Effects of Small Latency Variations in 2D Target Selection Tasks

Paper Title

Effects of Small Latency Variations in 2D Target Selection Tasks

Publication Info

• Topic area: Human-computer interaction and the effects of latency on user performance.
• Keywords: latency, latency variation, 2D pointing tasks, target selection, user performance, task load, human-computer interaction, Fitts' Law, moving targets, NASA-TLX.

Background and Problem

• Problem / challenge: Prior research has extensively studied the effects of constant latency and large latency variations, but the impact of small, frequent latency variations (±50 ms) on user performance and perceived task load remains unclear.
• Significance: Understanding the effects of small latency variations is critical for designing interactive systems, as such variations are common in real-world applications due to hardware, software, and network factors.
• Motivation and related work: Previous studies have shown that latency negatively impacts performance and user experience, but findings on latency variation are inconclusive. While large latency variations have been shown to degrade performance, small variations have been found to have negligible effects in complex tasks like first-person shooters. This study seeks to address the gap by isolating the effects of small latency variations in controlled 2D pointing tasks.

Solution

• Proposed approach: A controlled lab study investigating the effects of small latency variations (±50 ms) on performance and task load in two 2D target selection tasks: one with static targets and one with moving targets.
• Novelty:
  1. Focus on small, realistic latency variations (±50 ms) rather than large or sudden changes.
  2. Comparison of effects across tasks of varying complexity (static vs. moving targets).
  3. Detailed analysis of performance metrics (task time, error rate, distance ratio) and subjective task load (NASA-TLX).
• Procedure and key techniques:
  • Conducted a within-subjects study with 32 participants.
  • Tested two levels of base latency (50 ms and 150 ms) and two levels of latency variation (±0 ms and ±50 ms).
  • Measured task time, error rate, distance ratio, and NASA-TLX scores for both static and moving target tasks.
  • Used a custom software tool to introduce controlled latency and latency variation.

Results

• Concrete findings:
  • Static targets: High base latency significantly increased task time (ηp² = 0.83) and distance ratio (ηp² = 0.15). Latency variation also significantly increased task time (ηp² = 0.09) and distance ratio (ηp² = 0.32), but with smaller effect sizes than base latency.
  • Moving targets: High base latency significantly increased task time (ηp² = 0.96), error rate (ηp² = 0.84), and distance ratio (ηp² = 0.51). Latency variation had no significant effect on any performance measure.
  • Task load: High base latency increased perceived task load across all NASA-TLX sub-scales except temporal demand. Latency variation increased mental demand for moving targets and frustration for static targets under low base latency.
• Advantage over baselines:
  • Demonstrated that small latency variations have minimal effects on performance in more complex tasks (e.g., moving targets).
  • Highlighted that effects of latency variation are overshadowed by base latency in most cases.
• Experiments / evaluation:
  • Tasks: 2D Fitts' Law task with static targets and a custom task with moving targets.
  • Metrics: Task time, error rate, distance ratio, NASA-TLX scores.
  • Participants: 32 individuals with diverse gaming habits, using a balanced Latin square design to counter sequence effects.
• Limitations and future work:
  • Limited to uniform latency variation of ±50 ms; larger ranges or other distributions could reveal stronger effects.
  • Short task durations may not allow full adaptation to latency conditions.
  • Homogeneous participant sample (university students) limits generalizability.
  • Future work should explore longer tasks, adaptation over time, and effects of larger or sudden latency variations.

Summary

This study investigated the effects of small latency variations (±50 ms) on user performance and task load in 2D target selection tasks. High base latency consistently degraded performance and increased task load, while latency variation had small effects on static targets and no measurable impact on moving targets. These findings suggest that small latency variations are unlikely to affect performance in complex tasks but may influence simpler tasks under controlled conditions. The results provide foundational insights for designing low-latency systems and highlight the need for further research into adaptation and broader latency conditions.