The illusion of absence: how a common feature of magic shows can explain a class of road accidents

Abstract

The purpose of the present note is to draw attention to the potential role of a recently discovered visual illusion in creating traffic accidents. The illusion consists in a compelling and immediate experience that the space behind an occluding object in the foreground is empty. Although the illusion refers to a region of space, which is invisible due to occlusion (a blind spot), there is evidence to suggest that it is nevertheless driven by visual mechanisms and that it can be just as deceptive and powerful as ordinary visual illusions. We suggest that this novel illusion can make situations involving blind spots in a road user's field of view even more dangerous than one would expect based on the lack of visibility by itself. This could be because it erroneously makes the road user feel that (s)he has actually seen everything there is to see, and thus has verified that the blind spot is empty. This hypothesis requires further testing before definitive conclusions can be drawn, but we wish to make researchers and authorities involved in the analysis of traffic accidents and on-the-spot crash investigations aware of its potential role in order to encourage registration of relevant data and facilitate further research.

Keywords: A-pillar obstruction; Amodal completion; Blind zone; Illusion of absence; Improper lookout; LBFTS accidents; Magic; Perception; Road safety; View obstructions.

Fig. 1

Top panels: A demonstration of the illusion of absence. Although all the objects in panel (a) are hidden behind the violet ”bubbled” occluder in panel (b), it is curiously difficult to imagine that they are really there. Bottom panels: A demonstration of amodal completion. The two fingers are experienced as a single long finger when they are partially occluded by the box (panel d). Note that this illusory impression persists even though it is quite absurd and contradicts your conscious knowledge. Top row adapted from The Other Side of Magic: The Psychology of Perceiving Hidden Things by V. Ekroll, B. Sayim and J. Wagemans, 2017, Perspectives on Psychological Science, 12(1), p. 98. Copyright (2017) by SAGE Publications. Reprinted with permission. Bottom row adapted from “Never repeat the same trick twice—unless it is cognitively impenetrable” by V. Ekroll, E. De Bruyckere, L. Vanwezemael and J. Wagemans, (2018), i-Perception, 9(6), p. 3, used under CC BY

Fig. 2

An example of a visual illusion that can be explained based on the principle of generic views. The three panels show the same four cards photographed from three different viewpoints. The picture card is in the front in the bottom row, and in the back in the top row, but in panel (a), it appears to be in front also in the top row. Adapted from Adelbert Ames’ “overlay demonstration” (Ittelson, 1952)

Fig. 3

The A-pillars next to the windscreen can hide the view of other road users

Fig. 4

Schematic illustration of the binocular blind zone (gray regions) created by A-pillars (blue arrows) of different widths. a If the A-pillar is wider than the distance between the pupillary distance PD—which is the case in most extant cars—, the width (x) of the blind zone increases with the distance (d) from the observer. b If the width of the A-pillar were equal to the pupillary distance, the width of the binocular blind zone would be equal to the pupillary distance (typically about 6 cm) at any distance. c If the width of the A-pillar were less than the pupillary distance, the width of the blind zone would decrease with distance. Panel (a) also illustrates the definition of the binocular obstruction angle α. The equation underneath shows how the width x of the binocular blind zone at a given distance d can be calculated based on the binocular obstruction angle and the interpupillary distance. In (b), the binocular obstruction angle is zero, and in (c) it is negative

Fig. 5

Illustration of how car B may remain trapped in the A-pillar blind zone (red region) of car A until after they have passed a conservative estimate (reaction time 1.5 s., dry road) of the stopping distance for cars riding at 50 km/h (red dotted lines). The cars are shown at two different points of time. In this example, equal speeds are assumed. The A-pillar bearing is 45° and the A-pillar obstruction angle is 7.3°, which are realistic average values (see text). Note that the A-pillars of some vehicles have considerably larger obscuration angles, and that the obscuration angle may increase even further if the driver is sitting closer than the most rearward position of the seat. The cars are 4 m long and 1.75 m wide, which corresponds to the measures of a typical four-person car (e.g. VW Polo)

Fig. 6

Illustration of the CBDR principle. Two vehicles A and B are driving on straight paths that intersect at the point I, each with their own constant speed. If the bearing α of vehicle B viewed from vehicle A remains constant at all times, the vehicles are going to reach the intersection I simultaneously, i.e. they are going to collide. Note that, by symmetry, this also means that the bearing β of vehicle A is constant. If the bearing α decreases with time, vehicle B will have passed the intersection when vehicle reaches it (this is only true in a strict sense if we neglect the size of the vehicles). Conversely, if α increases, vehicle B will not yet have reached the intersection. Note that these rules are valid irrespective of the angle γ between the straight paths

Fig. 7

The front end loader on tractors or similar vehicles also creates forward-looking blind spots, which have similar basic properties as those created by A-pillars. From Ringen and Moss-Iversen (2017), reprinted with permission

Fig. 8

Schematic illustration of how the A-pillar blind zone (red area) of a left-turning bus (yellow) may sweep across a crosswalk and potentially obscure a crossing pedestrian until right before impact

Fig. 9

(Left) The narrow signpost in the middle can hide a motorcycle approaching the intersection over a long stretch (150 m, see Haakenstad, 2015) from the point of view of a driver halting at the entry to the main road. In this photo, a large truck is almost completely covered. This probably happened during a fatal accident at this intersection (Amundsen et al., 2015). Based on the findings of Øhrn et al. (2019), one may speculate that narrow obstructions of view like this signpost are particularly prone to evoking the illusion of absence, and thus a compelling, but potentially misleading conviction that it is safe to enter the main road. (Right) The signpost has later been removed. The photo on the left was taken by Pål Bjerke, Norwegian Public Roads Administration and is reprinted with permission