Mismatch between ERSP trial count from std_readersp and original EEG dataset trial count (EEGLAB)

[TWXinPing]

Hi everyone,

I'm currently encountering an issue while using std_readersp to extract single-trial ERSP data for ICA cluster analysis.

I’m analyzing an EEGLAB STUDY with ICA clusters, and I extracted ERSP data like this:

[STUDY, erspdata, times, freqs, erspbase] = std_readersp(STUDY, ALLEEG, ... 'design', design_idx, ... 'clusters', cluster_id, ... 'component', comp_idx, ... 'singletrials', 'on', ... 'subbaseline', 'off');

The resulting ERSP has shape:

size(erspdata) = [freqs × times × trials] = [83 × 200 × 175]

However, my original EEG dataset has:

ALLEEG(31).trials = 178 STUDY.datasetinfo(31).trialinfo = 1×178 struct

So I’m missing 3 trials in the ERSP output.

What I’ve checked: ALLEEG(31).reject is empty.

No error or warning was shown when running std_readersp.

The component used (comp_idx = 67) exists and works fine otherwise.

My question is: Where could the missing trials have gone? What internal mechanism in std_readersp or EEGLAB’s STUDY pipeline might cause this mismatch?

And how can I retrieve trial-by-trial ERSP data that fully matches my original behavioral trial info?

Additional Info: EEGLAB version: 2023.0

Dataset is epoched and ICA-decomposed

All trials were labeled with behavioral info (custom trialinfo fields)

Any suggestions would be very helpful. Thank you in advance!