Prof. Simon Carlile on Binaural Representations
Who: Prof. Simon Carlile (University of Sydney)
What: Six degrees of spatial separation - The portal for auditory perception
When: Friday October 31, 2014
Where: CCRMA Seminar Room (Top Floor of the Knoll at Stanford)
Why: Binaural hearing and representations are both critical!
Bring your favorite binaural processor to CCRMA on Halloween and we’ll make it less mysterious.
Six degrees of spatial separation - The portal for auditory perception.
Prof. Simon Carlile
University of Sydney
Our perception of auditory space depends on the analysis of acoustic cues produced at each ear by the surrounding sound sources (reviews Carlile, 1996; Carlile et al., 2005). Despite more than a century of research, the nature of the representation underlying this perception remains the subject of much debate (Grothe et al., 2010; Ashida and Carr, 2011). Strong evidence indicates that the early encoding of binaural time differences involves a two channel, opponent code rather than a labelled line code as suggested previously. In this lecture we will review the historical development of these ideas and, in that context, look at data from very recent experiments that take a different approach to probing this auditory representation using a variation of the two-point discrimination task. Subjects made a two-point separation judgment using concurrent speech sounds. Discrimination thresholds changed non-linearly as a function of the overall separation, with a minimum at 6° of separation. This ‘dipper’ function was seen for regions around the midline as well as for more lateral regions (30° and 45°). By contrast, the JNDs for the binaural cues to sound location (interaural time and level differences) were linear for matched base intervals.
These data suggest that the perceptual representation of auditory space involves a multi-channel mapping which emerges subsequent to the encoding of the binaural cues. Rather, it could be based on a logical representation of space that may operate as a network of neural interconnections rather than as a topographical ‘map’. There would be significant advantages to representing space through the logical relationships of ‘object locations’ rather than at the level of cues or features, especially when considering the challenge of efficiently integrating auditory and visual information. Audio-visual binding at the level of object representation would obviate the need to convert audition’s head coordinates to vision’s retinal coordinates on a feature by feature basis. Strongly corroborating this idea is our recent finding of a dipper function in a very similar two-point discrimination experiment but where one point
Ashida G, Carr CE (2011) Sound localization: Jeffress and beyond. Cur Op Neurobiol 21:745-751.
Carlile S (1996) The physical and psychophysical basis of sound localization. In: Virtual auditory space: Generation and applications. (Carlile S, ed), p Ch 2. Austin: Landes.
Carlile S, Martin R, McAnnaly K (2005) Spectral Information in Sound Localisation. In: Auditory Spectral Processing (Irvine DRF, Malmierrca M, eds), pp 399-434: Elsevier.
Grothe B, Pecka M, McAlpine D (2010) Mechanisms of Sound Localization in Mammals. Physiol Rev 90:983-1012.
Orchard-Mills E, Leung J, Burr D, Morrone MC, Wufong E, Carlile S, Alais D (2013) A Mechanism for Detecting Coincidence of Auditory and Visual Spatial Signals. Multisensory Research 26:333-345.
Prof. Simon Carlile is an Associate Professor, and head of the Auditory Neuroscience Laboratory, School of Medical Science, University of Sydney. Dr. Simon Carlile serves as Chief Executive Officer and Director at Personal Audio Pty Ltd. Dr. Carlile initiated his research in virtual space and 3D audio at Oxford University in 1980. He has a 25 year track record which has resulted in more than 85 refereed papers, chapters and a book "The Development and Applications of Virtual Auditory Space" which is a foundation monograph in the field. Between 1998 and 2003, he was also Chief Information Officer at the University of Sydney with responsibility for the implementation and management of strategic Enterprise Planning Resource systems throughout the University.