One critically important environmental property of a sound source is its physical location in space. The distance between a sound source and a listener is a critical factor shaping neural, physiological, and behavioural responses to sound sources. Specifically, sound sources that are approaching a listener (looming sources) initiate responses in neural populations that mediate attention to auditory space, assignment of appropriate responses, and even motor planning in response to looming sound sources. Analogous neural activity does not occur in response to receding sound sources. Physiological responses such as heart rate and galvanic skin response show similar differentiation between looming and receding sounds. Finally, behavioural responses to looming sources indicate a perceptual bias to hear sound sources as closer than actual and to underestimate the arrival time of a looming source. Taken together, these findings indicate the environmental salience of looming sound sources and demonstrate an important link between perception of a sound source and the potential to physically interact with the source. These findings provide indirect evidence that suggests the perceptual anisotropy in the perception of looming and receding sounds may be advantageous in evolutionary terms. PERCEIVING SOUND SOURCES AND SOUND SOURCE “PROPERTIES” Because of the relatively sparse history of investigating the perception of sound source properties, there is still little consensus over the precise terminology that should be used to describe the perception of sound sources. For example, when describing a “sound”, some researchers have developed entire theoretical paradigms around the term “auditory object” . Others prefer the term “auditory event” to describe very similar auditory phenomena . Still others have taken a slightly different approach to defining auditory objects and grappled with the very basic question “What is an auditory object?” . Nonetheless, the intent of many recent investigations into the perception of sound source properties has been to shift the traditional focus on the perception of the acoustic characteristics of the sound per se (such as pitch and loudness), to the perception of the physical properties of the object that is producing the sound (such as weight, shape, or size ). Sound source properties and spatial location Much of the work on the perception of sound source properties stems from the now classic papers by Gaver which proposed an innovative way of thinking about “what” and “how” we hear [5, 6]. The thrust of Gaver’s work suggested that in everyday listening situations, people don’t attend to “pitch” or “timbre”, or other acoustic properties of sound energy. Rather, they identify sound sources and the physical properties of objects that are producing sound. Gaver suggested that sound events could be divided into three main categories based on the physical properties of the objects that created the soundsolid, liquid, or gas. More complex sounds could be created by interactions between these main three categories. Although the physical materials that make up a sound source are fundamental to the perception of sound source properties, the location of the sound source relative to the listener is also a crucial property of a sounding object. Any object, be it auditory or visual, must occur at a location in space. Thus, spatial location is an inherent property of objects (or events). Generally speaking, the closer a sound source is to a listener, the more salient and ecologically relevant that source becomes. When sound sources are moving, those that are approaching a listener (or looming) are generally treated with greater urgency than those that are receding.