Chapter 2 Auditory Spatial Awareness 2.3 Navigating Space by Listening While everyone has the ability to hear space, only those with motivation, dedication, and aptitude become expert at decoding the aural attributes of objects and geometries. As with the training of sonar operators to identify underwater objects by how they modified incident sound waves, acquiring expertise at auditory spatial awareness requires hundreds of hours of practice. Why would someone invest so much effort to become proficient at auditory spatial awareness? Some individuals obviously benefit by having this ability. Musicians and composers include spatial attributes as a component of their art; acousticians depend on spatial awareness in the design of concert halls; and audio engineers create spatial illusions with synthesizers. But of the many groups who use auditory spatial awareness in their personal and professional life, individuals with a visual deficit have the strongest motivation: hearing is a way to orient and navigate space. Their reward is simply the possibility of leading a normal and fulfilling life. Blindness does not improve hearing. The auditory acuity of visually impaired people, as a population, is average, spanning the same range of abilities as found in the general population. However, no group is monolithic: some blind individuals are indeed motivated to enhance their spatial abilities far beyond the average. Practice is the most important predictor for achieving a high level of proficiency. With sufficient practice, some blind individuals become expert, often displaying skills that are so unbelievable as to border on magic. Examining such individuals illustrates what our species, in the limit, is capable of achieving. There is evidence that those individuals who practice a sensory or motor skill for thousands of hours change their brain wiring. Neurological studies show that the brains of conductors, musicians, and those with visual handicaps have enlarged cortical regions involving particular auditory cues. Enhanced auditory spatial acuity is entirely a property of specialized sections of the brain that have been trained to interpret particular audible cues. Individuals strengthen their neurological structure by repeated sensory exercise, just as athletes strengthen their muscles by physical exercise. While we can see the unique physique of Olympic swimmers, we cannot see the corresponding uniqueness of “sensory athletes,” except by observing their behavior while engaging in life’s activities. We are how we live—there is no generic human being. ... Echolocation is directly relevant to aural architecture because it conclusively demonstrates that our species has the neurological endowment to make judgments about objects and spatial geometries just by listening. Yet, most aural architects, both amateurs and professionals, are unfamiliar with the native ability of human beings to hear space. When a listener uses a cognitive strategy to transform auditory cues into an image of a space, we refer to the environment as having navigational spatiality. By sensing the doorway to the bathroom late at night, for example, an individual is experiencing navigational spatiality of aural architecture. 2.3.1 Experts at Hearing Objects and Geometries History is replete with anecdotal stories about blind individuals “seeing” space, but it was only in the mid 20th century that this ability came to be understood as an auditory skill. ... scientists now recognized that hearing space is more common than initially expected. Even though most animals and people with adequate vision and available light have little need to enhance this residual ability, hearing space remains a viable alternative for supplementing vision. The scholarly language describing orienting and navigating in a space through hearing is ambiguous and confused. For example, the literature incorrectly uses the word echolocation (hearing echoes) for all forms of spatial awareness. This name originated from studies of bats and dolphins, who have a synchronized means for both generating unique vocalization and decoding the responding echoes. Echolocation is now applied to sensing spatial attributes with any kind of sounds, rather than just with self-made vocalizations. Background noise, as well as clicking fingers or tapping canes, provides sufficient sonic illumination to “see” aspects of a space. Moreover, the concept of echolocation also applies to aural cues other than echoes. These confusions arose because the phenomenon of spatial awareness was recognized long before its physical and perceptual basis were understood. One of the earliest written records of face vision, the early name for echolocation, was recorded by Diderot (1749), who described the amazing ability of some blind individuals to perceive objects and their distances. More recently, Hayes (1935), using a scientific rather than philosophical perspective, reviewed and cataloged the evidence for echolocation as part of his work at the Perkins School for the Blind. In his review, Hayes noted that scientists began to study echolocation only after sufficient anecdotal evidence and personal testimonials demonstrated that it was a real phenomenon. ... the historic literature contains numerous testimonies from many periods and cultures. Accepting the introspective comments of those who are adept at echolocation provides the kind of insight that is not yet available from scientific studies, which reveal little about the underlying cognitive strategy for sensing space. These testimonies emphasize several important aspects of echolocation. First, the skill is not conscious, and even those who are have a highly developed skill cannot describe how they do what they do. Second, the exclusive use of echolocation for navigation requires great courage. Third, using hearing for navigation, at least at this high level of performance, is unusual; more frequently, blind individuals depend on their cane using echolocation only as a supplement to their tactile sense of space. How blind individuals acquire a cognitive strategy for echolocation is still somewhat of a mystery. ... Although the details of learning echolocation vary, there is common attitude shared by those who are determined to see with their ears. ... During the ensuing half-century, modern methods have evolved for teaching echolocation, but the assumption that it can be taught is still controversial. Many, if not most, schools for the blind have abandoned echolocation. What explains the current lack of interest in teaching echolocation? In reviewing the literature, I noted that, with the exception of Kish (1995) and a few others, those who teach echolocation are themselves fully sighted. Normal individuals are very unlikely to develop sophisticated echolocation abilities. In contrast, Kish was blind from childhood, and taught himself echolocation by an intuitive sense how to acquire that skill. He is now a licensed teacher for orientation and mobility. Along with a colleague, Kish founded TeamBat, a program that guides blind teenagers into the mountains on bicycle trips, shown in Figure 2. The answer to the earlier question is, in part, that echolocation is more a commitment than a teachable skill. Figure 2. Teenaged blind bicyclists in TeamBat Those blind individuals who use echolocation belong to a unique sensory subculture that has transformed the latent ability to hear navigational space into a high art form. There is no question that most individuals possess only the most rudimentary ability to detect spatial objects and geometries by ear. However, the difference between experts and beginners is only a matter of degree because the underlying cognitive and personal issues are the same. Experts are simply more illustrative of the phenomenon than beginners. Those who acquire an appreciation for aural architecture are, relatively speaking, beginners who cannot walk through the streets of a big city while blindfolded. Like ear training for musicians, acousticians, and audio engineers, learning echolocation also involves attending to the subtlest auditory cues. However, echolocation involves an additional step—using a cognitive strategy to convert binaural cues into spatial images. Those cues originate from a multiplicity of transient sound sources interacting with a range of moving objects and surfaces. Consider the number of sounds and surfaces on an urban street. The cognitive strategy of echolocation must process all of them. Acquiring this ability therefore requires an individual to practice in a real sound field in a real space. For this reason, echolocation is best learned as part of daily life in an actual environment, unlike other forms of ear training, which can take place in a studio or classroom. It is difficult, if not impossible, to artificially create or record teaching examples that faithfully replicate realistic sonic environments. The ability to create an internal picture of external objects and geometry is greatly enhanced when strong motivation, fortuitous skills, and an extended opportunity to practice are present. For blind individuals, enhanced echolocation ability correlates with several key factors. Engaging in echolocation, if begun in childhood when brain substrates are evolving, can readily adapt neural structures that might otherwise have been used for different purposes. A child without any residual vision is simply more likely to discover hearing as an alternative means for navigating a space if permitted to do so. Because practicing echolocation includes the risk of injury, the child needs to be comfortable taking risks, and the child’s parents must avoid excessive protectiveness. In fact, participating in activities that normally assume the adequate vision is the best predictor of acquiring auditory spatial awareness for navigating. See for example the comments of Kish (1995, 2001), who categorically rejected the guidance of those who urged him to learn to use the cane, and Ved Mehta (1957), who moved about the streets of Calcutta without supervision. Investing in auditory spatial awareness is always a free choice that any of us could make, but only a few do so. Even though there are numerous examples of individuals who learned echolocation, the rehabilitation literature is, at best, ambivalent about using hearing rather than the tactile sense for navigating space. When large numbers of soldiers returned from WW II with visual disabilities, formal training programs became a priority. After prolonged controversy and passionate debates, rehabilitation workers involved in helping blind soldiers eventually concluded that tactile navigation—using a cane—was simply easier to teach. Many soldiers could not, or would not, learn to sense subtle auditory cues and invent cognitive strategies. Moreover, most rehabilitation professionals were themselves sighted, and could not teach from experience. Scientific studies of blind individuals using echolocating do not reveal their underlying cognitive processes. As a generalization, cognitive strategies are learnable but not necessarily teachable. For those who cannot echolocate, that ability is more an abstraction rather than a way of life. The literature on echolocation actually illustrates a larger principle: sensory skills are always based on personal utility and life style. Such skills are acquired, rather than being biological imperatives. Those blind individuals who echolocate are merely one example of training, which happens to focus on a particular cognitive strategy for interpreting a particular set of spatial cues in particular situations. ... Those with the ability to echolocate are only an obvious example of a sensory subculture that has the ability to appreciate an aspect of aural architecture. 2.3.2 Hearing Specific Spatial Attributes Insights into the sensory and cognitive aspects of echolocation contribute to the intellectual foundation for aural architecture. And for this reason, it is worth shifting the discussion from anecdotes to research. By the mid 20th century, explaining the phenomenon of echolocation became a scientific challenge. As with many perceptual phenomena that are complex, researchers decomposed an intractable phenomenon into many small, yet simplified, questions or special cases. Theories about how one hears the distance to an isolated wall or how one judges the size of a door opening are examples of special cases. At the current state of knowledge, cognitive and perceptual science is more a collection of segmented theories and experiments than a unified whole. When a blind individual rides a bicycle in a city, he is merging numerous special cases into a holistic strategy. Navigating real spaces involves hearing walls, openings, passive objects, and extracting their relationship to the location and properties of sound sources. The whole is far larger than the sum of the parts. Space is experienced as a non-conscious unity rather than a collection of separable processes. To appreciate the acoustic complexity of an urban street, consider that the environment is composed of multiple objects and numerous sound sources, some stationary, some mobile. Each traffic sign, parked automobile, or telephone pole has a surface that produces both reflections when the sound source is in front of it and shadows when it is behind. A reflection may be heard as an echo if the sound is impulse-like and the surface is more than 10 meters away, or as tonal coloration if the source is continuous and the surface is nearby. A sonic shadow may be diffuse and blurred for low frequencies, or sharp and clear for high frequencies. Sonic illumination is the visual equivalent of a space illuminated with multiple lights: some bright, some dim, some colored, some blinking, and some moving. In a real environment, the sound field is indeed complex. Now consider that because a listener has two ears separated by the width of his head each ear senses sound at a slightly different location in space. By moving or rotating his head, a listener repositions his two ears at another location. The physical sound field actually varies in three dimensions: left-right, front-back, and up-down. Obviously, if we had more ears and if our heads were larger, the auditory cortex would acquire far more information about the spatial distribution of sound. But even with our limited abilities to sense a three-dimensional sound field, the sounds at the two ears are often sufficient for the auditory cortex to build a perceptual model of the objects and geometries that could have produced those particular sounds. Perception is a non-conscious inferential process that synthesizes a hypothetical collection of objects and geometries. This process is the result of having learned the relationship between auditory cues and spatial attributes. That relationship is subtle, ambiguous, and inexact. Those who have developed echolocation skills cannot describe how the spatial image suddenly appears in consciousness. Scientists are still probing for important clues and theories to explain the hidden processes of echolocation. Once the phenomenon of echolocation was recognized, beginning with Supa et al. (1944) at Cornell, the explaining it has been of periodic interest to small groups of researchers. The science of echolocation is far from the mainstream of auditory research, being supported mostly by those with an interest in rehabilitation of people with visual deficits. Before reviewing what science has learned about echolocation, we need to explain the tentativeness of research conclusions. Scientists wrestle with a confounding methodological problem: individuals are remarkably inconsistent in their abilities to hear space. Auditory spatial awareness ranges from total obliviousness to unbelievable magic, and this range corresponds to an equally wide variability in cognitive strategies and sensitivity to particular cues. Is a scientist actually studying a general phenomenon, or the unique ability of specific individuals on particular tasks? In practice, scientists ignore this question when they use randomly selected individuals. Even within the sorted population of blind individuals, there is a wide range of abilities. Human echolocation is actually a collection of independent phenomena. Hearing spectral changes produced by a nearby wall is not the same as hearing shadowing produced by a telephone pole or hearing reverberation from two coupled spaces. A given individual might be very good at one task but mediocre at another. Experiments are designed to focuses on a single task under controlled conditions. ... Although there are only a few studies designed to explore why some individuals performed better than others, Carlson-Smith and Wiener (1996) showed that two specific aspects of auditory acuity were partial predictors of echolocation ability. Those individuals who performed best at detecting spatial attributes were also better at sensing small changes in the amplitude and the frequency of continuous sounds. When a sound field is not uniform, moving through it converts spatial differences into time differences. As listeners move through the space, they hear spatial differences as temporal changes. Basic detection of soft sounds or high frequencies is not relevant to echolocation. Rather, hearing and interpreting small changes of loud sound is far more important. Ignoring the role of genetics in expert listeners, learning is the dominant component. However, we are not speaking of 20 hours of practice but of thousands of hours. By the age of 20, a young adult has already spent well over 100,000 hours listening to the physical world of spaces. If, during that time, an individual engages in self-directed practice exercises, as would a blind person moving through life’s spaces, he is likely to become very proficient at both improving his perceptual acuity to aural cues, as well as inventing cognitive strategies to incorporate those cues into spatial perception. Like athletes who love sports, those who want to become more proficient in echolocation engage in complex sensory activities that simultaneously exercise a wide range of skills and methods. They invent methods to teach themselves how to become proficient— customized pedagogy. Formal training managed by a teacher in a classroom is far more limited than a lifetime of training managed by the individual himself. Sensory practice changes the brain. When examining blind individuals who had engaged in extensive practice, Röder et al. (1999) found that their neurological responses to sounds in the peripheral field were significantly better than those of normal subjects. With enough practice, improved ability is observable in the neurological response of the relevant cortex. Similarly, Pantev et al. (2001) found that the brains of pianists who began their careers as children responded more intensely to piano notes than those who began later. Practice produces larger brain changes during early developmental periods because immature brains have additional plasticity in their neurological wiring. Learning is far more specific to the task being practiced than one would expect, and acquired skills do not readily transfer from one task to another. Just as exercising one muscle group does not strengthen other muscles, exercising one sensory skill does not enhance other skills because each sensory skill involves specific brain substrates. An audio engineer who has acquired enhanced acuity to the tonal coloration in reverberation is unlikely to transfer that skill to navigating a corridor without vision. Although the concept of task-specific learning is well understood, only a few isolated experiments confirm the phenomenon. ... scientific studies have not yet revealed the extent to which spatial cues can be learned with extensive practice. Conclusions, albeit somewhat speculative, have broad implications. First, extensive practice produces dramatic changes in perceptual ability, and those changes are observable using neurological imaging techniques. Brains reflect how individuals live their lives. Secondly, a culture that motivates and rewards individuals to learn auditory spatial awareness is likely to have a population that can better appreciate aural architecture. And conversely, without such a population, aural architecture is likely to be irrelevant to the culture. Third, auditory spatial awareness is a collection of independent sensitivities. Some individuals may be acutely aware of reverberation and the enclosed volume of a space, while others may be aware of local objects and geometries in a navigational space. Lastly, any discussion about aural architecture must include an understanding of the aural subculture, which has its own idiosyncratic investment in the ability to detect and appreciate particular attributes of spaces.