[open] Multiple correct button presses
I am currently making an IAT in Open Sesame in which there are two categories of images. After each button press, participants get the next image if the button press was correct, but a feedback-error-screen (sketchpad, show if [correct] = 0) in case they made a mistake. For one category of images, the correct response is either the 'z'-key or the 'm'-key. No problem in this case. However, the problem lies in the second category of images. In this category, participants can press both the 'z'-key or the 'm'-key and both responses are correct.
I have tried to code this in the correct_response variable, but don't know what to use. If I use "z;m", then both key responses are considered to be wrong. If I leave it open, both response keys are wrong too. However, in the category of images where only one response key is correct, there is no problem. I only get the error screen in case of a wrong answer.
Long story, short question: Is there a way to set two keys as the "correct_response"?