Ce. Kim et al., ACCURACIES OF SACCADES TO MOVING TARGETS DURING PURSUIT INITIATION AND MAINTENANCE, Experimental Brain Research, 113(2), 1997, pp. 371-377
The overall goals of the studies presented here were to compare (1) th
e accuracies of saccades to moving targets with either a novel or a kn
own target motion, and (2) the relationships between the measures of t
arget motion and saccadic amplitude during pursuit initiation and main
tenance. Since resampling of position error just prior to saccade init
iation can confound the interpretation of results, the target ramp was
masked during the planning and execution of the saccade. The results
suggest that saccades to moving targets were significantly more accura
te if the target motion was known from the early part of the trial (e.
g., during pursuit maintenance) than in the case of novel target motio
n (e.g., during pursuit initiation); both these types of saccades were
more accuate than those when target motion information was not availa
ble. Using target velocity in space as a rough estimate of the magnitu
de of the extra-retinal signal during pursuit maintenance, the saccadi
c amplitude was significantly associated with the extra-retinal target
motion information after accounting for the position error. In most s
ubjects, this association was stronger than the one between retinal sl
ip velocity and saccadic amplitude during pursuit initiation. The resu
lts were similar even when the smooth eye motion prior to the saccade
was controlled. These results suggest that different sources of target
motion information (retinal image velocity vs internal representation
of previous target motion in space) are used in planning saccades dur
ing different stages of pursuit. The association between retinal slip
velocity and saccadic amplitude is weak during initiation, thus explai
ning poor saccadic accuracy during this stage of pursuit.