ReferenceError: screen_text is not defined

Online experiments
13

Try

if key_resp_4:
     if "backspace" in key_resp_4.keys:
          key_resp_4.keys.remove("backspace")
          if len(key_resp_4.keys) > 0:
               key_resp_4.keys.pop()
     elif "return" in key_resp_4.keys:
          key_resp_4.keys.remove("return")
          thisExp.addData("recall_resp", screen_text)
          continueRoutine = False
     screen_text = ''.join(key_resp_4.keys)