PPSH (Pre/Post Stimulus Histogram) is a group of programs that, together, compute the autocorrelation and crosscorrelation functions for two concurrent sequences of events (e.g. , two simultaneously recorded neuron spike trains or one spike train and one stimulus series). PPSHDATA compiles the intervals in real time as a single mixed and labeled, double precision list of indefinite length. Intervals are numbered sequentially and stored, along with relevant identifying data, on a Linc Tape train file.

PPSH1 reads a selected interval list and generates either a first order interval distribution or an n order correlation (expectation density) function. The histogram is displayed and may be plotted along with a calibrated scale. Total event counts and histogram areas are typed out as octal numbers.

HISTDUMP temporarily saves the histogram in a reserved four block section of Linc Tape on unit 0 for subsequent printout by TAPEDUMP (DECUS 12-2).