[pymvpa] [mvpa-toolbox] Fast ER design (Dr. Aguirre please help ; -) )
yarikoptic at gmail.com
Fri Jul 15 01:41:50 UTC 2011
Thank you Geoff and sorry for the delay with forwarding ;-)
On Wed, 13 Jul 2011, Geoffrey K Aguirre wrote:
> On Jul 12, 2011, at 3:15 PM, Yaroslav Halchenko wrote:
> > But what about the choice of ISI given
> > the contrast(s) and possibly pre-set TR: am I correct that there is no
> > other way to figure out an optimal stimuli duration and ISI given
> > the constraint of number of categories and run-time, besides exploring a
> > set of choices and selecting the one with best "efficiency"/"detection
> > power" ?
> Generally, the best design will be one in which the frequency of appearance of a given stimulus versus the null trials falls between 0.1 and 0.01 Hz. In the context of a Type1, Index1 sequence, all the stimuli (including the null) are repeated within permuted blocks. Therefore, the optimal stimulus-onset-asynchrony in seconds would be the one that causes a given stimulus to repeat, on average, every 30-60 seconds. If there are k stimuli (including the null-trial), this would suggest that the SOA should be about 30 / k seconds long.
> This analysis presumes that the neural response to a stimulus is a step function that does not decay while the stimulus is on the screen.
> Note that the power of these designs is increased by doubling the duration of the null-trials (See Appendix A of Aguirre 2007).
Yaroslav O. Halchenko
Postdoctoral Fellow, Department of Psychological and Brain Sciences
Dartmouth College, 419 Moore Hall, Hinman Box 6207, Hanover, NH 03755
Phone: +1 (603) 646-9834 Fax: +1 (603) 646-1419
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