and mountain categories, whilst rushing water had the highest rating in the preference category. Analysis of the results identified three physical features that help explain the apparent split between tranquillity and preference. These were; mistiness, unstructured openness; which refers to how open the scene is and how difficult it is to establish a sense of depth or distance, and surface calmness. Mistiness and unstructured openness tended to depress preference relative to tranquillity whilst surface calmness tended to enhance it. Herzog and Barnes conducted a follow up study in which deserts and waterscapes were included in the setting types. In 2000, Herzog and Chernick conducted further research into the tranquillity construct when they investigated the relationship between tranquillity and danger in urban and rural settings. The key results that emerged from this research were that "setting care", which relates to how safe we feel in a particular setting, is more salient for judgments of danger in urban settings than natural ones and that openness was a significant predictor of danger but not of tranquillity. The authors concluded therefore that tranquillity and danger should not simply be viewed as polar opposites, but like preference and tranquillity as distinct constructs. The role of audio-visual interaction within the tranquillity construct Within tranquillity studies, much of the emphasis has been placed on understanding the role of vision in the perception of natural environments, which is probably not surprising, considering that upon first viewing a scene its configurational coherence can be established with incredible speed. Indeed, scene information can be captured in a single glance and the gist of a scene determined in as little as 100ms. The speed of processing of complex natural images was tested by Thorpe et al. using colour photographs of a wide range of animals (mammals, birds, reptiles and fish), in their natural environments, mixed with distracters that included pictures of forests, mountains, lakes, buildings and fruit. During this experiment, subjects were shown an image for 20ms and asked to determine whether it contained an animal or not. The electrophysiological brain responses obtained in this study showed that a decision could be made within 150ms of the image being seen, indicating the speed at which cognitive visual processing occurs. However, audition, and in particular the individual components that collectively comprise the soundscape, a term coined by Schafer to describe the ever-present array of sounds that constitute the sonic environment, also significantly