Visual experience, visual field size, and the development of nonvisual sensitivity to the spatial structure of outdoor neighborhoods explored by walking

Spatial Cognition of the Visually Impaired: A Case Study in a Familiar Environment

OBJECTIVES

This paper aims to explore the factors influencing the spatial cognition of the visually impaired in familiar environments.

BACKGROUND

Massage hospitals are some of the few places that can provide work for the visually impaired in China. Studying the spatial cognition of the visually impaired in a massage hospital could be instructive for the design of working environments for the visually impaired and other workplaces in the future.

METHODS

First, the subjective spatial cognition of the visually impaired was evaluated by object layout tasks for describing the spatial relationships among object parts. Second, physiological monitoring signal data, including the electrodermal activity, heart rate variability, and electroencephalography, were collected while the visually impaired doctors walked along prescribed routes based on the feature analysis of the physical environment in the hospital, and then their physiological monitoring signal data for each route were compared. The visual factors, physical environmental factors, and human-environment interactive factors that significantly impact the spatial cognition of visually impaired people were discussed.

CONCLUSIONS

(1) visual acuity affects the spatial cognition of the visually impaired in familiar environments; (2) the spatial cognition of the visually impaired can be promoted by a longer staying time and the more regular sequence of a physical environment; (3) the spatial comfort of the visually impaired can be improved by increasing the amount of greenery; and (4) the visual comfort of the visually impaired can be reduced by rich interior colors and contrasting lattice floor tiles.

How ageing and blindness affect egocentric and allocentric spatial memory

Egocentric (subject-to-object) and allocentric (object-to-object) spatial reference frames are fundamental for representing the position of objects or places around us. The literature on spatial cognition in blind people has shown that lack of vision may limit the ability to represent spatial information in an allocentric rather than egocentric way. Furthermore, much research with sighted individuals has reported that ageing has a negative impact on spatial memory. However, as far as we know, no study has assessed how ageing may affect the processing of spatial reference frames in individuals with different degrees of visual experience. To fill this gap, here we report data from a cross-sectional study in which a large sample of young and elderly participants (160 participants in total) who were congenitally blind (long-term visual deprivation), adventitiously blind (late onset of blindness), blindfolded sighted (short-term visual deprivation) and sighted (full visual availability) performed a spatial memory task that required egocentric/allocentric distance judgements with regard to memorised stimuli. The results showed that egocentric judgements were better than allocentric ones and above all that the ability to process allocentric information was influenced by both age and visual status. Specifically, the allocentric judgements of congenitally blind elderly participants were worse than those of all other groups. These findings suggest that ageing and congenital blindness can contribute to the worsening of the ability to represent spatial relationships between external, non-body-centred anchor points.

How can basic research on spatial cognition enhance the visual accessibility of architecture for people with low vision?

People with visual impairment often rely on their residual vision when interacting with their spatial environments. The goal of visual accessibility is to design spaces that allow for safe travel for the large and growing population of people who have uncorrectable vision loss, enabling full participation in modern society. This paper defines the functional challenges in perception and spatial cognition with restricted visual information and reviews a body of empirical work on low vision perception of spaces on both local and global navigational scales. We evaluate how the results of this work can provide insights into the complex problem that architects face in the design of visually accessible spaces.

How Persons with Visual Impairments Explore Novel Spaces: Strategies of Good and Poor Performers

The study presented here examined the videotaped search patterns and strategies that 65 persons with visual impairments used to locate and learn the arrangement of five objects in a novel space. Videotapes of the 15 best-performing and 15 worst-performing participants’ explorations were then compared to the participants’ verbal self-reports of the strategies they used. The best-performing participants used search patterns and strategies that were effective in locating objects quickly and that facilitated the development of object-to-object relationships.

Spotlights and Soundscapes

For persons with visual impairment, forming cognitive maps of unfamiliar interior spaces can be challenging. Various technical developments have converged to make it feasible, without specialized equipment, to represent a variety of useful landmark objects via spatial audio, rather than solely dispensing route information. Although such systems could be key to facilitating cognitive map formation, high-density auditory environments must be crafted carefully to avoid overloading the listener. This article recounts a set of research exercises with potential users, in which the optimization of such systems was explored. In Experiment 1, a virtual reality environment was used to rapidly prototype and adjust the auditory environment in response to participant comments. In Experiment 2, three variants of the system were evaluated in terms of their effectiveness in a real-world building. This methodology revealed a variety of optimization approaches and recommendations for designing dense mixed-reality auditory environments aimed at supporting cognitive map formation by visually impaired persons.

Early Loss of Vision Results in Extensive Reorganization of Plasticity-Related Receptors and Alterations in Hippocampal Function That Extend Through Adulthood

Although by adulthood cortical structures and their capacity for processing sensory information have become established and stabilized, under conditions of cortical injury, or sensory deprivation, rapid reorganization occurs. Little is known as to the impact of this kind of adaptation on cellular processes related to memory encoding. However, imaging studies in humans suggest that following loss or impairment of a sensory modality, not only cortical but also subcortical structures begin to reorganize. It is likely that these processes are supported by neurotransmitter receptors that enable synaptic and cortical plasticity. Here, we explored to what extent the expression of plasticity-related proteins (GABA-A, GABA-B, GluN1, GluN2A, GluN2B) is altered following early vision loss, and whether this impacts on hippocampal function. We observed that in the period of 2-4 months postnatally in CBA/J-mice that experience hereditary postnatal retinal degeneration, systematic changes of GABA-receptor and NMDA-receptor subunit expression occurred that emerged first in the hippocampus and developed later in the cortex, compared to control mice that had normal vision. Changes were accompanied by significant impairments in hippocampal long-term potentiation and hippocampus-dependent learning. These data indicate that during cortical adaptation to early loss of vision, hippocampal information processing is compromised, and this status impacts on the acquisition of spatial representations.

Performance of Blind and Sighted Persons on Spatial Tasks

This article reports on a study of the performance by congenitally blind, adventitiously blind, and sighted persons on three types of tasks: manipulatory, simple locomotion, and complex locomotion. The three groups of subjects tended to perform equivalently, and the results offer little evidence of a set of spatial processes that rely on past visual experience and are applicable to a broad variety of tasks.

Change in Visual Perceptual Detection Distances for Low Vision Travelers as a Result of Dynamic Visual Assessment and Training

This study evaluated the ability of a dynamic visual assessment and training protocol to improve the ability of 65 persons who were legally blind to detect environmental hazards. Training improved the ability of the majority of subjects to detect hazards, and the assessments identified those who did not need training or would not benefit from it.

Visual Experience is not Necessary for Efficient Survey Spatial Cognition: Evidence from Blindness

This study investigated whether the lack of visual experience affects the ability to create spatial inferential representations of the survey type. We compared the performance of persons with congenital blindness and that of blindfolded sighted persons on four survey representation-based tasks (Experiment 1). Results showed that persons with blindness performed better than blindfolded sighted controls. We repeated the same tests introducing a third group of persons with late blindness (Experiment 2). This last group performed better than blindfolded sighted participants, whereas differences between participants with late and congenital blindness were nonsignificant. The present findings are compatible with results of other studies, which found that when visual perception is lacking, skill in gathering environmental spatial information provided by nonvisual modalities may contribute to a proper spatial encoding. It is concluded that, although it cannot be asserted that total lack of visual experience incurs no cost, our findings are further evidence that visual experience is not a necessary condition for the development of spatial inferential complex representations.

Let me be your guide: physical guidance improves spatial learning for older adults with simulated low vision

Monitoring one's safety during low vision navigation demands limited attentional resources which may impair spatial learning of the environment. In studies of younger adults, we have shown that these mobility monitoring demands can be alleviated, and spatial learning subsequently improved, via the presence of a physical guide during navigation. The present study extends work with younger adults to an older adult sample with simulated low vision. We test the effect of physical guidance on improving spatial learning as well as general age-related changes in navigation ability. Participants walked with and without a physical guide on novel real-world paths in an indoor environment and pointed to remembered target locations. They completed concurrent measures of cognitive load on the trials. Results demonstrate an improvement in learning under low vision conditions with a guide compared to walking without a guide. However, our measure of cognitive load did not vary between guidance conditions. We also conducted a cross-age comparison and found support for age-related declines in spatial learning generally and greater effects of physical guidance with increasing age.

The Effects of Restricted Peripheral Field-of-View on Spatial Learning while Navigating

Recent work with simulated reductions in visual acuity and contrast sensitivity has found decrements in survey spatial learning as well as increased attentional demands when navigating, compared to performance with normal vision. Given these findings, and previous work showing that peripheral field loss has been associated with impaired mobility and spatial memory for room-sized spaces, we investigated the role of peripheral vision during navigation using a large-scale spatial learning paradigm. First, we aimed to establish the magnitude of spatial memory errors at different levels of field restriction. Second, we tested the hypothesis that navigation under these different levels of restriction would use additional attentional resources. Normally sighted participants walked on novel real-world paths wearing goggles that restricted the field-of-view (FOV) to severe (15°, 10°, 4°, or 0°) or mild angles (60°) and then pointed to remembered target locations using a verbal reporting measure. They completed a concurrent auditory reaction time task throughout each path to measure cognitive load. Only the most severe restrictions (4° and blindfolded) showed impairment in pointing error compared to the mild restriction (within-subjects). The 10° and 4° conditions also showed an increase in reaction time on the secondary attention task, suggesting that navigating with these extreme peripheral field restrictions demands the use of limited cognitive resources. This comparison of different levels of field restriction suggests that although peripheral field loss requires the actor to use more attentional resources while navigating starting at a less extreme level (10°), spatial memory is not negatively affected until the restriction is very severe (4°). These results have implications for understanding of the mechanisms underlying spatial learning during navigation and the approaches that may be taken to develop assistance for navigation with visual impairment.

Effects of Field-of-View Restrictions on Speed and Accuracy of Manoeuvring

Effects of field-of-view restrictions on the speed and accuracy of participants performing a real-world manoeuvring task through an obstacled environment were investigated. Although field-of-view restrictions are known to affect human behaviour and to degrade performance for a range of different tasks, the relationship between human manoeuvring performance and field-of-view size is not known. This knowledge is essential to evaluate a trade-off between human performance, cost, and ergonomic aspects of field-of-view limiting devises like head-mounted displays and night vision goggles which are frequently deployed for tasks involving human motion through environments with obstacles. In this study the speed and accuracy of movement were measured in 15 participants (8 men, 7 women, 22.9 ± 2.8 yr. of age) traversing a course formed by three wall segments for different field-of-view restrictions. Analysis showed speed decreased linearly with decreasing field-of-view extent, while accuracy was consistently reduced for all restricted field-of-view conditions. Present results may be used to evaluate cost and performance trade-offs for field-of-view restricting devices deployed to perform time-limited human-locomotion tasks in complex structured environments, such as night-vision goggles and head-mounted displays.

Blind and Sighted Children's Spatial Knowledge of Their Home Environments

The development of spatial knowledge of the home environment was longitudinally studied in three groups of school-age children who varied in their visual ability: totally blind, visually impaired, and normally sighted. The children were asked to judge which of three locations in their homes was the closest to a designated position: (1) judging by the routes necessary to get to the locations; and (2) judging by straight-line distances to the locations. Locations were either on the same floor as the designed position, on a different floor, or in the yard. Totally blind children were delayed in mastery of the tasks compared to the other children, particularly in judging straight-line distances between familiar locations. Their mistakes suggest that their spatial understanding of their home environments is based on their knowledge of routes between places rather than on their knowledge of the overall layout of the familiar space.

Spatial navigation by congenitally blind individuals

Spatial navigation in the absence of vision has been investigated from a variety of perspectives and disciplines. These different approaches have progressed our understanding of spatial knowledge acquisition by blind individuals, including their abilities, strategies, and corresponding mental representations. In this review, we propose a framework for investigating differences in spatial knowledge acquisition by blind and sighted people consisting of three longitudinal models (i.e., convergent, cumulative, and persistent). Recent advances in neuroscience and technological devices have provided novel insights into the different neural mechanisms underlying spatial navigation by blind and sighted people and the potential for functional reorganization. Despite these advances, there is still a lack of consensus regarding the extent to which locomotion and wayfinding depend on amodal spatial representations. This challenge largely stems from methodological limitations such as heterogeneity in the blind population and terminological ambiguity related to the concept of cognitive maps. Coupled with an over‐reliance on potential technological solutions, the field has diffused into theoretical and applied branches that do not always communicate. Here, we review research on navigation by congenitally blind individuals with an emphasis on behavioral and neuroscientific evidence, as well as the potential of technological assistance. Throughout the article, we emphasize the need to disentangle strategy choice and performance when discussing the navigation abilities of the blind population. WIREs Cogn Sci 2016, 7:37–58. doi: 10.1002/wcs.1375

For further resources related to this article, please visit the WIREs website.

Allocentric Spatial Performance Higher in Early-Blind and Sighted Adults Than in Retinopathy-of-Prematurity Adults

The question as to whether people totally blind since infancy process allocentric or external spatial information like the sighted has caused considerable debate within the literature. Due to the extreme rarity of the population, researchers have often included individuals with retinopathy of prematurity (RoP--over oxygenation at birth) within the sample. However, RoP is inextricably confounded with prematurity per se. Prematurity, without visual disability, has been associated with spatial processing difficulties. In this experiment, blindfolded sighted participants and two groups of functionally totally blind participants heard text descriptions from a survey (allocentric) or route (egocentric) perspective. One blind group lost their sight due to RoP and a second group before 24 months of age. The accuracy of participants' mental representations derived from the text descriptions was assessed via questions and maps. The RoP participants had lower scores than the sighted and early blind, who performed similarly. In other words, it was not visual impairment alone that resulted in impaired allocentric spatial performance in this task but visual impairment together with RoP. This finding may help explain the contradictions within the existing literature on the role of vision in allocentric spatial processing.

How does experience modulate auditory spatial processing in individuals with blindness?

Comparing early- and late-onset blindness in individuals offers a unique model for studying the influence of visual experience on neural processing. This study investigated how prior visual experience would modulate auditory spatial processing among blind individuals. BOLD responses of early- and late-onset blind participants were captured while performing a sound localization task. The task required participants to listen to novel “Bat-ears” sounds, analyze the spatial information embedded in the sounds, and specify out of 15 locations where the sound would have been emitted. In addition to sound localization, participants were assessed on visuospatial working memory and general intellectual abilities. The results revealed common increases in BOLD responses in the middle occipital gyrus, superior frontal gyrus, precuneus, and precentral gyrus during sound localization for both groups. Between-group dissociations, however, were found in the right middle occipital gyrus and left superior frontal gyrus. The BOLD responses in the left superior frontal gyrus were significantly correlated with accuracy on sound localization and visuospatial working memory abilities among the late-onset blind participants. In contrast, the accuracy on sound localization only correlated with BOLD responses in the right middle occipital gyrus among the early-onset counterpart. The findings support the notion that early-onset blind individuals rely more on the occipital areas as a result of cross-modal plasticity for auditory spatial processing, while late-onset blind individuals rely more on the prefrontal areas which subserve visuospatial working memory.

Activation of the hippocampal complex during tactile maze solving in congenitally blind subjects

Despite their lack of vision, congenitally blind subjects are able to build and manipulate cognitive maps for spatial navigation. It is assumed that they thereby rely more heavily on echolocation, proprioceptive signals and environmental cues such as ambient temperature and audition to compensate for their lack of vision. Little is known, however, about the neural mechanisms underlying spatial navigation in blind individuals in settings where these cues are absent. We therefore measured behavioural performance and blood oxygenation-level dependant (BOLD) responses using functional magnetic resonance imaging (fMRI) in congenitally blind and blindfolded sighted participants while they navigated through a tactile multiple T-maze. Both groups learned the maze task at a similar pace. In blind participants, tactile maze navigation was associated with increased BOLD responses in the right hippocampus and parahippocampus, occipital cortex and fusiform gyrus. Blindfolded sighted controls did not show increased BOLD responses in these areas; instead they activated the caudate nucleus and thalamus. Both groups activated the precuneus during tactile maze navigation. We conclude that cross-modal plastic processes allow for the recruitment of the hippocampal complex and visual cortex in congenital blindness.

The role of visual experience for the neural basis of spatial cognition

Blindness often results in the adaptive neural reorganization of the remaining modalities, producing sharper auditory and haptic behavioral performance. Yet, non-visual modalities might not be able to fully compensate for the lack of visual experience as in the case of congenital blindness. For example, developmental visual experience seems to be necessary for the maturation of multisensory neurons for spatial tasks. Additionally, the ability of vision to convey information in parallel might be taken into account as the main attribute that cannot be fully compensated by the spared modalities. Therefore, the lack of visual experience might impair all spatial tasks that require the integration of inputs from different modalities, such as having to represent a set of objects on the basis of the spatial relationships among the objects, rather than the spatial relationship that each object has with oneself. Here we integrate behavioral and neural evidence to conclude that visual experience is necessary for the neural development of normal spatial cognition.

Sequential vs simultaneous encoding of spatial information: a comparison between the blind and the sighted

The aim of this research is to assess whether the crucial factor in determining the characteristics of blind people's spatial mental images is concerned with the visual impairment per se or the processing style that the dominant perceptual modalities used to acquire spatial information impose, i.e. simultaneous (vision) vs sequential (kinaesthesis). Participants were asked to learn six positions in a large parking area via movement alone (congenitally blind, adventitiously blind, blindfolded sighted) or with vision plus movement (simultaneous sighted, sequential sighted), and then to mentally scan between positions in the path. The crucial manipulation concerned the sequential sighted group. Their visual exploration was made sequential by putting visual obstacles within the pathway in such a way that they could not see simultaneously the positions along the pathway. The results revealed a significant time/distance linear relation in all tested groups. However, the linear component was lower in sequential sighted and blind participants, especially congenital. Sequential sighted and congenitally blind participants showed an almost overlapping performance. Differences between groups became evident when mentally scanning farther distances (more than 5m). This threshold effect could be revealing of processing limitations due to the need of integrating and updating spatial information. Overall, the results suggest that the characteristics of the processing style rather than the visual impairment per se affect blind people's spatial mental images.

Colour, face, and visuospatial imagery abilities in low-vision individuals with visual field deficits

This study investigates to what extent visual perception integrity is necessary for visual mental imagery. Sixteen low-vision participants with severe peripheral visual field loss, 16 with severe central field loss, 6 left brain-damaged patients with right homonymous hemianopia, 6 right brain-damaged patients with left homonymous hemianopia, and 16 normally sighted controls performed perceptual and imagery tasks using colours, faces, and spatial relationships. Results showed that (a) the perceptual and mental image>ry disorders vary according to the type of visual field loss, (b) hemianopics had no more difficulties imagining spatial stimuli in their contralesional hemispace than in their ipsilesional one, and (c) the only hemianopic participant to have perceptual and mental imagery impairments suffered from attentional deficits. Results suggest that (a) visual memory is not definitively established, but rather needs perceptual practice to be maintained, and (b) that visual mental imagery may involve some of the attentional-exploratory mechanisms that are employed in visual behaviour.

The importance of a visual horizon for distance judgments under severely degraded vision

In two experiments we examined the role of visual horizon information on absolute egocentric distance judgments to on-ground targets. Sedgwick [1983, in Human and Machine Vision (New York: Academic Press) pp 425-458] suggested that the visual system may utilize the angle of declination from a horizontal line of sight to the target location (horizon distance relation) to determine absolute distances on infinite ground surfaces. While studies have supported this hypothesis, less is known about the specific cues (vestibular, visual) used to determine horizontal line of sight. We investigated this question by requiring observers to judge distances under degraded vision given an unaltered or raised visual horizon. The results suggest that visual horizon information does influence perception of absolute distances as evident through two different action-based measures: walking or throwing without vision to previously viewed targets. Distances were judged as shorter in the presence of a raised visual horizon. The results are discussed with respect to how the visual system accurately determines absolute distance to objects on a finite ground plane and for their implications for understanding space perception in low-vision individuals.

The role of visual experience in mental scanning of actual pathways: evidence from blind and sighted people

In this research we compare blind and normally sighted people in mental scanning of spatial maps using locomotor or visual/locomotor exploration of a real 3-D environment. Different types of visual experience were tested: early (congenital) and late (adventitious) onset of blindness, short-term deprivation (blindfolded-sighted), and full vision (sighted). Participants were asked to learn six positions in a large parking area with movement alone (congenital, adventitious, blindfolded-sighted) or with vision plus movement (sighted), and then to mentally scan between positions in the path. Finally, they had to describe how they imagined scanning the learned pathway. We found a significant linear relation between space and time, ie the classic mental scanning effect, in all tested groups. However, the linear component was lower in blind participants, especially congenital. Instead, short-term visual deprivation had minimal impact on mental scanning. Overall, blind participants had shorter scanning times than both sighted groups, and the effect was particularly evident with farther distances. These results suggest that there is a quantitative rather than a qualitative difference between the blind and the sighted. In addition, the mental scanning strategies reported by participants also affected mental scanning times. The theoretical implications of these findings are discussed.

Beyond core knowledge: Natural geometry

For many centuries, philosophers and scientists have pondered the origins and nature of human intuitions about the properties of points, lines, and figures on the Euclidean plane, with most hypothesizing that a system of Euclidean concepts either is innate or is assembled by general learning processes. Recent research from cognitive and developmental psychology, cognitive anthropology, animal cognition, and cognitive neuroscience suggests a different view. Knowledge of geometry may be founded on at least two distinct, evolutionarily ancient, core cognitive systems for representing the shapes of large-scale, navigable surface layouts and of small-scale, movable forms and objects. Each of these systems applies to some but not all perceptible arrays and captures some but not all of the three fundamental Euclidean relationships of distance (or length), angle, and direction (or sense). Like natural number (Carey, 2009), Euclidean geometry may be constructed through the productive combination of representations from these core systems, through the use of uniquely human symbolic systems.

Learning building layouts with non-geometric visual information: the effects of visual impairment and age

Previous studies suggest that humans rely on geometric visual information (hallway structure) rather than non-geometric visual information (eg doors, signs, and lighting) for acquiring cognitive maps of novel indoor layouts. In this study we asked whether visual impairment and age affect reliance on non-geometric visual information for layout learning. We tested three groups of participants-younger (<50 years of age) normally sighted; older (50-70 years of age) normally sighted; and low-vision (people with heterogeneous forms of visual impairment ranging in age from 18 to 67 years). 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.

Centred Egocentric, Decentred Egocentric, and Allocentric Spatial Representations in the Peripersonal Space of Congenital Total Blindness

The distinction between different spatial representations in the peripersonal space was examined in two experiments by requiring sighted blindfolded and blind participants to remember the locations of objects haptically explored. In experiment 1, object relocation took place from either the same position as learning—with the same (centred egocentric condition) or 90°-rotated (rotated egocentric condition) object array—or from a position different from the learning position (allocentric condition). Results revealed that, in both sighted and blind people, distance errors were higher in the allocentric and rotated conditions than in the centred egocentric condition, and that blind participants made more distance errors than sighted subjects only in the allocentric condition. Experiment 2 repeated rotated egocentric and allocentric conditions, while the centred egocentric condition was replaced by a decentred egocentric condition in which object relocation took place from the same position as learning (egocentric) but started from a decentred point. The decentred egocentric condition was found to remain significantly different from the rotated condition, but not from the allocentric condition. Moreover, blind participants performed less well in the allocentric condition, but were specifically impaired. Overall, our results confirm that different types of spatial constraints and representations, including the decentred egocentric one, can be distinguished in the peripersonal space and that blind people are as efficient as sighted in the egocentric and rotated conditions, but they encounter difficulties in recalling locations also in the peripersonal space, especially when an allocentric condition is required.

Memory for an imagined pathway and strategy effects in sighted and in totally congenitally blind individuals

The literature reports mixed results on the imagery abilities of the blind, at times showing a difference between sighted and blind individuals and at other times similarities. However, the possibility that the results are due to different strategies spontaneously used in performing the imagery tasks has never been systematically studied. A large group of 30 totally congenitally blind (TCB) individuals and a group of 30 sighted individuals matched for gender age and schooling were presented with a mental pathway task on a complex two-dimensional (5 x 5) matrix. After administering the task, participants were interviewed in order to establish the strategy they used. Results showed that both sighted and TCB may use a spatial mental imagery, a verbal or a mixed strategy in carrying out the task. Differences between the groups emerged only when last location and then entire pathway had to be remembered rather than just the last position, and were clearly affected by the type of strategy. Specifically, TCB performed more poorly than the sighted individuals when they used a spatial mental imagery strategy, whereas the two groups had a similar performance with a verbal strategy.

The role of visual experience on the representation and updating of novel haptic scenes

We investigated the role of visual experience on the spatial representation and updating of haptic scenes by comparing recognition performance across sighted, congenitally and late blind participants. We first established that spatial updating occurs in sighted individuals to haptic scenes of novel objects. All participants were required to recognise a previously learned haptic scene of novel objects presented across the same or different orientation as learning whilst they either remained in the same position to moved to a new position relative to the scene. Scene rotation incurred a cost in recognition performance in all groups. However, overall haptic scene recognition performance was worse in the congenitally blind group. Moreover, unlike the late blind or sighted groups, the congenitally blind group were unable to compensate for the cost in scene rotation with observer motion. Our results suggest that vision plays an important role in representing and updating spatial information encoded through touch and have important implications for the role of vision in the development of neuronal areas involved in spatial cognition.

Why Cyclops could not compete with Ulysses: monocular vision and mental images

The present research demonstrates that the limitations of congenitally blind people in tasks requiring the processing of mental images are specifically related to the absence of binocular vision and not to the absence of vision per se. We contrasted three different groups of participants: sighted; visually impaired, with reduced binocular vision; monocular, with a normal visual acuity although in one eye only. Visually impaired participants (i.e. blurred vision) show a pattern of performance comparable to that of the sighted. In contrast, monocular participants show a similar pattern of performance to congenitally blind individuals despite being able to see perfectly well. These results shed new light on the relationship between perception and imagery and on the characteristics of sequential and simultaneous processes in the human brain.

Optic-flow and egocentric-direction strategies in walking: Central vs peripheral visual field

The impact of a central or peripheral visual field loss on the vision strategy used to guide walking was determined by measuring walking paths of visually impaired participants. An immersive virtual environment was used to dissociate the expected paths of the optic-flow and egocentric-direction strategies by offsetting the walker's point of view from the actual direction of walking. Environments consisted of a goal within a forest, the goal alone, or the forest alone following a brief presentation of the goal. The first two environments allowed an evaluation of the visual information used in a goal-directed task whereas the third environment investigated the information used in a memory-guided task. Participants had either a central (CFL) or peripheral visual field loss (PFL) or were fully sighted (FS). Results showed that, for the goal-directed task, the CFL group was less influenced by optic flow than was an age-matched FS group. Optic flow decreased heading error by only 1.3 degrees (16%) in the CFL group compared to 3.6 degrees (42%) in the FS group. The PFL group showed an optic-flow influence (2.4 degrees or 26%) comparable to an older, age-matched FS group (2.9 degrees or 31%). For the memory-guided task, all but the PFL group had heading errors comparable to those obtained in the goal-alone scene, demonstrating the ability to use an egocentric-direction strategy with a stored representation of either the goal's position or an offset relative to a landmark instead of a visible goal. The paths of the PFL group veered significantly from the predicted paths of both the optic-flow and egocentric-direction strategies. The findings of this study suggest that central vision is important for using optic flow to guide walking, whereas peripheral vision is important for establishing and/or updating an accurate representation of spatial structure for navigation.

Anticipatory spatial representation of 3D regions explored by sighted observers and a deaf-and-blind-observer

Viewers who study photographs of scenes tend to remember having seen beyond the boundaries of the view [boundary extension; J. Exp. Psychol. Learn. Mem. Cogn. 15 (1989) 179]. Is this a fundamental aspect of scene representation? Forty undergraduates explored bounded regions of six common (3D) scenes, visually or haptically (while blindfolded) and then the delimiting borders were removed. Minutes later they reconstructed boundary placement. Boundary extension occurred: mean areas were increased by 53% (vision) and by 17% (haptics). A deaf-and-blind woman (KC) haptically explored the same regions. Although a "haptic expert", she too remembered having explored beyond the boundaries, with performance similar to that of the blindfolded-sighted. Boundary extension appears to be a fundamental aspect of spatial cognition. Possibly constrained by the "scope" of the input modality (vision>haptics), this anticipatory spatial representation may facilitate integration of successively perceived regions of the world irrespective of modality and the perceiver's sensory history.

Allocentric and Egocentric Updating of Spatial Memories

In 4 experiments, the authors investigated spatial updating in a familiar environment. Participants learned locations of objects in a room, walked to the center, and turned to appropriate facing directions before making judgments of relative direction (e.g., "Imagine you are standing at X and facing Y. Point to Z.") or egocentric pointing judgments (e.g., "You are facing Y. Point to Z."). Experiments manipulated the angular difference between the learning heading and the imagined heading and the angular difference between the actual heading and the imagined heading. Pointing performance was best when the imagined heading was parallel to the learning view, even when participants were facing in other directions, and when actual and imagined headings were the same. Room geometry did not affect these results. These findings indicated that spatial reference directions in memory were not updated during locomotion.

Path integration from optic flow and body senses in a homing task

We examined the roles of information from optic flow and body senses (eg vestibular and proprioceptive information) for path integration, using a triangle completion task in a virtual environment. In two experiments, the contribution of optic flow was isolated by using a joystick control. Five circular arenas were used for testing: (B) both floor and wall texture; (F) floor texture only, reducing information for rotation; (W) wall texture only, reducing information for translation; (N) a no texture control condition, and (P) an array of posts. The results indicate that humans can use optic flow for path integration and are differentially influenced by rotational and translational flow. In a third experiment, participants actively walked in arenas B, F, and N, so body senses were also available. Performance shifted from a pattern of underturning to overturning and exhibited decreased variability, similar responses with and without optic flow, and no attrition. The results indicate that path integration can be performed by integrating optic flow, but when information from body senses is available it appears to dominate.

Active, passive and snapshot exploration in a virtual environment: influence on scene memory, reorientation and path memory

We investigated the importance of active, passive and snapshot exploration on spatial memory in a virtual city. The exploration consisted in traveling along a series of streets. 'Active exploration' was performed by giving directions to the subject who controlled his displacement with a joystick. During 'passive' exploration, the travel was imposed by the computer. Finally, during 'snapshot exploration', simple views of the scene were presented sequentially every 4 m. Travel velocity was the same in all cases. The three visual exploration modes were compared with three spatial memory measures: (1) scene recognition, (2) at the end of the path, reorientation toward the departure point and (3) drawings of the path shape. Scene recognition and estimation of the direction of the starting point of the path were not affected by the mode of exploration. In contrast, reproduction of the shape of the path was affected: the errors of reproduction were greater for the snapshot exploration than for the other two conditions; there was no difference between the other two conditions. These results suggest that (1) 2D image features from a visual scene are memorized. Moreover, (2) pointing towards the origin of the path relies on motion duration integration or a frame of reference integrated during displacement. Finally, (3) drawing the path shape involves a deliberate reconstruction process.

Developmental lesions of visual cortex influence control of reaching

We examined visually guided reaching movements in a young adult (EW) who had extensive bilateral lesions in the visual cortex since birth. EW lacked a right occipital lobe and ventral portions of the left and had poor visual acuity (3/400), yet could point to visual targets as quickly as 9 controls with visual cortex lesions acquired in adulthood and 4 adults without neurological disease. However, EW's endpoint variability and hand movement path curvature were much greater, especially for left hand movements, in concert with large sensorimotor transformation errors. Experimental reduction of acuity (to 3/240 or worse) in the normal controls produced symmetric increases in endpoint variability but did not change hand path curvature, indicating that EW's impaired movements were not due to poor vision alone. Results suggest that visual cortex in early life supports the development of lifelong neural mechanisms for the planning and control of reaching movements.

Evidence of imagined passive self-motion through imagery-perception interaction

The existence of whole-body passive self-motion mental imagery was investigated by examining whether the perception of passive body accelerations can be affected by passive self-motion imagery. Twenty healthy subjects recognised target passive body acceleration. This recognition task was performed under three conditions: (1) a baseline condition without imagery; (2) a compatible imagery condition during which subjects imagined themselves passively moving in the same direction as the target acceleration; (3) a non-compatible imagery condition during which subjects imagined themselves passively moving in the direction opposite to that of the target acceleration. The recognition of the target acceleration was improved under compatible and degraded under non-compatible imagery. This interaction implies that perception and imaginary share common representations, and supports the existence of passive self-motion imagery.

Spatial hearing in children with visual disabilities

A study is reported of the effect of early visual experience on the development of auditory space perception. The spatial hearing of thirty-five children with visual disabilities (twenty-two with congenital total blindness) was compared with that of eighteen sighted children and seventeen sighted adults. The tests provided a comprehensive assessment of spatial-hearing ability, including psychophysical estimates of spatial resolution in the horizontal, vertical, and distance dimensions, as well as measures of reaching and walking to the locations of sound sources. The spatial hearing of the children with visual disabilities was comparable to or somewhat better than that of the sighted children and adults. This pattern held even when the group with visual disabilities was restricted to those children with congenital total blindness; in fact, some of those children had exceptionally good spatial hearing. These findings imply that the developmental calibration of human spatial hearing is not dependent on a history of visual experience. It seems likely that this calibration arises from the experience of changes in sound-localization cues arising from self-motion, such as turning the head or walking. As a practical matter, orientation and mobility instructors may reasonably assume that individuals with visual disabilities can use their hearing effectively in day-to-day travel situations.