[Eeglablist] How do I account for 100ms delay (from sound card) when looking at averaged files?

[Arnaud Delorme]

Dear Michelle,

In addition to Steve's recommendation, you can use the event editor (EEGLAB menu Edit > Event values) and change the latency of your time locking event by hand (add 100 ms to each of them).

Arno

On Oct 22, 2014, at 4:53 AM, Stephen Politzer-Ahles <spa268 at nyu.edu> wrote:

> Hello Michelle,
> 
> There are various ways to do this, and it depends somewhat on what you plan on doing with the data. The first question is whether or not you need to re-process the data. If you have a 100ms delay and you baseline-corrected from -200ms to 0ms (for example), then with the delay your baseline is really -300ms to -100ms, so you may or may not want to correct that. Likewise, if you epoched from -200ms to 500ms (for example) and you really need your epoch to go out to 500ms, then you would need to redo this because you really epoched from -300ms to 400ms (after accounting for the delay). If these things don't matter to you, then you may not need to redo any of the processing. If you do need to redo processing, you could probably accomplish this by either 1) using a loop to iterate over each event and change the event's latency (see http://sccn.ucsd.edu/wiki/Chapter_03:_Event_Processing#Event_latencies for information on how the event latency is represented); or 2) not actually change the events, but just choose epoch sizes that account for that (e.g., epoching from "-100ms" to "600ms), which is equivalent to -200 to 500ms after accounting for the delay).
> 
> If you don't need to reprocess, or you reprocess without actually changing the event latencies, then one thing you can do is just adjust your analyses later on (for example, changing the x-axis of plots to account for the shifted latency, and adjusting y your window of analysis--e.g. doing statistics on the "200ms - 300ms" time window if what you really want is the 100ms - 200ms window). Others on the list might have other suggestions for ways to actually change the times within EEGLAB without having to go back and re-process. It may depend on your format (e.g. whether or not you plan on using STUDY) and what EEGLAB functions you plan on using later.
> 
> Best,
> Steve
> 
> 
> 
> Stephen Politzer-Ahles
> New York University, Abu Dhabi
> Neuroscience of Language Lab
> http://www.nyu.edu/projects/politzer-ahles/
> 
> On Tue, Oct 21, 2014 at 6:05 PM, Downes, Michelle <michelle.downes at ucl.ac.uk> wrote:
> How do I account for 100ms delay (from sound card) when looking at averaged files? I've been told I can write a loop but I am not an experienced programmer and can't see anything online! 
> 
> Thank you!
> 
> Michelle Downes
> 
> Michelle Downes, Msc
> PhD Student
> Cognitive Neuroscience and Neuropsychiatry Section
> Developmental Neurosciences Programme
> UCL Institute of Child Health
> London
> WC1N 1EH
> 
> Tel: +44(0)20 7905 2644
> Email: michelle.downes at ucl.ac.uk
> 
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