Planning sequences of saccades.
Subjects used saccades to fixate a sequence of 1-5 stationary targets (separation = 90') located at the vertices of an imaginary pentagon. The latency of the first saccade in a sequence and the duration of intervals between subsequent saccades increased with sequence length at a rate of about 20 msec/target. Latency also varied with ordinal position in the sequence. These results were not due to directional differences in saccadic latency nor to latency-accuracy or to latency-precision trade-offs. Results were similar when targets were removed and saccades were directed to remembered locations. These effects may be best accounted for by models that have been proposed to account for similar effects of sequence length and ordinal position on other voluntary motor tasks, such as typing, speech and finger-tapping. In these models motor programs for a sequence of responses are planned before execution and then retrieved from memory during execution. These models are fundamentally different from the traditional saccadic models in which visual error signals evoke saccades. Instead, we propose that saccades are controlled by an organized plan for an entire sequence of saccades. Visual error signals may modify or elaborate the plans during the execution of a sequence. Our proposal is consistent with ideas developed by Lashley [Cerebral Mechanisms in Behavior: The Hixon Symposium. Wiley, New York (1951)] in his general treatment of the central organization that determines voluntary motor performance.
Department of Psychology, Rutgers University, New Brunswick, NJ 08903.
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Zingale
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Kowler
D005133:Eye Movements; D005260:Female; D005403:Fixation, Ocular; D006801:Humans; D008568:Memory / Q000502:physiology; D009043:Motor Activity / Q000502:physiology*; D012438:Saccades; D013997:Time Factors