Measuring distraction: the Peripheral Detection Task

The possibilities for measuring workload or driver distraction by means of the Peripheral Detection Task during driving with in-vehicle equipment were investigated in a driving simulator experiment. The results show that the Peripheral Detection Task is a very sensitive method of measuring peaks in workload, induced by either a critical scenario or messages provided by a driver support system. The more demanding the task, the more cues will be missed and the longer the response times to the Peripheral Detection Task. Also, the experiment showed that the hypothesis that PDT measures the width of the functional field of view (perceptual tunnelling) is not supported. The results favour the ‘cognitive tunnelling’ hypothesis. This is consistent with the hypothesis that the PDT measures the (cognitive) selectivity of attention. Introduction In-vehicle systems may have a negative effect on safety if they increase workload or distract the driver (Verwey, Brookhuis & Janssen, 1996). Sudden increases in workload can occur during the interaction of the driver with the in-vehicle system, since the driver has to divide his/her attention between the outer world and the system inside the vehicle. Even if the system does not require the driver to look inside the vehicle on a display, the system may distract by providing information to the driver (e.g. speech messages) or performing actions that the driver did not expect or initiate. Since distraction is basically the inability to pay sufficient attention to all present tasks, or one task requires attention to a degree that other things are missed, the present paper will discuss workload and distraction as similar concepts. Although the two phenomena are not equal, the principles of measuring workload could also be useful for measuring distraction, caused by in-vehicle systems (with either visual or auditive messages). Therefore, the paper discusses the possibilities for using sensitive measures of workload, which may also be applicable for measuring distraction of invehicle equipment. Most of this workload or distraction concerns short-lasting peaks that are often difficult to detect with the traditional methods for measuring workload. Especially the sudden increases in workload or even short but high peaks are potentially dangerous because they often cannot be predicted and anticipated. If workload is predictable, the driver will generally try to control workload by making the primary driving task easier if possible. This can be done by lowering the current driving speed (e.g. Harms, 1991). While driving, workload or distraction caused by a driver support system is added to the workload induced by the primary driving task. Although there are several methods for measuring workload, good methods for measuring variations in workload are lacking. Methods of workload are usually aggregated over time. This makes traditional subjective measures of workload sometimes difficult to interpret, because it is unclear whether the driver refers to overall workload or peaks in workload (De Waard, 1996). Especially with subjective measures of workload this results in problems of interpretation. Especially self-report and physiological measures are mainly suitable for measuring workload over longer periods of time while they are unable to detect short-lasting variations in workload or short distraction. A possible exception to this is the use of event-related electro-cortical indices such as