FIG. 6.

Comparison of activation widths for equal peak spike rates. Sustained activation widths versus peak spike rates are plotted for a monopolar stimulus channel (MP 5) at levels from 0 to 10 dB SL and for a 60 dB SPL, 8.5-kHz acoustic tone, which produced a peak excitation at roughly the same inferior colliculus depth. The acoustic tone evoked a peak spike rate of 83 spikes/s and an activation width of 250 μm. The monopolar activation width (114 μm) at that same peak spike rate was found by interpolating between the points at 0 dB SL and 2 dB SL. This procedure was also used for comparing acoustic to bipolar stimuli, and for comparing monopolar to bipolar stimuli at equal peak spike rates.