Perceptual and attentional factors in driving

The scale of the problem:

Road accidents are a major cause of death and injury worldwide.

U.K., 2009: 2,222 people deaths, 222,146 injuries;

472 motorcyclist deaths, 20,703 injuries (DFT 2010).

Gross underestimate - 298,687 accidents reported, but maybe 700,000 per year?

U.K., 1951-2006: 309,144 deaths and 17.6 million injuries on UK roads.

The major cause of death for under 25's, and the major cause of lost years of life.

By 2020, injuries due to road accidents are likely to be the third largest cause of disease worldwide.

Role of perception in driving:

Hills (1980): vision is the most important sense for driving.

DfT (2010): contributory factors in road accidents:

But - no correlation between acuity and accident risk (Hills and Burg 1977, Gresset and Meyer 1994, Charman 1997).

Vehicle type: Cycles Motorcycles Cars, vans, lorries, etc.

All types of accident:

17,036 25,869 323,286

At junctions: 12,266 17,008 191,332

At junctions as % of all accidents:

72% 66% 59%

Department for Transport statistics (2005):

A prototypical multi-vehicle motorcycle accident:

75% of motorcycle accidents are collisions with another road-user, 25% are solo accidents.

In 75% of collisions, the other road-user violated the motorcyclist's right-of-way.

Right turns at intersections (especially T-junctions) are the most dangerous.

Usual excuse is that the offending driver "looked, but failed to see" the approaching motorcyclist.

About 75% of motorcycle accidents occur during daylight, in urban areas (Janoff and Cassell, 1971).

Motorcyclists using daytime headlights are nearly three times less likely to have an accident than motorcyclists who don’t (Vaughan, Pettigrew and Luckin 1977).

Data such as these have led to the widespread belief that

(a) motorcyclists have a conspicuity problem,

(b) conspicuity aids (e.g., daytime lights and bright clothing) will reduce their risk of an accident.

A “solution” to the problem of motorcyclists’ poor conspicuity:

Why are motorcyclists difficult to detect?

(1) Sensory limitations - the motorcycle is too hard to see (e.g., too small, too dim, etc.)

Why are motorcyclists difficult to detect?

(2) Practical problems - motorcycle is obscured by other road-users, street furniture, etc. NB: reported in HALF of all collisions!

Why are motorcyclists difficult to detect?

(3) Cognitive/attentional limitations - the motorcycle is "seen" but not truly perceived. Noddy's retina

Noddy's brain

Problems with previous research:

Lots of research on conspicuous clothing (dayglo jackets), but problems with it -

Dubious methods -

(a) reaction times, without having to search for the motorcyclist and in the certain knowledge he is there (e.g. Williams and Hoffman 1979);

(b) gap acceptance studies (which are not measuring just motorcycle conspicuity);

(c) memory of road-users for a motorcycle that they had just passed (failure to remember does not necessarily imply that there was originally failure to detect) (e.g. Janoff and Cassel 1979).

Evidence against the “sensory limitations” idea:

Cercarelli et al (1992):

Right-of-way violation crashes, as % of daytime and night-time multi-vehicle accident totals:

Day: Night:

Car-motorcycle: 61.8% 50%

Car-car: 62.5% 52.2%

Car drivers are as likely to pull out in front of cars as they are to pull out in front of motorcycles.

Cairney and Catchpole (1993):

30% of casualty accidents in the Melbourne metropolitan area occur at intersections.

At least one driver failed to see the other vehicle in 78-90% of vehicle-vehicle collisions.

In 13-51% of these collisions, neither driver saw the other!

In many cases the driver looked in the appropriate direction, but failed to see the other vehicle.

Location of motorcycle accidents:

Location of car accidents:

Location of injury-producing accidents (Department of Transport 1998):

Snellen acuity:

Ability to detect MAR of 1 arc min = 6/6 (20/20)

Average acuity = 6/4 (20/16)

UK limit for driving is 6/15

Legally blind = 6/60

Acuity 5 deg. eccentricity = 6/18

Night - time acuity = 6/9

Hole and Tyrrell (1993): effects of headlights on drivers’ expectations about whether a motorcyclist is present: 55 slides, 23 containing bike, 32 not: last slide always contained bike.

OFF/OFF

ON/OFF

ON/ON

OFF/ON

87 28 7 600

700

800

900

1000

1100

1200lights-on lights-off

(a) "Urban" location:

distance (m)

225 113 29600

700

800

900

1000

1100

1200lights-on lights-off

(b) "Rural" location:

distance (m)

Effects of perceptual "set" on reaction times. experimental condition (n=28 per group)

mean difference score (standard deviation in brackets)

no. subjects slower on test slide (as % of total no. subjects in each group)

ON/ON: 69.1 (236.8) 8 (29%)

OFF/ON: 128.2 (157.7) 2 (7%)

ON/OFF: -106.8 (199.7) 19 (68%)

OFF/OFF: 111.3 (285.5) 7 (25%)

Results:

ON/OFF condition was significantly different from the other three: no differences between the latter.

ON/OFF: 68% slower on the final slide, OFF/ON: 93% faster on the final slide, so it's not just incongruity.

Expt. 2: ON/OFF, 60% ON/OFF and 96% ON/OFF were significantly different from OFF/OFF.

Physical conspicuity may not be the most important factor in causing accidents:

(a) Headlight use made no difference to motorcycle detection when the motorcycle was close - yet it is at close range that right-of-way violations cause accidents (at longer distances, either road-user can take corrective action).

(b) Road-users may readily adopt imperfect heuristic strategies and expectations (shorthand codes) in order to cope with the informational demands of driving.

Using simple perceptual attributes (e.g., headlight luminance) to "code" for complex perceptual stimuli may be not always be an effective strategy!

Motorcycles at close range are well above sensory thresholds:

Motorcycles are physically smaller than cars, but retinal image size determines sensory conspicuity:

Motorcycles at close range are well above sensory thresholds:

Motorcycles are physically smaller than cars, but retinal image size is more important in sensory conspicuity:

Brooks and Guppy (1999):

Car-driving motorcyclists (and their friends and family) are less likely to have LBFS accidents with motorcycles.

Hard to explain if motorcycles are physically hard to see.

Langham, Hole, Edwards and O’Neil (2002): Effects of parking orientation on police car detection:

Is it safer to park in-line with the traffic flow, or at an angle? Video, filmed from driver’s point of view.Hazard detection task.

UR N1KD

In-line Angle

(45 deg.)

Bri

dg

e o

ver

A27

A27 (eastbound)

A27 (westbound)

Condition Mean time to detect (sec.) SD

Angle/ Experienced 3.12 0.57

In-line/ Experienced 4.76 +1.64 0.99

Angle/ Inexperienced 4.56 +1.44 0.42

In-line/ Inexperienced 4.50 +1.38 0.46

Condition Mean time to detect (sec.) SD

Angle/ Undivided Attention 3.72 0.53

Angle/ Divided Attention 4.44 +0.72 0.77

In-line/ Undivided Attention 4.38 +0.66 0.94

In-line/ Divided Attention 5.13 +1.41 0.94

Results:

Experiment 1: orientation and experience:

Experiment 2: orientation and divided attention:

Results:

1.Experiment 1:

Car orientation affected RT only for experienced drivers – slower when car parked in-line.

2. Experiment 2:

Independent effects of orientation and divided attention: worst RT was the in-line/divided-attention condition.

Five participants failed to detect the parked car: four were in this condition.

Shows "looked but failed to see" errors can occur with objectively highly conspicuous vehicles in full view.

Conclusion: high “sensory” conspicuity does not ensure detection.

Adapted from"Ogri", © Paul Sample

Change blindness and inattentional blindness:

Failure to detect changes unless they receive focused attention (e.g. Grimes 1996; Rensink et al 1997; Simons and Levin 1992; Mack and Rock 1998; Simons and Chabris 1999).

Change blindness and inattentional blindness:

Velichovsky et al (2002): saccades and blinks take up 18% of our viewing time - a natural cause of change-blindness effects?

Conclusions:

1. Physical factors can be important:

Clothing and headlight use can affect detectability. Contrast may be important.

However, at close distances, these variables have little effect - and yet it is at close distances that most collisions occur.

2. The driver’s psychological state is more important:

Headlights aid conspicuity by acting as a shorthand code to a motorcyclist's presence, not by compensating for their sensory deficiencies (e.g. small size).

Drivers have expectations about what they will encounter, and use these as a basis for action.

Drivers need to navigate in real time, using a visual system that evolved to cope with far slower speeds (Rumar 1990).

To cope, drivers need “quick and dirty” solutions to questions such as: “is it safe to pull out?”

Drivers may use a very impoverished representation of their surroundings, based on expectations.

Accidents occur when expectations and reality do not match.

We carry in our heads predictive hypotheses of the external world…These brain-based hypotheses of perception are our most immediate reality” (Gregory, 1998)."We not only believe what we see, to some extent we see what we believe."