Changing keys in an experiment

I am writing to inquire about changing the response keys for one of the experiments in my survey. 
When I run the Mental Rotation experiment, I use the mouse to click on the right image that matches the target image when rotated. However, I want to change the response key from being input from the mouse to input from the right and left arrows keys.

I am able to assign to keys the arrow keys right and left so the task knows to anticipate those keys being pressed. My problem is I am unsure how to change the "readkey @3 20000" command. How do I access the table with all the images and their associated answers so that readkey can evaluate the left and right arrow keypresses instead of waiting for the click?


Thanks!