Quaia C, Joiner WM, FitzGibbon EJ, Optican LM & Smith MA (2010) Eye movement sequence generation in humans: motor or goal updating?
Journal of Vision, 10:1-31.
Abstract: Saccadic eye movements are often grouped in pre-programmed sequences. The mechanism underlying the
generation of each saccade in a sequence is currently poorly understood. Broadly speaking, two alternative
schemes are possible: first, after each saccade the retinotopic location of the next target could be estimated,
and an appropriate saccade could be generated. We call this the goal updating hypothesis. Alternatively,
multiple motor plans could be pre-computed, and they could then be updated after each movement. We call
this the motor updating hypothesis. We used McLaughlin’s intrasaccadic step paradigm to artificially create
a condition under which these two hypotheses make discriminable predictions. We found that in human
subjects, when sequences of two saccades are planned, the motor updating
hypothesis predicts the landing position of the second saccade in two-saccade sequences much better than
the goal updating hypothesis. This finding suggests that the human saccadic system is capable of executing
sequences of saccades to multiple targets by planning multiple motor commands, which are
then updated by serial subtraction of ongoing motor commands.