Visuomotor Adaptation in a Viewing Window Task Figure 4. Sample scan paths from representative participants. A) gradual rotation group and B) sudden rotation group. The line represents the pathway of the viewing window from image onset until participant signal of image identification. doi:10.1371/journal.pone.0048759.g004 of more relevance is how behaviour changes over the course of study, therefore, an examination of behaviour by phase was also conducted. When the trials were divided into four phases: pre, early, late, post distortion phases; no significant interaction between distortion type and phase of the experiment were found for movement velocities and scan times. However, a significant effect of phase was found. We anticipate that scan time is not only influenced by the ability to move the Viewing Window to the desired areas of the computer screen but also by the participant’s familiarity with the type of object. The item list contained a variety of everyday objects that most people would encounter including, fruits, vegetables, tools, office supplies, and musical instruments. However, how quickly these are identified can be expected to be influenced by how often a participant encounters these particular items. For example, a person who does not often interact with tools may have more difficulty identifying the image of the vice grips. The ability to recognize the objects may also be influenced by the perspective of the images. The items were displayed with variable orientation which could affect the difficulty of the task. Even though this strengthens the task in terms of increasing the variability of the location of valuable information on the computer screen, the changing perspective could also affective the ability to identify the objects. This is not something that was controlled, however, it was one reason for using counterbalanced lists in the two groups so that any effects would not drive the results of any particular phase of the study. In addition, it is possible that participants may have improved their scan times over the course of the experiment as they because more familiar with the task. We excluded the first items to account for practice trials. It is possible that subjects are more likely to hesitate in signalling their response at the start of the experiment while the task is still novel and answer more quickly later in the study when they become more confident. These influences contributed to the observation of decreased mean scan time between the late and post distortion phases (Figure 5B) despite the mean velocities also decreasing (Figure 5 A). The decreased velocity indicates increased difficulty in controlling the window movement, however, participants were still able to quickly identify the masked objects. In the analysis of time spent off the object, a significant difference between groups was found indicating larger after effects in the gradual rotation group. The present study demonstrates that the Viewing Window is capable of distinguishing performance of both strategic control and spatial realignment and therefore is a powerful tool for measuring visuomotor adaptation behaviour. Even though sub- jects in the gradual rotation group did not report observing a change during the distortion trials, the large after-effects observed in their scan behaviour indicate adaptation took place. This is consistent with previous studies investigating gradual rotations [8]. In addition to behavioural differences, the neural basis of strategic control and spatial realignment are believed to differ. Strategic control primarily recruits posterior parietal cortex PLOS ONE | www.plosone.org 6 November 2012 | Volume 7 | Issue 11 | e48759