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. 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. 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, 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., soundscapes) 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.
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