Figure 7. Large numbers of sites are needed to encompass the complete frequency range.

A. Single trial neural activity evoked by each of nine consonant sounds, organized by characteristic frequency and shown without any smoothing. As compared to the responses by 200 sites (see Figure 2), these responses are less distinct even without averaging or smoothing. 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. Although this smoothing does highlight evoked activity over spontaneous firing, responses from 60 sites are not sufficient to produce clearly distinguishable patterns, especially as compared to the responses from 200 sites (see Figure 2).