Ecolocación humana: Revisión histórica de un fenómeno particular - Segunda parte / Human echolocation: Historical review of a particular phenomenon - Second part

RESUMEN

La ecolocación es una habilidad que usaría inconscientemente la mayoría de las personas. Resulta crucial para la movilidad independiente de la persona ciega e implica utilizar sonidos autoproducidos y sus reflexiones para localizar y reconocer objetos que no se ven. Dos nuevos paradigmas han enriquecido el estudio de esta sorprendente habilidad el del acoplamiento sensoriomotor y el de la sustitución sensorial. El primero sostiene que los sistemas perceptivo y motor constituyen procesos acoplados que requieren un insoslayable tratamiento unificado. El segundo considera que es posible ver con los oídos o con la piel en virtud de la plasticidad cerebral. En esta segunda parte se presenta la temática en el contexto teórico de la cognición corporizada y de recientes avances en neurociencias; se desarrollan además los estudios realizados en el tercer período. En esta revisión se reflejan cambios paradigmáticos en las ciencias del comportamiento y el valor científico acrecentado de la ecolocación humana.

ABSTRACT

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 SIENTIFIC 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.