On-to-off-path gaze shift cancellations lead to gaze concentration in cognitively loaded car drivers: A simulator study exploring gaze patterns in relation to a cognitive task and the traffic environment

Emma J Nilsson,Trent Victor,Mikael Ljung Aust,Bo Svanberg,Per Lindén,Pär Gustavsson

doi:10.1016/j.trf.2020.09.013

Abstract

Appropriate visual behaviour is necessary for safe driving. Many previous studies have found that when performing non-visual cognitive tasks, drivers typically display an increased amount of on-path glances, along with a deteriorated visual scanning pattern towards potential hazards at locations outside their future travel path (off-path locations). This is often referred to as a gaze concentration effect. However, what has not been explored is more precisely how and when gaze concentration arises in relation to the cognitive task, and to what extent the timing of glances towards traffic-situation relevant off-path locations is affected. To investigate these specific topics, a driving simulator study was carried out. Car drivers’ visual behaviour during execution of a cognitive task (n-back) was studied during two traffic scenarios; one when driving through an intersection and one when passing a hidden exit. Aside from the expected gaze concentration effect, several novel findings that may explain this effect were observed. It was found that gaze shifts from an on-path to an off-path location were inhibited during increased cognitive load. However, gaze shifts in the other direction, that is, from an off-path to an on-path location, remained unaffected. This resulted in on-path glances increasing in duration, while off-path glances decreased in number. Furthermore, the inhibited off-path glances were typically not compensated for later. That is, off-path glances were cancelled, not delayed. This was the case both in relation to the cognitive task (near-term) and the traffic environment (far-term). There was thus a general reduction in the number of glances towards situationally relevant off-path locations, but the timing of the remaining glances was unaffected. These findings provide a deeper understanding of the mechanism behind gaze concentration and can contribute to both understanding and prediction of safety relevant effects of cognitive load in car drivers.

Highlights

Car driving is a largely visual task
We explored the gaze concentration effect on a high-resolution time scale in relation to both the traffic environment and the variations in cognitive load caused by the cognitive tasks
Because glances towards the hedge along the road appear to be searching for the exit, both the Exit and the Hedge along road areas of interest (AOIs) can be considered as glances towards the potential threat

Summary

Introduction

Car driving is a largely visual task. It can be described as a form of continuous adaptation to the traffic environment based on visual information. Maintaining a glance behaviour appropriate for the current traffic situation, where areas with important information are appropriately scanned, is crucial for safe driving. In naturalistic tasks, such as driving, gaze patterns are determined both by bottom-up mechanisms such as objects’ size, colour, luminance and movement, as well as by top-down mechanisms, or expectations (Itti & Koch, 2001; Wickens, 2015). Timing wise, guiding fixations lead the ongoing action by about one second, while occasional look-ahead-fixations appear to anticipate later actions and target objects or locations further into the future (Land, 2006; Mennie, Hayhoe, & Sullivan, 2007)

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