When   Tuesday, January 13, 2009   Time   2:00 PM - 3:00 PM  
Where   Technological Instit M416 2145 Sheridan Rd.   map it
Audience   - Faculty/Staff - Student - Public
Contact   Molly E Scanlon   +1 847 491 5586  
Group   McCormick-Colloquia Engineering Sciences and Applied Mathematics

Applied Math Colloquium

Title: Sparse time/frequency representations and the neural coding of sound

Speaker: Marcelo Magnasco, Rockefeller University

Abstract: It is widely believed that the auditory system identifies sounds on the basis of some form of time-frequency analysis, whereby the auditory stream is represented simultaneously along a temporal axis and a frequency axis. However, in addition to delicate spectral features, auditory neurons also preserve exquisite temporal information about sound features, but we do not know how the brain uses this temporal information to parse the rapidly changing sounds of the natural world. We forward a simple argument on how to make effective use of temporal information in the auditory nerve, which leads us to consider the reassignment class of time-frequency representations as a potential model of auditory processing. We show that these representations are sparse even for spectrally dense signals. Many details of complex sounds that are virtually undetectable in standard sonograms are readily perceptible and visible in reassignment; as the only known class of time-frequency representations that is always ‘‘in focus’’ this methodology may help explain the remarkable acuity of auditory perception.

We also consider how to determine, experimentally, when a neural code embeds information in the detailed timing of spikes. We show that standard ``spike-triggered'' receptive field constructions are inadequate to extract this level of information and present a new method, ``differential reverse correlations'', based on correlating small changes in spike timing due to small changes to the stimulus.

Special Note: Please note unusual day and time.