Visuomotor Adaptation in a Viewing Window Task Figure 2. Experimental design of the Viewing Window task. The first five trials were used as practise and therefore excluded from all analysis. No distortion was present in movement of the Viewing Window during trials 6–9. During trials 10–36, in two separate groups, participants either received a gradual progressive distortion of 2.5u in the counter-clockwise direction on each trial, or a large sudden distortion in either direction. For analysis, these trials were divided in half in two phases (early and late). On trial 37 the distortion was removed and control of the Viewing Window returned to normal for the remainder of the study to examine after-effects. doi:10.1371/journal.pone.0048759.g002 The first five trials were removed as practice trials. The remaining data sets were exported to SPSS 13.0. Data was filtered to exclude trials in which the object was incorrectly identified and to consider only data acquired after movement of the window was first initiated for each trial. Measures of movement behaviour examined included the velocity of the Viewing Window, time the image was viewed (scan time), and the percentage of the time the Viewing Window spent on the object. For each subject, trials were identified as outliers by calculating the Z scores for each of the examined behavioural measures and excluding data beyond 2.5 standard deviations from all subsequent analyses. To examine differences between groups during the distortion trials, the movement velocities, scan times and percentage of time spent off the object were analyzed with ANOVA with Bonferroni correction (alpha 0.05). To examine changes in behaviour over the course of the experiment the trials were then divided into the pre-distortion phase (trials 6–9), early distortion phase (trials 10–22), late distortion phase (trials 23–36), and post distortion phase (trials 37–40). To examine phase interactions within groups, a repeated- measures ANOVA was conducted. For each subject, data were normalized by subtracting the mean of the appropriate beha- vioural measure obtained during the pre-distortion period. For example, to normalize the measurement of mean scan time during the early distortion period for subject X, the mean scan time found during the pre-distortion phase (trials 6–9) was subtracted from the mean scan time found during the early distortion phase (trials 10– 22). This process was repeated for each phase, for each behavioural measure, and for each subject. The normalized data were then analyzed with a repeated measures ANOVA with Bonferroni correction using a factor structure for each behavioural measure of a 2 [Group:Gradual vs Sudden distortion] 6 3 [Phase: Early, Late, Post distortion]. The scan paths of Viewing Window movement were visually inspected. Results Group comparisons revealed several anticipated behavioural differences (Figure 3). Subjects in the gradual rotation group demonstrated significantly faster mean velocities of movement compared to the sudden rotation group (F(1,38) = 5.406, p,0.05 Figure 3A). No significant difference in scan times were identified (F(1,38) = 1.185, p.0.05, Figure 3B). The gradual rotation group spent significantly less time scanning areas off the object (F(1, 38) = 4.620, p,0.05, Figure 3C). The faster velocities and ability to keep the window on the object, suggest that the gradual rotation group experienced less difficulty in controlling the movement of the window and adapted easily to the distortions. The slower movement velocities and greater time off the object observed in the sudden rotation group suggest that participants did experience some difficulty in controlling the Viewing Window movement. When data were divided into pre, early, late, and post distortion periods, several behavioural differences between groups were visible. Figure 4 depicts sample scan paths from one representative subject in the gradual rotation group and another representative subject from the sudden rotation group. The gradual rotation subject demonstrates fairly simple scan paths during the distortion trials indicating good control over window movement. However, once the distortion is removed, the same participant shows after- effects in the form of difficultly in keeping the Viewing Window on the object. In contrast to this behaviour, the participant in the distortion group shows a complicated scan path and therefore more difficulty when the distortion is first introduced. By the last distortion trial, the same participant has adapted and shows PLOS ONE | www.plosone.org 4 November 2012 | Volume 7 | Issue 11 | e48759