[Eeglablist] baselining using 500ms from the inter-trial interval

[Nash, Hannah]

Hi,

I've read the tutorials and other post on the topic of baselining and I can't quite seem to find the solution to my problem.

In our experiment a letter prime (presented for 500ms) precedes (ISI 500ms) a phoneme target (variable duration 282ms - 428ms)

There is an inter-trial interval of 1000ms.

To summarise a trial
ITI (1000ms) - letter prime (500ms) - ISI (500ms) - sound target (282-428ms)

Both the primes and targets send triggers and so are events.

At the moment I am looking at ERPS to the targets (period of 500ms after event onset) and using the default of -100ms before event onset as the baseline period.

This is not resulting in a very good baseline at all and I'm wondering if this is related to both the length of the period (too short) and the fact that it's only 400ms after the offset of the letter prime.

Therefore I'd like to use a period of 500ms but from the inter-trial interval.

The problem is that I don't know how program this in eeglab.  Do the epoch limits have to be extended to include this period this would be variable from 2282ms - 2428ms?    I know that the baseline period would then be -1500 to -1000 but the epoch would include the prime and the ISI as well....

Perhaps this is straightforward for someone more familiar with eeglab.  Any help will be appreciated.

Thanks
Hannah

Dr Hannah Nash
Research Fellow, UCL - Division of Psychology & Language Sciences
Chandler House (room 115)
2 Wakefield Street
London
WC1N 1PF

Email: hannah.nash at ucl.ac.uk

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