# [FieldTrip] Calculate amplitudes and latencies

Stephen Politzer-Ahles politzerahless at gmail.com
Fri Oct 5 18:45:00 CEST 2012

Hi Daria,

I'm not aware of a built-in FieldTrip function that does these things, but
since it involves basic math you can do it with MATLAB functions (e.g.,
max() to find the maximum amplitude, and find() to get the latency of that
point).

However, see Steve Luck's (2005) *An Introduction to the Event-Related
Potential Technique* for a discussion of why peak latency and peak
amplitude measures are often not good. I would recommend using mean
amplitude (there is an example of how to do it in FieldTrip at
http://fieldtrip.fcdonders.nl/tutorial/eventrelatedstatistics#t-test_with_fieldtrip_function,
although it's also straightforward to do just in MATLAB) and fractional
area latency as your measures. Or, better yet, you could just do a cluster
test, which will tell you where and when significant clusters are without
your having to try and measure latencies (
http://fieldtrip.fcdonders.nl/tutorial/cluster_permutation_timelock).

Best,
Steve

Message: 1
> Date: Fri, 5 Oct 2012 17:10:31 +0200
> From: Daria Laptinskaya <daria.laptinskaya at googlemail.com>
> To: FieldTrip discussion list <fieldtrip at science.ru.nl>
> Subject: [FieldTrip] Calculate amplitudes and latencies
> Message-ID:
>         <
> Content-Type: text/plain; charset="iso-8859-1"
>
> Dear fieldtrippers,
>
> does anyone know how I can find the peak maximum of an erp?
> And how to calculate the latency until the maximum?
>
> Timelockanalysis and the grand average of all erps are already done.
>
> Best,
> Daria
>
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