[Eeglablist] erp analyses with unequal groups

[Christina Karns]

There are two methods to send a TTL pulse from E-prime. If you use the
writeport command there can be a delay between the stimulus and the
trigger. Instead, use the OnestSignalEnabled or OffsetSignalEnabled
commands to send the pulses which will be tied to the actual presentation
of the stimulus object. There is more about this in the critical timing
chapter of the E-prime manual. Other sources of delays are peripherals (a
non-optimal soundcard, USB ports etc.) Contact E-prime support for more
information.

**********************************
Christina M. Karns
Knight Lab
Helen Wills Neuroscience Institute
University of California, Berkeley
-----------------------------------
Tel: (510) 643-9744
Fax: (510) 642-1196
Mail: 132 Barker Hall
      Mail Code 3190
      Berkeley, CA 94720
***********************************

On Mon, 14 May 2007, [iso-8859-1] Kéfil LANDOU wrote:

> hello,
 I'm using Eprime to put a marker in my eeg data. When Eprime receive a ttl through a parallel port, it sends the corresponding marker to biosemi. But I have a delay in this operation. Does anyone know how can I measure this delay? Thank you!

Mohamed Kéfil LANDOU
M-5108
tél: (514)340-5121 # 7131
École Polytechnique de Montréal

----- Original Message ----
Wrom: HYUCDDJBLVLMHAALPTCXLYRWTQTIPWIGYOKS
To: Rob Anderson <roba at unm.edu>
Cc: eeglablist at sccn.ucsd.edu
Sent: Friday, May 11, 2007 6:27:27 PM
Subject: Re: [Eeglablist] erp analyses with unequal groups






Rob Anderson wrote:




  Hi. I am currently conducting
erp group comparisons of oddball and gonogo data for groups that have
been defined based on a cluster analysis of personality trait
variables. I would like to compare the erps for these
different clusters (4 of them), but have only been able to compare
groups of equal size (i.e., taking a subsample of the clusters). I do
not have the Matlab Statistical Toolbox installed, so the statistical
analyses are defaulting to the nonparametric permutation tests.




These tests are usually more rigorous as they do not rely on the
probability distribution of the data.






   If I install the statistical
toolbox, will that enable me to make erp comparisons for unequal groups?




Yes, it will. Note that you can still set a threshold p-value using the
parametric statistics in EEGLAB. The only thing EEGLAB will not do is
to compute the exact p-value itself as this is the part that requires
the statistics toolbox (fcdf() and tcdf() functions).




   If not, is there some other way to
get statistics based on unequal groups? If not, is there a relatively
easy way to do a bootstrap sort of analyses where the smaller groups
are formed with different membership and then tested statistically to
see if there is a difference within a given group when there are
different members in that group?




I am not sure I understand clearly what you want to say. The
statistical functions in EEGLAB can support group of equal size
(usually paired) or group of unequal size (unpaired). The command line
output indicates you what type of statistic is being used by default.



Best regards,



Arno




  Thanks for any help you can give me
with this.  Rob







  Rob Anderson, Ph.D.

Research Assistant Professor


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