Interstimulus interval

The interval construct provides a timed interval for use on the trials timeline with the following features:

  • explicit capture of start time, end time and (actual) duration.
  • ability to offset the start of the interval in relation to the ending of another item on the trials timeline.
  • variable duration intervals.
  • intervals defined by factors and levels.
  • used at the start of the trials timeline it acts as an interval between the end of one trial and the onset of the next (which is, strictly speaking, not an intertrial interval (ITI) as an ITI is measured from the onset of one trial to the onset of the next, thus including the duration of the trial itself).

Creating an interstimulus interval

Interstimulus intervals can be added to trials timelines. Click New item, select Interval from the type list and select one of the following creation options:

  • New: create a new interstimulus interval.
  • Copy: copy another interstimulus interval from the current study.
  • Clone (from a different trial): clone an existing interstimulus interval from another trial.

Editing interstimulus interval

Click anywhere along its row (Figure 1) to open the editor.

Figure 1. Open construct editor (Psychstudio)

Figure 1. Open construct editor

Editing timing

In edit mode, the following properties can be set via the timing table:

  • Start mode
    • Fixed: start time will be measured from the beginning of the trials timeline.
    • Offset from previous item: start time will be measured from the end of the previous item on the trials timeline. If there is no previous item, or the timeout of the previous item is set to nil(infinite), then start time will be measured from the beginning of the trial.
  • Start time (ms): when to initiate construct.
  • Duration mode
    • Fixed: duration will be a fixed time period.
    • Random: duration will be a random time period bound by minimum and maximum values.
    • Factor: duration will be a randomly chosen level from the factor selected.
    • Level: duration will be set to the value of the chosen level.
  • Timeout (ms): duration of construct presence.