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FAQ: How do events get assigned to Interest Areas if there are multiple Interest Areas?
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#1
09-03-2020, 07:23 AM (This post was last modified: 01-13-2026, 16:18 PM by Dan.)
When Interest Areas (IAs) overlap or are nested inside one another, it is crucial to understand how Data Viewer assigns fixations and reports the data.

IA Identifiers: Label, ID, and Index
Every Interest Area is defined by 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 (ranging from 1 to the total number of IAs) determined by the IA's order in the Inspector window. Note: In most cases, the ID and Index are identical.
   

How Fixations are Assigned
A fixation is assigned to an IA only if its average gaze position (represented as the center point of the fixation circle in the Spatial Overlay view) falls within the IA's boundaries. A simple overlap of the fixation circle's edge is insufficient.

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 all of them. Consequently, the fixation's duration contributes to the dwell time metrics for every relevant IA.

  • Assign to a Single IA (Alternate feature)
    You can override the default behavior so that each fixation is assigned to only one Interest Area.
    • Go to Edit > Preferences > Output / Analysis.
    • Enable Include Fixation in Single IA.
    When this is enabled, the fixation will be assigned exclusively to the overlapping IA with the lowest ID number.
How Overlaps Appear in Data Reports
When a fixation lands in multiple IAs, report variables handle the data differently:
  • Single-Value Variables: Variables like CURRENT_FIX_INTEREST_AREA_ID will report only the IA with the lowest ID.
  • List Variables: 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.