martes, 8 de noviembre de 2011

Argentinian research on human echolocation

This text is a english translation thru google translator from:

Argentine Research on human echolocation

Arias, C., Ramos, OA; Ortiz Skarp, AH

Acoustic Research Centre and Lighting, CIAL. National University of Córdoba. Postal Agency No. 4. C. Universitaria.5000 Cordoba Argentina

Research Centre of the Faculty of Philosophy and Humanities, CIFFyH. National University of Córdoba.

The person born or have a severe disability, is undergoing a painful life issues and complex. Visual impairment, for his profound connotations and implications, is one of the most destructuring and psychologically disabling effects that are evident in the area of mobility of the visually impaired person.
There are a variety of "electronic aids" to a blind person can navigate more easily in their daily lives. However, none has managed to replace or offer, the benefits are obtained from comprehensive systematic training of other's skills.
The research work we are doing since 1980 (Arias, 1996)-strongly interdisciplinary since 1991 - has been guided by the firm conviction that genuine development potential will effectuate the proper insertion of the visually impaired in society, from the perspective of a real correspondence between capabilities and opportunities.
Echolocation or perception of obstacles unaided vision, is such a genuine and untapped skills not surprising that one of the factors CONSTITUTE more important for the visually impaired person to achieve independent mobility and efficient.
In this presentation we briefly describe our work on human echolocation and describe some aspects of theoretical and methodological details of our new project, which aims to address auditory localization phase of virtual obstacles.
We hope that the progress and realize that we hope will serve to lay the foundations of a theoretical and practical training program in computer-aided echolocation, for the visually impaired (DV).
Echolocation is an active mode of perception that allows a kind of dialogue between the environment and the individual who, rather than responding with fixed schedules and automatic external stimulation seem spontaneous exercise control over their own behavior (Griffin, 1988). Strictly speaking it is defined as the ability to detect, discriminate and locate obstacles to process the information contained in the echoes produced when the subject self-generated sounds are reflected on the obstacles. By extension, it also speaks of echolocation when using electronic sounds and ambient sounds.The sounds generated by the subject are the direct signal while the echoes up the reflected signal, a paradigm of echolocation.
The entire process of perceiving auditory obstacle involves a first and indispensable object detection phase (there is "something" on the way), a phase of location (where it is and is perceived relative distance) and a phase of discrimination features to identify the physical barrier (known what that "something" detected and localized) Although little is known about it, we may assume various psychoacoustic mechanisms and psychoneurological identified in the 3 phases: a subcortical processing unconscious, seems to be involved in the first two. The last phase can only be achieved from the conscious cortical processing of information (Masterton, 1992).
We care to note that most of the DVs generated spontaneously and intuitively sounds, such as clicking with your fingers or tongue (impulse noise), hissing and knocking with his staff (noise), so focused and overcome obstacles in their way . They become thus generating activities and information processors.
This ability, especially in relation to the detection and location of obstacles, can be seen in any person with normal hearing in at least one ear that has been subjected to a brief but appropriate training.Individual differences among blind persons in relation to the ability of echolocation (also among subjects with normal vision) extend over a wide range, from an efficiency such that surprised the researchers (Rice, 1969; Kellogg, 1962) to almost complete dependence on total inefficiency and insecurity in walking.
Previous work on human echolocation
The echolocation research on national and international human are very rare and discontinuous.
Scientific experimentation in this field dates back to 1900, although by mid-1700 Diderot wrote about the "amazing" ability observed in some blind people to perceive and overcome obstacles.
In the 40's, from the rigorous and ingenious studies by Dallenbach group and collaborators at Cornell University, one of whom, Michael Supa, was blind, was able to elucidate important aspects: the sensory hearing is the basis of echolocation and the change in the pitch of the sounds is necessary and sufficient condition to detect and locate nearby obstacles (Dallenbach et al., 1944; Cotzin et al., 1950). Also dating from this decade the first formal relations were established between the animal echolocation-field of study in which significant progress has been made ​​(Nachtigall et al., 1988) - and human echolocation.
Further research including highlights Kellogg (op.cit.), Rice (1967b) and Kohler (1964) studied the discriminatory power of this skill. They noted that the subject both blind and sighted, accurate distance judgments made, size and material, and even managed to discriminate triangular, square and circular obstacles with the same surface.
Have described two basic and complementary mechanisms of echolocation supported on different psychoacoustic (Bilsen, 1980, Schenkman, 1985). The first mode-echolocation at far distances (between 2 / 3 m to 5 m between subject and obstacle) - is involved mainly in the detection phase and location of the obstacle.Information on presence of the obstacle is given by the presence of echo while its position and distance are extracted from the temporomandibular key spatial imaging. The second mode, the echolocation at close distances (less than 2 / 3 m between the subject and the obstacle), is involved in the phases of detection, localization and discrimination of obstacles. The direct and reflected signals are not perceived as separate, under certain conditions the auditory system combines both signals and processes them as one.The person perceives a change or shift the pitch of the direct signal or perceive that noise, if you use these guiding signals, acquires some characteristic tonal (pitch perceptual phenomenon called repetition, (repetition pitch)). The presence of the obstacle is determined by the presence or change of tonality of the direct signal while the information about position, distance and characteristics is contained in the spectral and spatial key vibrational pattern that results from the interference of the direct signal with the signal reflected (Bassett et al, 1964).
Sensory compensation
It has been held since ancient times, the lack or loss of vision caused an extraordinary development of other senses especially touch and hearing. A variant of this hypothesis suggests that there are fundamental differences in the ability of the remaining senses as a result of cortical reorganization during compensation. Another model holds that sensory compensation may be strategic rather than structural: the differences between blind subjects and sighted due to attentional effects and effects of training (Miller, 1992).
The sensory compensation hypothesis has led to numerous studies with controversial results. It could be shown that, in general, both groups similarly yielded a considerable number of tasks. However, blind subjects performed better on auditory localization (Rice, Schenkman, ops. Cit.) And auditory integration processes (Starlinger et al., 1981a, Niemeyer et al., 1981b; Arias et al., 1993b). Performed worse than subjects with normal vision in trial testing and maintenance of rhythm (Stankov et al., 1978; Juurmaa, 1967).
Stages fulfilled
We will seek, in the beginning of our research work, to study cognitive processes perceptual. We construct two sound problems as a special technique, using an artificial head space to play sound effects (Arias de Miranda, 1984, 1985). We manage 35 people problems DVs. Later (Arias de Miranda, 1987), we built another 4 problems and 4 sound problems tactile (haptic) with increasing difficulty, to study spontaneous learning and the effect of mode of presentation on performance in problem solving. Individually manage the 8 problems 40 adults and 32 children and adolescents DVs.
We interpret the results of both studies in support of previous findings that point for the potential utility of this technique as a valid tool for the training of cognitive skills.
Later, some of the controversial results of studies on sensory compensation motivated us to perform three new works. The first was to replicate an experiment on personnel tempo (Rimoldi et al., 1961) to analyze the performance of the subjects while performing a tracking task spontaneous rhythm (Arias, 1993a). Thirty DVs, 15 adults and 15 children and adolescents resolved the test.
Our results indicated for very consistent temporal factors adopted by the subjects when performing a task and run counter to the conclusions of some researchers in relation to a poorer performance observed in blind subjects, relative to subjects with normal vision in tasks similar (Stankov. et al; Juurmaa, ops. cit.).
The second work done, was to administer a test of skill in nonverbal acoustic material structure, a group of DVs formed by 22 adults, 16 adolescents and 13 children. In general, subjects used the strategy of passive recognition to solve the test items, similar to how some subjects proceeded with normal vision and without musical training who participated in another local study we conducted with common high school students (Arias and Biassoni, 1992).
The aim of the third study (Arias et al., 1993b), was to evaluate the peripheral and central auditory functioning responses evoked by stimuli including echolocation, a group of 8 subjects' good Ecoloc "and a control group of 8 subjects with normal vision.
We obtained evidence of better performance of blind subjects in relation to their peers with normal vision in several peripheral and central auditory tests administered, in agreement with previous findings. The results obtained in evoked potentials seem to indicate, first, that the echolocation signals are processed at low levels of the auditory pathway in the superior olivary complex of the pons. On the other, that the improvement observed by Starlinger et al. (Op.cit.) Late evoked potentials in congenitally blind subjects, already evident at the inferior colliculus of the midbrain.
We also conducted in our laboratory anechoic chamber with 6 subjects DVs "good detectors," a classic experiment of detection (presence / absence), location (position) and discrimination of characteristics (shape, size and material) of obstacles (Arias , 1987).Our results strongly agreed with those reported in previous experiments (Kellogg, Kohler, Rice, Hausfeld et al., 1982, Schenkman, ops. Cit): it was easier to detect the presence / absence of whites that their characteristics, size being the most easiest and the hardest way. We want to emphasize that in no case we observed erratic behavior in the participants, by contrast, emit sounds, movements performed "scanning" (head turn right / left) and listened carefully to the sound changes that were happening, and then respond.
New findings in neurophysiology of hearing
The auditory central nervous system of mammals contains a large number of subcortical auditory nuclei, far from mere relay stations as previously argued, have key roles in the processing of sound information. It seems that the auditory cortex is not necessary to discriminate the physical attributes of sound, just the intensity, pitch, timbre, duration. It is the ear which is responsible for analyzing and encoding, while the attributes of the sound source: the azimuth, elevation, distance and nature-guiding properties of the animal action in the environment rather than the sound in themselves, are analyzed coded and the superior olivary complex (Masterton, op.cit.).
The beeper
Man's ability to locate sound sources is very accurate even in adverse situations (eg, with only one ear). It refers to the perception of source position in the horizontal plane (azimuth) and vertical (elevation) and discrimination of the relative distance between subject and sound source. The man is very good locations in the horizontal plane, the less efficient in the vertical plane and distance judgments are poor (Moore, 1977).
The main key to determine the position of a sound source are interaural differences in arrival time of sound at the two ears, interaural differences in sound intensity and total filtering effect caused by the interaction of sound with folds of the pinna, head, torso and shoulders.
In sound localization experiments, the stimuli are presented under two conditions: through a set of loudspeakers arranged in a particular spatial arrangement (free field). The second condition involves the presentation of the sounds through headphones with the undeniable advantage of being able to exercise strict control of the stimulus. Its disadvantage is that the sounds are heard as if it originated in the head. The classic studies with headphones, also called for that reason, studies of "lateralization" or "location within the head," did not consider the effect of filtering. In the 70's pioneering work was done that could be a realistic perception of auditory space. In the late 80's, Wightman and Kistler (1989b) developed a procedure to locate virtual sound sources using headphones with the same precision with which real sound sources are located. These studies have led to devices called "virtual reality" that are being developed in this decade. They are potentially useful tools to investigate perceptual processes huge engines and for training of disabled people.
Sound localization studies in blind subjects
As already noted, in a paradigm of echolocation sounds generated by the subject are the direct signal and the echoes, the reflected signal.That is, the primary sound source is located in the subject itself and the obstacle that generates reflection behaves as secondary sound source.
In the literature, location sound and location of obstacles are taken as synonyms. But strictly speaking, the first process is involved in only one phase of echolocation, that is, when are discriminated obstacle position (azimuth and elevation) and their relative distance (phase tracking). In a real situation, a person can detect DV "something" on her way though I can not clarify its position, distance or nature. It is frequently observed that a "good Ecoloc" blind bypasses some obstacles without consciously realizing it.
Been little research reported in blind subjects on location of sounds presented via loudspeakers or headphones (Starlinger et al., Niemeyer et al., Ops. Cit.). In most studies described echolocation, we study the localization phase of real obstacles (Rice, 1969, Clarke et al., 1975, Strelow et al., 1982, Schenkman, 1985). For example, in a classic study which used a special device (Rice, op. Cit.), The task to be performed by the subject was to point the nose to where he judged that he was the center of the target. It was noted that early-blind individuals whose returns were higher than the performance of both late blind subjects and subjects with normal vision-emitted one or two clicks with the language that allowed a single "ear out" (auditory glance) to obtain accurate information about the presence and location of targets.
The system Rousettus
From the 91-to materialize the interdisciplinary team and subsidies for our developments, so far, we have forced into complete PC-based system, which we called Rousettus (the only genre Megachiroptera using echolocation to fly and feed, although much less efficiently than Microchiroptera).
Rousettus System Module consists of Simulator to emulate Obstacles "white ghost", the module that enables EcoTest build and administer tests and psychoacoustic module specifically designed Evoked Response in late stages of which we are still working, which will allow psychoneurological aspect of studying the echolocation and, among other applications, assess auditory functioning multi-disabled.
EcoTest design with a series of tests in order psychoacoustic study the echolocation mode at near distances, and the phenomenon of "facial vision" (Arias and Ramos, in press; Ramos and Arias, in press). To do this, we analyze the performance of subjects in detection and discrimination tasks of the pitch of repetition using echolocation signals as sound stimuli. Administer the tests to 30 subjects with normal hearing and vision, with and without musical training. A person 50 years of age, blind since adolescence, also met the test battery constructed.
The results indicated that musical training did not influence test performance, which would aim for a hearing "privileged" is not a necessary condition for Ecoloc. Also, that subjects actually perceive the pitch of repetition when they are stimulated with echolocation signals. In addition, signals were more effective noise signals in all tests clicks. The most relevant performance blind subject, in our opinion, it was the mating test the pitch of echolocation signals. He was the only subject without musical training who committed only 4 errors out of 16 trials. We want to stress that he never showed an erratic or confused when they solved this test, however, their mode of response could be explained in light of the concept of "auditory gestalt" (Terthardt, 1974).
Our aim with our new project is in Rousettus implentar, using advanced signal processing techniques involving the listening with headphones (Wightman et al., Ops. Cit.), The auditory spatial location phase of virtual obstacles. Acoustically validate the procedure used with a head-torso-art artificial. Additionally, the psycho validate the above procedure, through testing virtual sound source localization specially built, which will resolve occluded subjects with normal vision and blind subjects.
In short, once perfected the system will be in optimal conditions Rousettus to address the process of fully human echolocation in terms of both acoustic and psychoacoustic and psychoneurological.Projects designed echolocation critical experiments using virtual obstacles (Obstacles Simulator Module) to obtain subjective responses is, judgments about detection, discrimination and location of obstacles (EcoTest) simultaneously with objective responses (Evoked Response Module).
We strengthened our conviction that they are on a path of large and complex but promising approach and accept the commitment involved in our country have opened a line of research strongly interdisciplinary background which will correspond to the UBA Mouchet in 1938 and Fuchs, Foschi and White UNC in 1968.BIBLIOGRAPHY
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