Hello,
Yes, I got these values from FEAT (please see attachment; this example is
for 250 volumes). The Efficacy is the right most value in the diagonal (I
didn’t consider the others) and the Mean Effect Required is the mean of
Ci’s.
Kind regards,
Jose Paulo Santos
On Fri, 30 May 2008 08:19:03 +0100, Steve Smith <[log in to unmask]>
wrote:
>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
>Associate Director, Oxford University FMRIB Centre
>
>FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
>+44 (0) 1865 222726 (fax 222717)
>[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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