Page 40 - April 2008

He pointed out that, while hearing is a ubiquitous sense among vertebrates, there is a great need for models of effect that capture the idiosyncrasies of species auditory capabili- ties, a range of possible mechanisms of injury, and variable real-world noise environments.
Plotkin and his coworkers described key components of an adaptive management system for exposure to sonic booms that has been designed to ensure preservation of a highly valued ecosystem in Labrador, Canada. They described efforts to moni- tor, predict and manage military aircraft training activities at Goose Bay, a sensitive ecosystem under airspace that has been host to military flying operations since World War II. Since 1995, a local organization funded by a consortium of stakeholders, the Institute for Environmental Monitoring and Research, has con- ducted effects research and negotiated mitigation of the effects of low altitude flight operations, serving to protect the welfare of aboriginal people as well as the survival of wildlife species.
David Dall’Osto and Peter H. Dahl presented a pilot study to characterize environmental noise underwater in Puget Sound by describing different components of the noise budget, including injection of noise from airplane flyovers, and correlation between pressures above and below water. Their work emphasized that noise in real-world environ- ments comes from many different sources, sometimes including the target species themselves, and may involve characterization of transmission through a variety of media.
Panel discussions focused on commonalities between studies of noise effects on humans and animals. The search for metrics relating acoustic environment to outcome meas- ures was certainly a common concern. Commonalities were also easily understood in hearing loss. However, some pan- elists and authors saw a gap concerning cognitive, behavioral or social responses to noise.
Human actions are rarely interpreted as adaptive, nor are animal responses posited to be intelligent and flexible. However, the panelists considered that both perspectives are likely to be important in developing general models of effect. Recent reviews of the disturbance literature for animals have begun to characterize animal responses to disturbance as strategies, behaviors that are chosen based on context that
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minimize risk and cost and maximize benefits. Even though
effects on humans and animals are assessed very differently from a legal point of view, there was a consensus that noise could be conceptualized as an environmental challenge to be met with adaptive responses in both cases. In humans, adap- tive responses are constrained by economic or social needs, whereas animals are driven to maximize survival and repro- duction. However, whether human or animal, non-auditory impact is mediated by processes in the brain—perception, evaluation of risk, and response. A small first order list of predictors was agreed on during the panel discussion:
1. Acoustic features such as signal to noise ratio and absolute level, particularly those that differ greatly from background or expected noise;
2. Control and predictability;
3. Association with perceived threat (e.g., predatory or
social challenge);
4. Interference with function, such as sleep interfer- ence, masking of biologically-significant signals like speech, or competition for attention
During the discussion, there was agreement that effects on attention were particularly under-appreciated. In this view, attention should be modeled as a limiting resource that can be used up by noise. In the case of wild animals, it may distract attention from important activities such as vigilance against predators or socializing. In the case of humans, it may interfere with activities that require attention, such as learning.
The concept of “soundscapes” as differentiated from physical acoustic characteristics of the environment, various- ly called the acoustic environment or acoustic topology, came up repeatedly during the discussion. In the sense that the term soundscape describes sounds that vary predictably over an area, the two did not seem to differ greatly. However, soundscape was also linked to human conceptual and emo- tional perceptions of their acoustic environment. There was an extensive discussion about the value of treating acoustic measurements of the environment as objective, given that the best information available now suggests that mental process- es of both humans and animals are closely tied to effect. However, there did seem to be value in recognizing that the human-based concept of soundscape can be examined by conversing with humans, whereas animal perceptions must always be measured by indirect experimentation.
Based on this discussion, panelists noted that there was a continuum of noise exposure from completely natural to highly urban environ- ments. They noted an urgent need to develop quantitative measures at both individual and aggregate levels in both
humans and animals.
At the 156th Meeting of the Acoustical Society of America in Miami
38 Acoustics Today, April 2008
Fig. 5. Alerting response of Mexican spotted owl chick to dis- turbance. Responses of owls were documented during low-altitude training overflights by Tornado aircraft flown by the German Air Force in the Gila National Forest, New Mexico (photo by A. Bowles).
Fig. 6. In experimental trials, even domestic poultry evaluate disturbances cognitively before selecting a response. In this photo- graph, naïve turkey poults move to a location where they can see a low flying military jet and moni- tor its movements (photo by A. Bowles).