The reason that the responses are not being registered is because the audio event is set to end “Immediately after the event is presented” under the Input tab. To record all responses you should change this to end “Only after a time limit.” However, you will want to choose a time limit that is the same duration as the audio clip (or the same as the longest-running clip). Therefore, it might be best to use audio clips that are all the same length (for example having a duration of 10 seconds each).
Another alternative would be to use the “Variable” option on the time limit instead of “Fixed.” As long as the trials are not randomized in this experiment, you could create a Trial Variable with these levels:
These match the duration of clips p21 through p25. Then set that trial level to “Sequential” (so that the trial levels are not selected at random). You can find the Trial Variable option under the Experiment menu.