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Background STRF describes properties in frequency and time domains STRF describes properties in frequency and time domains Have been studied in many animals but not adequately in a computer model Have been studied in many animals but not adequately in a computer model
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Analysis of spectro-Analysis of spectro-temporal receptive temporal receptive fields in an auditory fields in an auditory
neural networkneural networkMadhav NandipatiMadhav Nandipati
PurposePurpose Compare computer model to Compare computer model to
biological systembiological system Evaluate utility of receptive fieldsEvaluate utility of receptive fields
BackgroundBackground STRF describes properties in STRF describes properties in
frequency and time domainsfrequency and time domains Have been studied in many animals Have been studied in many animals
but not adequately in a computer but not adequately in a computer modelmodel
Neural networkNeural network
Training setTraining set Different neurons trained on simple Different neurons trained on simple
soundssounds
0 Time (ms) 200 0 Time (ms) 2000 Time (ms) 200
Freq
uenc
y (k
Hz)
5
Freq
uenc
y (k
Hz)
5
Freq
uenc
y (k
Hz)
5
Upsweeps Pure tones Downsweeps
Training procedureTraining procedure Oja’s rule – modified Hebbian Oja’s rule – modified Hebbian
learninglearning Update rule:Update rule:
Some particulars:Some particulars: Training set of 276 stimuliTraining set of 276 stimuli 600 iterations through each stimulus600 iterations through each stimulus
Results – weightsResults – weights
210 Frequency (Hz) 14501320 22601920 3075
2650 38503460 44004270 5510
Generation of STRFsGeneration of STRFs Create ripple stimuli by equation:Create ripple stimuli by equation:
Generation of STRFs Generation of STRFs cont.cont.
Feed ripple into model and get Feed ripple into model and get outputoutput
Fit curve to outputFit curve to output
Generation of STRFs Generation of STRFs cont.cont.
Magnitude and phase shift become Magnitude and phase shift become one pixel of transfer function:one pixel of transfer function:
Generation of STRFs Generation of STRFs cont.cont.
2D inverse Fourier transform to 2D inverse Fourier transform to obtain STRFobtain STRF
Pad matrix with zeros to get Pad matrix with zeros to get smoother imagesmoother image
Use similar color schemes as Use similar color schemes as literatureliterature
Results - STRFsResults - STRFs
Comparison to tuning Comparison to tuning curvescurves
Depicts response intensity to Depicts response intensity to different freqs.different freqs.
Peak of curve = best frequency (BF)Peak of curve = best frequency (BF)
Comparison of BFsComparison of BFs Peak of tuning curve compared to Peak of tuning curve compared to
max value of STRFmax value of STRF
Temporal componentTemporal component Line of best fit around max areaLine of best fit around max area Different slopes means different Different slopes means different
temporal characteristicstemporal characteristics
Temporal component Temporal component cont.cont.
Discussion & ConclusionDiscussion & Conclusion Real STRFs look similar to Real STRFs look similar to
computational STRFscomputational STRFs Means underlying processing is also Means underlying processing is also
similarsimilar