[FieldTrip] Segment length choice and further analysis

[Schubert, E.S. (Sophie)]

Dear FieldTrip Support,

I am reaching out regarding a question I have encountered while using FieldTrip for preprocessing.

I am working on PSG analysis where sleep stages have already been marked (with markers for each sleep event, every 30 seconds). I have epoched the data into 30-second segments based on these markers, as well as into 5 and 3-second segments to test artifact detection and evaluate the percentage of data that would be lost. This choice was driven by the need for complete trial rejection upon artifact detection. The planned analyses include frequency domain analysis, time-frequency analysis, and examining specific characteristics of EEG.

As I delve deeper into specific analyses such as K-complex and sleep spindle detection, I have noticed that different studies use varying segment lengths to detect these events effectively. K-complex analyses often adhere to AASM criteria for sleep stages (20 or 30-second segments). Segmenting entire trials of 30 seconds and rejecting them outright could potentially discard valuable data.

If I am correct, FieldTrip operates under the premise of segmenting data, and once segmented, the data cannot be recombined into a continuous form or re-epoched. This has left me uncertain about how to proceed with future analyses that require other segment lengths. It seems imperative that such analyses could also be conducted on a continuous scale.

My concern is primarily about the impact of segment length choice on subsequent analyses. Would different segment lengths significantly affect the outcomes of analyses such as event detection or spectral analysis? How can I ensure that my choice of segment length aligns well with the requirements of these analyses?

I would greatly appreciate any insights, advice, or best practices regarding this matter. If there are specific tools or methodologies within FieldTrip or related software that could address these concerns, I would be eager to learn more about them.
Thank you in advance for your assistance.

Kind regards,

Sophie Schubert

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