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Echolocation is an ability that can be used daily by human beings, even without being conscious of it. It turns out to be crucial to the efficient independent mobility of the blind person, an aspect that is severely affected by blindness. It implies using the information that emerges from self-produced sounds and their reflexions in order to locate and recognize unseen objects. According to the new cognitive and ecological paradigms in perception, it is believed that the primary function of the auditory system is to determinate, i.e., to localize and recognize, the characteristics of the sound source through the sounds emitted by it. Within this context, it has been very recently argued that echolocation (i.e., the ability to locate and recognize biologically relevant secondary sound sources through the information contained in the direct-reflected couple) is a variant of that general process of primary sound sources determination. Two recently established scientific paradigms have specially enriched the study of this amazing ability: the sensorimotor contingency theory and the sensory substitution perspective. The first approach claims that the perceptual and motor systems are coupling processes that demand a thoroughly unified treatment. The second approach considers that, for example, vision loss does not mean loss of the ability to see since it is possible to see with the ears or the skin. The central idea is that the information usually captured by vision may instead be captured by touch or audition, on account of brain plasticity. In this way, in echolocation (which represents a kind of 'seeing with the ears' natural sensory substitution system that is part of the human endowment) action consists of the exploratory activity that the subject carries out through self-generation of sounds and head and/or cane movements while sensation refers to certain tonal or spatial percepts related to the presence and characteristics of the objects that the subject (implicitly) learns to perceive probably as auditory Gestalts. In the first part of this article the main theoretical aspects and a revision of the studies throughout two of the three delimited periods were developed: FIRST APPROACHES (1700 - 1935) and SCIENTIFIC STUDY OF HUMAN ECHOLOCATION (1940 - 1980). The questions that researchers formulated during these periods were firstly concerned with discovering if blind persons actually possessed this ability, which of the sense organs was involved and which sensory stimulation was its necessary and sufficient condition. Secondly, they inquired into the scopes of echolocation and its possible underlying psychoacoustic mechanisms. The thorough investigations carried out allowed to unequivocally establishing that audition is the sensory basis of this ability and that changes in pitch are its necessary and sufficient condition. It was also demonstrated that not only blind subjects but also appropriately trained sighted subjects were able to precisely localize and recognize the characteristics of the experimental objects. In this second part, we present the object of study within the context of theories of embodied cognition and recent developments in the field of the neurosciences; we also elaborate upon studies carried out during the third period, named RECENT STUDIES, that extends from 1990 to present days. We show how the blind person with good echolocation ability becomes an excellent experimental model to study behavioral and neurophysiological aspects involved in implicit learning. The article illustrates the paradigm shifts that occurred in recent scientific history through the study of this particular human ability that, within the mentioned recent theoretical context, has acquired a renewed interest. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]