Comparing Eye-Tracking Metrics with the Driver Activity Load Index

TL;DR

This study compares how eye-tracking and a subjective scale measure driver workload, finding that the scale mainly reflects perceptual strain.

Contribution

The study reveals that the Driver Activity Load Index (DALI) specifically captures perceptual overload rather than cognitive effort.

Findings

High-load driving scenes caused longer fixations, fewer blinks, and larger pupil dilation.

DALI scores increased with scene complexity and were linked to perceptual strain, not cognitive effort.

Eye-tracking metrics and DALI scores both support the specificity of DALI for measuring perceptual load.

Abstract

This study investigated how perceptual workload in driving situations is captured by subjective ratings versus eye-tracking metrics. Fifty participants completed low- and high-complexity conditions while fixation behavior, blinks, and pupil diameter were recorded, and workload was assessed using the DALI scale. High-load scenes elicited longer fixations, fewer fixations per minute, reduced blinking, and increased pupil dilation, indicating elevated attentional demand. DALI scores increased with scene complexity and were negatively associated with fixation duration, demonstrating that participants’ subjective ratings were driven primarily by perceptual strain rather than cognitive effort. Eye-tracking patterns supported this interpretation: fixation-based indicators tent to reflect the cognitive component of demand, whereas DALI selectively tracked perceptual overload. Together, these results show that DALI is highly sensitive to visual density, and that eye-movement measures provide converging evidence for its specificity as a perceptual load instrument.

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