It is the most natural and intuitive way to interact with objects directly using our hands. But by doing so, we're limited to be able to only interact with objects within reach. Because of this, researchers have been keen to explore ways to expand our ability to use our hands to interact with objects beyond our arm length. These kinds of methods are normally called hyper-natural interaction because it extends users' natural movements by giving them superpowers. For instance, we can extend user's arms. We can give the user much longer arms and linearly map the virtual hands' movement to their real hands. So, when my hands are 10 centimeters in front of me, my virtual hands are 40 centimeters away, and when my hands are 70 centimeters away, my virtual hands are 280 centimeters away. This might feel a bit weird and unnatural as generally we have a good sense of where our hands are and how much they have moved. We're in particular sensitive to discrepancies when we have our arm relatively close to our body. As for most of the tasks we do in everyday life, we have our hands within this range. A more carefully thought and very famous attempt to generate the illusion of arm extension is the go-go technique created by Poupyrev et al. in 1996. It defines a radius around the user about two thirds of their physical arm length, an area we're very sensitive and familiar with. And within this radius, the user has a direct one-to-one mapping of their physical hand to the virtual one. So I'll be interacting with objects within this range just like I do in real life. But beyond this radius, the virtual arm is designed to be mapped non-linearly to the real arm, which allows the virtual arm to be further away than the real arm. Just like when my arm is about 45 centimeters away from me, the virtual arm is also 45 centimeters long, but after this point, it starts to grow longer. And the further away my real arm is, the longer my virtual arm grows. So when I fully extend my arms, which is probably about 70 centimeters long, my virtual arm could be about 200 centimeters away from me, depending on how I set the parameters in the equation. This method enables the user to reach things further out and the parameters can be adjusted depending on the task and user's personal preference, but the equation itself limits the maximum distance the users could grow their arms, which reflects our limitation in selecting and manipulating distant objects. Finally, the equation also creates a smooth transition between the linear and non-linear mapping, which means that the arm will gradually increase and it will be very subtle and not noticeable. Overall, the go-go technique is very intuitive and easy to learn. And unlike some other methods which allow the user to grow their arms infinitely, this method puts constraints to how much and how quickly we should grow our arms. These constraints reflect our natural ability in dealing with objects from a distance and thus prevent this superpower from becoming out of control.
