# Movement Time and Subjective Rating of Difficulty in Real and Virtual Pipe Transferring Tasks
###### Abstract  
An experiment was performed to investigate the movement time (MT) and subjective rating of difficulty for real and virtual pipe transferring tasks. Thirty adults joined as human participants. The HoloPipes app in a Microsoft(r) Hololens 2 augmented reality (AR) device was adopted to generate virtual pipes. The participants performed pipe transferring trials, from one location to another on a workbench, in both lateral and anterior-posterior directions. For the lateral transferring tasks, pipes in three diameters with three transferring distances and two origins were tested. For the anterior-posterior transferring tasks, pipes with a diameter of 2.2 cm with three transferring distances and two origins were tested. It was found that the MT of transferring a virtual pipe was significantly (\(p<0.0001\)) shorter than that of transferring a real pipe. Moreover, male participants transferred the pipe significantly (\(p<0.0001\)) faster than their female counterparts. Thus, the hypothesis that transferring a virtual pipe is less efficient than transferring a real pipe was rejected. It was also found that the MT of transferring both a real and a virtual object was dependent upon gender, handedness, and the transferring direction. In addition, the subjective rating of difficulty in pipe transferring is positively correlated (\(r=0.48,p<0.0001\)) with the MT. Based on Fitts' law, additive MT models were proposed. These models could be used to predict the MT between handling real and virtual pipes under gender, handedness, and transferring direction conditions. augmented reality; movement time; object transfer; Fitts' law; human-virtual object interaction +
Footnote †: journal: Medical  
where a and b are constants which may be determined by experimental data. Mathematically, the ID in Equation (2) has no units and a \"bit\" is given to this term as the unit to indicate the quantity of information involved in the movement [22]. In [PERSON] study, it was defined as \(\log_{2}(2\)D/W) and ranged from 1 to 7 bit for the tapping tasks using a stylus, 4 to 10 bit for disc transfer tasks, and 3 to 10 bit for pin transfer tasks [2; 3]. The a and b in Equation (2) are the intercept and slope of the linear equation, respectively. They have been adopted to assess the interface of human-machine systems where movements of body segments are required. To determine these regression coefficients, tasks and scenarios with levels of ID were manipulated and the MT data under each ID level were collected to fit the regression formula [23]. Since the inception of the Fitts' law in 1954 [2], numerous studies discussing the fitness of this law in explaining MT have been reported. Some earlier studies have proposed revisions of the ID to remedy the negative ID problem since negative ID does not exist and is not allowed [24; 25]. The literature has proposed more than a dozen alternative ID definitions, including \(\log_{2}(\text{D/W})\), \(\log_{2}((\text{D/W})+0.5)\), \(\log_{2}((\text{D/W})+1)\), and so on [26; 27; 28]. Instead of logarithm functions, power functions have also been proposed to estimate the difficulty of the tasks [29; 30]. Some of the studies have shown that ID may be estimated simply using D or D\({}^{1/2}\) when it is less than three [31; 32]. This implies that target size may be neglected in determining ID under such circumstances. [PERSON] [33] has considered the width of the finger and adopted a pad size of the finger index in the ID equation. [PERSON] and [PERSON] [34] indicated that the ID in a pointing task could be decreased by expanding the target size, even at the final stage of hand movement. This implies that the ID, instead of a constant, might be changed before a body segment has reached the target in a Fitts' task. Even with so many ID variants proposed, the original definition of ID has still been widely adopted [35; 36]. In addition to the revisions of the ID, additive MT models based on the original Fitts' equation have also been proposed.