The time course of visual information accrual guiding eye movement decisions

doi:10.1073/pnas.0305329101

The time course of visual information accrual guiding eye movement decisions

^*Department of Psychology, University of California, Santa Barbara, CA 93106; and ^§National Aeronautics and Space Administration Ames Research Center, Moffett Field, CA 94035

Edited by George Sperling, University of California, Irvine, CA, and approved June 22, 2004 (received for review August 19, 2003)

Abstract

Saccadic eye movements are the result of neural decisions about where to move the eyes. These decisions are based on visual information accumulated before the saccade; however, during an ≈100-ms interval immediately before the initiation of an eye movement, new visual information cannot influence the decision. Does the brain simply ignore information presented during this brief interval or is the information used for the subsequent saccade? Our study examines how and when the brain integrates visual information through time to drive saccades during visual search. We introduce a new technique, saccade-contingent reverse correlation, that measures the time course of visual information accrual driving the first and second saccades. Observers searched for a contrast-defined target among distractors. Independent contrast noise was added to the target and distractors every 25 ms. Only noise presented in the time interval in which the brain accumulates information will influence the saccadic decisions. Therefore, we can retrieve the time course of saccadic information accrual by averaging the time course of the noise, aligned to saccade initiation, across all trials with saccades to distractors. Results show that before the first saccade, visual information is being accumulated simultaneously for the first and second saccades. Furthermore, information presented immediately before the first saccade is not used in making the first saccadic decision but instead is stored and used by the neural processes driving the second saccade.

Footnotes

↵ † To whom correspondence should be addressed. E-mail: avi.caspi{at}psych.ucsb.edu.
↵ ‡ Present address: The Leslie and Susan Gonda Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat Gan 52900, Israel.
This paper was submitted directly (Track II) to the PNAS office.
↵ ¶ We also investigated use of an alternative criterion to define saccadic decisions. This criterion required a saccade's endpoint to be a maximum spatial distance of 2° from a possible target location to be assigned to that location. The use of this second criterion did not lead to any significant changes in our results.
↵ ∥ Eckstein, M. P., Beutter, B. R. & Stone, L. S. (1999) Perception 29, Suppl., 101a (abstr.).