randomising stimuli without repeats

I have a simple experiment which should run like this:

  1. cue
  2. prime (picture of a face presented for specified time, no response required)
  3. mask (a Chinese ideograph to be rated by the participant. Moves back to cue once response made).
  4. Inter trial interval (ITI)

I have 40 face primes (each of which MUST be presented per participant) thus 40 trials in effect.

I need each participant to ‘see’ every face prime BUT the order in which they are presented should be randomised per participant.

I’ve tried creating 1 trial which uses two stim lists with items selected from the corresponding folders; one for faces and one for the ideographs. However, some items from the faces folder are being repeated (it doesn’t matter if this is the case with the ideographs) meaning that not all 40 faces are being shown per participant, despite checking the ‘randomise per participant’ box in the block editor.

I have since created 40 trials linked uniquely to each face prime set up as a unique event (thus 40 trials,each linked to 1 face event (selecting 'same file every time) plus cue, Chinese ideograph and ITI. Still getting repeats of the face events.

I have tried adding code values to each face event (presented, ‘yes’ or ‘no’, set to no.). In the feedback tab I have specified that code values should be changed to ‘yes’ always after the event and the remaining events in the trial should be presented. I have then requested that trials should be limited to those marked as ‘no’ in the block editor as well as that the number of events should be 40.

I hope this makes sense - basically I need participants to see all 40 face primes once, with no repeats. How can I achieve this? I have spent too many hours on this!

It would be helpful if you could post your experiment. Please post as an Experiment Package, which is found under the File menu.

Also, what is the exact number of Chinese ideographs you will be using?

Hi Monika,

I’m using a pool of 120 ideographs so that each participant hopefully sees a different face-ideograph pairing in the 40 trials

experiment package

Hi Monika

I’ve attached 2 versions of my experiment. The first is set up as 1 trial (novel images) which should take a image from the face file at random, and an image from the Chinese character file at random. As there are 40 faces, I’ve edited the block to show only 40 trials.

Although no response is required for the face file, I’ve had to check the ‘record and save response’ box in order to see which face has been presented in the output. Unfortunately this means that there are 2 separate lines for each trial but it’s not a major issue. However, as you will see from the corresponding output file, faces are being repeated (e.g. F3A.gif appears at lines 9 and 37 whilst M6A.gif appears at lines 13, 63 and 67).

I’ve also attached a version where I have set up individual trials which link to a specific face file under ‘events’. For example, trial F1A links to event F1A.gif. I hoped this would overcome the repeating problem but alas this hasn’t worked. Again, as you’ll see from the output, faces are being repeated (e.g. F2D.gif appears at lines 5 and 14, F8D.gif appears at lines 12 and 18).

The faces and Chinese character folders are also attached as zip files.

Many thanks for your help.

as1trial.sl4 (44.8 KB)

as1trial.txt (12.7 KB)

as20trials.sl4 (26.1 KB)

as20trials.txt (5.3 KB)

sorry - should also point out that the second version only contains 20 rather 40 trials to save me some time while I get this sorted!

I could not run the experiment because the stimuli were not attached. Please post as an Experiment Package, which is found under the File menu.