Sonic Device The other day, Dr. Robert Smith, who is blind, took a remarkable stroll through the campus of the University of California at Santa Barbara. As Dr. Smith walked along the campus, places and impediments (障碍物) in his path seemed to call out their names to him -- 'library here, library here', 'bench here, bench here'. Dr. Smith was testing a prototype (样机) navigation system for the blind that anounced the surrounding objects through stereo headphones that were mounted to a computer in his back-pack, creating a virtual reality landscape(仿真影像). The information came not from some miniature radar but from the signals broadcast by the military's network of gloal positioning satellites(全球定位卫星). One day, its developers hope, miniaturized(小型化的) versions of this navigation devices, which now weighs twenty-eight pounds, will help the blind navigate unfamiliar neighborhoods. 'With this system you do not need to know a thing in advance about where you are going', said Dr. Roberta Klatzky, a psychologist at Carnegie-Mellon University who is working with Dr. Smith to develop the navigating device. Dr. Michael Oberdor of the National Eye Institute said, 'A blind person could walk clown the street and know not just he was at 80th and Broadway, but what stores are around, and that Zabar's delicatessen(熟食店) was up ahead. This navigation system tells you not just where there are obstacles, but your overall location geographically. ' It lets blind users construct a mental map of new surroundings and learn their way around. The navigation system uses signals from a computerized map to create a 'virtual acoustic display(仿真声音显示). This is a talking map in which large objects seem to announce themselves in the headphones with the precise timing and loudness that would be the case if the objects were actually a sound. This allows the blind person to sense immediately his or her distance or direction, and use that information for guidance. While no one knows whether it is because blind people tend to develop a sharper sense of hearing, those who have tried the system say that they quickly adapt to locating an object through the sounds. 'One of the crucial features of this system is that it takes advantage of sensory paychophysics (感官心理物理学) -- how the brain interprets signals from outside to make a map of your surroundings so you can navigate, ' Dr. Oberdor said. Thanks to the help of this sonic device, blind people can hear obstacles in the way speaking out their names.