222 6 Mobility AT: The Batcane (UltraCane)

Figure 6.4. Prototype handedness arrangement

6.4.5 Cognitive Mapping

From the inspiration for the electronic cane, it is apparent that the bat builds a ‘spatial map’ of its surroundings using its ultrasound-based sensory capability. Human beings who have the sense of sight also build a ‘map’ of their surroundings. Physiologists have demonstrated that visually impaired people can also have an apparently identical capability, and this can also be present to some extent in those who have never had sight. In essence, human beings can typically visualise a scene in their mind. Thus information presented to a user, that includes appropriate range and direction information, may be implicitly used to form such a spatial map.

Various brain structures contribute to this ability. The midbrain structure, the superior colliculus, has the prime function to collate novel sensory input and organize the most appropriate motor response. It utilizes spatially aligned visual and auditory maps and the map of the body surface is superimposed over the same neural area (Stein and Meredith 1993). The electronic cane relies upon the sensory alignment in this brain structure by stimulating the near-space of the body map, in a spatially discrete manner. This is intended to give rise to an interpretation in the central nervous system of external spatial awareness.

The somatosensory cortex provides a further contributory proprioceptive knowledge of the position and attitude of our limbs. With practice a user will be aware of the orientation of a hand-held cane, and of the relative position in space of its extremity. Since the electronic cane has transducers to extend both range and dimension the new extents are similarly made available to allow the user to interrogate the space more precisely and complete the perceived spatial map. Clearly memory of known areas and their features will also provide further reinforcing information. The various factors that aid the cognitive process from the tactor stimuli are illustrated in Figure 6.5.

These cognitive processes are exploited in the electronic guide cane through the tactor devices to stimulate and harness the human perception system, and engender in the user’s brain a spatial map of their surroundings, offering increased mobility and independence.