Physical analysis of several organic signals for human echolocation: Oral vacuum pulses Juan Antonio Mart´ ınez Rojas, Jes´ us Alpuente Hermosilla, Roc´ ıo S´anchez Montero and Pablo Luis L´opez Esp´ ı Department of Signal Theory and Communications, Universidad de Alcal´a, Escuela Polit´ ecnica Superior, Campus Universitario, Ctra. de Madrid-Barcelona, km 33.600, 28871 Alcal´a de Henares, Spain juanan.martinez@uah.es September 3, 2008 Abstract Active human echolocation can be an extremely useful aid for blind people. Active echolocation can be trained with both artificial and organic signals. Organic signals offer some advantages over artificial ones. Very detailed studies of organic signals in animals have been done. However, in the case of humans, the scientific literature is very scarce and not system- atic. This is the first paper of a series on the properties of several suitable sounds for human echolocation. In this work, we offer a detailed analysis of these sounds, comparing their merits from a physical point of view. The results of this study have important applications to design systematic and optimized training protocols for accurate echolocation awareness. 1 Introduction Human echolocation is a very important factor for correct orientation in both blind and sighted people. More importantly, active echolocation, a kind of human sonar, can be trained to produce accurate spatial awareness and object detection in blind individuals. Some recent famous cases, like Dan Kish and Ben Underwood, prove the extremely high level of spatial information which can be achieved with this technique. The phenomenon of active echolocation in animals, specially bats and dol- phins, has been actively researched since World War II. These studies have important applications in biology, acoustics and sonar design. It is known that dolphins and the Egyptian Fruit Bat (Rousettus aegyptiacus ) make clicks for active sonar. In contrast, microbats use laryngeal sounds, generally CW and/or FM chirped ones, to echolocate. However, the study of the physical characteristics of the most accessible organic sounds for human echolocation is very scarce. Rice, [1], [2], found that 1