Indicates whether a button was released or pressed on a Cedrus Response Pad.
<xid>
This property returns 1 if the button was pressed, or 0 if the button was released or the event was generated from a TTL signal rather than a button.
The following defines any button press as a valid response:
<trial example>
/ isvalidresponse = [xid.responsebox.lasteventaction == 1]
</trial>