PMC

The STSF method generates and tests novel stimuli during the experiment based upon the contribution of frequencies to the receptive field. A The STRF (left) for an example site and two of the five target stimuli (spectrograms) are shown, along with neural responses (rasters). B When target stimuli were filtered at the 50% threshold to remove frequencies outside the RF (spectrograms; Tw), neural responses were similar to the unfiltered responses. C Adding a masker in the frequency bands within the STRF to the filtered stimuli (spectrograms; target within STRF, masker within STRF: TwMw) elicited different neural responses (rasters). D Adding a noise masker to the frequency bands outside the RF (spectrograms; target within STRF, masker outside STRF: TwMo) also degraded neural response timing.

After STRF calculation, the contribution of each frequency band to the receptive field is estimated. A Five example song spectrograms (power in each frequency versus time) are shown which elicited example field L responses (rasters). B Responses to 20 songs were used to generate the STRF, which estimated the stimulus features that increased (red) and decreased (blue) the firing probability of the example site. C The contribution of each frequency band (black line) was calculated by adding the minimum (inhibitory, blue) and maximum (excitatory, red) magnitude in each frequency band. Different receptive field inclusion thresholds (25%, 50%, and 75%) were calculated relative to the maximum contribution.

Frequencies outside the receptive field can be removed using site-specific filtering while preserving neural responses, and masking frequencies within the STRF disrupts neural responses. A–E When target stimuli (T) were filtered to contain only within-STRF frequency bands (Tw), there were significant changes in the stimulus intensity (A) but no significant change in the neural discriminability (B), spike timing reliability (C), sparseness (D), or firing rate (E), suggesting that the timing of neural responses was predominantly preserved by filtering. Once a masker was added to these within-STRF frequency bands (TwMw), the discriminability, reliability, and sparseness were all affected. Individual sites are gray, means (±1 SEM) in black; two outlier (very high rate) sites are omitted from the firing rate plot but included in the mean.

Adding a masker in frequency bands outside the receptive field can disrupt neural responses. A Three example field L sites’ spike trains change in response to site-specific filtered stimuli (spectrograms above each raster). The response from each site is preserved in filtering to remove outside-STRF frequencies (T → Tw), but degrades in response to a masker placed in those outside-STRF frequency regions (TwMo). B, C The neural discrimination (B) and the spike timing reliability (C) of responses significantly changed relative to the filtered stimuli (Tw) due to the addition of a noise masker to the frequency bands outside the STRF (TwMo). D, E The sparseness (D) and firing rate (E) for each site are shown; individual traces for two outlier (high rate) sites are not shown on the firing rate plot. B–E Individual sites (gray), plus sites 1–3 (red, blue, green) and the site from Figures  and (orange), with means (±1 SEM) in black.