Effect of task and eccentricity of the target on detection thresholds in mesopic vision:: Implications for road lighting

Objective: The aim of this work is to assess how adding a driving-related task affects the detection of objects in peripheral vision, under mesopic conditions. Background: The main index used to assess the quality of road lighting installations refers to simple detection tasks in foveal vision, which raises methodological and practical questions. Method: The experimental design consisted of a three-phase experiment. In the first phase, two groups (control and experimental) per-formed a peripheral detection task (simple task). Based on these results an individual detection threshold was computed for each participant and eccentricity. A tracking task was performed in Phase 2 for both groups (steering a tracking target along a circuit, on a screen). In the third phase, the control group performed the same task as in Phase 2. The experimental group performed a double task, with a tracking (primary) task and a peripheral detection (secondary) task. Results: The data show an effect of the tracking task and eccentricity on peripheral event detection. The tracking task caused detection performance to decrease from 84.2% to 67.5%, p < .001. Conclusion: The small target visibility model used in road lighting may be improved, taking into account the effects of task and eccentricity on target detection. Application: This study supports improved roadway lighting design by guiding consideration of sign eccentricity and task load.