Blind people's mental spatial maps

Mental mapping of space is crucial for moving and acting. Although vision plays a crucial role, much evidence suggests that vision is neither sufficient nor even necessary to form adequate spatial mental representations and that alternative sources of information based on audition, touch and kinaesthesis can be used. These considerations are important to understand blind people's mental spatial maps and to plan effective mobility and orientation aids. Here we present the results of two experiments that investigated these issues. In Experiment 1, blind people (congenital and adventitious) were compared with sighted participants in a task that required mentally scanning spatial maps of an actual environment explored through locomotion. The results showed that blind people's spatial maps represented external distances with good approximation. However, beyond 5 meters there was a decrease in the degree of similarity of these maps to external distances. Experiment 2 compared simultaneous visual and sequential kinesthetic perceptual modalities of spatial information. The results confirmed that when vision was sequentialized to resemble kinaesthetic exploration the task became as difficult for vision as it was for kinaesthesis. This difficulty was more evident beyond 5 meters, thereby confirming the metric threshold effect found in previous experiment. This effect may be regarded as a consequence of difficulty in spatial updating processes and suggests that there is need of intermittent aids within certain ranges of distance to favor efficient blind mobility strategies. Our results may represent a useful contribution to set up compensatory sensorial channels, such as acoustic echolocation.