An alternative to using the ! symbol is to define -1 as a valid response code on your trial. That way, only trials on which -1 is given as an option will continue automatically after the maximum time has been reached. Like other codes, if -1 is listed first, then it will be considered the correct response. This option can also be combined with the ! method if you want to define no
response as correct but have automatic continuation regardless of the response. You can think of -1 as an actual "no response" button which is pressed at the
maximum response time.