The interplay of drifts and flicks in binocular fixation

The contribution of microsaccades and drifts in the maintenance of binocular steady fixation

“…Even though the endpoints of 53.1% of the drift movements were found to be corrective towards the centre of the PRL, the mean distance was still 0.41°away from this point, not significantly closer than the mean post-microsaccadic distance. This result is in accordance with previous work by St Cyr and Fender [26], who found that the area circumscribed by the end-drift and end-microsaccadic positions, in two test persons, were equal. However, their study made no reference to the PRL.…”

“…The large microsaccades in this study were different from the medium and small microsaccades with respect to overshoot and main sequence [26]. The present study confirms that these large microsaccades may be different from the medium and small microsaccades, since 73.9% were coupled, 43.5% corrective, and the mean postmicrosaccadic distance to the PRL was significantly greater for the large microsaccadic fixation pattern than for the other two.…”

“…Previously, the scatter of end positions of microsaccades and drifts has been used to estimate the retinal area of fixation [21,26]. Our study confirms the strict correlation between the retinal area of fixation (RAF95) and both the mean post-microsaccadic and the mean post-drift distance to the centre of the PRL.…”

“…Cornsweet postulated that the microsaccades redirect the eye towards the PRL and that the drifts are oculomotor "noise". In later studies, however, drifts were found to be corrective [3,21], even to the same extent as the microsaccades [26]. Many test persons can voluntarily suppress the microsaccades for at least 10 s, and still perform delicate visually guided tasks, such as threading a needle, indicating that eye movements performed during the drifts (slow control) are sufficient to redirect the eye [13,28].…”

A compact field guide to the study of microsaccades: Challenges and functions

“…Early studies uniformly reported narrow amplitude distributions for fixational saccades, and correspondingly used the term microsaccades to indicate saccades smaller than a few minutes of arc, typically 12′ (Ditchburn and Ginsborg, 1953; Nachmias, 1959; Boyce, 1967; Ditchburn and Foley-Fisher, 1967; St.Cyr and Fender, 1969). In contrast, several recent studies have reported substantially broader distributions of fixational saccades, which has led to a considerable increment in the microsaccade amplitude threshold.…”