Spectrally specific temporal analyses of spike-train responses to complex sounds: A unifying framework
Fig 10
The harmonicgram can be used to visualize formant tracking in synthesized nonstationary speech.
Neural harmonicgrams for fibers with a CF below 1 kHz (A, N = 16) and for fibers with a CF between 1 and 2.5 kHz (B, N = 29) in response to the dynamic vowel, s2. Stimulus intensity = 65 dB SPL. The formant frequencies mimic formant trajectories of a natural vowel [21]. A 20-Hz bandwidth was employed to low-pass filter the demodulated signal for each harmonic. The harmonicgram for each AN-fiber pool was constructed by averaging the Hilbert-phase PSTHs of all AN fibers within the pool. PSTH bin width = 50 μs. Data are from one chinchilla. The black, purple, and red lines represent the fundamental frequency (F0/F0), the first formant (F1/F0) and the second formant (F2/F0) contours, respectively. The time-varying formant frequencies were normalized by the time-varying F0 to convert the spectrotemporal representation into a harmonicgram.