Space representation in the absence of sight in the human brain

Despite the lack of vision, blind individuals are capable to move independently in space, to represent identity and to localize objects and relate with them, to catch other people’s intentions and feelings, to develop a social communication. More than that, blind individuals very often make us notice some specific sensorial aspects that we are simply ‘unable to see’: a specific timbre of the voice that conveys information of one’s feelings, a sudden mild change of temperature while walking around the corner, a peculiar scent in front of a grocery store, an unusual texture of a textile. Since the early days, sight has always been regarded as the most important sense for humans to interact with the environment and to acquire knowledge. In the ancient Greek language the verb ‘to know’ (oi\da) was the past tense of the verb ‘to see’ (oJravw), that is, “I saw and thus I know”. Similarly, everyday linguistic uses such as “can you see my point?” or “I see what you mean” suggest a predominant role of vision. Furthermore, from a neuro-anatomical perspective, almost one third of the whole cortex in primates is devoted to visual function. These few considerations alone are enough to raise some fundamental questions. How do individuals with congenital blindness form a representation of a world that they have never seen? How is non-visual sensory information processed in the brain in sighted and congenitally blind individuals? What happens to the “visual” brain in congenitally blind individuals? To what extent is vision really necessary for the human brain to develop and function? In the last two decades, behavioural and functional brain studies in individuals with congenital blindness have provided a powerful approach to understand how the external world is represented, and how the brain functional organization develops in the absence of sight. In this chapter, we will discuss findings from studies conducted in sighted and congenitally blind humans relative to spatial abilities and representation.