Human auditory ecology (HAE) is a research program in hearing sciences studying the interactions between humans and their acoustic environments.
Concept HAE studies the "relationship between the acoustic environments in which people live and their auditory needs in these environments.Gatehouse S., Elberling C., Naylor G. (1999) Aspects of auditory ecology and psychoacoustic function as determinants of benefits from and candidature for non-linear processing in hearing aids. In A. N. Rasmussen, P. A. Osterhammel, T. Anderson, & T. Poulsen (Eds.), Auditory models and non-linear hearing instruments (18th Danavox Symposium) (pp. 221–233). Copenhagen, Denmark: Holmens Trykkeri This auditory ecology, a concept initially coined by Stuart Gatehouse, therefore refers to the auditory environments in which humans live and function, the tasks to be undertaken by humans in these complex acoustic environments and the importance of these tasks in daily life and daily routines. The use of this concept was initially restricted to the case of urban life. However, urban habitats are relatively recent in humankind history and evolution, and natural soundscapes have preceded the apparition of Homo sapiens, some 300,000 years ago. For this reason, the concept of auditory ecology was extended to study a different and evolutionary-based question, namely how humans perceive ecological processes at work in natural habitats through their peripheral and central auditory system.
Auditory perception of natural soundscapes Natural soundscapes correspond to the complex arrangements of biological (animal vocalizations) and geophysical (wind, rain, stream) sounds shaped by sound propagation through non-anthropogenic habitats.Farina A., Gage S.H. (2017) Ecoacoustics: The ecological role of sounds (John Wiley & Sons, Hoboken). ISBN 978-1-119-23069-4Acoustic ecology According to its most recent definition, human auditory ecology (HAE) is a multidisciplinary research programme attempting to map and explain the ability of normal-hearing and hearing-impaired human listeners to perceive natural soundscapes. In this specific case, HAE aims at characterizing how and to which extent humans perceive ecological processes underlying habitats marginally affected by human activity through their ears and their auditory brain, with a life-span perspective. HAE could be considered as a field of auditory psychophysics, auditory neurosciences and audiology. More broadly, HAE aims to encourage hearing scientists who traditionally work on speech and music perception in urban settings to collaborate with soundscape ecologists, ecoacousticians and neuro-ethologists, and share expertise with environmental and architectural acousticians, anthropologists, philosophers and geographers.
Extended definition of human auditory ecology HAE studies the (presumably ancestral) monitoring functions of the human auditory system. These monitory auditory functions are used by human auditory system to build a perceptual representation of the close environment, orient and navigate, assess resources (food, water, shelter) and danger (e.g., flooding, predators), opportunities for action, and the general health of the environment. These monitoring functions are assumed to help human listeners build a sense of place and time and operate in their acoustic environment.
From such a perspective, HAE is based on (i) concepts derived from soundscape ecology such as the acoutic adaptation and acoustic niche hypothesis,Sueur, J., Farina, A. Ecoacoustics: the Ecological Investigation and Interpretation of Environmental Sound. Biosemiotics 8, 493–502 (2015). https://doi.org/10.1007/s12304-015-9248-x and (ii) psychophysical and neuroscientific models and methods. HAE operates on the large acoustic databases of natural soundscapes collected by soundscape ecologists and eco-acousticians using standardized procedures and recording material. HAE aims to characterize the monitoring functions of the human auditory system through ordinary listening behaviors (listening to animal vocalisations such as bird songs or insect stridulations, detecting presence of water or rain, assessing water discharge or wind strength ...). Moreover, HAE investigates the extent to which these monitoring functions are adapted to specific information conveyed by natural soundscapes, whether they operate throughout the life span or whether they emerge through individual learning or cultural transmission.
HAE aims to identify testable working hypotheses guided by computational models of the human auditory system, in order to (i) unveil low and high-level auditory mechanisms engaged in the auditory perception of soundscapes associated with natural habitats, green or blue species within or outside cities, (ii) how they develop through life and (iii) the extent to which they are affected by exposure, learning and culture. Although HAE aims to improve fundamental knowledge on the human auditory system and how humans interact with natural environments, it also aims at providing novel solutions to screen and rehabilitate hearing loss via hearing aids and cochlear implants.
Acoustical aspects
Contribution of soundscape ecology and ecoacoustics Because most vertebrate species send and receive sound for essential life functions (e.g., navigation, courtship, foraging), the collection of sounds perceived in an environment (i.e., soundscapesSchafer, R.M., The tuning of the world. 1977, New York, NY, USA: Knopf) can reflect ecological processes. Thus, by studying the structure of the soundscape over space and time, soundscape ecology and ecoacoustics aim to study the dynamics of ecological processes. Soundscape ecology is predicated on two key hypotheses: the acoustic niche hypothesis, where signals have evolved to partition in acoustic space to minimize overlap between species and the acoustic adaptation hypothesis, which states that species' optimize transmission of vocalizations to overcome habitat constraints. Although, the acoustic adaptation hypothesis has received limited support in experimental studies. Recent developments in passive sound collection offer the opportunity to cost-effectively monitor soundscapes at enormous scales. For example, the Australian Acoustic Observatory comprises 360 permanent recording stations and the National Park Service's Natural Sounds and Night Skies division have collected recordings at over 490 sites across the United States. Extracting relevant biological information from resulting enormous datasets remains challenging. Species vocalizations of interest may be manually or automatically extracted, using listening, visualizations of spectrograms, or recognition algorithms. Alternatively, acoustic indices can be used to summarize the properties of the soundscape.
Contribution of computational auditory sciences The pioneering work of Singh and Theunissen suggests that high spectral modulations (harmonicity) and slow amplitude modulations distinguish biological (animal vocalizations) from geophysical sounds (wind, rain, stream sounds) in natural scenes. Subsequent work by McDermott and Simoncelli showed that geophysical sounds such as wind, rain or stream sounds can be distinguished from other sounds by their textural properties. The latter are reflected in specific regularities or "statistics" of amplitude-modulation patterns computed by the human auditory system in response to these sounds.
The statistics of these sounds and scenes could be characterized further using the large, ecologically valid databases collected by soundscape ecologists and ecoacousticians, allowing to test further efficient-coding principles positing that perceptual systems (e.g., the auditory system) have evolved to encode environmental stimuli in the most efficient way, and that the properties of auditory mechanisms closely match the statistical properties of natural sounds and scenes.Attias H., Schreiner C. E. (1997) Temporal low-order statistics of natural sounds. Advances in Neural Information Processing Systems 9 : 27–33. MIT Press The first studies based on this approach indicate that the central auditory system of humans has access to sufficient sensory information in the spectro-temporal domain to achieve accurate auditory discrimination of terrestrial biomes and their changes across moments of the day and seasons.
Psychoacoustical aspects
Historical background HAE aims to understand human auditory perception of natural (i.e. biophonic and geophonic) acoustic environments. In contrast, the majority of experimental studies of human auditory perception have utilized parametrically generated stimuli which lack acoustic complexity of natural environmental sounds. The prevailing methodological paradigms of psychoacoustics have traditionally focused on investigating how sounds' physical properties relate to the perception of abstract sound qualities such as pitch, loudness and duration without considering sounds' semantic or referential aspects. Furthermore, traditional psychoacoustic methods have relied primarily on detection and discrimination tasks in which a specific acoustic parameter is manipulated (e.g. frequency or intensity) under conditions of low stimulus uncertainty and performed by trained listeners. Overall, traditional psychoacoustics has been highly successful in describing human auditory abilities in relationship to underlying anatomy and physiology, leading to tremendous breakthroughs and achievements in communication and audio technology.Plomp, R. (2002). The intelligent ear: On the nature of sound perception. Lawrence Erlbaum Associates Publishers However, this approach has had limited utility for understanding the perception of meaningful acoustically complex environmental sounds in everyday life, which typically involves perception of sound producing objects and events along with associated materials and actions.Neuhoff JG. Ecological Psychoacoustics. 1st ed. New York, NY: Elsevier Academic Press; 2004
Ecological psychoacoustics A growing awareness of these limitations to ecological validity in traditional psychoacoustics has led to the broadening of theoretical approaches and modifications of experimental procedures used in the studies of auditory perception to include tasks involving sound identification, categorization and comprehension. Later efforts explored principles of perceptual organization of complex auditory scenes (under the general framework of auditory scene analysis) and formulated questions in terms of actionable and behaviorally relevant properties of specific sound (under the framework of ecological psychology). A further attempt to bridge the gap between investigations of auditory perception utilizing traditional psychoacoustic paradigms and those pertaining to everyday listening (ordinary listening behaviors) has been proposed under the general heading of ecological psychoacoustics. Ecological psychoacoustics generally considers auditory perception in terms of the ecologically relevant behavioral goals of the listener in specific tasks, situational contexts and environments (e.g. cognition-perception-action loop), while employing psychoacoustic experimental methods to maintain high internal validity.