Target motion direction influence on tracking performance and head tracking strategies in head-unrestrained conditions

Abstract

We examined subjects' behavior when they tracked periodic oscillating targets moving along a randomly oriented ramp with the head free to move. This study focuses on the effect of target motion direction on pursuit performance and on head tracking strategies used by human subjects to coordinate eye and head movements. Our analyses revealed that the gaze tracking gain was modulated by both target oscillation frequency and target motion direction. We found that pursuit gain was modulated by the target motion direction: vertical pursuit being less accurate than horizontal pursuit. While gaze tracking was sensitive to target frequency and orientation, head behavior was less modulated by a change of target frequency than by a change of target motion direction. Additionally, subjects had two main strategies for moving their head: They oriented their head to favor rotations around either the head dorsoventral (target motion directions <20 deg) or mediolateral axis (target motion directions >70 deg). In between, the subjects did not choose a consistent rotation axis for identical target motion directions.

Catch-up saccades in head-unrestrained conditions reveal that saccade amplitude is corrected using an internal model of target movement

“…The experimental setup used in this study has been described elsewhere (Daye et al, 2010(Daye et al, , 2012. The analyses in this study used the same dataset as in Daye et al (2010Daye et al ( , 2012.…”

“…The analyses in this study used the same dataset as in Daye et al (2010Daye et al ( , 2012. Briefly, human participants sat in front of a 1-m distant translucent tangential screen in a completely dark room after giving informed consent.…”

“…The paradigm used in this study is the same as in Daye et al (2010Daye et al ( , 2012 and was composed of two parts. The first part was the pursuit part.…”

“…Finally, participants had to maintain their gaze at this position until the appearance of the end-of-trial fixation at the center of the screen. Whereas Daye et al (2012) analyzed the tracking performance of the participants, this study focuses on the catch-up saccades during the pursuit part of the movement before the flash presentation or the offset of the pursuit target, whichever occurred first.…”

“…Studies of saccades (e.g., Freedman & Sparks, 1997;Goossens & Van Opstal, 1997;Guitton, Munoz, & Galiana, 1990;Tomlinson & Bahra, 1986) and pursuit (e.g., Collins & Barnes, 1999;Daye, Blohm, & Lefèvre, 2012;Lanman, Bizzi, & Allum, 1978) with the head free to move did not account for saccade-pursuit interactions, except for Daye, Blohm, and Lefèvre (2010) and Herter and Guitton (1998). The present study sought to analyze saccade-pursuit interactions in head-unrestrained conditions, which introduces several challenges.…”