resulting movement of the Viewing Window. Subjects were divided into two groups according to the way in which this distortion was presented. To evoke strategic control, distortions had to be presented large enough to be noticeable, and in enough variety to avoid becoming predictable. In a previous pilot study we had utilized two large distortions in the counter-clockwise direction, pseudo-randomized with no distortion. However, to an adapted subject, a change from a counter-clockwise distorted trial to one with no distortion is similar to adapting to a change in the clockwise rotation. More problematic was that with only three conditions it was difficult to pseudo-randomize the change in control from one trial to another. In the present study, we aimed to pseudo-randomize the change experienced by the subject and so used two large distortions, but in either direction (four in total). Therefore, the group in which we aimed to evoke strategic control in, received large noticeable distortions of 0u, 34u, or 68u in either direction, so that the change in rotation from the previous trial was pseudo-randomized. In the second group, distortions incremen- tally increased in each trial by 2.5u in the counter-clockwise direction. In this distortion group, changes were cumulative in one direction as we wanted to end the distortion period at a large rotation, so that return to normal control in the post-distorted trial would be evident. Subjects received verbal instruction to try to identify the images as quickly and accurately as possible by using the trackball to move the window around the computer screen. Once subjects knew the identity of the object, they were to press the space bar on a keyboard and enter the name in a text box that appeared on the computer screen. The task would then move onto the next trial with a new masked image. The task therefore proceeded at the Visuomotor Adaptation in a Viewing Window Task subject’s own pace. Feedback regarding accuracy was not provided to the participant. To account for order effects, two lists of objects were used that were counterbalanced. Therefore, in each rotation group, ten subjects received one list of items and the other ten received the same list but the order of items in the experimental (distortion) period was reversed. Data Analysis All participants knew that the task was self-paced and so while they received the instruction to identify the object ‘‘as quickly and accurately as possible’’, time was not a limiting factor. It is possible that participants, motivated by the goal to identify the object, guessed at the object identity. To account for this, an accuracy threshold of 60% was applied to consider data from participants who were fully engaged in the task and the highest performing. This type of threshold was selected because it was the most objective. The use of a threshold more specific to the motor component of the task rather than the perceptual component may be more desirable in examining adaptation behaviour such as movement velocity, or the time off the object. However, establish- ing the level of this threshold is subjective. This is an interesting topic for further examination. As a result of the accuracy threshold, 18 subjects were excluded and so a total of 58 participants had to be recruited to obtain group sizes of 20 subjects for each experimental group. The resulting data analyzed was from 40 participants (14 male, mean age 19.561.9 years, range 18–26 years). An additional analysis of all 58 participants is presented in Supplementary Information S1. Figure 1. Experimental setup of the Viewing Window task. Subjects sat at a desktop workstation and viewed masked images on a 190 monitor. In order to identify the images, subjects used a trackball to control the movement of the Viewing Window that would allow part of the image to be seen clearly. Subjects were instructed to, upon identification of the image, press the space bar on the keyboard and enter the name of the object in a text box that would appear on the computer screen. The photographed subject has given written informed consent, as outlined in the PLoS consent form, to publication of their photograph. doi:10.1371/journal.pone.0048759.g001 PLOS ONE | www.plosone.org 3 November 2012 | Volume 7 | Issue 11 | e48759