consumers to minimize the expenditure of cognitive energy according to the principle of Occam’s Razor. This means that the consumer seeks as simple of a solution as possible for a problem requiring decision-making. In addition, this resource-rational approach to decision-making emphasizes the role of inductive inference and Bayesian reasoning. Together, the principle of Occam’s Razor, inductive inference, and Bayesian reasoning illuminate the dynamic human-environment relationship. This paper analyzes these concepts from a contextual perspective and introduces the Consumer Contextual Decision-Making Model (CCDMM). Based on the CCDMM, two hypothetical strategies of consumer decision-making will be presented. First, the SIMilarity-Strategy (SIMS) is one in which most of a consumer’s decisions in a real-life context are based on prior beliefs about the role of a commodities specific to real-life situation being encountered. Because beliefs are based on previous experiences, consumers are already aware of the most likely consequences of their actions. At the same time, they do not waste time on developing contingencies for what, based on previous experience, is unlikely to happen. Second, the What-is-Out-there-in-the-World-Strategy (WOWS) is one in which prior beliefs do not work in a real-life situation, requiring consumers to update their beliefs. The principle argument being made is that most experimental consumer research describes decision-making based on the WOWS, when participants cannot apply their previous knowledge and situation-based strategy to problems. The article analyzes sensory and cognitive biases described by behavioral economists from a CCDMM perspective, followed by a description and explanation of the typical intention-action gap based on the model. Prior to a section dedicated to discussion, the neuroeconomic approach will be described along with the valuation network of the brain, which has evolved to solve problems that the human has previously encountered in an information-rich environment. The principles of brain function will also be compared to CCDMM. Finally, different approaches and the future direction of consumer research from a contextual point of view will be presented.

Mechanisms underlying simultaneous brightness contrast: Early and innate

In the phenomenon of simultaneous brightness contrast, two patches, one on a dark background and the other on a light one, appear to have different brightness despite being physically equi-luminant. Elucidating the phenomenon's underlying mechanisms is relevant for the larger question of how the visual system makes photometric judgments in images. Accounts over the past century have spanned low-, mid- and high-level visual processes, but a definitive resolution has not emerged. We present three studies that collectively demonstrate that the computations underlying this phenomenon are low-level, instantiated prior to binocular fusion, and available innately, without need for inferential learning via an individual's visual experience. In our first two studies, we find that strong brightness induction is obtained even when observers are unaware of any luminance differences in the neighborhoods of the probe patches. Results with dichoptic displays reveal that eye of origin, although not evident consciously, has a marked influence on the eventual brightness percept of the probe patches, thereby localizing brightness estimation to a site preceding binocular fusion. The third study uses conventional simultaneous brightness contrast displays, but an unusual group of participants: Congenitally blind children whom we were able to treat surgically. The results demonstrate an immediate susceptibility to the simultaneous brightness illusion after sight onset. Together, these data strongly constrain the search for mechanisms underlying a fundamental brightness phenomenon.

Critical periods of brain development

Brain plasticity is maximal at specific time windows during early development known as critical periods (CPs), during which sensory experience is necessary to establish optimal cortical representations of the surrounding environment. After CP closure, a range of functional and structural elements prevent passive experience from eliciting significant plastic changes in the brain. The transition from a plastic to a more fixed state is advantageous as it allows for the sequential consolidation and retention of new and more complex perceptual, motor, and cognitive functions. However, the formation of stable neural representations may pose limitations on future revisions to the circuitry. If sensory experience is abnormal or absent during this time, it can have profound effects on sensory representations in adulthood, resulting in quasi-permanent adaptations that can make it nearly impossible to learn certain skills or process certain stimulus properties later on in life. This chapter begins with a brief introduction to experience-dependent plasticity throughout the lifespan (Section Introduction). Next, we define what constitutes a CP (Section What Are Critical Periods?) and review some of the key CPs in the visual and auditory systems (Section Key Critical Periods of Sensory Systems). We then discuss the mechanisms whereby cortical plasticity is regulated both locally and through neuromodulatory systems (Section How Are Critical Periods Regulated?). Finally, we highlight studies showing that CPs can be extended beyond their normal epochs, closed prematurely, or reopened during adult life by merely altering sensory inputs (Section Timing of Critical Periods: Can CP Plasticity Be Extended, Limited, or Reactivated?).

Responses in area hMT+ reflect tuning for both auditory frequency and motion after blindness early in life

Previous studies report that human middle temporal complex (hMT+) is sensitive to auditory motion in early-blind individuals. Here, we show that hMT+ also develops selectivity for auditory frequency after early blindness, and that this selectivity is maintained after sight recovery in adulthood. Frequency selectivity was assessed using both moving band-pass and stationary pure-tone stimuli. As expected, within primary auditory cortex, both moving and stationary stimuli successfully elicited frequency-selective responses, organized in a tonotopic map, for all subjects. In early-blind and sight-recovery subjects, we saw evidence for frequency selectivity within hMT+ for the auditory stimulus that contained motion. We did not find frequency-tuned responses within hMT+ when using the stationary stimulus in either early-blind or sight-recovery subjects. We saw no evidence for auditory frequency selectivity in hMT+ in sighted subjects using either stimulus. Thus, after early blindness, hMT+ can exhibit selectivity for auditory frequency. Remarkably, this auditory frequency tuning persists in two adult sight-recovery subjects, showing that, in these subjects, auditory frequency-tuned responses can coexist with visually driven responses in hMT+.

Alterations in cortical and thalamic connections of somatosensory cortex following early loss of vision

Early loss of vision produces dramatic changes in the functional organization and connectivity of the neocortex in cortical areas that normally process visual inputs, such as the primary and second visual area. This loss also results in alterations in the size, functional organization, and neural response properties of the primary somatosensory area, S1. However, the anatomical substrate for these functional changes in S1 has never been described. In the present investigation, we quantified the cortical and subcortical connections of S1 in animals that were bilaterally enucleated very early in development, prior to the formation of retino-geniculate and thalamocortical pathways. We found that S1 receives dense inputs from novel cortical fields, and that the density of existing cortical and thalamocortical connections was altered. Our results demonstrate that sensory systems develop in tandem and that alterations in sensory input in one system can affect the connections and organization of other sensory systems. Thus, therapeutic intervention following early loss of vision should focus not only on restoring vision, but also on augmenting the natural plasticity of the spared systems.

Link Between Facial Identity and Expression Abilities Suggestive of Origins of Face Impairments in Autism: Support for the Social-Motivation Hypothesis

Individuals with autism spectrum disorder (ASD) often have difficulties with processing identity and expression in faces. This is at odds with influential models of face processing that propose separate neural pathways for the identity and expression domains. The social-motivation hypothesis of ASD posits a lack of visual experience with faces as the root cause of face impairments in autism. A direct prediction is that identity and expression abilities should be related in ASD, reflecting the common origin of face impairment in this population. We tested adults with and without ASD ( ns = 34) in identity and expression tasks. Our results showed that performance in the two domains was significantly correlated in the ASD group but not in the comparison group. These results suggest that the most likely origin for face impairments in ASD stems from the input stage impacting development of identity and expression domains alike, consistent with the social-motivation hypothesis.

Visual loss alters multisensory face maps in humans

Topographically organised responses to visual and tactile stimulation are aligned in the ventral intraparietal cortex. The critical biological importance of this region, which is thought to mediate visually guided defensive movements of the head and upper body, suggests that these maps might be hardwired from birth. Here, we investigated whether visual experience is necessary for the creation and positioning of these maps by assessing the representation of tactile stimulation in congenitally and totally blind participants, who had no visual experience, and late and totally blind participants. We used a single-subject approach to the analysis to focus on the potential individual differences in the functional neuroanatomy that might arise from different causes, durations and sensory experiences of visual impairment among participants. The overall results did not show any significant difference between congenitally and late blind participants; however, single-subject trends suggested that visual experience is not necessary to develop topographically organised maps in the intraparietal cortex, whilst losing vision disrupted topographic maps' integrity and organisation. These results discussed in terms of brain plasticity and sensitive periods.

Probing Human Visual Deficits with Functional Magnetic Resonance Imaging

Much remains to be understood about visual system malfunction following injury. The resulting deficits range from dense, visual field scotomas to mild dysfunction of visual perception. Despite the predictive value of anatomical localization studies, much patient-to-patient variability remains regarding (a) perceptual abilities following injury and (b) the capacity of individual patients for visual rehabilitation. Visual field perimetry is used to characterize the visual field deficits that result from visual system injury. However, standard perimetry mapping does not always precisely correspond to underlying anatomical or functional deficits. Functional magnetic resonance imaging can be used to probe the function of surviving visual circuits, allowing us to classify better how the pattern of injury relates to residual visual perception. Identifying pathways that are potentially modifiable by training may guide the development of improved strategies for visual rehabilitation. This review discusses primary visual cortex lesions, which cause dense contralateral scotomas.

Learning to see again: biological constraints on cortical plasticity and the implications for sight restoration technologies

The 'bionic eye'-so long a dream of the future-is finally becoming a reality with retinal prostheses available to patients in both the US and Europe. However, clinical experience with these implants has made it apparent that the visual information provided by these devices differs substantially from normal sight. Consequently, the ability of patients to learn to make use of this abnormal retinal input plays a critical role in whether or not some functional vision is successfully regained. The goal of the present review is to summarize the vast basic science literature on developmental and adult cortical plasticity with an emphasis on how this literature might relate to the field of prosthetic vision. We begin with describing the distortion and information loss likely to be experienced by visual prosthesis users. We then define cortical plasticity and perceptual learning, and describe what is known, and what is unknown, about visual plasticity across the hierarchy of brain regions involved in visual processing, and across different stages of life. We close by discussing what is known about brain plasticity in sight restoration patients and discuss biological mechanisms that might eventually be harnessed to improve visual learning in these patients.

Emergence of categorical face perception after extended early-onset blindness

It is unknown whether the ability to visually distinguish between faces and nonfaces is subject to a critical period during development. Would a congenitally blind child who gains sight several years after birth be able to acquire this skill? This question has remained unanswered because of the rarity of cases of late sight onset. We had the opportunity to work with five early-blind individuals who gained sight late in childhood after treatment for dense bilateral cataracts. We tested their ability to categorize patterns as faces, using natural images that spanned a spectrum of face semblance. The results show that newly sighted individuals are unable to distinguish between faces and nonfaces immediately after sight onset, but improve markedly in the following months. These results demonstrate preserved plasticity for acquiring face/nonface categorization ability even late in life, and set the stage for investigating the informational and neural basis of this skill acquisition.

Changing What You See by Changing What You Know: The Role of Attention

Attending is a cognitive process that incorporates a person's knowledge, goals, and expectations. What we perceive when we attend to one thing is different from what we perceive when we attend to something else. Yet, it is often argued that attentional effects do not count as evidence that perception is influenced by cognition. I investigate two arguments often given to justify excluding attention. The first is arguing that attention is a post-perceptual process reflecting selection between fully constructed perceptual representations. The second is arguing that attention as a pre-perceptual process that simply changes the input to encapsulated perceptual systems. Both of these arguments are highly problematic. Although some attentional effects can indeed be construed as post-perceptual, others operate by changing perceptual content across the entire visual hierarchy. Although there is a natural analogy between spatial attention and a change of input, the analogy falls apart when we consider other forms of attention. After dispelling these arguments, I make a case for thinking of attention not as a confound, but as one of the mechanisms by which cognitive states affect perception by going through cases in which the same or similar visual inputs are perceived differently depending on the observer's cognitive state, and instances where cuing an observer using language affects what one sees. Lastly, I provide two compelling counter-examples to the critique that although cognitive influences on perception can be demonstrated in the laboratory, it is impossible to really experience them for oneself in a phenomenologically compelling way. Taken together, the current evidence strongly supports the thesis that what we know routinely influences what we see, that the same sensory input can be perceived differently depending on the current cognitive state of the viewer, and that phenomenologically salient demonstrations are possible if certain conditions are met.

Postretinal Structure and Function in Severe Congenital Photoreceptor Blindness Caused by Mutations in the GUCY2D Gene

Purpose

To examine how severe congenital blindness resulting from mutations of the GUCY2D gene alters brain structure and function, and to relate these findings to the notable preservation of retinal architecture in this form of Leber congenital amaurosis (LCA).

Methods

Six GUCY2D-LCA patients (ages 20–46) were studied with optical coherence tomography of the retina and multimodal magnetic resonance imaging (MRI) of the brain. Measurements from this group were compared to those obtained from populations of normally sighted controls and people with congenital blindness of a variety of causes.

Results

Patients with GUCY2D-LCA had preservation of the photoreceptors, ganglion cells, and nerve fiber layer. Despite this, visual function in these patients ranged from 20/160 acuity to no light perception, and functional MRI responses to light stimulation were attenuated and restricted. This severe visual impairment was reflected in substantial thickening of the gray matter layer of area V1, accompanied by an alteration of resting-state correlations within the occipital lobe, similar to a comparison group of congenitally blind people with structural damage to the retina. In contrast to the comparison blind population, however, the GUCY2D-LCA group had preservation of the size of the optic chiasm, and the fractional anisotropy of the optic radiations as measured with diffusion tensor imaging was also normal.

Conclusions

These results identify dissociable effects of blindness upon the visual pathway. Further, the relatively intact postgeniculate white matter pathway in GUCY2D-LCA is encouraging for the prospect of recovery of visual function with gene augmentation therapy.

Visual Field Map Clusters in High-Order Visual Processing: Organization of V3A/V3B and a New Cloverleaf Cluster in the Posterior Superior Temporal Sulcus

The cortical hierarchy of the human visual system has been shown to be organized around retinal spatial coordinates throughout much of low- and mid-level visual processing. These regions contain visual field maps (VFMs) that each follows the organization of the retina, with neighboring aspects of the visual field processed in neighboring cortical locations. On a larger, macrostructural scale, groups of such sensory cortical field maps (CFMs) in both the visual and auditory systems are organized into roughly circular cloverleaf clusters. CFMs within clusters tend to share properties such as receptive field distribution, cortical magnification, and processing specialization. Here we use fMRI and population receptive field (pRF) modeling to investigate the extent of VFM and cluster organization with an examination of higher-level visual processing in temporal cortex and compare these measurements to mid-level visual processing in dorsal occipital cortex. In human temporal cortex, the posterior superior temporal sulcus (pSTS) has been implicated in various neuroimaging studies as subserving higher-order vision, including face processing, biological motion perception, and multimodal audiovisual integration. In human dorsal occipital cortex, the transverse occipital sulcus (TOS) contains the V3A/B cluster, which comprises two VFMs subserving mid-level motion perception and visuospatial attention. For the first time, we present the organization of VFMs in pSTS in a cloverleaf cluster. This pSTS cluster contains four VFMs bilaterally: pSTS-1:4. We characterize these pSTS VFMs as relatively small at ∼125 mm² with relatively large pRF sizes of ∼2-8° of visual angle across the central 10° of the visual field. V3A and V3B are ∼230 mm² in surface area, with pRF sizes here similarly ∼1-8° of visual angle across the same region. In addition, cortical magnification measurements show that a larger extent of the pSTS VFM surface areas are devoted to the peripheral visual field than those in the V3A/B cluster. Reliability measurements of VFMs in pSTS and V3A/B reveal that these cloverleaf clusters are remarkably consistent and functionally differentiable. Our findings add to the growing number of measurements of widespread sensory CFMs organized into cloverleaf clusters, indicating that CFMs and cloverleaf clusters may both be fundamental organizing principles in cortical sensory processing.

Visual BOLD Response in Late Blind Subjects with Argus II Retinal Prosthesis

Retinal prosthesis technologies require that the visual system downstream of the retinal circuitry be capable of transmitting and elaborating visual signals. We studied the capability of plastic remodeling in late blind subjects implanted with the Argus II Retinal Prosthesis with psychophysics and functional MRI (fMRI). After surgery, six out of seven retinitis pigmentosa (RP) blind subjects were able to detect high-contrast stimuli using the prosthetic implant. However, direction discrimination to contrast modulated stimuli remained at chance level in all of them. No subject showed any improvement of contrast sensitivity in either eye when not using the Argus II. Before the implant, the Blood Oxygenation Level Dependent (BOLD) activity in V1 and the lateral geniculate nucleus (LGN) was very weak or absent. Surprisingly, after prolonged use of Argus II, BOLD responses to visual input were enhanced. This is, to our knowledge, the first study tracking the neural changes of visual areas in patients after retinal implant, revealing a capacity to respond to restored visual input even after years of deprivation.

Stimulus-Response Compatibility Effect in the Near-Far Dimension: A Developmental Study

The present study investigates the developmental aspect of stimulus-response compatibility (SRC) effect in 8-11-years-old children. The task consisted in manually responding to the color of a pawn presented on a chessboard at different distances. Manual responses were provided by reaching a proximal or distal location depending on the color of the stimulus. We found that reaction time was affected by the conflict generated by the response suggested by the location of the stimulus and the response required according to its color. This was not the case for movement time despite we found a higher rate of long duration movements in the incongruent than in the congruent spatial condition. The SRC effect was, however, observed in children older than 10 years old. These findings provide additional evidence for a reorganization of the perceptual system during the period of 8-10 years, integrating progressively multimodal information and preparing more efficiently the body to act in the environment.

Low Vision and Plasticity: Implications for Rehabilitation

Low vision is any type of visual impairment that affects activities of daily living. In the context of low vision, we define plasticity as changes in brain or perceptual behavior that follow the onset of visual impairment and that are not directly due to the underlying pathology. An important goal of low-vision research is to determine how plasticity affects visual performance of everyday activities. In this review, we consider the levels of the visual system at which plasticity occurs, the impact of age and visual experience on plasticity, and whether plastic changes are spontaneous or require explicit training. We also discuss how plasticity may affect low-vision rehabilitation. Developments in retinal imaging, noninvasive brain imaging, and eye tracking have supplemented traditional clinical and psychophysical methods for assessing how the visual system adapts to visual impairment. Findings from contemporary research are providing tools to guide people with low vision in adopting appropriate rehabilitation strategies.

Visual motion serves but is not under the purview of the dorsal pathway

Visual motion processing is often attributed to the dorsal visual pathway despite visual motion's involvement in almost all visual functions. Furthermore, some visual motion tasks critically depend on the structural integrity of regions outside the dorsal pathway. Here, based on numerous studies, I propose that visual motion signals are swiftly transmitted via multiple non-hierarchical routes to primary motion-dedicated processing regions (MT/V5 and MST) that are not part of the dorsal pathway, and then propagated to a multiplicity of brain areas according to task demands, reaching these regions earlier than the dorsal/ventral hierarchical flow. This not only places MT/V5 at the same or even earlier visual processing stage as that of V1, but can also elucidate many findings with implications to visual awareness. While the integrity of the non-hierarchical motion pathway is necessary for all visual motion perception, it is insufficient on its own, and the transfer of visual motion signals to additional brain areas is crucial to allow the different motion perception tasks (e.g. optic flow, visuo-vestibular balance, movement observation, dynamic form detection and perception, and even reading). I argue that this lateral visual motion pathway can be distinguished from the dorsal pathway not only based on faster response latencies and distinct anatomical connections, but also based on its full field representation. I also distinguish between this primary lateral visual motion pathway sensitive to all motion in the visual field, and a much less investigated optic flow sensitive medial processing pathway (from V1 to V6 and V6A) that appears to be part of the dorsal pathway. Multiple additional predictions are provided that allow testing this proposal and distinguishing between the visual pathways.

Early Blindness Results in Developmental Plasticity for Auditory Motion Processing within Auditory and Occipital Cortex

Early blind subjects exhibit superior abilities for processing auditory motion, which are accompanied by enhanced BOLD responses to auditory motion within hMT+ and reduced responses within right planum temporale (rPT). Here, by comparing BOLD responses to auditory motion in hMT+ and rPT within sighted controls, early blind, late blind, and sight-recovery individuals, we were able to separately examine the effects of developmental and adult visual deprivation on cortical plasticity within these two areas. We find that both the enhanced auditory motion responses in hMT+ and the reduced functionality in rPT are driven by the absence of visual experience early in life; neither loss nor recovery of vision later in life had a discernable influence on plasticity within these areas. Cortical plasticity as a result of blindness has generally be presumed to be mediated by competition across modalities within a given cortical region. The reduced functionality within rPT as a result of early visual loss implicates an additional mechanism for cross modal plasticity as a result of early blindness—competition across different cortical areas for functional role.