Optic flow speed modulates guidance level control: New insights into two-level steering.

Abstract

Responding to changes in the road ahead is essential for successful driving. Steering control can be modeled using 2 complementary mechanisms: guidance control (to anticipate future steering requirements) and compensatory control (to stabilize position-in-lane). Drivers seem to rapidly sample the visual information needed for steering using active gaze patterns, but the way in which this perceptual information is combined remains unclear. Influential models of steering capture many steering behaviors using just ‘far’ and ‘near’ road regions to inform guidance and compensatory control respectively (Salvucci & Gray, 2004). However, optic flow can influence steering even when road-edges are visible (Kountouriotis, Mole, Merat, & Wilkie, 2016). Two experiments assessed whether flow selectively interacted with compensatory and/or guidance levels of steering control, under either unconstrained gaze or constrained gaze conditions. Optic flow speed was manipulated independent of the veridical road-edges so that use of flow would lead to predictable understeering or oversteering. Steering was found to systematically vary according to flow speed, but crucially the Flow-Induced Steering Bias (FISB) magnitude depended on which road-edge components were visible. The presence of a guidance signal increased the influence of flow, with the largest FISB in ‘Far’ and ‘Complete’ road conditions, whereas the smallest FISB was observed when only ‘Near’ road-edges were visible. Gaze behaviors influenced steering to some degree, but did not fully explain the interaction between flow and road-edges. Overall the experiments demonstrate that optic flow can act indirectly upon steering control by modulating the guidance signal provided by a demarcated path.

A Unifying Theory of Driver Perception and Steering Control on Straight and Winding Roads

“…The following prefilter dynamics are consistent with the estimated FRFs in Fig. 5, and are identical to the preview model of [29], [30]: (10) with K f the scaling gain, T l,f the low-pass (smoothing) filter time-constant, 1 and τ f the look-ahead time.…”

“…2 For the data in Fig. 9, the standard deviation of the vehicle's lateral position deviation from the centerline σ y e ≈ 0.1 m, which is sufficiently low for safe lane keeping on most roads; measured deviations on real roads are typically higher [10], because the current model analysis lacks external disturbances (y d , ψ d ) and human remnant (n).…”

“…Expressions similar to (1) can be derived for other optical cues (e.g., see [6] for details), but are not further investigated here, as various researchers have suggested that the bearing angle is a key perceptual feedback that guides driver steering [26], [33]. Possible bearing angle aim-points are the tangent point, points on the road's lane edge or centerline, or points on the future vehicle path [2], [10], [22], [33], [35].…”

“…The information-centered approach predominantly studies the visual cues used by drivers. Using experimental tools such as eye-trackers and visual occlusion, evidence has been provided that drivers rely on patterns of the optical flow [3], [4], [8]- [10], both "near" and "far" visual regions [10]- [13], and the road's curvature or tangent point [14]- [16]. In contrast, the controltheoretic approach mostly ignores driver perception and focuses on understanding and modeling the driver's control dynamics.…”

Visual control of steering in curve driving

“…Thus, although the path may be occluded, participants can still get visual feedback, in the form of optic flow, regarding how their steering actions move them through the environment. Others have demonstrated that biased optic flow can influence steering Kountouriotis, Mole, Merat, & Wilkie, 2016;Mole, Kountouriotis, Billington, & Wilkie, 2016), though in those studies path information was continuously available. Here, the selective manipulation of path occlusion and optic flow enabled us to experimentally control the information that was available to the driver.…”