Open AccessAngular offset distributions during fixation are, more often than not, multimodal
Author(s) -
Lee Friedman,
Dillon Lohr,
Timothy Hanson,
Oleg V. Komogortsev
Publication year - 2021
Publication title -
journal of eye movement research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.25
H-Index - 20
ISSN - 1995-8692
DOI - 10.16910/jemr.14.3.2
Subject(s) - offset (computer science) , fixation (population genetics) , eye tracking , multimodality , computer science , artificial intelligence , eye movement , computer vision , mathematics , medicine , population , environmental health , world wide web , programming language
Typically, the position error of an eye-tracking device is measured as the distance of the eye-position from the target position in two-dimensional space (angular offset). Accuracy is the mean angular offset. The mean is a highly interpretable measure of central tendency if the underlying error distribution is unimodal and normal. However, in the context of an underlying multimodal distribution, the mean is less interpretable. We will present evidence that the majority of such distributions are multimodal. Only 14.7% of fixation angular offset distributions were unimodal, and of these, only 11.5% were normally distributed. (Of the entire dataset, 1.7% were unimodal and normal.) This multimodality is true even if there is only a single, continuous tracking fixation segment per trial. We present several approaches to measure accuracy in the face of multimodality. We also address the role of fixation drift in partially explaining multimodality.