Three experiments investigated the acquisition and retention of structural and object landmarks in virtual indoor environments. The experiments investigated the rate of acquisition and memory retention for hallway structure (structural landmarks) and pictures (object landmarks). The experiments investigated the rate of acquisition, the role of information content, and memory retention of this information when participants were trained and tested in novel virtual indoor environments. The results from these experiments suggest that (a) even initially, participants are biased toward encoding building structure over object landmarks; (b) participants are sensitive to the information content of landmarks and will allocate memory resources to landmarks that are more informative; and (c) information about these landmarks is retained even after a 1-year delay.

Visual plasticity peaks during early critical periods of normal visual development. Studies in animals and humans provide converging evidence that gains in visual function are minimal and deficits are most severe when visual deprivation persists beyond the critical period. Here we demonstrate visual development in a unique sample of patients who experienced extended early-onset blindness (beginning before 1 y of age and lasting 8-17 y) before removal of bilateral cataracts. These patients show surprising improvements in contrast sensitivity, an assay of basic spatial vision. We find that contrast sensitivity development is independent of the age of sight onset and that individual rates of improvement can exceed those exhibited by normally developing infants. These results reveal that the visual system can retain considerable plasticity, even after early blindness that extends beyond critical periods.brain plasticity | sensitive periods | sight restoration | visual impairment | childhood blindness

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Background Cataracts are a major cause of childhood blindness globally. Although surgically treatable, it is unclear whether children would benefit from such interventions beyond the first few years of life, which are believed to constitute `critical' periods for visual development. Aims To study visual acuity outcomes after late treatment of early-onset cataracts and also to determine whether there are longitudinal changes in postoperative acuity. Methods We identified 53 children with dense cataracts with an onset within the first half-year after birth through a survey of over 20 000 rural children in India. All had accompanying nystagmus and were older than 8 years of age at the time of treatment. They underwent bilateral cataract surgery and intraocular lens implantation. We then assessed their best-corrected visual acuity 6 weeks and 6 months after surgery. Results 48 children from the pool of 53 showed improvement in their visual acuity after surgery. Our longitudinal assessments demonstrated further improvements in visual acuity for the majority of these children proceeding from the 6-week to 6-month assessment. Interestingly, older children in our subject pool did not differ significantly from the younger ones in the extent of improvement they exhibit. Conclusions and relevance Our results demonstrate that not only can significant vision be acquired until late in childhood, but that neural processes underlying even basic aspects of vision like resolution acuity remain malleable until at least adolescence. These data argue for the provision of cataract treatment to all children, irrespective of their age.

Previous studies suggest that humans rely on geometric visual information (hallway structure) rather than non-geometric visual information (e.g., doors, signs and lighting) for acquiring cognitive maps of novel indoor layouts. This study asked whether visual impairment and age affect reliance on nongeometric visual information for layout learning. We tested three groups of participants-younger (< 50 years) normally sighted, older (50-70 years) normally sighted, and low vision (people with heterogeneous forms of visual impairment ranging in age from 18-67). Participants learned target locations in building layouts using four presentation modes: a desktop virtual environment (VE) displaying only geometric cues (Sparse VE), a VE displaying both geometric and non-geometric cues (Photorealistic VE), a Map, and a Real building. Layout knowledge was assessed by map drawing and by asking participants to walk to specified targets in the real space. Results indicate that low-vision and older normally-sighted participants relied on additional non-geometric information to accurately learn layouts. In conclusion, visual impairment and age may result in reduced perceptual and/or memory processing that makes it difficult to learn layouts without non-geometric visual information.Keywords spatial navigation; wayfinding; visual impairment; low vision; aging; virtual environments; geometric visual information; cognitive maps; landmarks; environmental learning A typical building contains abundant visual features for aiding navigation, from geometric cues about the structural layout of the floor plan to cues unrelated to the layout geometry such as the presence of objects (e.g., pictures, water fountains) and image characteristics (e.g., textures, color and lighting). The current study addresses how two important participant characteristics, visual impairment and age, influence the types of visual information needed for developing an accurate mental representation of a novel virtual environment (VE). First, we ask whether rendering of purely geometrical information is sufficient for navigation in virtual buildings with visual impairment, and whether the addition of non-geometric visual features helps or hinders. Second, because the prevalence of visual impairment is much higher in old age, we ask whether age influences the use of geometric and non-geometric visual information.Correspondence concerning this article should be addressed to Amy A. Kalia, University of Minnesota Twin-Cities, Department of Psychology, N218 Elliott Hall, 75 East River Road, Minneapolis, MN 55455. Email: kali0080@umn.edu. NIH Public Access Author ManuscriptPerception. Author manuscript; available in PMC 2009 October 1. Published in final edited form as:Perception. 2008 ; 37(11): 1677-1699. doi:10.1068/p5915. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript Geometric and Non-geometric CuesIn this study, geometric cues refer to the spatial configuration of hallways, specifically their length and intersection connectivity. In F...

This study investigated navigation with route instructions generated by digital-map software and synthetic speech. Participants, either visually impaired or sighted wearing blind folds, successfully located rooms in an unfamiliar building. Users with visual impairment demonstrated better route-finding performance when the technology provided distance information in number of steps rather than walking time or number of feet.

This study investigated the interaction between remembered landmark and path integration strategies for estimating current location when walking in an environment without vision. We asked whether observers navigating without vision only rely on path integration information to judge their location, or whether remembered landmarks also influence judgments. Participants estimated their location in a hallway after viewing a target (remembered landmark cue) and then walking blindfolded to the same or a conflicting location (path integration cue). We found that participants averaged remembered landmark and path integration information when they judged that both sources provided congruent information about location, which resulted in more precise estimates compared to estimates made with only path integration. In conclusion, humans integrate remembered landmarks and path integration in a gated fashion, dependent on the congruency of the information. Humans can flexibly combine information about remembered landmarks with path integration cues while navigating without visual information.

Objective Many blind children in the developing world are unable to obtain timely treatment due to lack of financial and medical resources. Can public health programs that identify and treat such children several years after the onset of blindness enhance their quality of life? The notion that visual development is subject to an early ‘critical period’ argues against this possibility. However, there are inadequate empirical data from humans on this issue. To address this need, we examined the quality of life of children living in India and who were treated for early-onset blindness (before one year of age), due to cataracts or corneal opacities. Study Design Survey study. Methods As part of an ongoing scientific effort named Project Prakash, we screened over 40,000 children in rural northern India to identify those suffering from early onset blindness. They were provided eye surgeries in a tertiary care ophthalmic center in New Delhi. We subsequently surveyed sixty-four Prakash children, ranging in age from 5 to 22 years, and obtained their responses on a multi-dimensional Quality of Life questionnaire. Results Nearly all of the subjects indicated that their quality of life had improved after treatment. Children reported marked enhancement in their mobility, independence and safety, as also in social integration. Surprisingly, we found no significant correlations between quality of life metrics and factors such as age at treatment, gender, time since treatment, and pre- and post- surgery acuity. Conclusions A key question for public health policy makers is whether a program of surgical intervention for older blind children is likely to be beneficial, or if the resources are better spent on rehabilitation via vocational training and assistive devices. The marked improvements in quality of life we find in our data strongly argue for the provision of surgical care regardless of a child’s age.