FAQ: How do events get assigned to Interest Areas if there are multiple Interest Areas?

[SR-SUPPORT]

When Interest Areas (IAs) overlap or are nested inside one another, it's important to understand how Data Viewer assigns fixations and reports the data.

IA Identifiers: Label, ID, and Index
Each IA has three identifiers:

• Label: The descriptive text name (e.g., Left_Eye).
  
• ID: A numerical identifier that you can assign. Multiple IAs can share the same ID.
  
• Index: A unique number (from 1 to the total number of IAs) based on the IA's order in the Inspector window. In most cases, the ID and Index are identical.
  

   

How Fixations are Assigned
As a reminder, a fixation is assigned to an IA only if its average gaze position (the center point of its circle in the Spatial Overlay view) falls within the IA's boundaries. An overlap of the circle's edge is not enough.

Managing Overlap

• Fixation is Counted in All Overlapping IAs (Default Behavior)
  By default, if a fixation's center point falls within multiple IAs, it is counted towards every single one of them. The fixation's duration will contribute to the dwell time measures for all relevant IAs.
  
  
• Assign to a Single IA (Alternate feature)
  Instead, you can change the default behavior by modifying the preferences to have each fixation assigned to only a single interest area.
  • Go to Edit > Preferences > Output / Analysis.
    
  • Check the box for Include Fixation in Single IA.
    
  When this is enabled, the fixation will be assigned only to the overlapping IA with the lowest ID number.
  

How Overlaps Appear in Data Reports
When a fixation falls in multiple IAs, different report variables will show different information:

• Most IA variables (like CURRENT_FIX_INTEREST_AREA_ID) will only report the IA with the lowest ID.
  
• The *_INTEREST_AREAS variables will return a list of all IAs the fixation landed in.
  

To get detailed metrics for each specific Interest Area regardless of overlap, you should generate an Interest Area Report.