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Launchscan skip scans

Hi everyone,
I wonder what the skip function in launchScan actually does. I assumed it was the number of pulses that would be skipped before continuing the script, but a brief test taught me that the script will continue on the very first (emulated) pulse.

I know that scanner usually performs a couple (typically 5) scans without sending a triggering pulse to stabilise the recording, but what is the point in informing the PsychoPy script about this number, when it has no significance for its functioning, as it just waits for the first pulse to continue? Or am I missing something here?

Thanks in advance,


Because not all scanners work the same way. Some scanners send a pulse on every single TR, some just on the initial TR, even if it will be a discarded disdaq image, and others only on the first “real” volume.

Yes, I realise that. But that still make me wonder what the skip command does. Is there any functional difference is setting it to 0, 5 or 100? In a little test script (have not tested it at the scanner yet) it continues after the very first pulse (i.e. me pressing the sync key on the keyboard)

To all future readers who wonder the same thing: I think I understand now. The ‘Skip’ command only applies to ‘Test’ mode, and allows you to match your test and scan setup in terms of timing. In ‘Test’ mode skip doesn’t do anything.