How do I set a certain duration for a stimuli presentation?

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I have a small white spot presented on a grey background. I would like to have the spot stimuli on for 2 secs and then switch to only the grey background for 5 secs. I need help in setting the duration for each stimuli presentation. Also, I need the timing to be as accurate as possible.
  1 Comment
Chris McComb
Chris McComb on 4 Mar 2015
Edited: Chris McComb on 4 Mar 2015
Are you after something like this?
% Number of stimuli
n = 5;
for i=1:1:n
% Plot the spot
h = plot(x_spot, y_spot);
% Pause for 2 seconds
pause(2);
% Delete the spot
delete(h);
% Wait for 5 seconds
pause(5);
end

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Answers (1)

Jos (10584)
Jos (10584) on 4 Mar 2015
I suggest you do not use delete and pause. Here is an alternative
x = [1 2 6 8 3] ;
y = [7 1 3 9 6] ;
stimtime = 1 ; % time to show a spot
waittime = 2 ; % time to wait between spots
% create a plot
clf ; % clear current figure
h = plot(NaN,NaN,'bo','markerfacecolor','r') ;
set(gca,'xlim',[0 10],'ylim',[0 10]) ;
for k=1:numel(x),
set(h,'xdata',x(k),'ydata',y(k),'visible','on') ;
drawnow ;
tic ;
while toc < stimtime, end
set(h,'visible','off') ;
drawnow ;
while toc < stimtime+waittime, end
end
  2 Comments
Kathryn Fransen
Kathryn Fransen on 6 Mar 2015
Thank you for your answer. I see how tic and toc work for the example you presented, however, I am having a hard time getting it to work with my stimuli code. I have attached the stimuli code (I use the psychophysics toolbox, so I am not sure if this function will work without the toolbox?). I need to add a timing element to this code allowing for the spot image to be presented for 2 seconds, and then I will add in code for a blank grey background for 5 seconds. I then would like to make this loop 5 times. Do you have any suggestions on how I can use tic and toc with the stimuli I am working with? I have tried many things, but can't get anything to work.
Jos (10584)
Jos (10584) on 7 Mar 2015
I suggest you take a look at the help of the toolbox, and perhaps ask your question over there. This seems to be a very basic problem more related to psychophysics than to matlab itself.

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