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How does sensory experience shape the development of the visual brain? To answer this eluding question, we examine brain responses to visual categories in a rare group of cataract-reversal individuals who experienced a short transient period of early blindness. Encoding of low-level visual properties is impaired in the early visual cortex (EVC) of cataract-reversal participants, whereas categorical responses in downstream ventral occipito-temporal cortex (VOTC) are preserved. In controls, degrading visual input to mimic the visual deficits of cataracts produces cascading disruptions extending from EVC to VOTC, unlike in the cataract group. A deep neural network trained on altered visual input reproduces this dissociation, supporting the brain findings. These results demonstrate that while EVC is permanently affected by early deprivation, categorical coding in VOTC shows resilience, highlighting different sensitive periods for specific brain regions and computations. This study shows that transient blindness at birth leaves lasting effects on early visual functions, while higher visual regions encoding categories remain unaffected, revealing different sensitive periods for different functions in vision.

Visual problems can negatively affect visual development and learning but often go undetected. We assessed the feasibility of scaling up a school-based screening program to identify and treat kindergarten children with visual problems. We conducted a prospective cohort study offering vision screening to junior (JK) and senior kindergarten (SK) children attending 43 schools in 15 Ontario communities. Screening comprised photoscreeners and tests of visual acuity, stereoacuity and eye alignment. Children who failed any test were referred for a comprehensive eye examination, with treatment as needed (e.g., glasses). Using a passive consent model, 89% of children were screened compared with 62% using an active consent model (p < 0.001). Referral rates to an optometrist varied across schools (mean referral rate for children in JK 53%, range 25%–83%; mean referral rate for children in SK 34%, range 12%–61%). Among 4811 children who were screened, a visual problem was detected in 516 (10.7%), including 164 (3.4%) with amblyopia and 324 (6.7%) with clinically significant refractive errors. For 347 (67.2%) of the children with a visual problem, this was their first eye examination. Rescreening in Year 2 did not lead to detection of additional problems among children who passed screening in Year 1. Regardless of location (child’s school or optometrist’s office), 1563 (68.9%) of children attended the follow-up optometry examination. Most of the children who were surveyed (291 of 322, 90.4%) indicated that they enjoyed vision screening. Many children in Ontario with a visual problem were not being identified by the status quo in 2015–2017. We found that in-school vision screening with follow-up eye examinations is an effective strategy for identifying at-risk children and placing them in eye care before grade 1.

ObjectivesTo assess the diagnostic accuracy of five vision screening tools used in a school setting using sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV).DesignWe compared the results of the five best evidence-based screening tools available in 2014 to the results of a comprehensive eye exam with cycloplegic refraction by a licenced optometrist. Screening included Cambridge Crowded Acuity Cards, Plusoptix S12 and Spot photoscreeners, Preschool Randot Stereoacuity Test and the Pediatric Vision Scanner (PVS). Referral criteria followed AAPOS (2013) guidelines and published norms.SettingA large school in Toronto, Canada, with 25 split classrooms of junior kindergarten (JK: 4 year olds) and senior kindergarten (SK: 5 year olds) children.ParticipantsOver 2 years, 1132 eligible children were enrolled at the school. After obtaining parental consent, 832 children were screened. Subsequently, 709 children had complete screening and optometry exam data.Main outcome measuresThe presence/absence of a visual problem based on optometrist’s assessment: amblyopia, amblyopia risk factors (reduced stereoacuity, strabismus and clinically significant refractive errors) and any other ocular problem (eg, nystagmus).ResultsOverall, 26.5% of the screened children had a visual problem, including 5.9% with amblyopia. Using all five tools, screening sensitivity=84% (95% CI 78 to 89), specificity=49% (95% CI 44 to 53), PPV=37% (95% CI 33 to 42), and NPV=90% (95% CI 86 to 93). The odds of having a correct screening result in SK (mean age=68.2 months) was 1.5 times those in JK (mean age=55.6 months; 95% CI 1.1 to 2.1), with sensitivity improved to 89% (95% CI 80 to 96) and specificity improved to 57% (95% CI 50 to 64) among SK children.ConclusionsA school-based screening programme correctly identified 84% of those kindergarten children who were found to have a visual problem by a cyclopleged optometry exam. Additional analyses revealed how accuracy varies with different combinations of screening tools and referral criteria.

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

Synesthesia is a neurologic trait in which specific inducers, such as sounds, automatically elicit additional idiosyncratic percepts, such as color (thus “colored hearing”). One explanation for this trait—and the one tested here—is that synesthesia results from unusually weak pruning of cortical synaptic hyperconnectivity during early perceptual development. We tested the prediction from this hypothesis that synesthetes would be superior at making discriminations from nonnative categories that are normally weakened by experience-dependent pruning during a critical period early in development—namely, discrimination among nonnative phonemes (Hindi retroflex /d̪a/ and dental /ɖa/), among chimpanzee faces, and among inverted human faces. Like the superiority of 6-mo-old infants over older infants, the synesthetic groups were significantly better than control groups at making all the nonnative discriminations across five samples and three testing sites. The consistent superiority of the synesthetic groups in making discriminations that are normally eliminated during infancy suggests that residual cortical connectivity in synesthesia supports changes in perception that extend beyond the specific synesthetic percepts, consistent with the incomplete pruning hypothesis.

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

Unlike most objects, faces are processed holistically: They are processed as a whole rather than as a collection of independent features. We examined the role of early visual experience in the development of this type of processing of faces by using the composite-face task, a measure of holistic processing, to test patients deprived of visual experience during infancy. Visually normal control subjects showed the expected composite-face effect: They had difficulty perceiving that the top halves of two faces were the same when the top halves were aligned with different bottom halves. Performance improved when holistic processing was disrupted by misaligning the top and bottom halves. Deprived patients, in contrast, showed no evidence of holistic processing, and in fact performed significantly better than control subjects when top and bottom halves were aligned. These findings suggest that early visual experience is necessary to set up or maintain the neural substrate that leads to holistic processing of faces.

Hebb's (1949) book The Organisation of Behaviour presented a novel hypothesis about how the baby learns to see. This article summarizes the results of my research program that evaluated Hebb's hypothesis: first, by studying infants' eye movements and initial perceptual abilities and second, by studying the effect of visual deprivation (e.g., congenital cataracts) on later perceptual development. Collectively, the results support Hebb's hypothesis that the baby does indeed learn to see. Early visual experience not only drives the baby's initial scanning of objects, but also sets up the neural architecture that will come to underlie adults' perception. L'ouvrage de Hebb (1949) intitulé The Organisation of Behaviour présentait une hypothèse novatrice selon laquelle le bébé apprend à voir. Le présent article résume les résultats de mon programme de recherche qui consistait à évaluer l'hypothèse de Hebb : premièrement, en étudiant les déplacements de l'oeil du bébé et ses capacités perceptuelles initiales et deuxièmement, en étudiant l'effet de la privation visuelle (par ex. en raison de cataractes congénitales) sur le développement perceptuel ultérieur. Collectivement, les résultats appuient l'hypothèse de Hebb suggérant que le bébé apprend effectivement à voir. Les expériences visuelles précoces entraînent non seulement le balayage initial des objets par le bébé mais aussi, établit l'architecture neurale qui servira de base à la perception de l'adulte.

Previous studies of face perception during early infancy are difficult to interpret because of discrepant results and procedural differences. We used a standardized method based on the Teller acuity card procedure to test newborns, 6-week-olds, and 12-week-olds with three pairs of face and nonface stimuli modified from previous studies. Newborns' preferences were influenced both by the visibility of the stimuli and by their resemblance to a human face. There appears to be a mechanism, likely subcortical, predisposing newborns to look toward faces. Changes in preferences at 6 and 12 weeks of age suggest increasing cortical influence over infants' preferences for faces.

Objective To assess the effectiveness of a kindergarten vision screening program by randomly assigning schools to receive or not receive vision screening, then following up 1.5 years later. Methods Fifty high-needs elementary schools were randomly assigned to participate or not in a vision screening program for children in senior kindergarten (SK; age 5‒6 years). When the children were in Grade 2 (age 6‒7 years), vision screening was conducted at all 50 schools. Results Contrary to expectations, screened and non-screened schools did not differ in the prevalence of suspected amblyopia in Grade 2 (8.6% vs. 7.5%, p  = 0.10), nor prevalence of other visual problems such as astigmatism (45.1% vs. 47.1%, p  = 0.51). There was also no difference between screened and non-screened schools in academic outcomes such as the proportion of children below grade level in reading (33% vs. 29%) or math (44% vs. 38%) ( p  = 0.86). However, more children were wearing glasses in screened than in non-screened schools (10.2% vs. 7.8%, p  = 0.05), and more children reported their glasses as missing or broken (8.3% vs. 4.7%, p  = 0.01), suggesting that SK screening had identified successfully those in need of glasses. Examination of individual results revealed that 72% of children diagnosed and treated for amblyopia in SK no longer had amblyopia in Grade 2. Conclusion The prevalence of amblyopia and other visual problems was not reduced in Grade 2 by our SK vision screening program, perhaps because of poor treatment compliance and high attrition. The results suggest that a single screening intervention is insufficient to reduce visual problems among young children. However, the data from individuals with amblyopia suggest that continuing vision care and access to glasses benefits children, especially children from lower socioeconomic class.