Sounds have an ‘out-there-ness’ – they appear to come from ‘somewhere’. That this seems matter-of-fact makes it no less remarkable; how the brain separates out sources into distinct objects appearing and disappearing, moving over space and changing over time, represents one of the particularly difficult challenges in neuroscience today. We know that by comparing sound energy at the two ears – literally, small differences in the air pressure at each ear drum generated by the waves of sound roiling about us – our brains construct a representation of the spatial world. This sensation of auditory space, i.e., knowing the location of objects or where events are occurring, is a critical feature of human experience, enabling us to attend to important events, experience the world beyond our line of sight (including behind us) and to communicate effectively; ‘cocktail party listening’ depends in part on spatial hearing.
No less important than the sources of sounds themselves, however, are the spaces they inhabit. Spaces Speak – Are You Listening?, the title of a book by Barry Blesser, an engineer, and Linda-Ruth Salter, a sociologist (they also happen to be married to each other), sets out to explain how our feeling of connectedness to the world about us, and our sense of well-being in that world, comes through our sense of spatial hearing, particularly in terms of the space in which we are listening. Sound reflected from the walls, floor and ceiling, for example, merges to become the sound of the environment in which we are listening; we ‘hear’ the spaces we inhabit, and can place sound objects and events into these acoustic spaces, spaces whose features are just as (re-)memorable as the objects and events themselves. The interaction of sound with the physical environment and the ability to reproduce virtual soundscapes using binaural recordings, for example, open up new ways of generating a narrative, connecting events and objects with the spaces in which they occurred, even in the absence of visual information.
The short sound segment you will hear was recorded using binaural microphones (one placed at the entrance to each ear). By listening to these sounds over stereo headphones you hear not only the recorded sound objects (in this case, words spoken by a single talker), but also something of the environment in which that talker spoke and how they moved through that environment. Even with this simple example, it becomes obvious that recording the spatial aspect of sound provides for a compelling recreation of events ‘out there’ in the real world.
A native of Belfast, David McAlpine was raised between Northern Ireland and Perth, Australia, where he studied Physiology at the University of Western Australia. Returning to the UK for graduate studies at Oxford University, he became fascinated by the brain’s ability to represent the spatial world through sound. Following completion of his PhD, he undertook further scientific training at the Medical Research Council’s Institute of Hearing Research, in Nottingham, before striking out on an academic career. Today, as Professor of Auditory Neuroscience and Director of the UCL Ear Institute, David runs a multi-disciplinary research programme that seeks to understand how the spatial world is represented in the brain. Working with theatre groups, directors and artists, David is also exploring how a scientific understanding of the auditory world can be employed to provide a more vivid acoustic experience for audiences. By working together, David believes that scientists and artists can enhance each other’s inherent creativity to explore new ways of understanding the world about us.