This study reports an investigation of the ability of subject to estimate the velocity of the vehicle in which they travel. Previous investigations of absolute velocity have left uncontrolled, i.e., under the control of the subject, the sensory stimulation, the time available for observation and the acceleration of the vehicle. The situation of interest from the safety point of view is the one where the situation has to be reappraised quickly. Toward this end equipment was developed to control the locus of visual stimulation and the time that the stimulation was available for observation. The acceleration of the vehicle was a parameter of the experiment. Stimulation time was held constant at one second. Results show that, with time limitation, the locus of visual stimulation is significant in determining the accuracy of the estimates. Peripheral visual stimulation results in more accurate estimates of the absolute velocity of the vehicle than stimulation of the frontal visual field. The higher acceleration rate used to attain velocities also partially destroys the gain in accuracy attributed to the locus of visual stimulation. It is hypothesized that fixation of the frontal field in "normal" driving may be a factor in highway hypnosis, i.e., gross under-estimation of absolute velocity. The significance of absolute velocity appreciation for steering behaviour and multiple car manoeuvres is pointed out.
Abstract