Efficient Coding of Natural Sounds Grace Wang HST 722 Topic Proposal.
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Transcript of Efficient Coding of Natural Sounds Grace Wang HST 722 Topic Proposal.
Background
Our natural environment consists of multiple sound sources and background noises with complex harmonic and temporal structuresStationary harmonic structure (vocalizations)Nonstationary structure (crunchy)
Have our brains developed to be optimized for processing natural sounds efficiently?
Efficient coding hypothesis
Shannon’s model for transferring data in communication systems (info theory)
Barlow applied info theory to model neural behavior Proposed spikes of neural populations was optimized to
efficiently represent naturally occurring images and sounds
Efficiency = reduce redundancy to maximize independence
Largely consistent with early stages of visual processing Is the same true for the auditory system?
Information in adjacent filters is highly redundant
Nearly identical statistics across filters and across sound types
Suggested natural sounds may be associated with bandwidth and translation invariance
from Attias and Schreiner (1997), “Temporal low-order statistics of natural sounds”
How do we remove redundancy to achieve statistically independent neural responses?
from Schwartz and Simoncelli (2000), “Natural sound statistics and divisive normalization in the auditory system”
Sound pressure waveform decomposition
Differs from spectrograms by retaining the phase information
from Smith and Lewicki (2005), “Efficient coding of time-relative structure using spikes”
1 1
( ) ( ) ( )mnM
m mi m i
m i
x t s t t
Time-frequency distribution of optimal filter
shapes Fourier transform
may be sufficient for animal vocalizations
Need wavelet analysis for environmental sounds and speech
from Lewicki (2002), “Efficient coding of natural sounds”
Decompose into modulation spectra
from Singh and Theunissen (2003), “Modulation spectra of natural sounds and ethological theories of auditory processing”
from Singh and Theunissen (2003), “Modulation spectra of natural sounds and ethological theories of auditory processing”
Discarding a lot of energy in white noise
from Singh and Theunissen (2003), “Modulation spectra of natural sounds and ethological theories of auditory processing”
from Singh and Theunissen (2003), “Modulation spectra of natural sounds and ethological theories of auditory processing”
Neural responses
Increasing selectivity along ascending pathway for songs in zebra finches
Optimal stimulus set in grasshoppers does not coincide completely with their natural soundsSuggested neurons are optimized for
behaviorally relevant sounds (Machens et al 2005)
Papers Background
Smith and Lewicki 2005: Efficient coding
Discussion Attias and Schreiner 1997: Demonstrate redundant
representation in peripheral auditory system Lewicki 2002: Fourier vs wavelet representation Singh and Theunissen 2003: Modulation spectra
Further reading Machens et al 2005: grasshoppers, behaviorally
relevant sounds Hsu et al 2004: zebra finches, increasing selectivity