====== Psychtoolbox ======

===== Timing =====

It is necessary to log onset timing of stimuli for [[:mr:analysis|first level analysis]], and important to be aware of how time is recorded.
==== Docs ====
  * http://psychtoolbox.org/docs/Screen-Flip <code>
Flip (optionally) returns a high-precision estimate of the system time (in seconds)
 when the actual flip has happened in the return argument ‘VBLTimestamp’.
 ....
‘FlipTimestamp’ is a timestamp taken at the end of Flip’s execution.
 Use the difference between FlipTimestamp and VBLTimestamp to get an estimate of 
 how long  Flips execution takes. [in what units!?]</code>
  * [[https://github.com/Psychtoolbox-3/Psychtoolbox-3/wiki/FAQ%3A-Explanation-of-Flip-Timestamps|PTBs Timestamp FAQ]] <code>
FlipTimestamp, which is not much more than a GetSecs taken at end of Flip, can and
 often will be earlier than StimulusOnsetTimestamp, as flip processing usually already
  completes while the display is still in VBLANK, preparing for display of the new stimulus 
  frame, that's why StimulusOnsetTimestamp == VBLTimestamp > FlipTimestamp.

</code>
==== Examples ====

<code=matlab>
w = Screen('OpenWindow', 0, [0 0 0], [0 0 800 600]); 
for i=1:3; 
   [vts(i,1), vts(i,2)] = Screen('Flip',w); 
   vts(i,3) = GetSecs(); 
end;
sca
format longG
vts,
</code>

On linux (+ octave), ''GetSecs()'' as well as Flip's ''VBLTimestamp'' and ''StimulusOnsetTime''
are in epoch seconds.

<code>
vts =

       1738935521.40479        1738935521.40479       1738935521.405101
       1738935521.421465       1738935521.421465      1738935521.421387
       1738935521.438137       1738935521.438137      1738935521.438507
</code>


On windows, these numbers or clock ticks since start up. Similar to [[:mr:task:EPrime]].

<todo @foran> windows output </todo>