try
    screens = Screen('Screens');
    whichscreen = max(screens);
    [w, rect] =Screen('Openwindow', whichscreen);
    disc = CenterRect([0, 0, 20, 20], rect);
    Screen('FillOval', w, 0, disc);
    Screen('Flip', w);
    space = KbName('space');
    firsttouch = 0;
    WaitSecs(1)+rand*2;
    t0 = GetSecs;
    for i = 1:200
        Screen('FillOval', w, 0, [disc(1)+i, disc(2), disc(3)+i, disc(4)]);
        Screen('Flip', w);
        [keyIsDown, secs, keyCode] = KbCheck;
        if keyCode(space) == 1 && firsttouch == 0
            rt = secs-t0;
            firsttouch = 1;
        end
    end
    Screen('CloseAll');
catch
    Screen('CloseAll')
    rethrow(lasterror)
end