Is the eye-movement field confused about fixations and saccades? A survey among 124 researchers

Abstract

Eye movements have been extensively studied in a wide range of research fields. While new methods such as mobile eye tracking and eye tracking in virtual/augmented realities are emerging quickly, the eye-movement terminology has scarcely been revised. We assert that this may cause confusion about two of the main concepts: fixations and saccades. In this study, we assessed the definitions of fixations and saccades held in the eye-movement field, by surveying 124 eye-movement researchers. These eye-movement researchers held a variety of definitions of fixations and saccades, of which the breadth seems even wider than what is reported in the literature. Moreover, these definitions did not seem to be related to researcher background or experience. We urge researchers to make their definitions more explicit by specifying all the relevant components of the eye movement under investigation: (i) the oculomotor component: e.g. whether the eye moves slow or fast; (ii) the functional component: what purposes does the eye movement (or lack thereof) serve; (iii) the coordinate system used: relative to what does the eye move; (iv) the computational definition: how is the event represented in the eye-tracker signal. This should enable eye-movement researchers from different fields to have a discussion without misunderstandings.

Studying Gaze Behaviour during Collision Avoidance with a Virtual Walker: Influence of the Virtual Reality Setup

“…According to Parasuraman and Rizzo [34], the gaze behaviour can be described as a succession of fixations separated by fast eye movement called saccades. An important task in eyetracking studies is to well define these two movements [19]. Depending on the task and situation different definitions can be found in the literature, and we therefore used the definition of fixations given by Kitazawa and Fujiyama [23], whose experimental task shared common properties with ours: a fixation was defined as a continuous gaze on the same object for more than 80ms.…”

Binocular coordination and return-sweep saccades among skilled adult readers

“…Saccadic eye movements direct gaze from one word to another. Saccades are followed by momentary periods of stillness, called fixations, during which specific regions of the text are projected to a relatively constant location on the retina and information is encoded (Hessels, Niehorster, Nyström, Andersson, & Hooge, 2018). Saccades typically move the eyes' gaze seven to nine character spaces for English readers.…”

Visual Exploration of Omni-Directional Panoramic Scenes

“…There is substantial confusion in the eye-movement field regarding the definition of fixations and saccades, in particular when eye movements are combined with free head movements (see e.g., Hessels, Niehorster, Nyström, Andersson & Hooge, 2018). In our study, participants were seated inside a virtual sphere and looked at the panoramic scenes from approximately the center of the sphere.…”