How Fitts' Fits in 3D: A Tangible Twist on Spatial Tasks

TL;DR

This work extends Fitts' Law to 3D object manipulation within PointARs by evaluating how tangible cube size and spacing affect interaction metrics. It implements a Tangible Fitt’s Law Test Program with hand-tracking (MediaPipe Hands), real-time object detection (YOLOv5s), and UDP-based feedback, across nine cube-size/distance configurations and three participants, measuring movement time ($MT$), error rate, and throughput ($TP$). The results partially corroborate Fitts' Law: increased distance raises task difficulty, but larger object sizes unexpectedly increase $MT$ due to tracking limitations, with a weak $ID$–$MT$ relationship ($R^2 \approx 0.047$). The authors propose practical design guidelines—cube sizes of 1.5–2 inches and inter-cube spacing ≤2 inches—and call for broader configuration testing and refinement of the 3D $ID$ formulation to better predict performance in mixed reality spatial tasks. This work has potential to inform MR interface design and tangible interaction strategies for 3D pointer skills.

Abstract

Expanding Fitts' Law into a 3D context, we analyze PointARs, a mixed reality system that teaches pointer skills through an object manipulation task. Nine distinct configurations, varying in object sizes and distances, were explored to evaluate task complexity using metrics such as completion time, error rate, and throughput. Our results support Fitts' Law, showing that increased distances generally increase task difficulty. However, contrary to its predictions, larger objects also led to higher complexity, possibly due to the system's limitations in tracking them. Based on these findings, we suggest using tangible cubes between 1.5" and 2" in size and limiting the distance between objects to 2" for optimal interaction in the system's 3D space. Future research should explore additional configurations and shapes to further validate Fitts' Law in the context of 3D object manipulation in systems like PointARs. This could help refine guidelines for designing mixed reality interfaces.

Figures (8)

• Figure 1: Current actual space setup of the PointARs prototype.
• Figure 2: A photo of some of the tangibles in the current PointARs system.
• Figure 3: Overview of the steps in the evaluation protocol.
• Figure 4: Tangible space schematics of the experiment setup during data collection
• Figure 5: Average completion times per object size and distance.