experiment. In their task, participants moved a marker to one of four targets while having no vision of their moving arm or hand. Klassen et al. [10] used an out-and back target task to one of eight targets where in a gradual condition increments of 0.125u were introduced to a maximum of 30u in a gradual distortion group. Even though these tasks have revealed important information regarding visuomotor adaptation behaviour and its neural basis, they are simplistic as they require one trajectory of movement therefore limiting the internal model a participant is capable of building during adaptation. In order to investigate visuomotor adaptation in a more natural, enriched setting, our lab has developed a computer-based task, the Viewing Window [12,13,14]. The paradigm is a visuomotor experiment hidden within a perceptual task. Subjects view a blurred or masked image of an object on a computer screen with the instruction to identify the object as quickly and accurately as possible. To accomplish this, they must move a small, circular region, the Viewing Window, around the screen using a touch sensitive screen, trackball or joystick. The task has previously been used during reading and text comprehension tasks [15,16], as well as scene exploration [17], to investigate visual attention and perception. More recently, our lab has used to this task to investigate visuomotor adaptation by manipulating the relationship between the actions of the participant and the resulting movement of the window [14]. By restricting the region of an object that can be viewed clearly, the visuomotor scanning pattern can be analyzed. The benefits of the Viewing Window over traditional prism experiments is that this task requires minimal experimenter instruction, distortions can be presented in finer and progressive increments, it can be performed on a compact tablet PC therefore it is highly portable, and precise timing and spatial information regarding viewing window movement and object identification can be recorded. Our previous studies with the Viewing Window task have utilized large distortions in the form of flips in Viewing Window movement in the horizontal and vertical direction and so it would be anticipated that strategic control would be the predominant mechanism of visuomotor adaptation [12,13,14]. The use of this task has revealed novel recruitment of the claustrum, not found in previous studies of visuomotor adaptation [12]. The purpose of the present study is to demonstrate that the viewing window paradigm can be used to investigate both strategic control and spatial realignment. We hypothesize that distinct behaviours between participants using strategic control and those who adapt using spatial realignment can be measured using the Viewing Window paradigm. In line with our previous Viewing Window studies, we anticipate participants in the sudden rotation group will demonstrate difficulty in controlling the window when the distortion is initially introduced, which will be reflected by more complicated paths of movement, slower velocities of movement, and more time spent off the object during the first half (early phase) of the trials. As the experiment progresses, we hypothesize the participants will adapt and their performance evaluated by these measures will improve during the second half of the distortion trials (late phase) and will continue to do so once the distortion is removed. In contrast, we hypothesize that participants in the gradual rotation group will not notice the introduced distortion and so changes in behaviour in the form of movement velocities, the time taken to identify the viewed object (scan time), and the time that the Viewing Window spent on areas that did not contain object image (time off object), will be minimal during the early and late phase distortion trials and the paths of window movement will be more simple with fewer changes in direction compared to the sudden rotation group. However, once the distortion is removed in the post-distortion Visuomotor Adaptation in a Viewing Window Task phase, we hypothesize that participants in the gradual rotation group will show greater after-effects in the form of decreased performance of these measures. The ability to distinguish and measure behavioural differences between groups will demonstrate that the Viewing Window task can be used to evaluate performance of both strategic control and spatial realignment. The ability to use the Viewing Window to measure behaviour during strategic control and spatial realignment would provide a novel, powerful tool for examining visuomotor adaptation. This would expand the repertoire of experimental designs available for investigating visuomotor adaptation in healthy individuals and in decline due to natural aging, and neural injury and degenerative disease. Methods Subjects Written informed consent was obtained from all subjects prior to the study. Fifty-eight right-handed, first year psychology students with normal or corrected-to-normal vision (15 male) were recruited from the University of Manitoba psychology participant pool. Subjects received course credit for participating in the study. This research was approved by the Human Research Ethics Board at the University of Manitoba. Prior to start of the experiment, subjects were familiarized with the response equipment, a track ball, used in the study. Participants were presented with a medium difficulty maze (set 5) acquired from www.printablemazes.net and asked to guide a computer cursor through the maze to get acquainted with the sensitivity of the trackball. Participants were aware that no data were being collected during this time and that it was self-paced. The Viewing Window Task The Viewing Window task [14], is an in-house software program written in MatlabH (2007b, MathWorks, Natick, MA), run on a Dell tablet computer and presented to the participant on a 190 LCD monitor. During the present study our methods were modified slightly from our previously published studies [12,13,14]. During pilot testing, the sudden rotation distortions were not apparent to all subjects when a blurred image was presented. Therefore, clear images of the objects were overlaid with a black mask. As a result, subjects could not obtain any additional cues as to where useful information may be, resulting in a much more difficult task. The number of trials therefore had to be reduced to maintain an acceptable duration of experiment and prevent subject fatigue. In the present study, 40 trials were presented which all subjects completed in less than one hour. During each trial a masked picture of an everyday object would appear at 1280 6 1024 resolution. All participants viewed the same 40 images however, to control for order effects, 2 counterbalanced lists were used so that half the participants in each experimental group would view the list in one order, and the other half would view the list in the reverse order. No images were viewed more than once by each participant. Even though there was some variation in the size of the image of the object, all images were larger than the size of the Viewing Window so that no object could be seen in its entirety without moving the Window. The goal of the task was to identify the object as quickly and accurately as possible. To do this, subjects used a trackball to control the Viewing Window, a small circular region through which part of the object could be seen completely clearly (Figure 1). During the first 9 and last 4 trials the movement of the viewing window was controlled normally by the trackball (Figure 2). During the 27 trials in between, a distortion was introduced between the movement of the trackball and the PLOS ONE | www.plosone.org 2 November 2012 | Volume 7 | Issue 11 | e48759