Here are two versions of a self-paced N-back task I have used extensively in my lab.
The first goes from 0-back to 2-back using orthographic stimuli.
The second uses visual stimuli (named for letters--since I based this on the orthographic version) and also runs from a 0-back to 2-back. I have included 2 sample stimuli. Our pilots suggested that using contiguous dot patterns and no more than 2 dots ensured non-random performance. If anybody wants the rest of the visual stimuli I will mail them or post them.
Response is via mouse button press in both.
I will post a reference for the task once I get one in press.
Lori Altmann
University of Florida