Directional differences in saccades

Though saccades are believed to be generated by similar neural mechanisms in all directions, measurements show directional differences in movement characteristics. The mechanisms and causes of these differences remain unclear.

This study investigated directional differences in saccades in 48 healthy participants (28 males, 20 females; mean age 40.38 years). An EyeSeeCam Sci 2 video-oculography system with a sampling rate of 500 Hz was used to measure centrifugal and centripetal horizontal (5 °, 10 °, 15 °, and 20 °) and vertical (5 °, 10 °, and 15 °) visually guided saccades.

Horizontally, when amplitude was large (15 ° and 20 °), saccades in the medial hemifield were faster than in the lateral hemifield in both centrifugal and centripetal directions. Centripetal saccades were significantly faster than centrifugal ones. Vertically, with large amplitude (15 °), saccades in the upper hemifield were significantly faster than in the lower hemifield in both directions. As horizontally, centripetal saccades were faster than centrifugal ones in the upper hemifield. No clear trends appeared in horizontal saccade latency and amplitude. However, shorter latencies for centripetal saccades and larger amplitudes for upward saccades were noted vertically.

The medial-lateral eye position difference likely relates to saccade-vergence interaction. Other directional saccade asymmetries are attributed to physical properties, like the elastic restoring force in the centripetal direction and viscous resistance from eyelid coverage in the lower eye position, rather than neural mechanisms. Saccade motor characteristics are strongly influenced by periocular tissues.