The smaller the EPSP component the more likely the AP component will fail.

The first row (A-D) shows the individual spike waveforms for 4 different amplitude ranges for the EPSP component for a single unit (Unusual unit; BF = 1.15kHz). Dotted lines are for visual guide only. For the lowest amplitude (A) the AP-component occurs only occasionally whereas for the highest amplitude (D) the AP-component never fails. This is summarised in the figure in the second row (E). The EPSP-AP interval decreases with increasing EPSP-amplitude (F). G shows the distribution of EPSP-amplitudes when accompanied by an AP-component (red bars) or not followed by an AP component (i.e. failures–blue bar). The dotted black line is the ratio of failures. At high EPSP- amplitudes the unit doesn’t fail.