This paper studies how driving performance, including visual search behaviours are affected by concurrent mental verbal or imagery tasks. Ten participants drove an instrumented car in real traffic and normal daylight conditions, in two road environments: a four lane highway and a conventional two lane road. For each type of road the participants performed a control condition of ordinary driving and drove also while performing different mental tasks: two verbal tasks and two imagery tasks. The results show: (1) compared with ordinary driving, fixation duration was lower for verbal tasks and higher for imagery tasks; (2) a significant reduction in variability of fixation along the horizontal axis with respect to ordinary driving: 24% for verbal and 43% for imagery tasks; (3) a higher reduction in vertical variability: 45% for verbal tasks and 67% for imageries; (4) for both secondary tasks a pupillary dilation response was observed. The results were reproduced in both road types and for most cases are significant individually. Other effects associated with secondary tasks were a reduction in the number of fixations in both rear-view mirrors (offfside-external and internal) and on the dashboard. This reduction was higher for imagery tasks than for verbal tasks. Driving speed was not affected. The results were analysed considering the limitations of attentional capacity and specific resources theories of attention. (A)
Abstract