[Eeglablist] Error STUDY: Cannot compute ERSPS because datasets do not have the same number of data points

[Bethel Osuagwu]

Hi Nynke,
>From your explanation, your conditions have different epoch lengths. One cause of this is that you did not supply the same epoch time length when you epoched your data 

1: Use pop_epoch() to reduce the length of the longer ones to match the length of the shorter ones

2: Re-epoch your data making sure that you supply the same epoch time for all conditions

Bethel
________________________________________
From: eeglablist-bounces at sccn.ucsd.edu [eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Laan, L.N. van der (Nynke) [L.N.vanderLaan at uu.nl]
Sent: 14 November 2013 14:26
To: eeglablist at sccn.ucsd.edu
Subject: [Eeglablist] Error STUDY: Cannot compute ERSPS because datasets do not have the same number of data points

Hello all,

I am using EEGlab to calculate and plot grand mean ERP’s (over multiple subjects) for two conditions. However, when I precompute the channel measures I get a message saying: ‘Cannot compute ERSPS because datasets do not have the same number of data points’. Afterwards I am not able to plot the channel measures (nothing happens) so I guess that the channel measures were not precomputed.

Some background information: The input datasets for the study are epoched (and preprocessed/filtered/etc.) so for each subject I have two files (Subject1_conditionA and Subject1_conditionB). I have not performed ICA.

The only thing that I want is an ERPimage from both conditions (for a few channels of interest).

Does anyone know what is causing the problem? Is it a problem when the number of epochs is not equal (i.e., in some subjects I have 1-2 more trials of condition A or B)?

Best regards,
Nynke