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Classify Fixations by Velocity Threshold
classify_ivt R Documentation
Classify each gaze point based on their velocities as calculated by
calculate_velocity.
classify_ivt(data, velocity_threshold = 100)
data Data frame of the eye tracking data we want to process
velocity_threshold Velocity threshold in degrees per second (°/s) over which the gaze point should be classified as saccade
Input data frame columns
velocity
: Velocity of the current gaze point
Additional columns in output
classification
: Classification of this gaze point
eventIndex
: Index of the event in which the gaze point lies
eventType
: Type of the current event
eventDuration
: Duration of the current event
fixation_x
: X coordinate of the current fixation (if eventType is a fixation)
fixation_y
: Y coordinate of the current fixation (if eventType is a fixation)
fixation_z
: Z coordinate of the current fixation (if eventType is a fixation)
This is an implementation of the fixation identification by velocity threshold (I-VT) as documented in the Tobii Pro I-VT fixation filter. It compares the velocity of each gaze point against the threshold and classifies the gaze point as saccade if the velocity is equal or above it. Additionally it groups gaze points of the same classification into an event.
The default velocity threshold is 100 degrees per second, as described by Tobii for their mobile eye trackers. For stationary eye trackers the default threshold by Tobii is 30 degrees per second.
The input data frame with the classification columns added