Abstract
Our recent study has shown that simian saccadic adaptation is accelerated by preceding adaptation and that this facilitatory effect is nullified by repetition of zero-error movements. This suggests that a memory of learning is erased by such movements. In the present study, we examined effects of zero-error movements on the metrics of saccades. Using intrasaccadic target step (ISS) paradigm, we decreased the gain of saccades to 10 deg target steps in one horizontal direction (1st adaptation). We reversed ISS to bring the gain back to ∼1.0 (recovery), after which we required the animal to make zero-error saccades for 30 min (zero-error block). Then we reversed ISS again to induce another gain decrease (2nd adaptation). Saccades with sizes of 9.1-10.0 deg were sorted into 0.1 deg bins, and the duration and peak velocity of saccades having a similar amplitude were compared. For a given amplitude, the duration decreased during 1st adaptation and was still shorter in the early zero-error block than in preadaptation block. However, by the late zero-error block, the duration returned to a preadaptation level. Duration then decreased in subsequent 2nd adaptation as in 1st adaptation. Correspondingly, the peak velocity showed opposite changes. Saccades in non-adapted direction did not exhibit similar changes. Results are consistent with our previous suggestion that repetition of zero-error movements erases the memory of preceding learning and returns the saccadic system to a preadaptation state. [Jpn J Physiol 55 Suppl:S173 (2005)]
