findcontrolstimulus

  FINDCONTROLSTIMULUS - find the corresponding 'control' stimulus for a set of stimuli

  CONTROLSTIMNUMBER = FINDCONTROLSTIMULUS(STIMID, CONTROLSTIMID)

  Given an array of STIMID values that indicate stimulus presentation, and an array of
  CONTROLSTIMID value(s) that indicate the identification number of a 'control' stimulus
  (such as a blank screen), this function finds the control stimulus id that corresponds
  to each STIMID presentation.

  If the stimulus presentation is regular (stimuli are presented from 1...numstims in 
  some order, followed by a second presentation of 1...numstims in some order, etc, with only
  a single control stimulus), then the control stimulus for each stimulus is the control
  stimulus that corresponds to the same stimulus repetition.

  If the stimulus presentation is not regular, then the 'closest' control stimulus is taken 
  to be the control stimulus; if 2 stimuli are equally close, then the first stimulus will be taken
  as the control stimulus.

  CONTROLSTIMNUMBER will always be returned as a column vector.

  See also: STIMIDS2REPS

  Example:
    stimid = [ 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 ];
    cs=findcontrolstimulus(stimid,3)'
       % cs == [ 3 3 3 6 6 6 9 9 9 12 12 12 15 15 15 ]