Effects of object size and task goals on reaching kinematics in a non-immersive virtual environment

Object size (large vs. small) and task goal (reach at a comfortable pace vs. reach as fast as possible) are well-accepted task constraints that influence reaching kinematics. However, it is unclear whether these two constraints affect reaching in the virtual environment (VE). The purpose of this study was to examine the effects of these two task constraints in VE. Forty-one healthy adults (11 males; mean age 24.9 years old) participated in this study. All adults were asked to play bubble popping games that ran on our virtual reality (VR) platform (SuperPop VR™), which can precisely measure reaching kinematics (including duration, straightness, jerkiness, and speed) in real time. Participants were blinded to the study purposes, and two task constraints were manipulated: bubble size (small vs. large) and goal (comfortable vs. fast). Participants began with their dominant hand for each condition and alternated hands after each condition was tested three times. A repeated ANOVA was used for analyses. Reaches for small bubbles had longer duration, faster speed, and jerkier with more curved trajectories than reaches for large bubbles; reaches for small bubbles also had larger elbow and shoulder range of motion than reaches for large bubbles. In addition, reaches during participants' comfortable pace had longer duration, slower speed, and larger shoulder range of motion than reaches during their fast pace. Additionally, participants' non-dominant hands had faster speed than their dominant hands. Our findings confirmed that object size and task goals affected reaching kinematics even during VR games. When designing a VR evaluation and intervention program for clinical populations, it is important to consider the virtual object size and task goals as factors in influencing a participant's performance.