versión On-line ISSN 1668-7027
ARIAS, Claudia et al. Human echolocation: An extensive review of the literature - First part. Interdisciplinaria [online]. 2010, vol.27, n.2, pp. 335-348. ISSN 1668-7027.
Echolocation is a genuinely human though greatly unexploited ability that is closely related to the localization of reflected sounds. It is part of the scarcely studied and promising field of the percept-cognitive processes involved in everyday audition of non-verbal sounds. It implies self-producing sounds (original or direct signal) with the specific purpose of obtaining auditory information (reflected signal) to detect, locate and recognize unseen objects. This ability turns out to be crucial to the blind person's independent mobility, an aspect that is severely affected by blindness. We present an historical revision of the main studies that have been carried out on this particular phenomenon, describing the paradigm changes that occurred in scientific history. The historical conceptualizations of echolocation are specially revealing: while it was initially considered a paranormal phenomenon, a kind of sixth sense, now it is treated as an ability that could be unconsciously used by most of us. In this first part of this paper we present relevant theoretical aspects and the studies carried out during two of the three periods this historical revision has been divided in: (a) First approaches (1700 - 1935) and (b) Scientific study of human echolocation (decades from 40s to 80s). The third period, named recent studies, is developed in the second part of this article. The questions that were initially asked were concerned the explanation of which of the sense organs was involved and which sensory stimulation was the necessary and sufficient condition for this ability. Some researchers and many blind persons were inclined to look for the answer in the sense of touch, from stimuli such as differences in pressure, air currents or differences in temperature upon the skin of the face; this originated the name of facial vision with which echolocation is also known. During the 40s a vast and rigorous research program was put forward in order to elucidate the sensory basis of echolocation. Experimental subjects (blind and blindfolded sighted participants) that took part of the program had to walk through a corridor and halt at the moment they perceived the presence of an obstacle (mobile panel); then they kept on walking approaching the obstacle as near as possible without making contact (first perception and final appraisal, respectively). A series of ingenious tests was designed in which tactile or auditory input was artificially suppressed, one at a time. None of the subjects was able to perceive the object in the case of auditory input suppression. To confirm this finding, other tests were conducted in extreme conditions: for example, the subject was in another room using a telephone communication device and he / she had to perform the same task but this time it was the experimenter that walked across the corridor instead of him / her. The performance was not significantly affected in this extreme condition. In this way, it was unequivocally established that audition is the sensory basis of this particular kind of ability and that changes in pitch are its necessary and sufficient condition. Later studies inquired into the discriminatory power of echolocation and its scopes. It was demonstrated that, on the one hand, blind subjects and appropriately trained blindfolded sighted subjects were able to accurately judge the position, distance, size, material and shape of the objects. On the other hand, for the first time, research about the spontaneous generation of sounds by blind persons was carried out. It was observed that they used clicks or vocalizations to detect presence /absence of the object and continuous sibilant sounds to perceive its borders. Their performance was not significantly affected when they used artificial sounds that mimicked their own or sound signals that they had described as not preferred. Around the end of the second period the underlying psychoacoustic mechanisms were studied and two auditory fusion phenomena were postulated: repetition pitch and the precedence effect.
Palabras llave : Human echolocation; Facial vision; Repetition pitch; Precedence effect.