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Junghyun Park, Shinsuke Shimojo; Corrective saccades drive saccadic adaptation independently of explicit interpretation of retinal error. Journal of Vision 2007;7(9):142. doi: 10.1167/7.9.142.
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Systematic displacements of saccade targets while the eye is in mid-flight lead to a gradual change in saccade amplitudes. A) What drives this saccadic adaptation: post-saccadic retinal error signals or secondary corrective saccades? B) How susceptible is this process to explicit knowledge regarding the source of the retinal error?
Participants (N=10) were tested in a 3×2 manipulation. A) Three conditions tested the effect of explicit cues signaling that post-saccadic retinal error was due to a target shift rather than saccade inaccuracy. In the conventional saccadic adaptation condition, the target spot simply stepped from 10° to 7°. In the color condition, the target shift was marked by a color change. In the bar condition, a long vertical bar was presented throughout the trial in-between the original and final target positions. B) Participants were either encouraged to make corrective saccades, following the target wherever it is; or prohibited from making corrective saccades, stopping wherever the first saccade landed. Each of the 6 condition combinations was tested on different days to prevent transfer of adaptation.
A) Saccadic adaptation occurred in all encouraged conditions and in about half of prohibited conditions where participants unconsciously and unwillingly made secondary saccades. Six participants successfully ([[gt]]95% of trials) suppressed secondary saccades in [[gt]]1 of the prohibited conditions. When secondary saccades were suppressed, saccadic adaptation was abolished despite of the presence of retinal errors. B) Explicit knowledge did not affect saccadic adaptation: secondary saccades to the shifted target location resulted in saccadic adaptation even in color and bar conditions where participants could clearly tell that the target had assumed a new position and thus the movement wouldn't “correct” the error.
These results suggest that the adaptive change in saccade amplitude involves implicit processes arising from the corrective saccade, and is independent of explicit knowledge of the source of visual error.
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