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Steffen Klingenhoefer, Frank Bremmer; Foveation Time as a Driving Factor of Saccade Adaptation. Journal of Vision 2010;10(7):501. doi: 10.1167/10.7.501.
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It is well known that the oculomotor system is able to maintain its accuracy despite of changing conditions that otherwise would lead to movement inaccuracy and poor vision. In the laboratory this effect - usually termed saccade adaptation - is typically studied by a perisaccadic displacement of the saccade target either in (forward adaptation) or against the saccade direction (backward adaptation). Both conditions induce a change in saccade gain. Initially, however, errors due to the perisaccadic target step are compensated for by corrective saccades. In general, backward adaptation builds up more quickly and reaches larger adaptation amplitudes than forward adaptation. At present, the reason for this asymmetry is not fully understood. Previous studies suggested that the oculomotor system strives to minimize the saccadic flight time thereby maximizing the time of high resolution vision. In this vein the adaptation process should also be governed by temporal optimization. Accordingly, a faster adaptation would be required in case of longer latencies for corrective saccades. In a first experiment, we measured the latencies of subjects' corrective saccades. To this aim, we displaced the saccade target perisaccadically by a small amount to a random position, thus promoting corrective saccades of different directions and amplitudes. Additionally, we tested the subjects' behavior in forward and backward saccade adaptation paradigms. Our results confirm previous findings. Forward adaptation was slower and less complete than backward adaptation. In line with our hypothesis, we observed shorter latencies for corrective saccades in forward direction compared to those in the opposite direction. The inter-subject variability for the difference in latencies correlated with the observed asymmetry in gain adaptation. Therefore, we suggest foveation time as a driving factor of saccadic gain adaptation.
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