[Abstract Title]. - Society for Neuroscience

Abstract: When generating saccades toward a moving target, the target displacement that occurs
during the period preceding saccade end must be taken into account in order to accurately
foveate the target. Previous studies have shown that these saccades are characterized by a
prolonged deceleration phase. In some cases, a second peak eye velocity appears during the
deceleration, presumably reflecting the late influence of a mechanism that compensates for the
target motion. The goal of this work is to further determine the dynamics of this compensatory
mechanism.
Saccades were studied in 3 head restrained rhesus monkeys trained to track a small Gaussianblurred
disk (diam. 0.5°). After a 200 ms gap, the target stepped from a central (straight ahead)
position toward a peripheral one (8° or 16°) along the cardinal axes (horizontal or vertical).
Then, the target started to move at a constant speed after a delay that ranged between 0 and 300
ms. The target motion was always orthogonal to the target step (e.g. rightward or leftward
motion after an upward or downward step). This arrangement was designed in order to easily
decompose the saccade into two components: a component induced by the target step and
another induced by the target motion. Different target speeds (7, 14 or 21°/s) were tested in order
to estimate when the build-up of the motion-induced component was completed. Oblique
saccades to stationary targets located at positions comparable to those reached by saccades
toward moving targets were also tested.
Our results show that the amplitude of the step-induced component did not vary with the presaccadic
exposure duration, i.e. the period during which the target moved before the saccade is
launched. In contrast, the motion-induced component, which was saccadic, increased with the
pre-saccadic exposure duration. The temporal increase in amplitude differed between the three
target speeds. For exposure durations longer than 70 ms, the motion-induced amplitude was
clearly larger for faster target motions. The changes in amplitude started to differ from baseline
approx. 50 ms after the onset of target motion. Interestingly, the motion-induced component was
often delayed relative to the step-induced component, leading to a curvature of saccades. This
asynchrony contrasted with the synchronized onsets of horizontal and vertical components
during oblique saccades.
Our study provides a direct estimate of the time taken for visual motion-related signals to update
the programming and execution of saccades. The difference in saccade curvature between
stationary and moving targets provides another illustration of the dynamic control of saccade
trajectory by visual input.
Disclosures: J. Fleuriet, None; S. Hugues , None; L. Goffart, None.
Poster
265. Nociceptors II
Time: Sunday, November 16, 2008, 1:00 pm - 5:00 pm
Program#/Poster#: 265.1/EE2