Hi - I'm not sure where these Efficacy numbers come from - not from
the FEAT efficiency calculations I think? I'm not sure what these
are.......
Cheers.
On 28 May 2008, at 19:10, Jose Paulo Santos wrote:
> Hello,
>
> I'm trying to establish some kind of method to achieve to the optimal
> length in event-related paradigms.
>
> I designed a paradigm were I collected 500 volumes. The participant
> reported at the end that he was exhausted. So I know that 500
> volumes were
> too much in the human perspective. By the end of the session, the
> probability of the participant still being concentrated in the task
> was
> quite low.
>
> With fslsplit and fslmerge commands, I reconstructed several files,
> until
> 250 volumes, and I analyzed each of them with Feat. The numerical
> data was:
>
> Volumes Efficacy Mean Effect Required
> 250 0.253 0.938
> 312 0.241 0.847
> 375 0.251 0.752
> 438 0.245 0.740
> 500 0.243 0.722
>
> The rule of thumb for the Efficacy determines that it must be more
> than
> 0.200, and it was for all volumes. The rule of thumb for the Effect
> Required determines that it must be less than 0.800. This
> requirement is
> true only for 375 volumes or more. When this data is plotted, it seems
> that there aren’t significant increases in the Effect Required for
> more
> than 375 volumes. This is in line when the maps are analyzed: the 375
> volumes map has activations more intense (just a bit) and more
> extended
> (just a bit) than the 438 and 500 maps. So, 375 volumes would be the
> optimal length (and duration) of the session. If there is some
> clearance,
> it would be better to increase the inter stimulus interval (null
> event)
> than to show more stimuli.
>
> Is this acceptable? Why the Efficacy didn’t change so much? Increasing
> ISIs would increase the Efficacy?
>
> Thanks in advance,
> Jose Paulo Santos
>
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Stephen M. Smith, Professor of Biomedical Engineering
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