presenting events from a list

When runing trials that pick events from a list I get some of the events repeated and the number of trials in the block increased for no apparent reason.

Any ideas?

This sounds like confusion over what happens when you use a stimulus list. When you use a stimulus list, the trial gets duplicated–once for each stimulus in the list. Basically, when one event in a trial uses a stimulus list, that makes the trial a template for how to create additional trials. You can see what SuperLab will do by selecting “Expand Events that use Lists…” from the “Experiment” window. This will create a copy of your experiment, showing exactly what trials and events will be generated when you run the experiment.

As a simple example, you can check out the Letter Rotation Experiment.