**Abstract**

Several pieces of evidence indicate that visual experience during development is fundamental to acquire long-term spatial capabilities. For instance, reaching abilities tend to emerge at 5 months of age in sighted infants, while only later at 10 months of age in blind infants. Moreover, other spatial skills such as auditory localization and haptic orientation discrimination tend to be delayed or impaired in visually impaired children, with a huge impact on the development of sighted-like perceptual and cognitive asset. Here, we report an overview of studies showing that the lack of vision can interfere with the development of coherent multisensory spatial representations and highlight the contribution of current research in designing new tools to support the acquisition of spatial capabilities during childhood.

**Keywords:** blindness, visual impairment, child development, rehabilitation, innovation

## **1. Introduction**

Spatial competence is essential in everyday life for numerous human activities, as it entails the ability to understand and internalize the representation of the structure, entities, and relations of space with respect to one's own body [1, 2]. Despite the fact that spatial competence encompasses a diverse set of skills, research in the field has generally focused on identifying the developmental steps that are necessary to acquire from an early age the ability to reason about spatial properties of the environment.

There is a general consensus on the crucial role of visual experience in guiding the maturation of spatial competence [3]. Vision takes advantages respect to other senses in encoding spatial information because it ensures the simultaneous perception of multiple stimuli in the environment despite the apparent motion of the array on the retina during locomotion enabling us to extract more invariant spatial properties from the surrounding layout [4, 5]. Indeed psychophysical data indicate that when sensorial conflict occurs, audition and touch are strongly biased by simultaneously presented visuospatial information, suggesting that sighted people tend to organize spatial information according to a visual frame of reference [6–12]. Neurophysiological data further confirm the view by suggesting that the visual feedback is fundamental for spatial learning [13–18], i.e., visual experience allows the alignment and thus the integration of auditory and visuospatial cortical maps [19–22]. Thus, research on sighted individuals suggests that vision typically provides the most accurate and reliable information about the spatial properties

of the external world, therefore it dominates spatial perception. Consequently, if visual experience is necessary to adequately represent spatial information, we would expect blind people to perform worse than sighted people in spatial tasks. This would be especially true if the visual impairment emerges at birth, when multisensory communication is fundamental for the sensorimotor feedback loop that contributes to the development of spatial representations [23, 24].

Despite valuable insights into the important guiding role of vision on spatial development, contrasting results indicate that visually impaired people can manifest or enhanced either impaired skills depending on the spatial aspects investigated, leading to the hypothesis that vision could have an essential or facilitating role depending on the nature of the spatial task that individuals carry out [14]. A clearer definition of the underlying processes involved in spatial competence enhancements and deficits caused by visual loss is important not only to quantify to what extent the perceptual consequences of early blindness translate to realworld settings but also to develop effective rehabilitation tools and technologies to improve their spatial skills [25]. Indeed, scientific findings related to spatial competence development in the absence of visual experience have important implications for clinical outcomes and for the design of new rehabilitation activities meant to activate compensatory strategies since an early age.

#### **2. Development of spatial competence with vision**

The first developmental theory of spatial competence was proposed by Jean Piaget and his colleagues [26–28], who hypothesized that spatial understanding gradually improves with age thanks to a progressively more conscious interaction with the external world that permits to accumulate sensorimotor experiences such as reaching. Nonetheless, the identification of the starting points for spatial development remains one of the most debated topics within the literature of spatial competence.

While some researchers argue for innate knowledge of spatial understanding in humans [29] by reporting impressive spatial abilities in infants, other researchers advocate for a gradual acquisition of spatial competence during childhood [30] by reporting significant limitation of early spatial skills during infancy. For instance, several studies have demonstrated that already at 3 months infants are able to represent categorical spatial information by distinguishing between above vs. below and left vs. right [31, 32] and that by 5 months of age babies are sensitive to metric properties of space being able to code spatial object dimensions such as height [33–35], distance location [36], and angles [37]. Conversely, other studies indicate that while sensitivity to spatial properties appears in early infancy, further refinement of spatial accuracy emerges later during development. For instance, coding of categorical and metrical information improves through the primary school years [38–40] as well as capabilities of estimating and reproducing object size and location [41, 42].

The question of whether spatial capabilities are innate or acquired is of central importance to understand if an early sensory deprivation can negatively impact on the acquisition of adult-like competences. In the case of blindness, a key developmental acquisition is the ability to code auditory and tactile spatial properties of the environment in order to independently orient and navigate in space. Research on auditory spatial perception has shown that sighted infants already possess the ability to differentiate acoustic information and perform adequate actions in different dimensions [43]. Indeed they can turn their heads toward a sound from the moment they are born [44, 45] and at the age of 4–5 months, head-orientation movements

**253**

*The Role of Vision on Spatial Competence DOI: http://dx.doi.org/10.5772/intechopen.89273*

that is later consolidated through concrete experience.

instead of combining them as adults usually do [62].

The second distinction in the spatial cognition domain is between categorical and metric spatial representations, which, respectively, represent the coding of spatial information in a relative manner by means of comparisons among entities

become even faster and more precise than in the neonatal period. Further improvements in the ability to code the location of sonorous objects in space manifest at 6 months of age, when infants are sensitive to changes in the location of sounds as small as 13–19 degrees [46, 47]. Nonetheless, this reflexive orientation to sound sources is present at birth but disappears during the first month if large movements of the head are required [48] to appear again at 4–5 months of age: for this reason, it has been hypothesized that the early orientation reflex represents the activity of lower brain stem and provides an initial stage to acquire spatial competence [49]

In the spatial cognition domain, two main distinctions can be made about spatial representations of the environment [50]. The first distinction is between the egocentric and allocentric frame of reference which indicates the strategy to code location of objects, respectively, in a viewer-dependent or a viewer-independent manner. While the egocentric representation is tied to the observer and can be used either when the observer remains stationary or when the observer moves keeping track of the movement (dead reckoning or path integration), the allocentric representation does not depend on the viewer's current position but on external landmarks that can be adjacent (cue learning) or distal (place learning). Although early spatial representations were originally described as purely egocentric [51], several studies indicated that infants can make use of both intrinsic and external features of the environment to locate objects. There is evidence that infants can update egocentric representations by keeping track of their movement and thus locate objects from novel positions within the first year of life: indeed by 9 months, infants can compensate for simple changes in their position, such as translation along a straight line [52] or rotational movements [53]. Nonetheless, for more complex displacements, infants manifest a general difficulty in keeping track of their changing relation to target location. For example, at 12 months of age, they start to solve complex problems involving both translation and rotation but they perform better when they can make use of adjacent landmarks embedded in the environment [54], and this ability seems to show little improvement between 16 and 36 months [55]. Moreover, previous research has shown that sighted infants reach for sounding objects in the absence of visual clues [47, 56–59], implying that a sense of auditory space is well consolidated at this stage since sounding objects are localized in relation to one's body. The allocentric strategy seems to emerge quite early in the development together with the egocentric strategy, but with different maturational rates for cue learning and place learning types of coding. Indeed, studies employing paradigms where the direction of looking from a novel position indicate where infants expect to see an engaging stimulus demonstrate that by 8.5 months of age, infants use an adjacent salient landmark to locate the stimulus, whereas only at 12 months of age, they consistently use relational information of distal landmarks [54]. Several studies confirm the idea that egocentric and allocentric strategies continue to refine during childhood by showing that at 18–24 months of age, toddlers become able to use geometrical cues such as shape to orient themselves [60, 61]. Nonetheless, an important milestone such as the ability to integrate different reference frames within a common system of spatial representation in order to increase accuracy and reduce the variability of spatial judgments emerge only later during the development. Indeed, children aged between 4 and 8 years old are not able to use both self-motion and external landmarks as egocentric and allocentric information, respectively, to reproduce object location because they alternated both strategies

#### *The Role of Vision on Spatial Competence DOI: http://dx.doi.org/10.5772/intechopen.89273*

*Visual Impairment and Blindness - What We Know and What We Have to Know*

that contributes to the development of spatial representations [23, 24].

activate compensatory strategies since an early age.

**2. Development of spatial competence with vision**

of the external world, therefore it dominates spatial perception. Consequently, if visual experience is necessary to adequately represent spatial information, we would expect blind people to perform worse than sighted people in spatial tasks. This would be especially true if the visual impairment emerges at birth, when multisensory communication is fundamental for the sensorimotor feedback loop

Despite valuable insights into the important guiding role of vision on spatial development, contrasting results indicate that visually impaired people can manifest or enhanced either impaired skills depending on the spatial aspects investigated, leading to the hypothesis that vision could have an essential or facilitating role depending on the nature of the spatial task that individuals carry out [14]. A clearer definition of the underlying processes involved in spatial competence enhancements and deficits caused by visual loss is important not only to quantify to what extent the perceptual consequences of early blindness translate to realworld settings but also to develop effective rehabilitation tools and technologies to improve their spatial skills [25]. Indeed, scientific findings related to spatial competence development in the absence of visual experience have important implications for clinical outcomes and for the design of new rehabilitation activities meant to

The first developmental theory of spatial competence was proposed by Jean Piaget and his colleagues [26–28], who hypothesized that spatial understanding gradually improves with age thanks to a progressively more conscious interaction with the external world that permits to accumulate sensorimotor experiences such as reaching. Nonetheless, the identification of the starting points for spatial development remains one of the most debated topics within the literature of spatial

While some researchers argue for innate knowledge of spatial understanding in humans [29] by reporting impressive spatial abilities in infants, other researchers advocate for a gradual acquisition of spatial competence during childhood [30] by reporting significant limitation of early spatial skills during infancy. For instance, several studies have demonstrated that already at 3 months infants are able to represent categorical spatial information by distinguishing between above vs. below and left vs. right [31, 32] and that by 5 months of age babies are sensitive to metric properties of space being able to code spatial object dimensions such as height [33–35], distance location [36], and angles [37]. Conversely, other studies indicate that while sensitivity to spatial properties appears in early infancy, further refinement of spatial accuracy emerges later during development. For instance, coding of categorical and metrical information improves through the primary school years [38–40] as well as capabilities of estimating and reproducing object size and loca-

The question of whether spatial capabilities are innate or acquired is of central importance to understand if an early sensory deprivation can negatively impact on the acquisition of adult-like competences. In the case of blindness, a key developmental acquisition is the ability to code auditory and tactile spatial properties of the environment in order to independently orient and navigate in space. Research on auditory spatial perception has shown that sighted infants already possess the ability to differentiate acoustic information and perform adequate actions in different dimensions [43]. Indeed they can turn their heads toward a sound from the moment they are born [44, 45] and at the age of 4–5 months, head-orientation movements

**252**

competence.

tion [41, 42].

become even faster and more precise than in the neonatal period. Further improvements in the ability to code the location of sonorous objects in space manifest at 6 months of age, when infants are sensitive to changes in the location of sounds as small as 13–19 degrees [46, 47]. Nonetheless, this reflexive orientation to sound sources is present at birth but disappears during the first month if large movements of the head are required [48] to appear again at 4–5 months of age: for this reason, it has been hypothesized that the early orientation reflex represents the activity of lower brain stem and provides an initial stage to acquire spatial competence [49] that is later consolidated through concrete experience.

In the spatial cognition domain, two main distinctions can be made about spatial representations of the environment [50]. The first distinction is between the egocentric and allocentric frame of reference which indicates the strategy to code location of objects, respectively, in a viewer-dependent or a viewer-independent manner. While the egocentric representation is tied to the observer and can be used either when the observer remains stationary or when the observer moves keeping track of the movement (dead reckoning or path integration), the allocentric representation does not depend on the viewer's current position but on external landmarks that can be adjacent (cue learning) or distal (place learning). Although early spatial representations were originally described as purely egocentric [51], several studies indicated that infants can make use of both intrinsic and external features of the environment to locate objects. There is evidence that infants can update egocentric representations by keeping track of their movement and thus locate objects from novel positions within the first year of life: indeed by 9 months, infants can compensate for simple changes in their position, such as translation along a straight line [52] or rotational movements [53]. Nonetheless, for more complex displacements, infants manifest a general difficulty in keeping track of their changing relation to target location. For example, at 12 months of age, they start to solve complex problems involving both translation and rotation but they perform better when they can make use of adjacent landmarks embedded in the environment [54], and this ability seems to show little improvement between 16 and 36 months [55]. Moreover, previous research has shown that sighted infants reach for sounding objects in the absence of visual clues [47, 56–59], implying that a sense of auditory space is well consolidated at this stage since sounding objects are localized in relation to one's body. The allocentric strategy seems to emerge quite early in the development together with the egocentric strategy, but with different maturational rates for cue learning and place learning types of coding. Indeed, studies employing paradigms where the direction of looking from a novel position indicate where infants expect to see an engaging stimulus demonstrate that by 8.5 months of age, infants use an adjacent salient landmark to locate the stimulus, whereas only at 12 months of age, they consistently use relational information of distal landmarks [54]. Several studies confirm the idea that egocentric and allocentric strategies continue to refine during childhood by showing that at 18–24 months of age, toddlers become able to use geometrical cues such as shape to orient themselves [60, 61]. Nonetheless, an important milestone such as the ability to integrate different reference frames within a common system of spatial representation in order to increase accuracy and reduce the variability of spatial judgments emerge only later during the development. Indeed, children aged between 4 and 8 years old are not able to use both self-motion and external landmarks as egocentric and allocentric information, respectively, to reproduce object location because they alternated both strategies instead of combining them as adults usually do [62].

The second distinction in the spatial cognition domain is between categorical and metric spatial representations, which, respectively, represent the coding of spatial information in a relative manner by means of comparisons among entities in space and the coding of spatial information in external coordinates by means of metric cues such as distance or length. It has been shown that at 7 months of age, infants spontaneously show categorical dichotomous discrimination of auditory space by differentiating objects within and beyond reach [57, 58] and by distinguishing spatial categories such as above vs. below and left vs. right [32, 63]. Early sensitivity to metric cues has been observed in 4.5–6.5 months old infants for the dimension of objects [64] and distance [36]. Nonetheless, methodological issues have been raised for the interpretation of such results since experimental paradigms typically used with infants employ observational measures of the infant's behavior that may reveal more low-level perceptual rather than conceptual representation. Indeed, it has been shown that at the age of 2 years, children are able to match objects by height when these objects are presented in containers of a fixed height, but not when they are presented without containers, indicating that toddlers make use of distance cues only when they can rely on relative cues [65]. A considerable improvement in the ability to code object size and location can be observed between the ages of 4 and 12 [40–42, 66], for example, in tasks that require to use a configuration of distal landmarks to infer object location [67]. This could be due to the development of a hierarchical coding system, which integrates metrics and categorical information [68]. Given the time course of spatial cognition development and the discrepancy between early and later acquisition of spatial skills, an interactionist approach has been proposed that acknowledges strong potentiality and tries to identify underlying mechanisms implicated in the transformation of early abilities into mature competence [69]. The underlying mechanisms responsible for the refinement of spontaneous spatial orientation skills might be found both in the biological and environmental experiences. Within the biological context, many improvements in spatial functioning have been associated with the maturation of specific brain regions such as the hippocampus. For instance, the maturation of the hippocampus-mediated ability to encode relations among multiple objects may determine an increase in the number of stimuli that children rely on during reorientation and navigation tasks [70]. Within the environmental context, experience involves interactions with objects in the physical world and learning conventional information about symbolic spatial representations, such as maps and models. Spatial competence is strictly dependent on experiential factors such as exploratory activities which are in turn related to the development of locomotor activities. For example, it has been suggested that the emergence of allocentric coding in the form of cue learning might derive from the onset of crawling around 8–9 months, while further locomotor experiences may facilitate place learning by stimulating children to observe and approach object arrays from different directions. Indeed, locomotion is not simply a maturational precursor to psychological changes, but it plays a crucial role in their genesis [71]. For example, crawling provides the infant with concrete experiences that may change his coding strategy, for example, permitting the infant to abandon an egocentric body-oriented localization of objects to one based on the use of environmental landmarks. Recent findings suggest that sighted children acquire spatial capabilities thanks to the reciprocal influence between visual perception and execution of movements [72]: children monitor the success of action through a sensory-motor feedback by matching expected and observed changes of visual information. Indeed, self-generated movements commonly help to perceive the space acoustically because they convey the proprioceptive sensation corresponding to the movement of the ears toward sound sources [73]. In other words, using the dichotomy between the body and its exterior, an individual acquires spatial competence through observation of the body's actions and the resulting sensory consequences: through self-generated movements, the nervous system learns sensorimotor contingencies [74], which reveal the spatial properties

**255**

fundamental for the development of self-concept.

*The Role of Vision on Spatial Competence DOI: http://dx.doi.org/10.5772/intechopen.89273*

of the auditory space. Moreover, acting successfully entails affordances for action: since affordances change according to action capabilities and bodily characteristics, experiential factors are necessary especially during infancy when new skills are

These results suggest that early interaction between the visual input and other sensory and motor signals provides a powerful background to shape the development of spatial cognition in sighted children. But if vision is so important, how

While the development of spatial cognition has been extensively studied in sighted individuals [50], less effort has been spent in understanding how the sense of space changes during development in children with visual impairment. Specifically, scientific research on the development of auditory localization skills in visually impaired children has provided contrasting results. For example, it has been shown that children with visual disabilities have an excellent spatial hearing, measured as the ability to discriminate differences in sound localization in the horizontal and vertical plane as well as the ability to reach or walk toward the sound source position [76]. On the contrary, several studies suggested that infants and children with severe congenital blindness have a developmental delay in sound localization abilities [23, 77–79] and motor responses to sound [80, 81]. For example, blind children do not reach for objects that produced sounds until the end of the first year, while sighted children start around 5 months [82]. Similarly, blind children show worse performances than sighted children in auditory bisection, minimum audible angle tasks [23], and audio depth tasks [78]. Other studies show mixed results, indicating that children with congenital visual disabilities show an initial neuromotor developmental delay but compensate for the lack of vision developing good manipulatory and walking skills thanks to the exploration of sounding objects in the environment [83]. Studies of proprioceptive localization of immediate and memorized targets have been used to compare the proprioceptive performance of sighted and blind individuals. For instance, it has been shown that early visual deprivation does not necessarily prevent the development of spatial representations in both early blind children [84] and adults [85]. Considering that spatial competence emerges gradually thanks to the reciprocal influence between visual perception and execution of movements [72], it is evident that visually impaired children not only lack the visual input necessary to establish the sensorimotor feedback that typically promotes spatial development, but also manifests a general delay in the acquisition of important locomotor and proprioceptive skills, which may cause them to accumulate much less spatial experience compared to their sighted peers [79, 86, 87]. It has long been known that the development of blind infants is delayed in self-initiated postures and locomotion [79, 88, 89]. While sighted children typically start to perform first individual actions and navigation from the first year of age, blind children without cognitive and motor impairments start to walk at about 30–32 months of age [90]. Moreover, from the first month of life, blind infants show delays in the vestibular and proprioceptive functions due to the lack of integration with the visual inputs typically provided during the development [91]. Finally, since visual feedback represents the most important incentive for actions and thus for the development of locomotion and mobility skills, the onset of several motor milestones (e.g., rolling, crawling, standing, and balancing) can be delayed in visually impaired infants [92, 93], suggesting that the visual feedback of the body is

constantly appearing and bodily dimensions are changing rapidly [75].

**3. Development of spatial competence in the absence of vision**

spatial development changes when the visual input is missing?

#### *The Role of Vision on Spatial Competence DOI: http://dx.doi.org/10.5772/intechopen.89273*

*Visual Impairment and Blindness - What We Know and What We Have to Know*

in space and the coding of spatial information in external coordinates by means of metric cues such as distance or length. It has been shown that at 7 months of age, infants spontaneously show categorical dichotomous discrimination of auditory space by differentiating objects within and beyond reach [57, 58] and by distinguishing spatial categories such as above vs. below and left vs. right [32, 63]. Early sensitivity to metric cues has been observed in 4.5–6.5 months old infants for the dimension of objects [64] and distance [36]. Nonetheless, methodological issues have been raised for the interpretation of such results since experimental paradigms typically used with infants employ observational measures of the infant's behavior that may reveal more low-level perceptual rather than conceptual representation. Indeed, it has been shown that at the age of 2 years, children are able to match objects by height when these objects are presented in containers of a fixed height, but not when they are presented without containers, indicating that toddlers make use of distance cues only when they can rely on relative cues [65]. A considerable improvement in the ability to code object size and location can be observed between the ages of 4 and 12 [40–42, 66], for example, in tasks that require to use a configuration of distal landmarks to infer object location [67]. This could be due to the development of a hierarchical coding system, which integrates metrics and categorical information [68]. Given the time course of spatial cognition development and the discrepancy between early and later acquisition of spatial skills, an interactionist approach has been proposed that acknowledges strong potentiality and tries to identify underlying mechanisms implicated in the transformation of early abilities into mature competence [69]. The underlying mechanisms responsible for the refinement of spontaneous spatial orientation skills might be found both in the biological and environmental experiences. Within the biological context, many improvements in spatial functioning have been associated with the maturation of specific brain regions such as the hippocampus. For instance, the maturation of the hippocampus-mediated ability to encode relations among multiple objects may determine an increase in the number of stimuli that children rely on during reorientation and navigation tasks [70]. Within the environmental context, experience involves interactions with objects in the physical world and learning conventional information about symbolic spatial representations, such as maps and models. Spatial competence is strictly dependent on experiential factors such as exploratory activities which are in turn related to the development of locomotor activities. For example, it has been suggested that the emergence of allocentric coding in the form of cue learning might derive from the onset of crawling around 8–9 months, while further locomotor experiences may facilitate place learning by stimulating children to observe and approach object arrays from different directions. Indeed, locomotion is not simply a maturational precursor to psychological changes, but it plays a crucial role in their genesis [71]. For example, crawling provides the infant with concrete experiences that may change his coding strategy, for example, permitting the infant to abandon an egocentric body-oriented localization of objects to one based on the use of environmental landmarks. Recent findings suggest that sighted children acquire spatial capabilities thanks to the reciprocal influence between visual perception and execution of movements [72]: children monitor the success of action through a sensory-motor feedback by matching expected and observed changes of visual information. Indeed, self-generated movements commonly help to perceive the space acoustically because they convey the proprioceptive sensation corresponding to the movement of the ears toward sound sources [73]. In other words, using the dichotomy between the body and its exterior, an individual acquires spatial competence through observation of the body's actions and the resulting sensory consequences: through self-generated movements, the nervous system learns sensorimotor contingencies [74], which reveal the spatial properties

**254**

of the auditory space. Moreover, acting successfully entails affordances for action: since affordances change according to action capabilities and bodily characteristics, experiential factors are necessary especially during infancy when new skills are constantly appearing and bodily dimensions are changing rapidly [75].

These results suggest that early interaction between the visual input and other sensory and motor signals provides a powerful background to shape the development of spatial cognition in sighted children. But if vision is so important, how spatial development changes when the visual input is missing?
