Hazard anticipation of young novice drivers - SWOV

of the visual acuity in the fovea. In order to recognize what objects in a scene
precisely are, eye movements are necessary. Fixations are also necessary
because the limited capacity of our cognitive systems do not allow us to
process all information from the environment around a fixation even when
visual acuity would not have been a problem. The maximum area around a
fixation of which information can be processed is called the functional or
useful field of view (e.g. Ball et al., 1988). However, to understand the gist of
a total (traffic) scene (e.g.: 'I'm driving on a motorway.') one short fixation in
the centre of about 200 ms is sufficient (Oliva & Torralba, 2006). Note that the
distinction between the 'overall picture' and what is exactly going on in that
picture resembles the distinction between context aspects (the overall
picture) and content aspects (objects in the scene) made by Brouwer &
Schmidt (2002) (see Section 3.6). In 1935 with the aid of rudimentary eye
tracking equipment, Buswell already concluded that fixations in scenes are
not random (cited in Henderson & Ferreira, 2004). Some regions in a scene
receive more and longer fixations because of their visual salience such as
colour, intensity, contrast, orientation, movement, and because of their
cognitive salience. Cognitive salience means that persons have learned that
an area is salient within a certain context, independent of the visual features
of that area. A fixation made because of visual salience is called bottom-up
selection (Itti & Koch, 2001; Parkhurst, Law, & Niebur, 2002) and a fixation
made because of cognitive salience is called top-down selection (Henderson
et al., 2007). Different brain circuits are probably active for gaze control when
a fixation is top-down and a fixation is bottom-up (Hahn, Ross, & Stein,
2006). Most fixations are bottom-up, but some are top-down. Henderson &
Ferreira (2004) assume that schemata and task knowledge play an important
role in top-down selection. This is relevant for fixations in relation to covert
latent hazards. If a driver fixates at an empty region, this cannot be because
of bottom-up selection, as this area has no visual salience. The area however
can have meaning to the driver because based on the selected dominant
schema the driver expects that a yet invisible hazard could materialize in that
region. Fixations on other road users in a traffic situation that could start to
act dangerously (overt hazards), however do not necessarily indicate that the
driver has recognized the overt latent hazard. A fixation on a visible other
road user could also be the result of bottom-up selection. This is the case
when attention is drawn to a particular road user in the scene because of its
visual salience (size, movement, contrast, and so forth). A fixation on another
road user can also be top-down independent of hazard anticipation. A driver
may for instance be interested in how that other road user looks. In the
experiment reported in this chapter, fixations of participants while watching
125