Fig. 5.

ISI histogram and joint interval histogram of the afferent spike train shown in Figure 1 (column A) and surrogate spike trains obtained from the afferent data (columnsB–D). A1–D1, Show the first-order ISI histograms I₁(j), and A2–D2 show the joint interval histogram I(j₁, j₂) of adjacent ISIs. Size of thecircle is proportional to joint probability. B, The binomial spike train matches the mean ISI $\overline{I}$₁, but it does not match either the ISI or joint ISI distributions. C, The zeroth-order Markov spike train (M₀) matches only ISI, but not the joint interval distribution. D, The first-order Markov spike train (M₁) matches both the ISI and joint ISI of the afferent spike train. ISI sequences for B and M₀ are renewal processes, whereas M₁ is a nonrenewal process.