What experiment in a simple decision task should we run to obtain one million trials?
I like this idea! I think the task should be one where the data could be used by many analytic tools. Hence, the data would not only be beneficial for one particular question, for example parameter estimations, but also for other tools such as Systems Factorial Technology (see Townsend &amp; Nozawa, 1995), which provides a deeper understanding of the underlying cognitive sub-processes architecture, and other interesting information such as the process' capacity.

I suggest that the task at least respect a double factorial paradigm. This design is very simple: you have four conditions in a 2 x 2 design, where you vary two variables. It could be any variable, the only restriction is that you have to vary them independently one from another. In other words, each variable should reflect a cognitive sub-process. In one condition, both variables are in scenario where the sub-process should work very effectively (or optimally). In an other condition, both variables are in a scenario where the sub-process should work less effectively (or sub-optimally). And in the two remaining conditions, one variable works optimally and the other sub-optimally, and vice-versa.

As for the very details of the task, such as the stimuli that will be used and the specific variables, I do not have preferences. Letters are very manipulable, but they do carry semantic (more or less). Abstract stimuli could work. We could play with color, shapes, complexity, etc. At Psychonomics this year, they were many experiments which have use this design.

Reference for citation:
Townsend, J. T. &amp; Nozawa, G. (1995). Spatio-temporal properties of elementation perception an investigation of parallel, serial, and coactive theories. Journal of Mathematical Psychology, 39(4), 321–359. doi: 10.1006/jmps.1995.1033