Three-Dimensional Mapping of Exploratory Priority in a Full-Sphere Workspace Using Immersive Virtual Reality

Technical Summary: Three-Dimensional Mapping of Exploratory Priority in a Full-Sphere Workspace Using Immersive Virtual Reality

Problem Statement

Traditional assessments of spatial attention, such as paper-and-pencil tests or 2D computer monitors, fail to capture exploratory behavior across a full three-dimensional (3D) workspace. These methods introduce geometric confounders where peripheral targets are physically farther from the eye than central targets, modulating attention based on viewing distance rather than pure spatial priority. Furthermore, while spatial attention is known to be non-uniform in 2D planes (e.g., "pseudoneglect" or leftward bias), the attentional organization at the top, bottom, back, and lateral poles of a fully surrounding 3D environment remains largely unexplored. Existing immersive virtual reality (iVR) paradigms are often limited to frontal arcs or hemispheres, or they rely on complex ecological environments that introduce uncontrolled confounders like varying visual salience and semantic associations. There is a critical lack of normative data and a standardized framework for quantifying 3D spatial attention in a rigorously controlled, full-sphere volume.

Methodology

The study employed a novel, head-position-anchored spherical iVR paradigm to map exploratory priority in healthy adults.

• Participants: The study involved 60 healthy adults (mean age 21.0 ± 0.5 years). To ensure mathematical comparability for sequence-based scoring, the primary analysis focused on an omission-free subset of right-handed participants (n=44 for the left-hand task; n=47 for the right-hand task).
• Apparatus: The environment was built in Unity and delivered via an HTC Vive HMD with a Leap Motion Controller for markerless hand tracking.
• Stimuli and Layout: 62 non-symbolic spherical targets (50 mm diameter) were arranged on a virtual sphere with a fixed radius of 0.4 m relative to the participant's head. The layout utilized randomized irregular offsets to prevent predictable patterns while maintaining equidistant spacing from the user. This design necessitated active multiaxial exploration (head and body rotation) to access all targets.
• Task Procedure: Participants performed two separate trials (right-hand and left-hand tasks) in randomized order. They were instructed to search for and touch all 61 white targets (excluding the red start pole) using the index fingertip of the designated hand. The task had no time limit; the primary metric was the sequence of contact.
• Scoring and Analysis: Targets were scored by contact order (1 = first contacted, 61 = last contacted). Higher scores indicate lower attentional priority (later contact).
  • Omission Analysis: Conducted on the full cohort (n=60) to identify missed targets.
  • Cluster Analysis: Hierarchical clustering (Ward method) was performed on the omission-free dataset to identify spatial groupings. Optimal cluster numbers were determined using Calinski–Harabasz, Silhouette, and Davies–Bouldin indices.
  • Statistical Testing: Kruskal–Wallis and Friedman tests were used for overall effects, followed by Dunn's post-hoc comparisons. Laterality (hand) differences were assessed using Wilcoxon matched-pairs signed rank tests with False Discovery Rate (FDR) correction.

Key Results

The study identified three primary patterns of 3D exploratory priority:

1. Vertical Omission Concentration and Variability:

   • 21.7% of participants failed to contact at least one target. Omissions were non-uniformly distributed, heavily concentrated in the lower peripersonal space (approximately 0.2 m below head level) and the overhead region.
   • The vertical poles (Top and Bottom) exhibited the highest inter-individual variability (standard deviation) compared to horizontal poles, suggesting that vertical exploration is highly sensitive to individual differences in spatial cognitive styles or motor strategies.

2. Horizontal Asymmetry (Pseudoneglect-like Pattern):

   • A consistent leftward bias was observed at the horizontal poles and within the rear workspace. In the right-hand task, the Right pole received significantly higher scores (later contact) than the Left pole, indicating a priority for the left field.
   • In the rear workspace, the back-left cluster showed significantly lower scores (higher priority) than the back-right cluster.
   • This asymmetry was present but statistically attenuated when using the non-dominant (left) hand, suggesting that motor factors (e.g., right hemisphere activation) may modulate the magnitude of the bias.

3. Frontal Gradients and Spatial Organization:

   • Within the frontal workspace, scores followed a medial-to-lateral increase, meaning targets closer to the midline were contacted earlier than those in the lateral periphery.
   • A robust front-to-back gradient was observed, with scores increasing progressively from the front-medial region to the back regions. This suggests a proximity-based search strategy where participants prioritize nearby targets first.
   • Hand Dissociation: A spatial dissociation of hand advantage was identified relative to a horizontal boundary at -0.2 m. Above this boundary, hand advantages followed an ipsilateral pattern (right hand better on the right, left hand better on the left). Below this boundary, the pattern reversed to a contralateral advantage.

Significance and Claims

The authors claim that this study provides a preliminary reference dataset and a controlled framework for quantifying 3D exploratory behavior in healthy young adults.

• Methodological Contribution: The study demonstrates that iVR can successfully extend the logic of classic 2D cancellation tasks into a full-sphere volumetric space, revealing attentional priorities (such as rear-space leftward bias) that are often masked by ceiling effects or limited spatial ranges in 2D assessments.
• Theoretical Insight: The findings reveal a non-uniform spatial organization of 3D exploratory priority across both vertical and horizontal dimensions. The consistency of spatial patterns across right- and left-hand tasks supports the interpretation that these distributions reflect robust attentional priorities rather than purely effector-related motor strategies, although the study acknowledges it does not fully separate the two.
• Clinical and Practical Application: The authors posit that this framework serves as a foundation for future validation studies in clinical populations with spatial disorders, such as hemispatial neglect. Additionally, the results may inform the placement of critical information in everyday 3D environments by aligning displays with regional human attentional priorities.

The paper remains modest in its claims, noting that the findings are hypothesis-generating and that the observed patterns represent associations rather than sharp anatomical boundaries. It highlights the need for future studies with age-diverse cohorts and randomized starting positions to further isolate intrinsic attentional bias from biomechanical factors.