Eye Movements in Darkness Modulate Self-Motion Perception

Abstract

During self-motion, humans typically move the eyes to maintain fixation on the stationary environment around them. These eye movements could in principle be used to estimate self-motion, but their impact on perception is unknown. We had participants judge self-motion during different eye-movement conditions in the absence of full-field optic flow. In a two-alternative forced choice task, participants indicated whether the second of two successive passive lateral whole-body translations was longer or shorter than the first. This task was used in two experiments. In the first (n = 8), eye movements were constrained differently in the two translation intervals by presenting either a world-fixed or body-fixed fixation point or no fixation point at all (allowing free gaze). Results show that perceived translations were shorter with a body-fixed than a world-fixed fixation point. A linear model indicated that eye-movement signals received a weight of ∼25% for the self-motion percept. This model was independently validated in the trials without a fixation point (free gaze). In the second experiment (n = 10), gaze was free during both translation intervals. Results show that the translation with the larger eye-movement excursion was judged more often to be larger than chance, based on an oculomotor choice probability analysis. We conclude that eye-movement signals influence self-motion perception, even in the absence of visual stimulation.

Causal inference for spatial constancy across whole-body motion

“…The distribution m for the internally-updated position of the pre-motion target cannot be assumed to be accurate: it has been established that, under the conditions of our experiment, passive self-motion amplitude is underestimated [16]. We allow for such underestimation by introducing a gain factor α.…”

“…Participant’s displacement was operated by a custom-made sled, consisting of a chair mounted on an 800-mm track (see [16] for more details). The sled was powered by a linear motor (TB15N, Technotion, Almelo, The Netherlands) and controlled by a Kollmorgen S700 drive (Danaher, Washington, DC).…”

“…During passive self-motion, the brain must rely on vestibular and other sensory signals to infer the motion [12–16]. Various studies suggested that there is a clear compensation for passive self-motion in the updating of visual space, although compensation is not always perfect [17–20].…”

Eye movements during path integration

“…On the one hand, it can be related to a recent result which shows that eye movements are able to influence the perception of self‐motion even without visual stimuli (Clemens et al. ). Thus, the reproduction of the eye movements generated in the encoding phase could be a useful strategy during reproduction to keep this influencing factor constant between the two phases.…”

Vestibular contributions to high-level sensorimotor functions

“…In a recent study, we asked human subjects to estimate their displacement when the motion was accompanied by fixation on a world-fixed, or on a body-fixed fixation point or without a fixation point at all (allowing free gaze). Our results show that extra-retinal eye movement signals are used as a cue in the perception of body motion, weighting for about 25% into the percept, even in the absence of optic flow (Clemens et al, 2017). This novel result implies that any study concerned with self-motion estimation cannot ignore the possible influence of eye movements.…”