FAQ: What happens when my Interest Period boundary falls in the middle of a gaze event?

[SR-SUPPORT]

A Spanned Event is a fixation or saccade that crosses the start or end boundary of your Interest Period. For example, a fixation that starts before the Interest Period begins but ends inside it is a spanned fixation.

   

How to Handle Spanned Events: Hiding vs. Trimming
Data Viewer gives you two main ways to handle these events, which you can configure in the Inspector > Preferences > Data Filters tab.

• Hiding: This completely excludes the spanned event from all reports and calculations. For example, its duration will not contribute to metrics like IA_DWELL_TIME.
  
• Trimming (Default): This includes the event in reports, but its duration is trimmed to only the portion that falls inside the Interest Period. This trimmed duration is what contributes to metrics like IA_DWELL_TIME.
  

Preference Settings
You can control this behavior separately for the start and end of your Interest Period with the following settings:

   

• Hide Spanned Events at Start of IP: Excludes any event that crosses the start boundary from all reports.
  
• Hide Spanned Events at End of IP: Excludes any event that crosses the end boundary from all reports.
  
• Trim Spanned Fixation Duration at Start of IP: For fixations spanning the start boundary, only the duration inside the IP is used in calculations.
  
• Trim Spanned Fixation Duration at End of IP: For fixations spanning the end boundary, only the duration inside the IP is used.
  

Note: Mutually Exclusive: Hiding and trimming are mutually exclusive. An event can either be hidden or trimmed, but not both.

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Pro Tip: A common use case for these settings is to exclude the very first fixation in each trial. To do this, simply check the Hide Spanned Events at Start of IP option.