Could the Stylus Be Mightier Than the Controller?

Recent advancements in extended reality have enabled new peripheral types beyond standard controllers. Devices such as 3D-tracked styluses emulate the feel of traditional pens, offering a more familiar interaction style and higher precision. However, these spatial input devices are susceptible to the Heisenberg Effect of Spatial Interaction, where involuntary cursor movement is caused by the physical act of selection (e.g., button pressing), reducing selection accuracy. We present an exploratory investigation into the Heisenberg Effect using a 3D-tracked stylus (Logitech MX Ink) and a standard controller (Meta Quest Touch Plus). Through selection tasks across varying target widths, amplitudes, and actuation fingers, results indicate that styluses are less susceptible to the Heisenberg Effect than controllers. However, choice of actuation finger matters: thumb-based input produces significantly more unintended movement than index. We present these findings to open a discussion on the future of XR peripheral design to enable both fast and precise input.