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EDA background and analysis by Biopac
Here Biopac EDA presentation slides including setup, data quality considerations and further information:
Biopac EDA presentation slides
In order to establish a baseline against which responses will be compared/measured, we need a time window of resting right before responses start. Below you see the “EDA Preferences” window (Analysis → Electrodermal activity → Preferences) and the software asks how many seconds (or desired time unit) you want to use to establish the baseline. Let’s say, we are looking at the Stroop task (see below): instead of having regular individual events, we are looking at time periods that last up to several minutes. You can see that this person’s EDA starts to peak even before the beginning of the first Stroop block. Therefore, we need the time scale to start at least one minute, if possible more, before the task begins.
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Processing
· The little ‘I’ (info) button on the right hand bar of a channel is not there right after data collection, it only appears after something has been done to the data. You can check what has been done. This one shows that the data has already been resampled from 2,000Hz to 100Hz (Biopac samples everything at 2,000Hz by default)
· Missed the exact data selection and filtering option: remove high-frequency noise, happens if contact between electrode and skin is poor
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· Usually creates a new channel with filtered data to preserve original data but this can be turned off if desired
· Now convert peaks of stimulus presentation into stimulus event markers
· If you only have a handful of stimulus events, you don’t need to use the latency option (use zero); you can use it if you have hundreds of different ones, pick this option
· Now we have light bulbs à in event palette, you see stimulus types 1 and 2 (1=happy, 2=sad)
Preferences
· The first time you use the EDA option, you are asked to set your preferences; set those and then use these presets for ALL participants!
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o A response needs to happen AFTER the stimulus presentation; at least 1 second (signal transmission) and less than 4 seconds. If you see an immediate response, that is likely due to something that happened previously; i.e. exclude responses too close (minimum) or too far away (max) from your stimulus presentationo Either report within a time window (e.g. 10 or 20 seconds), or report per event
o Using the time period option, we get a summary of all different types of analyses; by event would be better for block designo Event markers now show “1” and “2” for type of stimulus (happy and sad, respectively)
Summary measures
o How many responses occur within an area?
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