Tutorial: Standard Priming (19/21)


…\DirectRT\samples\4 applications\standard priming\priming.csv


This sample illustrates a standard priming paradigm with very short priming intervals. Open the input file and notice that the entire session is performed by randomly drawing text stimuli from text files located in the experiment's stim folder. Remember that $ instructs DirectRT to randomly select from a StimList without replacement until all the stimuli have been used.

Now open the stim folder to view the StimLists that are accessed: pos.txt, neg.txt, and neu.txt. Note that the prime is both forward and backward masked by using two different text stimuli: ~XXXXXXXXXX, and ~&&&&&&&&&&. To change the masks, just change the characters.

As an exercise, play with the display times. Currently, the first mask is displayed for 500ms and the second mask for 200. Try changing the mask characters and see what effect that has on your ability to view the prime.

See also that the order of the valid keys is different for the trials that have positive versus negative targets. This is done because the first key defines what is the "correct" response. This is not required but it is sometimes useful for data analysis becasuse whether or not the "correct" key was pressed is written to the data file.

Note also, that this input file utilizes Optional Fields. In this case, 2 additional columns have been inserted, !prime and !target, that contain stimulus factor information. These are handy for data analysis and are included in the short version of the data file.

Another important thing to note is the stimulus duration of the prime. It is currently set to 10ms. Remember that DirectRT displays stimuli for a number of screen display cycles. If your monitor takes 16ms to refresh its screen, then this is the minimum a stimulus can be displayed. However, you can enter whatever value you want. DirectRT will round the display time to the nearest screen refresh. Actual display times can be viewed in the log data file. This way you can see if your system is capable of the display rates you are requesting.