A common space for action: behavioral study on visual and auditory affordance in sighted and congenitally blind subject

The capability of human beings to map and interact with the world is rooted into visual perception. But what happen to individuals that are born without any visual experience? Are they able to represent and interact with surrounding environment like sighted people? The principal aim of this study is to understand if our action-space representation, the portion of space that we consider reachable, could develop independently from visual modality and how interaction with other people could modulate its boundaries. To test these hypotheses we designed a series of behavioural experiments with visual and auditory stimuli in a sample of sighted and congenitally blind subjects. We systematically examined the modulation of action-space borders though the evaluation of the spatial alignment effect, that occurs only when the target stimulus is perceived reachable by the subject. Results showed that sighted and congenitally blind participants discriminate reachable from non-reachable space in the same way and furthermore spatial alignment effect is present also if the target stimulus is inside the action-space of a possible agent but outside the reachable range for the subject. These evidences contribute to the idea that human brain builds an action- space representation that is independent from sensorial modalities and more functional related to action possibilities and interaction, explaining also how congenitally blind people are so proficient in orienting and mapping external world without sight.