Figure 5. A Gaussian filter was necessary for highlighting evoked activity.

A. Single trial neural activity patterns in A1 without any smoothing. The first 40 ms of average evoked activity from each site is organized by characteristic frequency. Each consonant evoked a unique pattern of activity such that each group of neurons fire at a different latency depending on the characteristic frequency of the group. B. Average activity over 20 trials plotted without smoothing. Red lines mark the onset response of each frequency group. C. The same neural activity plotted in panel B after a Gaussian filter has been applied to the spectral dimension. We used a filter with a half width of 15% of the total number of sites. This ensured that spontaneous activity is not as influential on the classifier as evoked activity.