Requiring 2 button responses within event

I am designing an experiment in which subjects will be responding with 4 buttons on an RB-834 response pad.
They will be required to respond by making two simultaneous responses, one with each hand (pushing either 2 upper buttons at the same time, or two lower buttons at the same time).

Ideally, I would like to present feedback so that if a subject ever responds with only 1 hand (ie., only one button is pushed) or if the time elapsed between the first button being pushed and the second button being pushed is too long (greater than 50ms), there is some sort of error feedback displayed, to encourage consistent, simultaneous, two-handed responses.

To my knowledge, Superlab can only be set to look for a single button press response. Is there any way that I can require two button presses, where it does not matter which was first, but once a response has been selected, a specific response must then also be selected very rapidly?

To try and hack around this problem I have made a simple program (attached) and tried to make an event loop with feedback. Such that feedback for the first event has 4 possible responses (buttons 1-4) with the feedback:
If button 1 is pressed, start event that looks for button 3
If button 3 is pressed, start event that looks for button 1
If button 2 is pressed, start event that looks for button 4
If button 4 is pressed, start event that looks for button 2

The second event then begins based on the initial response and ends at a correct response, or after a time limit.
I then have feedback on that second event stating that:
If the response is correct (e.g, the button that it was “looking for” was pressed, present event (which is text that says GOOD)
If there is no response after the events time limit has elapsed then: present event (that event is a text event that says ERROR. )

When I run this set-up the first response leads to the proper second event, but the correct response to the second event doesn’t seem to trigger any of the feedback, and the next trial just starts.

I have also tried to make trial rules based on the last participant response, but as I don’t know what order the response buttons will be pressed in, this just leads to an endless loop!

If you have any suggestions please advise!


TestProgram.sl5 (6.7 KB)