Mean (SEM) PPI values as a function of the ISI. Three prepulse conditions were compared: 1) a 180° change in the location of a wide band noise (WBN) from right to left; 2) the offset of WBN that had been presented in the right hand speaker, the ES being presented in quiet for prepulse trials and in a background of WBN for control trials; and 3) the onset of the WBN in the left hand speaker, the ES being presented in a background of quiet in control trials and in the presence of the WBN for prepulse trials. (Experiment 1, n = 9, 11, and 6).