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Neil R Mennie, Mary M Hayhoe, Brian T Sullivan, Carol Walthew; Look ahead fixations and visuo-motor planning. Journal of Vision 2003;3(9):123. doi: https://doi.org/10.1167/3.9.123.
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In studies of eye movements in natural tasks, fixations are tightly linked to the immediate action, with few fixations on irrelevant objects or locations (Land et al, Perception, 1999). Additionally, several studies have reported the frequent occurrence of “look-ahead” fixations. These are fixations on an object in the few seconds prior to a second fixation that guides a reaching movement to grasp the object. One possibility is that these fixations indicate that the subject is planning a reach, and fixating the object in order to acquire spatial location for guiding the next movement. We investigated this possibility in a toy construction task that required picking up and connecting components in a pre-determined sequence. We found that all of N subjects produce look-ahead fixations, in up to 40 % of the reaches for some subjects. By manipulating the extent to which planning was required in the task, we modulated the frequency of occurrence of look-aheads. This supports the suggestion that look-ahead fixations reflect planning of the next reaching movement. Thus the programming of the reach is influenced by information acquired in prior fixations. This information must be in a reference frame independent of eye position. This conflicts with many descriptions of information integrated across saccades, which emphasize semantic properties and lack of spatial precision. It also suggests that planning movements several seconds ahead are a frequent component of natural behavior. Thus the underlying control structure of the task is not strictly sequential, and can perhaps be modeled as a set of loosely coupled micro-tasks that are capable of running on an opportunistic basis.
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