I suggest having your cue screen in a separate trial before the music and picture trial. By splitting them, the cue and music won't start simultaneously, however it will allow you to randomize the picture files.
- Under the audio event, the setting will be "Stop audio: when the trial ends"
Randomization will be done under the Trial Editor
- Under the Trial Editor, go to the Randomize tab
- Select Randomize the events in this trial
- At the bottom of the screen under, "Randomize All the Events in This Trial," check Except the first one
This is done so the audio event does not get randomized.