Beyond the tangent point: Gaze targets in naturalistic driving

Abstract

Moving in natural environments is guided by looking where you are going. When entering a bend, car drivers direct their gaze toward the inside of the curve, in the region of the curve apex. This behavior has been analyzed in terms of both "tangent point models," which posit that drivers are looking at the tangent point (TP), and "future path models," which posit that drivers are visually targeting a point on the desired trajectory or future path (FP). This issue remains unresolved, partly due to the challenge of representing the changing visual projection of the trajectory into the driver's field of view. This paper reports a study of naturalistic driving, in which the FP in the field of view is explicitly modeled, and the TP and reference points on the FP are simultaneously analyzed as potential gaze targets. We argue that traditional area-of-interest methods commonly interpreted as supporting the TP hypothesis are problematic when the interest is contrasting multiple gaze targets. This prompts a critical reassessment of the empirical case for the ubiquity of looking at the TP and the generality of the TP hypothesis as an account of where people look when they steer. As a basis for representing driver gaze behavior, the FP is an equally valid point of departure. There are no overwhelming theoretical or empirical reasons for favoring the TP models over the FP models.

Systematic Observation of an Expert Driver's Gaze Strategy—An On-Road Case Study

“…Chattington et al (2007) report gaze lead time (peak of gaze-steering cross correlation) of 0.98 s for 60 s epochs. We have observed similar cross correlations on the same road as used in this study for seven participants ( unpublished data from Lappi et al, 2013a). …”

“…For a good portion of the time, this gives as good qualitative characterization of where we look when “we look where we are going” on the road 1 . The Occlusion Point (OP) is the point furthermost part of the road to which a continuous, unobstructed preview of a possible trajectory (future path) is visible (Lappi et al, 2013a), i.e., the point where “the road disappears from view.” Like the TP, OP also is a travel point ; it moves ahead as the observer travels along the road and does not follow the local optic flow (Figure 3; clear illustrations are e.g., 17:28:16.79–17:20:28.15 and 17:30:40.29–17:30:46.02).…”

“…This is according to the definition in the original Land and Lee (1994) study 2 . As a methodological side comment, note that because of the visual projection of road geometry into the forward-looking visual field can bring these points very near to one another, making the definite determination of the actual gaze target of many individual fixations difficult, and traditional AOI methods unreliable (Lappi et al, 2013a; Lappi, 2014). But while in many individual cases the classification of a given single fixation could be ambiguous bases on instantaneous gaze position alone, the overall pattern of multiple gaze targets in the Far Zone is clear.…”

“…Note, however, that as with the distance and time distance of TP the size and the shape of this AOI will vary dramatically, making any statistical analysis of gaze catch percentages or dewll times problematic. (For the related AOI overlap problem of fixed-size AOI gaze catch percentage/dwell time analysis see Lappi et al, 2013a; Lappi, 2014). There appears to be no straightforward and general way to bring the traditional AOI method from controlled lab studies to dynamic tasks.…”

Sensorimotor basis of motor vehicle control

“…During such experiments, participants are typically required to move within an artificially generated force field with unfamiliar dynamics, a task they appear able to master even when (Kandil, Rotter et al 2009, Lappi, Lehtonen et al 2013, Lehtonen, Lappi et al 2014, Vansteenkiste, Van Hamme et al 2014, Itkonen, Pekkanen et al 2015. These studies help address issues related to many steering models, as introduced above, but they…”