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

Adults' spatial scaling of tactile maps: Insights from studying sighted, early and late blind individuals

The current study investigated spatial scaling of tactile maps among blind adults and blindfolded sighted controls. We were specifically interested in identifying spatial scaling strategies as well as effects of different scaling directions (up versus down) on participants' performance. To this aim, we asked late blind participants (with visual memory, Experiment 1) and early blind participants (without visual memory, Experiment 2) as well as sighted blindfolded controls to encode a map including a target and to place a response disc at the same spot on an empty, constant-sized referent space. Maps had five different sizes resulting in five scaling factors (1:3, 1:2, 1:1, 2:1, 3:1), allowing to investigate different scaling directions (up and down) in a single, comprehensive design. Accuracy and speed of learning about the target location as well as responding served as dependent variables. We hypothesized that participants who can use visual mental representations (i.e., late blind and blindfolded sighted participants) may adopt mental transformation scaling strategies. However, our results did not support this hypothesis. At the same time, we predicted the usage of relative distance scaling strategies in early blind participants, which was supported by our findings. Moreover, our results suggested that tactile maps can be scaled as accurately and even faster by blind participants than by sighted participants. Furthermore, irrespective of the visual status, participants of each visual status group gravitated their responses towards the center of the space. Overall, it seems that a lack of visual imagery does not impair early blind adults' spatial scaling ability but causes them to use a different strategy than sighted and late blind individuals.

Developmental changes in the visual, haptic, and bimodal perception of geometric angles

Geometrical knowledge is typically taught to children through a combination of vision and repetitive drawing (i.e. haptics), yet our understanding of how different spatial senses contribute to geometric perception during childhood is poor. Studies of line orientation suggest a dominant role of vision affecting the calibration of haptics during development; however, the associated multisensory interactions underpinning angle perception are unknown. Here we examined visual, haptic, and bimodal perception of angles across three age groups of children: 6 to 8 years, 8 to 10 years, and 10 to 12 years, with age categories also representing their class (grade) in primary school. All participants first learned an angular shape, presented dynamically, in one of three sensory tracing conditions: visual only, haptic only, or bimodal exploration. At test, which was visual only, participants selected a target angle from four possible alternatives with distractor angle sizes varying relative to the target angle size. We found a clear improvement in accuracy of angle perception with development for all learning modalities. Angle perception in the youngest group was equally poor (but above chance) for all modalities; however, for the two older child groups, visual learning was better than haptics. Haptic perception did not improve to the level of vision with age (even in a comparison adult group), and we found no specific benefit for bimodal learning over visual learning in any age group, including adults. Our results support a developmental increment in both spatial accuracy and precision in all modalities, which was greater in vision than in haptics, and are consistent with previous accounts of cross-sensory calibration in the perception of geometric forms.

Multisensory training improves the development of spatial cognition after sight restoration from congenital cataracts

Spatial cognition and mobility are typically impaired in congenitally blind individuals, as vision usually calibrates space perception by providing the most accurate distal spatial cues. We have previously shown that sight restoration from congenital bilateral cataracts guides the development of more accurate space perception, even when cataract removal occurs years after birth. However, late cataract-treated individuals do not usually reach the performance levels of the typically sighted population. Here, we developed a brief multisensory training that associated audiovisual feedback with body movements. Late cataract-treated participants quickly improved their space representation and mobility, performing as well as typically sighted controls in most tasks. Their improvement was comparable with that of a group of blind participants, who underwent training coupling their movements with auditory feedback alone. These findings suggest that spatial cognition can be enhanced by a training program that strengthens the association between bodily movements and their sensory feedback (either auditory or audiovisual).

Exploiting the haptic and audio channels to improve orientation and mobility apps for the visually impaired

Orientation and mobility apps for visually impaired people are well known to be effective in improving the quality of life for this target group. A mobile application that guides a visually impaired person step-by-step through a physical space is a valuable aid, but it does not provide an overview of a complex environment "at a glance," as a traditional hard-copy tactile map does. The aim of this study is to investigate whether a smartphone GPS map, enriched with haptic and audio hints, can facilitate cognitive mapping for visually impaired users. Encouraged by a preliminary study conducted in co-operation with two visually impaired volunteers, we designed and developed an Android prototype for exploration of an urban area. Our goal was to provide an affordable, portable and versatile solution to help users increase awareness of an environment through the positions of its landmarks and points of interest. Vibro-tactile and audio hints were linked to the coordinates on the map via the GeoJSON data format and were issued exploiting the text-to-speech and vibration features of the mobile device, as they were displayed through the operating system's APIs. Test sessions and interviews with visually impaired users produced encouraging results. Results, to be verified by more extensive testing, overall confirm the validity of our approach and are in line with results found in the literature.

Neural substrates of spatial processing and navigation in blindness: An activation likelihood estimation meta-analysis

Even though vision is considered the best suited sensory modality to acquire spatial information, blind individuals can form spatial representations to navigate and orient themselves efficiently in space. Consequently, many studies support the amodality hypothesis of spatial representations since sensory modalities other than vision contribute to the formation of spatial representations, independently of visual experience and imagery. However, given the high variability in abilities and deficits observed in blind populations, a clear consensus about the neural representations of space has yet to be established. To this end, we performed a meta-analysis of the literature on the neural correlates of spatial processing and navigation via sensory modalities other than vision, like touch and audition, in individuals with early and late onset blindness. An activation likelihood estimation (ALE) analysis of the neuroimaging literature revealed that early blind individuals and sighted controls activate the same neural networks in the processing of non-visual spatial information and navigation, including the posterior parietal cortex, frontal eye fields, insula, and the hippocampal complex. Furthermore, blind individuals also recruit primary and associative occipital areas involved in visuo-spatial processing via cross-modal plasticity mechanisms. The scarcity of studies involving late blind individuals did not allow us to establish a clear consensus about the neural substrates of spatial representations in this specific population. In conclusion, the results of our analysis on neuroimaging studies involving early blind individuals support the amodality hypothesis of spatial representations.

The power of vision: calibration of auditory space after sight restoration from congenital cataracts

Early visual deprivation typically results in spatial impairments in other sensory modalities. It has been suggested that, since vision provides the most accurate spatial information, it is used for calibrating space in the other senses. Here we investigated whether sight restoration after prolonged early onset visual impairment can lead to the development of more accurate auditory space perception. We tested participants who were surgically treated for congenital dense bilateral cataracts several years after birth. In Experiment 1 we assessed participants' ability to understand spatial relationships among sounds, by asking them to spatially bisect three consecutive, laterally separated sounds. Participants performed better after surgery than participants tested before. However, they still performed worse than sighted controls. In Experiment 2, we demonstrated that single sound localization in the two-dimensional frontal plane improves quickly after surgery, approaching performance levels of sighted controls. Such recovery seems to be mediated by visual acuity, as participants gaining higher post-surgical visual acuity performed better in both experiments. These findings provide strong support for the hypothesis that vision calibrates auditory space perception. Importantly, this also demonstrates that this process can occur even when vision is restored after years of visual deprivation.

Flexible cue anchoring strategies enable stable head direction coding in both sighted and blind animals

Vision plays a crucial role in instructing the brain’s spatial navigation systems. However, little is known about how vision loss affects the neuronal encoding of spatial information. Here, recording from head direction (HD) cells in the anterior dorsal nucleus of the thalamus in mice, we find stable and robust HD tuning in rd1 mice, a model of photoreceptor degeneration, that go blind by approximately one month of age. In contrast, placing sighted animals in darkness significantly impairs HD cell tuning. We find that blind mice use olfactory cues to maintain stable HD tuning and that prior visual experience leads to refined HD cell tuning in blind rd1 adult mice compared to congenitally blind animals. Finally, in the absence of both visual and olfactory cues, the HD attractor network remains intact but the preferred firing direction of HD cells drifts over time. These findings demonstrate flexibility in how the brain uses diverse sensory information to generate a stable directional representation of space.

Vision plays an important role in the head direction cell system in animals. Here the authors recorded from head direction cells in rd1 mice that show retinal degeneration at 1 month, and find that they use smell cues to maintain stable HD tuning.

Cognitive map formation supported by auditory, haptic, and multimodal information in persons with blindness

For efficient navigation, the brain needs to adequately represent the environment in a cognitive map. In this review, we sought to give an overview of literature about cognitive map formation based on non-visual modalities in persons with blindness (PWBs) and sighted persons. The review is focused on the auditory and haptic modalities, including research that combines multiple modalities and real-world navigation. Furthermore, we addressed implications of route and survey representations. Taking together, PWBs as well as sighted persons can build up cognitive maps based on non-visual modalities, although the accuracy sometime somewhat differs between PWBs and sighted persons. We provide some speculations on how to deploy information from different modalities to support cognitive map formation. Furthermore, PWBs and sighted persons seem to be able to construct route as well as survey representations. PWBs can experience difficulties building up a survey representation, but this is not always the case, and research suggests that they can acquire this ability with sufficient spatial information or training. We discuss possible explanations of these inconsistencies.

Cognitive map formation through tactile map navigation in visually impaired and sighted persons

The human brain can form cognitive maps of a spatial environment, which can support wayfinding. In this study, we investigated cognitive map formation of an environment presented in the tactile modality, in visually impaired and sighted persons. In addition, we assessed the acquisition of route and survey knowledge. Ten persons with a visual impairment (PVIs) and ten sighted control participants learned a tactile map of a city-like environment. The map included five marked locations associated with different items. Participants subsequently estimated distances between item pairs, performed a direction pointing task, reproduced routes between items and recalled item locations. In addition, we conducted questionnaires to assess general navigational abilities and the use of route or survey strategies. Overall, participants in both groups performed well on the spatial tasks. Our results did not show differences in performance between PVIs and sighted persons, indicating that both groups formed an equally accurate cognitive map. Furthermore, we found that the groups generally used similar navigational strategies, which correlated with performance on some of the tasks, and acquired similar and accurate route and survey knowledge. We therefore suggest that PVIs are able to employ a route as well as survey strategy if they have the opportunity to access route-like as well as map-like information such as on a tactile map.

Viewing Strategies in Children With Visual Impairment and Children With Normal Vision: A Systematic Scoping Review

Viewing strategies are strategies used to support visual information processing. These strategies may differ between children with cerebral visual impairment (CVI), children with ocular visual impairment, and children with normal vision since visual impairment might have an impact on viewing behavior. In current visual rehabilitation practice a variety of strategies is used without consideration of the differences in etiology of the visual impairment or in the spontaneous viewing strategies used. This systematic scoping review focuses on viewing strategies used during near school-based tasks like reading and on possible interventions aimed at viewing strategies. The goal is threefold: (1) creating a clear concept of viewing strategies, (2) mapping differences in viewing strategies between children with ocular visual impairment, children with CVI and children with normal vision, and (3) identifying interventions that can improve visual processing by targeting viewing strategies. Four databases were used to conduct the literature search: PubMed, Embase, PsycINFO and Cochrane. Seven hundred and ninety-nine articles were screened by two independent reviewers using PRISMA reporting guidelines of which 30 were included for qualitative analysis. Only five studies explicitly mentioned strategies used during visual processing, namely gaze strategies, reading strategies and search strategies. We define a viewing strategy as a conscious and systematic way of viewing during task performance. The results of this review are integrated with different attention network systems, which provide direction on how to design future interventions targeting the use of viewing strategies to improve different aspects of visual processing.

Spatial perspective-taking: insights from sensory impairments

Information can be perceived from a multiplicity of spatial perspectives, which is central to effectively understanding and interacting with our environment and other people. Sensory impairments such as blindness are known to impact spatial representations and perspective-taking is often thought of as a visual process. However, disturbed functioning of other sensory systems (e.g., vestibular, proprioceptive and auditory) can also influence spatial perspective-taking. These lines of research remain largely separate, yet together they may shed new light on the role that each sensory modality plays in this core cognitive ability. The findings to date reveal that spatial cognitive processes may be differently affected by various types of sensory loss. The visual system may be crucial for the development of efficient allocentric (object-to-object) representation; however, the role of vision in adopting another's spatial perspective remains unclear. On the other hand, the vestibular and the proprioceptive systems likely play an important role in anchoring the perceived self to the physical body, thus facilitating imagined self-rotations required to adopt another's spatial perspective. Findings regarding the influence of disturbed auditory functioning on perspective-taking are so far inconclusive and thus await further data. This review highlights that spatial perspective-taking is a highly plastic cognitive ability, as the brain is often able to compensate in the face of different sensory loss.

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.

Cognitive map formation through haptic and visual exploration of tactile city-like maps

In this study, we compared cognitive map formation of small-scale models of city-like environments presented in visual or tactile/haptic modalities. Previous research often addresses only a limited amount of cognitive map aspects. We wanted to combine several of these aspects to elucidate a more complete view. Therefore, we assessed different types of spatial information, and consider egocentric as well as allocentric perspectives. Furthermore, we compared haptic map learning with visual map learning. In total 18 sighted participants (9 in a haptic condition, 9 visuo-haptic) learned three tactile maps of city-like environments. The maps differed in complexity, and had five marked locations associated with unique items. Participants estimated distances between item pairs, rebuilt the map, recalled locations, and navigated two routes, after learning each map. All participants overall performed well on the spatial tasks. Interestingly, only on the complex maps, participants performed worse in the haptic condition than the visuo-haptic, suggesting no distinct advantage of vision on the simple map. These results support ideas of modality-independent representations of space. Although it is less clear on the more complex maps, our findings indicate that participants using only haptic or a combination of haptic and visual information both form a quite accurate cognitive map of a simple tactile city-like map.

Allocentric spatial perception through vision and touch in sighted and blind children

Vision and touch play a critical role in spatial development, facilitating the acquisition of allocentric and egocentric frames of reference, respectively. Previous works have shown that children's ability to adopt an allocentric frame of reference might be impaired by the absence of visual experience during growth. In the current work, we investigated whether visual deprivation also impairs the ability to shift from egocentric to allocentric frames of reference in a switching-perspective task performed in the visual and haptic domains. Children with and without visual impairments from 6 to 13 years of age were asked to visually (only sighted children) or haptically (blindfolded sighted children and blind children) explore and reproduce a spatial configuration of coins by assuming either an egocentric perspective or an allocentric perspective. Results indicated that temporary visual deprivation impaired the ability of blindfolded sighted children to switch from egocentric to allocentric perspective more in the haptic domain than in the visual domain. Moreover, results on visually impaired children indicated that blindness did not impair allocentric spatial coding in the haptic domain but rather affected the ability to rely on haptic egocentric cues in the switching-perspective task. Finally, our findings suggested that the total absence of vision might impair the development of an egocentric perspective in case of body midline-crossing targets.

Core knowledge of geometry can develop independently of visual experience

Geometrical intuitions spontaneously drive visuo-spatial reasoning in human adults, children and animals. Is their emergence intrinsically linked to visual experience, or does it reflect a core property of cognition shared across sensory modalities? To address this question, we tested the sensitivity of blind-from-birth adults to geometrical-invariants using a haptic deviant-figure detection task. Blind participants spontaneously used many geometric concepts such as parallelism, right angles and geometrical shapes to detect intruders in haptic displays, but experienced difficulties with symmetry and complex spatial transformations. Across items, their performance was highly correlated with that of sighted adults performing the same task in touch (blindfolded) and in vision, as well as with the performances of uneducated preschoolers and Amazonian adults. Our results support the existence of an amodal core-system of geometry that arises independently of visual experience. However, performance at selecting geometric intruders was generally higher in the visual compared to the haptic modality, suggesting that sensory-specific spatial experience may play a role in refining the properties of this core-system of geometry.

Virtual Haptic Perception as an Educational Assistive Technology: A Case Study in Inclusive Education

The traditional educational process of blind people is a complex practice that relies on the haptic perception (tactile perception) of physical models. However, physical models may be costly, inaccessible or may require a large storage space. To overcome these difficulties, in this article a virtual haptic perception approach to support the teaching and learning process of blind people is proposed. The proposed approach combines the use of virtual reality and haptic technologies. The research aim is to objectively evaluate the feasibility and effectiveness of using virtual haptic perception in the education of blind children. For this purpose, an experimental methodology was defined and used to teach maths, in particular fundamental three-dimensional (3D) shapes, to blind children. The results are analysed in terms of the participants' ability to explore and recognize virtual objects, and the knowledge gain after the virtual perception learning period. From this analysis it is concluded that haptic virtual perception is a valid and effective assistive technology for the education of blind children.

Adults' spatial scaling: evidence from the haptic domain

The current study investigated adults' spatial-scaling abilities using a haptic localization task. As a first aim, we examined the strategies used to solve this haptic task. Secondly, we explored whether irrelevant visual information influenced adults' spatial-scaling performance. Thirty-two adults were asked to locate targets as presented in maps on a larger or same-sized referent space. Maps varied in size in accordance with different scaling factors (1:4, 1:2, 1:1), whereas the referent space was constant in size throughout the experimental session. The availability of irrelevant, non-informative vision was manipulated by blindfolding half of the participants prior to the experiment (condition without non-informative vision), whereas the other half were able to see their surroundings with the stimuli being hidden behind a curtain (condition with non-informative vision). Analyses with absolute errors (after correcting for reversal errors) as the dependent variable revealed a significant interaction of the scaling factor and non-informative vision condition. Adults in the blindfolded condition showed constant errors and response times irrespective of scaling factor. Such a response pattern indicates the usage of relative strategies. Adults in the curtain condition showed a linear increase in errors with higher scaling factors, whereas their response times remained constant. This pattern of results supports the usage of absolute strategies or mental transformation strategies. Overall, our results indicate different scaling strategies depending on the availability of non-informative vision, highlighting the strong influence of (even irrelevant) vision on adults' haptic processing.

Audio Feedback Associated With Body Movement Enhances Audio and Somatosensory Spatial Representation

In the last years, the positive impact of sensorimotor rehabilitation training on spatial abilities has been taken into account, e.g., providing evidence that combined multimodal compared to unimodal feedback improves responsiveness to spatial stimuli. To date, it still remains unclear to which extent spatial learning is influenced by training conditions. Here we investigated the effects of active and passive audio-motor training on spatial perception in the auditory and proprioceptive domains on 36 healthy young adults. First, to investigate the role of voluntary movements on spatial perception, we compared the effects of active vs. passive multimodal training on auditory and proprioceptive spatial localization. Second, to investigate the effectiveness of unimodal training conditions on spatial perception, we compared the impact of only proprioceptive or only auditory sensory feedback on spatial localization. Finally, to understand whether the positive effects of multimodal and unimodal trainings generalize to the untrained part, both dominant and non-dominant arms were tested. Results indicate that passive multimodal training (guided movement) is more beneficial than active multimodal training (active exploration) and only in passive condition the improvement is generalized also on the untrained hand. Moreover, we found that combined audio-motor training provides the strongest benefit because it significantly affects both auditory and somatosensory localization, while the effect of a single feedback modality is limited to a single domain, indicating a cross-modal influence of the two domains. Therefore, the use of multimodal feedback is more efficient in improving spatial perception. These results indicate that combined sensorimotor signals are effective in recalibrating auditory and proprioceptive spatial perception and that the beneficial effect is mainly due to the combination of auditory and proprioceptive spatial cues.

Mental Imagery Follows Similar Cortical Reorganization as Perception: Intra-Modal and Cross-Modal Plasticity in Congenitally Blind

Cortical plasticity in congenitally blind individuals leads to cross-modal activation of the visual cortex and may lead to superior perceptual processing in the intact sensory domains. Although mental imagery is often defined as a quasi-perceptual experience, it is unknown whether it follows similar cortical reorganization as perception in blind individuals. In this study, we show that auditory versus tactile perception evokes similar intra-modal discriminative patterns in congenitally blind compared with sighted participants. These results indicate that cortical plasticity following visual deprivation does not influence broad intra-modal organization of auditory and tactile perception as measured by our task. Furthermore, not only the blind, but also the sighted participants showed cross-modal discriminative patterns for perception modality in the visual cortex. During mental imagery, both groups showed similar decoding accuracies for imagery modality in the intra-modal primary sensory cortices. However, no cross-modal discriminative information for imagery modality was found in early visual cortex of blind participants, in contrast to the sighted participants. We did find evidence of cross-modal activation of higher visual areas in blind participants, including the representation of specific-imagined auditory features in visual area V4.

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.

The severity of the visual impairment and practice matter for drawing ability in children

BACKGROUND AND AIMS

Astonishing drawing capacities have been reported in children with early visual impairments. However, most of the evidence relies on single case studies. Hitherto, no study has systematically jointly investigated, in these children, the role of (1) the severity of the visual handicap, (2) age and (3) practice in drawing. The study aimed at revealing the specificities of the drawing in children deprived from vision, as compared to children with less severe visual handicap and to sighted children performing under haptic or usual visual control.

METHOD

148 children aged 6-14 years had to produce 12 drawings of familiar objects. 38 had a severe visual impairment, 41 suffered from low vision, and 69 were sighted children performing either under visual condition or blindfolded under haptic control.

RESULTS

Recognizability and other characteristics of the drawings were highly dependent on the child's degree of vision and level of drawing practice, and progressed with chronological age more clearly in the sighted children or those with low vision than in those deprived of vision.

CONCLUSION

The study confirmed that all groups showed significant drawing ability, even the group totally deprived of visual experience. Furthermore, the specificities of the drawings produced by visually-impaired children appeared clearly related to their practice and the severity of their visual impairment. This should incite parents and professionals to encourage these children to practice drawing as early as possible.

On my right or on your left? Spontaneous spatial perspective taking in blind people

Spatial perspective taking is a human ability that permits to assume another person's spatial viewpoint. Data show that spatial perspective taking might arise even spontaneously by the mere presence of another person in the environment. We investigated whether this phenomenon is observable also in blind people. Blind and blindfolded sighted participants explored a tridimensional tactile map and memorized the localization of different landmarks. Then, after the presentation of sounds coming from three landmarks-positioned on the right, on the left, and in front-participants had to indicate the reciprocal position of the two lateral landmarks. Results showed that when the sound coming from the frontal landmark suggested the presence of a speaking (voice) or moving person (footsteps), several blind and sighted people adopted this person's perspective. These findings suggest that auditory stimuli can trigger spontaneous spatial perspective taking in sighted as well as in blind people.

Haptic aesthetics in the blind: A behavioral and fMRI investigation

Understanding perception and aesthetic appeal of arts and environmental objects, what is appreciated, liked, or preferred, and why, is of prime importance for improving the functional capacity of the blind and visually impaired and the ergonomic design for their environment, which however so far, has been examined only in sighted individuals. This paper provides a general overview of the first experimental study of tactile aesthetics as a function of visual experience and level of visual deprivation, using both behavioral and brain imaging techniques. We investigated how blind people perceive 3D tactile objects, how they characterize them, and whether the tactile perception, and tactile shape preference (liking or disliking) and tactile aesthetic appreciation (judging tactile qualities of an object, such as pleasantness, comfortableness etc.) of 3D tactile objects can be affected by the level of visual experience. The study employed innovative behavioral measures, such as new forms of aesthetic preference-appreciation and perceptual discrimination questionnaires, in combination with advanced functional Magnetic Resonance Imaging (fMRI) techniques, and compared congenitally blind, late-onset blind and blindfolded (sighted) participants. Behavioral results demonstrated that both blind and blindfolded-sighted participants assessed curved or rounded 3D tactile objects as significantly more pleasing than sharp 3D tactile objects, and symmetric 3D tactile objects as significantly more pleasing than asymmetric 3D tactile objects. However, as compared to the sighted, blind people showed better skills in tactile discrimination as demonstrated by accuracy and speed of discrimination. Functional MRI results demonstrated that there was a large overlap and characteristic differences in the aesthetic appreciation brain networks in the blind and the sighted. As demonstrated both populations commonly recruited the somatosensory and motor areas of the brain, but with stronger activations in the blind as compared to the sighted. Secondly, sighted people recruited more frontal regions whereas blind people, in particular, the congenitally blind, paradoxically recruited more 'visual' areas of the brain. These differences were more pronounced between the sighted and the congenitally blind rather than between the sighted and the late-onset blind, indicating the key influence of the onset time of visual deprivation. Understanding of the underlying brain mechanisms should have a wide range of important implications for a generalized cross-sensory theory and practice in the rapidly evolving field of neuroaesthetics, as well as for 'cutting-edge' rehabilitation technologies for the blind and the visually impaired.

Allocentric and contra-aligned spatial representations of a town environment in blind people

Evidence concerning the representation of space by blind individuals is still unclear, as sometimes blind people behave like sighted people do, while other times they present difficulties. A better understanding of blind people's difficulties, especially with reference to the strategies used to form the representation of the environment, may help to enhance knowledge of the consequences of the absence of vision. The present study examined the representation of the locations of landmarks of a real town by using pointing tasks that entailed either allocentric points of reference with mental rotations of different degrees, or contra-aligned representations. Results showed that, in general, people met difficulties when they had to point from a different perspective to aligned landmarks or from the original perspective to contra-aligned landmarks, but this difficulty was particularly evident for the blind. The examination of the strategies adopted to perform the tasks showed that only a small group of blind participants used a survey strategy and that this group had a better performance with respect to people who adopted route or verbal strategies. Implications for the comprehension of the consequences on spatial cognition of the absence of visual experience are discussed, focusing in particular on conceivable interventions.

The Impact of Early Visual Deprivation on Spatial Hearing: A Comparison between Totally and Partially Visually Deprived Children

The specific role of early visual deprivation on spatial hearing is still unclear, mainly due to the difficulty of comparing similar spatial skills at different ages and to the difficulty in recruiting young blind children from birth. In this study, the effects of early visual deprivation on the development of auditory spatial localization have been assessed in a group of seven 3–5 years old children with congenital blindness (n = 2; light perception or no perception of light) or low vision (n = 5; visual acuity range 1.1–1.7 LogMAR), with the main aim to understand if visual experience is fundamental to the development of specific spatial skills. Our study led to three main findings: firstly, totally blind children performed overall more poorly compared sighted and low vision children in all the spatial tasks performed; secondly, low vision children performed equally or better than sighted children in the same auditory spatial tasks; thirdly, higher residual levels of visual acuity are positively correlated with better spatial performance in the dynamic condition of the auditory localization task indicating that the more residual vision the better spatial performance. These results suggest that early visual experience has an important role in the development of spatial cognition, even when the visual input during the critical period of visual calibration is partially degraded like in the case of low vision children. Overall these results shed light on the importance of early assessment of spatial impairments in visually impaired children and early intervention to prevent the risk of isolation and social exclusion.

Learning to echolocate in sighted people: a correlational study on attention, working memory and spatial abilities

Echolocation can be beneficial for the orientation and mobility of visually impaired people. Research has shown considerable individual differences for acquiring this skill. However, individual characteristics that affect the learning of echolocation are largely unknown. In the present study, we examined individual factors that are likely to affect learning to echolocate: sustained and divided attention, working memory, and spatial abilities. To that aim, sighted participants with normal hearing performed an echolocation task that was adapted from a previously reported size-discrimination task. In line with existing studies, we found large individual differences in echolocation ability. We also found indications that participants were able to improve their echolocation ability. Furthermore, we found a significant positive correlation between improvement in echolocation and sustained and divided attention, as measured in the PASAT. No significant correlations were found with our tests regarding working memory and spatial abilities. These findings may have implications for the development of guidelines for training echolocation that are tailored to the individual with a visual impairment.

Touching and Hearing Unseen Objects: Multisensory Effects on Scene Recognition

In three experiments, we investigated the influence of object-specific sounds on haptic scene recognition without vision. Blindfolded participants had to recognize, through touch, spatial scenes comprising six objects that were placed on a round platform. Critically, in half of the trials, object-specific sounds were played when objects were touched (bimodal condition), while sounds were turned off in the other half of the trials (unimodal condition). After first exploring the scene, two objects were swapped and the task was to report, which of the objects swapped positions. In Experiment 1, geometrical objects and simple sounds were used, while in Experiment 2, the objects comprised toy animals that were matched with semantically compatible animal sounds. In Experiment 3, we replicated Experiment 1, but now a tactile-auditory object identification task preceded the experiment in which the participants learned to identify the objects based on tactile and auditory input. For each experiment, the results revealed a significant performance increase only after the switch from bimodal to unimodal. Thus, it appears that the release of bimodal identification, from audio-tactile to tactile-only produces a benefit that is not achieved when having the reversed order in which sound was added after having experience with haptic-only. We conclude that task-related factors other than mere bimodal identification cause the facilitation when switching from bimodal to unimodal conditions.

Bilateral Coordination of Children who are Blind

The purpose of this study was to evaluate the bilateral coordination in children and adolescents with visual impairments aged 7 to 18 years in comparison to their sighted peers. An additional objective was to identify the influence of sex and age on bilateral coordination. Seventy-five individuals with congenital severe visual impairment (40 girls and 35 boys) comprised the visually impaired group. The Sighted group comprised 139 youth without visual impairment. Subtest 4 of the Bruininks-Oseretsky Test of Motor Proficiency was administered to test bilateral coordination. To analyze the effect of the independent variables in the results obtained in the Subtest 4, four linear regression models were applied according to group and sex. The results indicated that severe visual impairment and lack of visual sensation had a negative effect on the development of participants' bilateral coordination, which however did not depend on sex or age.

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

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Auditory and proprioceptive spatial impairments in blind children and adults

It is not clear what role visual information plays in the development of space perception. It has previously been shown that in absence of vision, both the ability to judge orientation in the haptic modality and bisect intervals in the auditory modality are severely compromised (Gori, Sandini, Martinoli & Burr, 2010; Gori, Sandini, Martinoli & Burr, 2014). Here we report for the first time also a strong deficit in proprioceptive reproduction and audio distance evaluation in early blind children and adults. Interestingly, the deficit is not present in a small group of adults with acquired visual disability. Our results support the idea that in absence of vision the audio and proprioceptive spatial representations may be delayed or drastically weakened due to the lack of visual calibration over the auditory and haptic modalities during the critical period of development.

Visuo-haptic multisensory object recognition, categorization, and representation

Visual and haptic unisensory object processing show many similarities in terms of categorization, recognition, and representation. In this review, we discuss how these similarities contribute to multisensory object processing. In particular, we show that similar unisensory visual and haptic representations lead to a shared multisensory representation underlying both cross-modal object recognition and view-independence. This shared representation suggests a common neural substrate and we review several candidate brain regions, previously thought to be specialized for aspects of visual processing, that are now known also to be involved in analogous haptic tasks. Finally, we lay out the evidence for a model of multisensory object recognition in which top-down and bottom-up pathways to the object-selective lateral occipital complex are modulated by object familiarity and individual differences in object and spatial imagery.

Are there relationships among different spatial skills of individuals with blindness?

The aim of this study was to detect the possible relationships between various spatial skills of individuals with blindness. Twenty-eight individuals with blindness participated in five experiments that examined the body knowledge, laterality, directionality, perspective-taking, spatial coding of the near space and spatial knowledge of the far space. According to the results a positive correlation between body knowledge and directionality has emerged. Moreover, body knowledge and spatial coding of near space are found to be predictors of perspective-taking, while directionality and perspective-taking are found to be predictors of spatial coding of near space, and directionality and perspective-taking predictors of spatial knowledge of far space. This finding suggest that future studies should seriously take into account the possibility that the development of a certain skill could in fact be the result of the development of another skill/s. Moreover, the findings support the notion that a delay in the development of a spatial skill may not necessarily be a result of the visual impairment itself but of the incomplete development of another spatial skill.

Impaired visual size-discrimination in children with movement disorders

Multisensory integration of spatial information occurs late in childhood, at around eight years (Gori, Del Viva, Sandini, & Burr, 2008). For younger children, the haptic system dominates size discrimination and vision dominates orientation discrimination: the dominance may reflect sensory calibration, and could have direct consequences on children born with specific sensory disabilities. Here we measure thresholds for visual discrimination of orientation and size in children with movement disorders of upper limbs. Visual orientation discrimination was very similar to the age-matched typical children, but visual size discrimination thresholds were far worse, in all eight individuals with early-onset movement disorder. This surprising and counterintuitive result is readily explained by the cross-sensory calibration hypothesis: when the haptic sense is unavailable for manipulation, it cannot be readily used to estimate size, and hence to calibrate the visual experience of size: visual discrimination is subsequently impaired. This complements a previous study showing that non-sighted children have reduced acuity for haptic orientation, but not haptic size, discriminations (Gori, Sandini, Martinoli, & Burr, 2010). Together these studies show that when either vision or haptic manipulation is impaired, the impairment also impacts on complementary sensory systems that are calibrated by that one.

Spatial updating depends on gaze direction even after loss of vision

Direction of gaze (eye angle + head angle) has been shown to be important for representing space for action, implying a crucial role of vision for spatial updating. However, blind people have no access to vision yet are able to perform goal-directed actions successfully. Here, we investigated the role of visual experience for localizing and updating targets as a function of intervening gaze shifts in humans. People who differed in visual experience (late blind, congenitally blind, or sighted) were briefly presented with a proprioceptive reach target while facing it. Before they reached to the target's remembered location, they turned their head toward an eccentric direction that also induced corresponding eye movements in sighted and late blind individuals. We found that reaching errors varied systematically as a function of shift in gaze direction only in participants with early visual experience (sighted and late blind). In the late blind, this effect was solely present in people with moveable eyes but not in people with at least one glass eye. Our results suggest that the effect of gaze shifts on spatial updating develops on the basis of visual experience early in life and remains even after loss of vision as long as feedback from the eyes and head is available.

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.

The impact of vision in spatial coding

The aim of this study is to examine the performance in coding and representing of near-space in relation to vision status (blindness vs. normal vision) and sensory modality (touch vs. vision). Forty-eight children and teenagers participated. Sixteen of the participants were totally blind or had only light perception, 16 were blindfolded sighted individuals, and 16 were non-blindfolded sighted individuals. Participants were given eight different object patterns in different arrays and were asked to code and represent each of them. The results suggest that vision influences performance in spatial coding and spatial representation of near space. However, there was no statistically significant difference between participants with blindness who used the most effective haptic strategy and blindfolded sighted participants. Thus, the significance of haptic strategies is highlighted.

Piaget's water-level task: the impact of vision on performance

In the present study, the aim was to examine the differences in performance between children and adolescents with visual impairment and sighted peers in the water-level task. Twenty-eight individuals with visual impairments, 14 individuals with blindness and 14 individuals with low vision, and 28 sighted individuals participated in the present study. Fourteen sighted individuals participated blindfolded and 14 were able to use their sight. The findings indicate that use of vision can influence the performance in water-level task. However, in the restriction of visual ability (participants with blindfold), individuals with blindness might present better performance than blindfolded sighted participants.

Functional equivalence of spatial images from touch and vision: evidence from spatial updating in blind and sighted individuals

This research examined whether visual and haptic map learning yield functionally equivalent spatial images in working memory, as evidenced by similar encoding bias and updating performance. In 3 experiments, participants learned 4-point routes either by seeing or feeling the maps. At test, blindfolded participants made spatial judgments about the maps from imagined perspectives that were either aligned or misaligned with the maps as represented in working memory. Results from Experiments 1 and 2 revealed a highly similar pattern of latencies and errors between visual and haptic conditions. These findings extend the well-known alignment biases for visual map learning to haptic map learning, provide further evidence of haptic updating, and most important, show that learning from the 2 modalities yields very similar performance across all conditions. Experiment 3 found the same encoding biases and updating performance with blind individuals, demonstrating that functional equivalence cannot be due to visual recoding and is consistent with an amodal hypothesis of spatial images.

Prior visual experience, and perception and memory of shape in people with total blindness

The aim of this study was to explore the role of prior visual experience for tactile differentiation of object shapes. The study investigated whether people who lost their vision later in life were able to identify and recognize object shapes more accurately and faster than those who were blind from their birth. Four experiments were conducted. The first two were concerned with tactile shape differentiation, the second two with shape recognition. The hypotheses were only partially confirmed. The ‘late’ blind participants distinguished shapes more accurately than the congenitally blind (particularly in ‘simple’ perception tasks). This finding may suggest that people who have prior visual experience use an allocentric strategy when visualizing object shapes in their imagery. The ‘late’ blind participants performed the tasks more slowly than those who were congenitally blind. This may be explained by the complexity of the task, the time needed to create an allocentric representation, and discrepancy in the tactile experiences between the congenitally and late blind groups. A number of implications for further research are outlined.