It has been proposed in the past that adaptation to rotated visual feedback is based on directionally tuned modules. Here, we investigate whether adaptation depends on the number of modules that are concurrently activated. To disambiguate the number of modules and their spatial overlap, we decided to vary the number of target directions and their spacing independently. In light of recent work on the existence of fast and slow adaptive processes, we analyzed the role of target number and spacing separately for the first eight movements under rotated visual feedback and for later movements. We found that during the first eight movements, adaptation progressed three times faster when targets were spaced across a 42° rather than across a 360° range, irrespective of their number. During the subsequent movements, adaptation progressed 1.66 times faster with two than with eight targets, irrespective of their spacing. This differential dependence of early and late adaptation on target metrics confirms the existence of adaptive processes with different time scales and suggests that those processes differ not only by their clocking speed, but also by their functional properties. Specifically, the speed of fast processes seems to be constrained by the directional tuning width of adaptive modules, and the speed of slow processes by the number of presentations per target direction.
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Randomization was performed with the in C++ statement “rand” after seeding with “srand”.
Movement onset was defined by a velocity threshold of 30 mm/s.
We decided for eight movements to represent fast adaptive processes since all target directions were presented equally often within eight movements (see "Procedures"). This is slightly less than the ten or twelve movements selected in earlier studies on adaptation to mirror reversals (Stratton et al. 2007) and force fields (Smith et al. 2006), respectively. Since the first eight adaptation movements in the present study took about 30 s, our choice is comparable to the value determined for fast adaptation to visual rotations in psychophysical experiments (Inoue et al. 2000). We are therefore confident that our analysis didn’t exceed the temporal limits of fast processes.
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This work was supported by the German Space Agency DLR on behalf of the Bundesministeriu für Wirtschaft und Technologie (Grant 50WB0625). Thanks are due to Dipl.-Ing. (FH) L. Geisen for software development and to V. Rohde, K. Friederichs, and M. Hinrichs for their help with data collection and analysis.
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Bock, O., Schmitz, G. Adaptation to rotated visual feedback depends on the number and spread of target directions. Exp Brain Res 209, 409–413 (2011). https://doi.org/10.1007/s00221-011-2564-8
- Motor learning
- Tuning curves