Investigating How Physical Surfaces Can Serve as Common-Region Cues for Perceptual Grouping of Virtual Elements in Augmented Reality

Paper Title

Investigating How Physical Surfaces Can Serve as Common-Region Cues for Perceptual Grouping of Virtual Elements in Augmented Reality

Publication Info

• Topic area: Perceptual grouping of virtual elements in augmented reality environments.
• Keywords: perceptual grouping, augmented reality, common region, physical surfaces, proximity cues, 3D interaction, user studies, virtual elements, spatial factors, AR system design.

Background and Problem

• Problem / challenge: The role of physical surfaces as extrinsic grouping cues for virtual elements in augmented reality (AR) is not well understood, particularly in 3D environments where physical and virtual elements coexist.
• Significance: Understanding how physical contexts influence perceptual grouping can improve AR system design, enhance grouping clarity, and reduce ambiguities in user interpretation.
• Motivation and related work: Prior studies have explored intrinsic and extrinsic grouping principles (e.g., proximity, common region) in 2D and 3D contexts, but gaps remain in understanding how physical surfaces interact with virtual elements in AR. This paper builds on these principles to investigate the effects of physical surfaces as grouping cues in AR environments.

Solution

• Proposed approach: Two user studies were conducted to investigate how physical surfaces influence perceptual grouping of virtual elements in 3D and how these cues interact with intrinsic grouping principles like proximity in AR.
• Novelty:
  1. Systematic evaluation of physical surfaces as common-region cues in 3D using a repetition discrimination task in VR.
  2. Investigation of the interaction between extrinsic (common region) and intrinsic (proximity) grouping cues in AR environments.
  3. Design recommendations for AR systems to leverage physical environments for grouping tasks.
• Procedure and key techniques:
  1. Study 1: Conducted in VR to examine how spatial properties of surfaces (direction, distance, size) influence grouping using a repetition discrimination task (N=24).
  2. Study 2: Conducted in a video see-through AR (VST-AR) environment to explore interactions between proximity and common-region cues under cooperative, interfering, and competitive conditions (N=24).
  3. Measurements included response time (RT), subjective ratings, and user behavior during grouping tasks.

Results

• Concrete findings:
  1. In Study 1, surfaces served as common-region cues, with grouping effects stronger for vertical surfaces aligned with the viewing direction and weaker for distant or oblique surfaces.
  2. In Study 2, conflicting proximity and common-region cues led to slower RTs and higher subjective difficulty ratings, indicating perceptual challenges.
  3. Participants adopted diverse strategies to resolve ambiguities, including leveraging physical boundaries, seeking clean backgrounds, and adjusting proximity cues.
• Advantage over baselines:
  • Study 1 confirmed that spatial properties (e.g., surface direction, distance) significantly impact grouping in 3D.
  • Study 2 demonstrated that AR systems must account for interactions between physical and virtual grouping cues to reduce ambiguity.
• Experiments / evaluation:
  • Study 1: 24 participants, 1008 trials per participant, controlled VR environment, analysis of RT and dwell time.
  • Study 2: 24 participants, 84 trials per participant, VST-AR environment, analysis of RT, subjective ratings, and user behavior.
• Limitations and future work:
  • Limited exploration of large distance variations and diverse physical surface types.
  • Abstract tasks may restrict generalizability to real-world scenarios.
  • Future work should investigate thresholds for effective grouping cues, interactions with other grouping principles, and more complex AR scenarios.

Summary

This paper investigates how physical surfaces act as common-region cues for perceptual grouping of virtual elements in AR. Two user studies reveal that spatial properties like surface direction and distance influence grouping in 3D, and that conflicting grouping cues (proximity vs. common region) create perceptual challenges in AR. Participants employed various strategies to resolve ambiguities, highlighting the need for AR systems to align physical and virtual grouping cues. The findings inform design recommendations for leveraging physical environments in AR to enhance grouping clarity and reduce user confusion.