This paper examines the nature of visual representations that direct o
ngoing performance in sensorimotor tasks. Performance of such natural
tasks requires relating visual information from different gaze positio
ns. To explore this we used the technique of making task relevant disp
lay changes during saccadic eye movements. Subjects copied a pattern o
f colored blocks on a computer monitor, using the mouse to drag the bl
ocks across the screen. Eye position was monitored using a dual-purkin
je eye tracker, and the color of blocks in the pattern was changed at
different points in task performance. When the target of the saccade c
hanged color during the saccade, the duration of fixations on the mode
l pattern increased, depending on the point in the task that the chang
e was made. Thus different fixations on the same visual stimulus serve
d a different purpose. The results also indicated that the visual info
rmation that is retained across successive fixations depends on moment
by moment task demands. This is consistent with previous suggestions
that visual representations are limited and task dependent. Changes in
blocks in addition to the saccade target led to greater increases in
fixation duration. This indicated that some global aspect of the patte
rn was retained across different fixations. Fixation durations reveale
d effects of the display changes that were not revealed in perceptual
report. This can be understood by distinguishing between processes tha
t operate at different levels of description and different time scales
. Our conscious experience of the world may reflect events over a long
er time scale than those underlying the substructure of the perceptuo-
motor machinery. (C) 1997 Elsevier Science Ltd.