title: PsychoPy: "Conditional" but random selection from list across two dimensions
body: <p>In my experiment, I am presenting images (faces) that are different across 2 dimensions: <strong>face identity and emotion</strong>. </p>
  
  <p>There are 5 faces displaying 5 different emotional expressions; making 25 unique stimuli in total. These only need to be presented once (so 25 trials). </p>
  
  <p>After I present one of the faces, the next face has to be different on only the emotion OR the identity, but the same on the other.</p>
  
  <p><strong>Example:</strong></p>
  
  <pre><code>Face 1, emotion 1 -&gt; face 3, emotion 1 -&gt; face 3, emotion 4 -&gt; ... etc.
  </code></pre>
  
  <p>1: is psychopy up to this task? I have mostly worked with the builder so far, except for some data-logging code, but I'd be happy to get more experienced with the coder.</p>
  
  <p>My hunch is that I would need to add two columns to the list of trials, one for identity and one for emotion. Then use the getEarlierTrial call somehow, but I pretty much get lost at this point.</p>
  
  <p>2: Would anyone be willing to point me in the right direction please?</p>
  
  <p>Many thanks in advance.</p>