Spectrally specific temporal analyses of spike-train responses to complex sounds: A unifying framework
Fig 3
Lower spectral-estimation variance can be achieved using apPSTHs (with multiple tapers) compared with difcor correlograms.
(A) Spectrum for the 100-ms segment in the speech sentence s3 (F0 ∼ 98 Hz, F1 ∼ 630 Hz) used for analysis. (B) Example spectra for an AN fiber (CF = 900 Hz, high SR) with spikes from 25 randomly chosen repetitions per polarity. The first two discrete-prolate spheroidal sequences were used as tapers corresponding to a time-bandwidth product of 3 to estimate D(f), the spectrum of d(t). No taper (i.e., rectangular window) was used to estimate the difcor spectrum. The AN fiber responded to the 6th, 7th and 8th harmonic of the fundamental frequency. (C) Error-bar plots for fractional power (PowerFrac) at the frequency (green triangle) closest to the 6th harmonic. Error bars were computed for 12 randomly and independently drawn sets of 25 repetitions per polarity. The same spikes were used to compute the spectra for d(t) (blue) and difcor (red). (D) Diamonds denote the ratio of variances for the difcor-based estimate to the d(t)-based estimate. This ratio was greater than 1 (i.e., above the dashed gray line) for all units considered, which demonstrates that the variance for the multitaper-d(t) spectrum was lower than the difcor-spectrum variance. AN fibers with CFs between 0.3 and 2 kHz and with at least 75 repetitions per polarity of the stimulus were considered. Bin width = 0.1 ms for PSTHs. Sampling frequency = 10 kHz for FFRs. Stimulus intensity = 65 dB SPL.