drawISI(params, window, isi_dur)
DRAWISI is called by various easyFunctions to display an inter-stimulus interval (ISI) after a trial is complete, consisting of a fixation cross (plus character) displayed in the centre of the screen using the preferred session font display information. This function can also be called directly from experiment code, although handing control of ISIs to easyFunctions is advantageous, as it allows for trial bookkeeping events to occur during rather than before the ISI itself, yielding more exact trial offset times.
All inputs are required inputs: params: structure of experiment parameters as supplied by easyLaunch window: window token, also supplied by easyLaunch in tokens.main_window isi_dur: length of the ISI in seconds