Head-up displays: A dead-end street to more safety?
“Drivers need to split their attention to deal with the added visual information” says professor Ian Spence from the department of psychology of the university of Toronto. Spence conducted research on what happens when two information sources appear within the same visual range. “Not only will drivers – as they always did – have to concentrate on what is happening on the road, but they will have to attend to whatever information pops up on the windshield in front of them”.
Along with two students, Spence developed two tests to measure how additional information in the field of vision will affect drivers reaction. Participants of the test were shown between one and nine randomly arranged spots at the windshield, and the participants had to report number and position of the spots as exactly as they could. In some tests the participants were shown a black square as an additional stimulus. The exactness of the test person’s report always was higher when the black square has not been shown. This led Spence to the conclusion that little attention as required to confirm that the square did not appear. However when the square was shown along with a low number of spots, it remained unnoticed in an albeit low percentage of cases – in one out of 15 occurrences. If more spots have been displayed in the field of vision, the number of incorrect reports increased significantly. The researchers concluded that when ever the attentiveness of the test persons was occupied by their primary task they had difficulties attending the secondary stimulus. In addition, the accuracy of the reports decreased as the number of spots shown increased. The researchers concluded in this case that if the primary tasks become more demanding, the test persons found it increasingly challenging to carry out both tasks.
In real-world driving this means that more visual information is experienced by drivers as more stressful. They for instance have to differentiate between warnings of a collision and a recommendation to make a turn, Spence explained. “Otherwise competing warnings may be more dangerous than no warning at all”. To verify this assertion, the researchers asked test persons to identify the appearance of the of random shapes like triangles, squares or diamonds among the spots. Again, in tests with larger numbers of spots the shape of the random figures was frequently misidentified or missed. Like in the first test, the participants had problems to estimate the number of spots when the random shape appeared. “Observwers made both judgements more slowly when the shape appeared among the spots by as much as 200 percent”, noted Spence. “The two visual tasks interfered with each other and impaired both reaction and speed and accuracy.” He added “Missed warnings and slowed reaction times present real threats to safety.”
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