2002 Abstract

CATCH-UP SACCADES IN TWO DIMENSIONS

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

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

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

During visual tracking of a moving stimulus, primates orient their visual axis by combining smooth pursuit and catch-up saccades. A quantitative analysis of catch-up saccades has been done for horizontal movements (de Brouwer et al., 2002). In this study, we investigate the properties of catch-up saccades made to visual stimuli moving in two dimensions (2D).
We measured 2D eye movements in 4 human subjects (search coil technique). Each trial started with a 2D Rashbass step-ramp stimulus (velocity [10..20 deg/s], direction [0..360 deg], duration [600..1100 ms]). This was followed by a second step-ramp of the target [500..700 ms]. Both the direction of the position step (PS, [-10..10 deg]) and the velocity step (VS, [-40..40 deg/s]) varied randomly in 2D. We analysed the first catch-up saccades after the second step of the target.
We found that catch-up saccades to the second ramp were characterized by latencies as short as 100 ms with respect to the second target step (mean 185 ms). The average gain of catch-up saccades was 0.84 (n=1175). However, when data were restricted to moderate values of retinal slip (RS<20 deg/s), the average gain was 0.9 (n=569). A multiple linear regression analysis was performed to find the parameters determining the amplitude of catch-up saccades. For both horizontal and vertical components of saccades, we found the best correlation with position error (PE) and RS as independent variables : Amp=0.9*PE+0.11*RS (R>0.97, n=569). We conclude that both position error and retinal slip are taken into account for programming 2D catch-up saccades.
Supported by: FNRS, SSTC and FSR (Belgium)

Citation:
C. Schreiber, G. Blohm, M. Missal, P. Lefèvre. CATCH-UP SACCADES IN TWO DIMENSIONS Program No. 265.8. 2002 Abstract Viewer/Itinerary Planner. Washington, DC: Society for Neuroscience, 2002. Online.