Positive effects of variable practice conditions on subsequent motor memory consolidation and generalization are widely accepted and described as the contextual interference effect (CIE). However, the general benefits of CIE are low and these benefits might even depend on decreased retest performances in the blocked-practicing control group, caused by retroactive inhibition. The aim of this study was to investigate if CIE represents a true learning phenomenon or possibly reflects confounding effects of retroactive inhibition. We tested 48 healthy human participants adapting their reaching movements to three different force field magnitudes. Subjects practiced the force fields in either a Blocked (B), Random (R), or Constant (C) schedule. In addition, subjects of the Blocked group performed either a retest schedule that did (Blocked-Matched; BM) or did not (Blocked-Unmatched; BU) control for retroactive inhibition. Results showed that retroactive inhibition did not affect the results of the BU group much and that the Random group showed a better consolidation performance compared to both Blocked groups. However, compared to the Constant group, the Random group showed only slight benefits in its memory consolidation of the mean performance across all force field magnitudes and no benefits in absolute performance values. This indicates that CIE reflects a true motor learning phenomenon, which is independent of retroactive inhibition. However, random practice is not always beneficial over constant practice.

14Positive effects of variable practice conditions on subsequent motor memory consolidation and 15 generalization are widely accepted and described as the contextual interference effect (CIE). 16However, the general benefits of CIE are low and these benefits might even depend on decreased 17 retest performances in the blocked-practicing control group, caused by retroactive inhibition. The 18 aim of this study was to investigate if CIE represents a true learning phenomenon or possibly 19 reflects confounding effects of retroactive inhibition. We tested 48 healthy human participants 20 adapting their reaching movements to three different force field magnitudes. Subjects practiced the 21 force fields in either a Blocked (B), Random (R), or Constant (C) schedule. In addition, subjects of 22 the Blocked group performed either a retest schedule that did (Blocked-Matched; BM) or did not 23 (Blocked-Unmatched; BU) control for retroactive inhibition. Results showed that retroactive 24 inhibition did not affect the results of the BU group much and that the Random group showed a 25 better consolidation performance compared to both Blocked groups. However, compared to the 26 Constant group, the Random group showed only slight benefits in its memory consolidation of the 27 mean performance across all force field magnitudes and no benefits in absolute performance 28 values. This indicates that CIE reflects a true motor learning phenomenon, which is independent 29 of retroactive inhibition. However, random practice is not always beneficial over constant practice. 30 31