Spatial representation and visual impairement - Developmental trends and new technological tools for assessment and rehabilitation

It is well known that perception is mediated by the five sensory modalities (sight, hearing, touch, smell and taste), which allows us to explore the world and build a coherent spatio-temporal representation of the surrounding environment. Typically, our brain collects and integrates coherent information from all the senses to build a reliable spatial representation of the world. In this sense, perception emerges from the individual activity of distinct sensory modalities, operating as separate modules, but rather from multisensory integration processes. The interaction occurs whenever inputs from the senses are coherent in time and space (Eimer, 2004). Therefore, spatial perception emerges from the contribution of unisensory and multisensory information, with a predominant role of visual information for space processing during the first years of life. Despite a growing body of research indicates that visual experience is essential to develop spatial abilities, to date very little is known about the mechanisms underpinning spatial development when the visual input is impoverished (low vision) or missing (blindness). The thesis's main aim is to increase knowledge about the impact of visual deprivation on spatial development and consolidation and to evaluate the effects of novel technological systems to quantitatively improve perceptual and cognitive spatial abilities in case of visual impairments. Chapter 1 summarizes the main research findings related to the role of vision and multisensory experience on spatial development. Overall, such findings indicate that visual experience facilitates the acquisition of allocentric spatial capabilities, namely perceiving space according to a perspective different from our body. Therefore, it might be stated that the sense of sight allows a more comprehensive representation of spatial information since it is based on environmental landmarks that are independent of body perspective. Chapter 2 presents original studies carried out by me as a Ph.D. student to investigate the developmental mechanisms underpinning spatial development and compare the spatial performance of individuals with affected and typical visual experience, respectively visually impaired and sighted. Overall, these studies suggest that vision facilitates the spatial representation of the environment by conveying the most reliable spatial reference, i.e., allocentric coordinates. However, when visual feedback is permanently or temporarily absent, as in the case of congenital blindness or blindfolded individuals, respectively, compensatory mechanisms might support the refinement of haptic and auditory spatial coding abilities. The studies presented in this chapter will validate novel experimental paradigms to assess the role of haptic and auditory experience on spatial representation based on external (i.e., allocentric) frames of reference. Chapter 3 describes the validation process of new technological systems based on unisensory and multisensory stimulation, designed to rehabilitate spatial capabilities in case of visual impairment. Overall, the technological validation of new devices will provide the opportunity to develop an interactive platform to rehabilitate spatial impairments following visual deprivation. Finally, Chapter 4 summarizes the findings reported in the previous Chapters, focusing the attention on the consequences of visual impairment on the developmental of unisensory and multisensory spatial experience in visually impaired children and adults compared to sighted peers. It also wants to highlight the potential role of novel experimental tools to validate the use to assess spatial competencies in response to unisensory and multisensory events and train residual sensory modalities under a multisensory rehabilitation

Tactual perception: a review of experimental variables and procedures

This paper reviews literature on tactual perception. Throughout this review we will highlight some of the most relevant variables in touch literature: interaction between touch and other senses; type of stimuli, from abstract stimuli such as vibrations, to two- and three-dimensional stimuli, also considering concrete stimuli such as the relation between familiar and unfamiliar stimuli or the haptic perception of faces; type of participants, separating studies with blind participants, studies with children and adults, and an analysis of sex differences in performance; and finally, type of tactile exploration, considering conditions of active and passive touch, the relevance of movement in touch and the relation between exploration and time. This review intends to present an organised overview of the main variables in touch experiments, attending to the main findings described in literature, to guide the design of future works on tactual perception and memory.This work was funded by the Portuguese “Foundation for Science and Technology” through PhD scholarship SFRH/BD/35918/2007

Keep an eye on your hands: on the role of visual mechanisms in processing of haptic space

The present paper reviews research on a haptic orientation processing. Central is a task in which a test bar has to be set parallel to a reference bar at another location. Introducing a delay between inspecting the reference bar and setting the test bar leads to a surprising improvement. Moreover, offering visual background information also elevates performance. Interestingly, (congenitally) blind individuals do not or to a weaker extent show the improvement with time, while in parallel to this, they appear to benefit less from spatial imagery processing. Together this strongly points to an important role for visual processing mechanisms in the perception of haptic inputs

The role of visual experience in the emergence of cross-modal correspondences

Cross-modal correspondences describe the widespread tendency for attributes in one sensory modality to be consistently matched to those in another modality. For example, high pitched sounds tend to be matched to spiky shapes, small sizes, and high elevations. However, the extent to which these correspondences depend on sensory experience (e.g. regularities in the perceived environment) remains controversial. Two recent studies involving blind participants have argued that visual experience is necessary for the emergence of correspondences, wherein such correspondences were present (although attenuated) in late blind individuals but absent in the early blind. Here, using a similar approach and a large sample of early and late blind participants (N=59) and sighted controls (N=63), we challenge this view. Examining five auditory-tactile correspondences, we show that only one requires visual experience to emerge (pitch-shape), two are independent of visual experience (pitch-size, pitch-weight), and two appear to emerge in response to blindness (pitch-texture, pitch-softness). These effects tended to be more pronounced in the early blind than late blind group, and the duration of vision loss among the late blind did not mediate the strength of these correspondences. Our results suggest that altered sensory input can affect cross-modal correspondences in a more complex manner than previously thought and cannot solely be explained by a reduction in visually-mediated environmental correlations. We propose roles of visual calibration, neuroplasticity and structurally-innate associations in accounting for our findings

Impaired Visual Size-Discrimination in Children with Movement Disorders.

Abstract 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

What we thought we knew: Intellectual assessment of individuals who are blind

Throughout the history of intellectual assessment, research involving individuals who are blind has often been scarce. Currently, there are no intellectual assessment procedures based on the Cattell-Horn-Carroll (CHC) theory of intelligence available to individuals who are blind. CHC theory is considered to be the gold standard of intellectual assessment and many government and diagnostic policies rely upon CHC theory. The proposed research sought to extend the current reach of CHC theory to individuals who are blind by developing a new measure of tactile performance ability. The Tactile Assessment of Performance (TAP) was developed and administered to participants who were blind and participants who were sighted. A total of 64 participants completed the research procedure, 32 participants who were sighted and 32 participants who were blind. A modified multitrait-multimethod design was employed. Most of the TAP subtests correlated positively with the Wechsler Adult Intelligence Scale – Fourth Edition (WAIS-IV), which is a widely used and accepted measure of intellectual functioning. The subtests of the TAP failed to correlate with measures of achievement striving and conscientiousness, which is indicative of discriminant validity. Results suggest the TAP is capturing aspects of CHC abilities and may prove useful as a measure of intelligence in individuals who are blind

Adults' spatial scaling from memory: Comparing the visual and haptic domain

The current study compared adults' spatial scaling from memory in the visual and haptic domain. Adults (N = 32, ages 19-27 years) were presented with a spatial-scaling task in a visual condition as well as a haptic condition (in which participants were blindfolded throughout the experimental session). In both conditions, they were presented with an embossed graphic including a target (i.e., a map). Then, they were asked to encode this map and to place a disc at the same spot on an empty referent space from memory. Maps had three different sizes whereas the referent space had a constant size, resulting in three different scaling factors (1:1, 1:2, 1:4). Participants' response times and absolute errors were measured. Order of perceptual condition was counterbalanced across participants. Analyses indicated that response times and absolute errors increased linearly with higher scaling factors in the visual as well as the haptic perceptual condition. In analogy to mental imagery research, these results suggest the usage of mental transformation strategies for spatial scaling

The role of visual processing in haptic representation - Recognition tasks with novel 3D objects

In perceiving and recognizing everyday objects we use different senses combined together (multisensory process). However, in the past authors concentrated almost completely on vision. However, it is also true that we can touch objects in order to acquire a whole series of information. Moreover, the combination of these two sensory modalities provides complete information about the explored object. So, I first analyzed the available literature on visual and haptic object representation and recognition separately; then, I concentrated on crossmodal visuo-haptic object representation. Finally I exposed and discussed the results obtained with the three experiments I conducted during my Ph.D. studies. These seem to be in line, as already previously proposed by different authors (Newell et al., 2005; Cattaneo et al. 2008; Lacey et al., 2009), with the existence of a supramodal object representation, which is unhooked from the encoding sensory moodality