Phantom responses being recorded by Lumina 3G (using PsychoPy)

Hi there,

I have a somewhat weird problem that I’m hoping someone could help me with! We are using the LS-Pair button boxes with the Lumina 3G controller for an fMRI experiment, with stimuli that are presented via PsychoPy3. The pyxid library works well mostly, and accurately records the response and timing. However, we are also getting phantom responses in that when the participant does not need to respond (i.e., no buttons on the boxes are pressed at all), PsychoPy still records ‘3’ as the response for every single trial in which there is meant to be no response! When the participant does respond (i.e., a button is pressed), then PsychoPy records that response instead (one of ‘0’ or ‘1’ or ‘2’ or ‘3’). So the biggest problem is that we cannot distinguish the correct ‘3’ response (as in the participant pressed that button) from the phantom ‘3’ responses (whenever no response is recorded).

The strange thing about this is that when we run the exactly same experiment without the scanner running, this does not happen (as in there are no phantom responses of any kind, and for the non-response trials, the responses get recorded as ‘None’, which is correct). I was wondering if anyone knew why this might be at all? We’ve tried running the experiment with the screen/hardware set-up away from the bore of the scanner (in case of signal interference) and nothing ever changes the phantom responses - except when the scanner is not running.

Any help or advice would be greatly appreciated - thank you in advance!

PS - our scanner is a Philips Ingenia CX T MRI.