A Review of Occlusion as a Tool to Assess Attentional Demand in Driving

Kujala, Tuomo; Kircher, Katja; Ahlström, Christer · 2021 · Crossref

DOI: 10.1177/00187208211010953

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Summary

This review paper examines the visual occlusion technique as a method for assessing attentional demand and spare visual capacity in driving. Developed by Senders et al. (1967), the technique involves intermittently blocking a driver’s forward visual field to estimate the frequency and duration of visual sampling required for safe vehicle control. The authors aim to synthesize findings from studies published between 1967 and 2020, evaluating the method’s utility, limitations, and contributions to understanding how drivers manage visual information. The review highlights that while occlusion provides unique insights into the temporal requirements of driving, it has been underutilized compared to eye-tracking methods, despite offering complementary data on when visual input is unnecessary. The authors conducted a systematic literature search using Google Scholar, identifying 2,130 results. After applying inclusion criteria—specifically requiring studies where the forward visual field was temporally occluded during active driving to assess visual demands—57 studies across 52 publications were included in the qualitative synthesis. The review categorizes these studies based on experimental settings, distinguishing between system-paced occlusion (where the experimenter controls timing) and self-paced occlusion (where the driver controls timing), as well as default states (occluded vs. unoccluded). This classification allows for an analysis of how different methodological approaches influence the measurement of spare visual capacity, defined as the fraction of time a driver can drive without visual input. The results indicate that spare visual capacity varies significantly based on situational and individual factors. Situational demands, such as higher speeds, narrower lanes, sharper curves, and complex road geometries, consistently reduce the amount of time drivers can safely occlude their vision. Conversely, simpler maneuvers and environments afford greater spare capacity. Driver assistance systems, such as adaptive cruise control and lane-keeping assistance, also reduce visual demand, though this may increase the risk of distraction. Inter-individual differences are substantial; older drivers generally require more frequent visual sampling than younger drivers, and experienced drivers demonstrate more proactive and efficient visual sampling strategies than novices. However, the review notes a lack of objective benchmarks to define the threshold between safe spare capacity and insufficient visual sampling, complicating the interpretation of occlusion data. The significance of this review lies in its argument for integrating visual occlusion with eye-tracking to achieve a more comprehensive understanding of driving attention. While eye-tracking identifies *what* drivers look at, occlusion reveals *when* visual information is strictly necessary, highlighting redundancy in visual sampling. The authors propose combining these methods with the Minimum Required Attention (MiRA) theory to better define attentional requirements in dynamic traffic scenarios. This approach has practical implications for human factors research, particularly in developing distraction detection algorithms and testing guidelines for in-vehicle systems. By accounting for individual variability and situational complexity, researchers can establish more accurate thresholds for safe driver attention, improving the design of automated systems and regulatory standards.

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Topics

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• visual occlusion
• visual
• attention
• useful field of view
• inattentional change blindness
• gaze based attention detection

Information type

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• Methodological Resource: measurement protocol, tool software
• Theoretical Contribution: theory or model