How to collect reaction times in a RSVP detection task

Hi All,

I'm using Psychtoolbox to run an RSVP detection task, but I have a problem in collecting reaction times (RT) while the RSVP sequence is running. What the code do at the moment is to present 16 stimuli in sequence, with one target presented in random position among distractors. Stimulus duration is 133 ms with an inter stimulus interval (blank screen) of 367 ms:

vStimuli = [2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1]; %stimuli vector, 2=target stimulus
vStimuli_shuffled = randperm(numel(vStimuli))

for i = 1:nStimuli % number of stimuli
            if Stimuli_shuffled(1,i) == 1 %DISTRACTOR
               Screen('FillRect', window, [255 255 255], stimulus_position);
               Screen('Flip', window);
               WaitSecs(durStim);
            elseif Stimuli_shuffled(1,i) == 2 % TARGET
               Screen('FillRect', window, [0 0 0], square_position); 
               Screen('Flip', window);
               WaitSecs(durStim);
            end

              Screen(window, 'FillRect', [128, 128, 128]); % Blank screen (ISI)
              Screen('Flip', window);
              WaitSecs(durISI);
  end

The code I use to record RT is:

for i = 1:nStimuli % number of stimuli 
           if Stimuli_shuffled(1,i) == 2 %TARGET
              Screen('FillRect', window, [0 0 0], stimulus_position);
              [starttime]= Screen('Flip',window);
              endtime=KbQueueWait();  % Wait a Keypress
              StimTime=GetSecs; 
              while (StimTime-starttime)<=StimTime
               [KeyIsDown, endtime, KeyCode]=KbCheck;
               if KeyIsDown
                 RT= round(1000*(endtime-starttime)); %Compute reaction time in second
                 PressBt=KbName(KeyCode);
                 break;
               end
          end

The problem is that this code wait for a key press to present the next stimulus, while I want a fixed timing in the RSVP presentation, and to record any keypress from the onset of the target stimulus to the next stimulus (500 ms). Moreover, I don't want that the keypress determines a short stimulus or ISI duration.

Any suggestion?