Quantitative Analysis of Catch-Up Saccades During Sustained Pursuit

Abstract

During visual tracking of a moving stimulus, primates orient their visual axis by combining two very different types of eye movements, smooth pursuit and saccades. The purpose of this paper was to investigate quantitatively the catch-up saccades occurring during sustained pursuit. We used a ramp-step-ramp paradigm to evoke catch-up saccades during sustained pursuit. In general, catch-up saccades followed the unexpected steps in position and velocity of the target. We observed catch-up saccades in the same direction as the smooth eye movement (forward saccades) as well as in the opposite direction (reverse saccades). We made a comparison of the main sequences of forward saccades, reverse saccades, and control saccades made to stationary targets. They were all three significantly different from each other and were fully compatible with the hypothesis that the smooth pursuit component is added to the saccadic component during catch-up saccades. A multiple linear regression analysis was performed on the saccadic component to find the parameters determining the amplitude of catch-up saccades. We found that both position error and retinal slip are taken into account in catch-up saccade programming to predict the future trajectory of the moving target. We also demonstrated that the saccadic system needs a minimum period of approximately 90 ms for taking into account changes in target trajectory. Finally, we reported a saturation (above 15 degrees /s) in the contribution of retinal slip to the amplitude of catch-up saccades.

Inactivation and stimulation of the frontal pursuit area change pursuit metrics without affecting pursuit target selection

“…We detected saccades using velocity and acceleration thresholds (Krauzlis and Miles 1996). During tracking, these thresholds were applied relative to the average eye velocity and acceleration to avoid erroneously flagging periods of smooth tracking with nonzero velocity as saccades (de Brouwer et al 2002). All detected saccades were visually verified, and saccades during ongoing pursuit were excised from velocity traces.…”

The relative timing between eye and hand in rapid sequential pointing is affected by time pressure, but not by advance knowledge

“…Saccadic onset and offset were determined for the left eye only. Saccadic onset was defined as the time when eye acceleration exceeded 750°/s 2 ; saccadic offset was calculated as the time when eye deceleration dropped below this threshold (De Brouwer et al 2002). When multiple saccades were used to shift gaze between two targets, onset was defined relative to the first saccade, whereas offset was defined relative to final saccade.…”

Predictive saccade in the absence of smooth pursuit: interception of moving targets in the archer fish

“…One feature of these saccades is revealed by examining the ratio G between the saccade amplitude and the gaze-lag just prior to the saccade, a measure known as the saccadic gain (de Brouwer et al, 2001). Note that a gain of GϷ1, where the animal essentially compensates for the gazelag, is expected in animals with a narrow fovea, whereas animals with wide area centralis but no fovea could tolerate other (and in particular, smaller) (de Brouwer et al, 2002) gain values. Surprisingly, we found that the saccadic gain in the archer fish varied up to ~2 (P0, t-test, null hypothesis is the gain equals 1) for fastmoving targets (Fig.3D), an exceptionally high value that is approximately twice that observed in mammals (de Brouwer et al, 2001;Temple et al, 2010).…”