Flip timing test

run_fliptest.m

function [expt] = run_fliptest()

%% setup
ntrials = 50;                % number of trials per block
stimdur = .1;                % time stim is on screen, in seconds
interstimdur = .05;            % minimum time between stims, in seconds
interstimjitter = .05;         % maximum extra time between stims (jitter)

% psychtoolbox
AssertOpenGL; % Running on PTB-3? Abort otherwise.
while KbCheck; end; % Wait for release of all keys on keyboard

%% experiment
try
    % setup screen
    screens=Screen('Screens');
    screenNumber=max(screens);
    win = Screen('OpenWindow', screenNumber);
    Screen('FillRect', win, [0 0 0]);
    Screen('TextFont', win, 'Arial');
    Screen('TextSize', win, 50);
    
    % display experiment text
    WaitSecs(1);
    for t=1:ntrials
        DrawFormattedText(win,'test','center','center',[255 255 255]); % put text in buffer
        rectimes(t) = GetSecs;
        schedtimes(t) = rectimes(t) + .1; % schedule flip
        [vbltimes(t), stimonsettimes(t), fliptimes(t), missed(t), beampos(t)] = Screen('Flip',win,schedtimes(t)); % draw text to screen
        WaitSecs(stimdur);
        Screen('Flip',win); % clear screen
        WaitSecs(interstimdur);
        WaitSecs(rand*interstimjitter); % add jitter
    end
    
    [monitorFlipInterval,nrValidSamples,stddev] = Screen('GetFlipInterval',win);
    Screen('CloseAll');
    
catch
    Screen('CloseAll');
    psychrethrow(psychlasterror);
end

% plot differences in scheduled vs. measured times
figure;
plot(vbltimes-schedtimes,'b'); hold on;
plot(stimonsettimes-schedtimes,'r--');
plot(fliptimes-schedtimes,'g.')
legend({'VBLTimes - When', 'StimOnsets - When', 'FlipTimes - When'});
xlabel('trial number'); ylabel('ms past scheduled time')

% output
expt.schedtimes = schedtimes;
expt.vbltimes = vbltimes;
expt.stimonsettimes = stimonsettimes;
expt.fliptimes = fliptimes;
expt.rectimes = rectimes;
expt.missed = missed;
expt.beampos = beampos;
expt.monitorFlipInterval = monitorFlipInterval;
expt.nrValidSamples = nrValidSamples;
expt.stddev = stddev;