2003 Abstract

MEMORY GUIDED SACCADES DURING AND AFTER SMOOTH PURSUIT.

G.Blohm^1,2*; M.Missal²; P.Lefèvre^1,2

1. CESAME, Universite catholique de Louvain, Louvain-la-Neuve, Belgium

2. Lab. Neurophysiol., Universite catholique de Louvain, Brussels, Belgium

To orient towards a flashed target during self-movement, the oculomotor system has to combine retinal with extra-retinal information about motion. In this study, we investigated how retinal and extraretinal motion signals are used to localize a target flashed during or after sustained pursuit.
In the flash during ramp condition (FDR), a green target moved at a random velocity (10-40deg/s) and direction to initiate a smooth pursuit response. 500-1500 ms after the target started to move, a red target was flashed for 10 ms at a random position ±10deg around the expected eye position. In the flash after ramp condition (FAR), the green pursuit target disappeared after 500-1000 ms. The red target was flashed 0-500 ms later. In both conditions, human subjects were instructed to pursue the green target and to orient their gaze towards the flash immediately after its occurrence.
A sequence of 1-3 saccades was typically observed after the flash. Only the first orientation saccade and the time course of the position error were analyzed. In both conditions, short latency saccades (< 200 ms) were programmed using position error at the moment of the flash (PEf). Saccades with longer latencies (> 200 ms) used in addition to PEf an estimation of the smooth eye displacement (SED) from the moment of the flash. At the end of the orientation process, the consecutive saccades largely accounted for PEf (FAR: 85%; FDR: 100%) and partially for the total SED (FAR: 35%; FDR: 50%).
In conclusion, the saccadic system uses extra-retinal signals to compensate for SED for targets flashed during or after sustained pursuit. However, the fact that the compensation for self motion is not present shortly after the flash reveals the time course of this compensation process (latency > 200 ms).
Support Contributed By: FNRS, SSTC and FSR (Belgium)

Citation:
G. Blohm, M. Missal, P. Lefèvre. MEMORY GUIDED SACCADES DURING AND AFTER SMOOTH PURSUIT. Program No. 72.17. 2003 Abstract Viewer/Itinerary Planner. Washington, DC: Society for Neuroscience, 2003. Online.