The duration of an event should be the length you expect the neurons to be active. However, as Jonathan pointed out in the case of everything less than 1 (and up to possibly 2 seconds) the duration will have a small impact.

 

The difference between block/event-related designs is simply the duration of the stimuli (or more accurately the duration of the neual active). One other difference is that the rest periods are more similar in length in block designs and are thus longer. Roughly the cut off is 10-15 seconds. There are exceptions such as slow event-related designs.

 

I've done event-related designs with stimuli lasting 7 seconds before (search Burton, McLaren, blind on pubmed).

Best Regards, Donald McLaren
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D.G. McLaren
University of Wisconsin - Madison
Neuroscience Training Program
Office: (608) 520-0586
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