Noise-invariant Neurons in the Avian Auditory Cortex: Hearing the Song in Noise
Responses of two neurons (Cell A and Cell B) to song presented alone and over noise. The top row shows the spectrogram of the same zebra finch song used in the two recordings. Song starts at 0s. Below the spectrogram are raster plots and corresponding smoothed PSTHs. The first raster and PSTH correspond to the response of each neuron to the song alone presented at 70 dB SPL. Clear temporal synchrony across the four trials can be seen illustrative of an equally robust response to song stimuli. The second raster and PSTH correspond to the responses to song+ modulation limited noise (ml-noise) presented at 3dB signal to noise ratio. Ml-noise is synthesized by low-pass filtering white noise in the space of temporal and spectral modulations (see methods). The pink highlights show the duration of the stimulus (song + noise). The onset and offset of the stimulus is different in each trial because the trials are aligned to the onset of the song and the noise masker began and ended with a different delay in each trial. The noise was also different in each trial. This addition of naturalistic noise destroys the cross-trial synchrony in the response for the neuron shown in the left column but not for the neuron shown in the right column.